One possible origin for GRB 211211A, shown in this illustration, is a pair of compact stars merging (bright dots in the center) and emitting jets of radiation (green and purple beams). Heavy elements forming in the clouds of matter surrounding the stars emit light that is known as a kilonova. SAMUELE RONCHINI/GSSI 2022

By Lisa Grossman
8.12.2022

Astronomers have spotted a bright gamma-ray burst that upends previous theories of how these energetic cosmic eruptions occur.

For decades, astronomers thought that GRBs came in two flavors, long and short — that is, lasting longer than two seconds or winking out more quickly. Each type has been linked to different cosmic events. But about a year ago, two NASA space telescopes caught a short GRB in long GRB’s clothing: It lasted a long time but originated from a short GRB source.

“We had this black-and-white vision of the universe,” says astrophysicist Eleonora Troja of the Tor Vergata University of Rome. “This is the red flag that tells us, nope, it’s not. Surprise!”

This burst, called GRB 211211A, is the first that unambiguously breaks the binary, Troja and others report December 7 in five papers in Nature and Nature Astronomy.

Prior to the discovery of this burst, astronomers mostly thought that there were just two ways to produce a GRB. The collapse of a massive star just before it explodes in a supernova could make a long gamma-ray burst, lasting more than two seconds (SN: 10/28/22). Or a pair of dense stellar corpses called neutron stars could collide, merge and form a new black hole, releasing a short gamma-ray burst of two seconds or less.

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Still from a NASA animation of a magnetar emitting a powerful flare. (NASA)

24 September 2022
By MICHELLE STARR

We have detected a strange new signal from across the chasm of time and space.

A repeating fast radio burst source detected last year was recorded spitting out a whopping 1,863 bursts over 82 hours, amid a total of 91 hours of observation.

This hyperactive behavior has allowed scientists to characterize not just the galaxy that hosts the source and its distance from us, but also what the source is.

The object, named FRB 20201124A, was detected with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China and described in a new paper led by astronomer Heng Xu of Peking University in China.

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Interactions between a planet and a magnetic neutron star (illustrated) might be the source of repeating, millisecond-long bursts of cosmic radio waves. MARK GARLICK/SCIENCE PHOTO LIBRARY/GETTY

It’s one more hypothesis among many for the source of these flares

By Liz Kruesi
APRIL 18, 2022

Fragmenting planets sweeping extremely close to their stars might be the cause of mysterious cosmic blasts of radio waves.

Milliseconds-long fast radio bursts, or FRBs, erupt from distant cosmic locales. Some of these bursts blast only once and others repeat. A new computer calculation suggests the repetitive kind could be due to a planet interacting with its magnetic host star, researchers report in the March 20 Astrophysical Journal.

FRBs are relative newcomers to astronomical research. Ever since the first was discovered in 2007, researchers have added hundreds to the tally. Scientists have theorized dozens of ways the two different types of FRBs can occur, and nearly all theories include compact, magnetic stellar remnants known as neutron stars. Some ideas include powerful radio flares from magnetars, the most magnetic neutron stars imaginable (SN: 6/4/20). Others suggest a fast-spinning neutron star, or even asteroids interacting with magnetars (SN: 2/23/22).

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Biggish bang Artist's impression of neutron stars merging, producing gravitational waves and resulting in a kilonova explosion. (Courtesy: University of Warwick/Mark Garlick/CC BY 4.0)

05 Apr 2022

A massive and exotic type of neutron star could be formed by the merger of two neutron stars and avoid becoming a black hole – at least temporarily. That is the conclusion of Arthur Suvorov at Manly Astrophysics in Australia and Kostas Glampedakis at Germany’s University of Tübingen who have calculated that magnetically supramassive neutron stars could stave off gravitational collapse, despite lying above the theoretical mass limit for black hole formation.

In 2017 the LIGO–Virgo collaboration detected the first gravitational waves emanating from two neutron stars as they spiralled into each other, and eventually merged. This event provided important opportunities for astronomers to study the aftermath of the merger using a range of different telescopes, but key questions remain about the object that was created.

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Collisions of two neutron stars (illustrated) probably produce more of the universe’s heavy elements than similar collisions of a black hole and neutron star. A. SIMONNET/SONOMA STATE UNIV., LIGO, NSF (EDITED BY MIT NEWS)

By Emily Conover NOVEMBER 3, 2021 

The cosmic origins of elements heavier than iron are mysterious. One elemental birthplace came to light in 2017 when two neutron-rich dead stars collided and spewed out gold, platinum and other hefty elements (SN: 10/16/17). A few years later, a smashup of another neutron star and a black hole left scientists wondering which type of cosmic clash was the more prolific element foundry (SN: 6/29/21).

Now, they have an answer. Collisions of two neutron stars probably take the cake, scientists report October 25 in Astrophysical Journal Letters.

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A black hole (illustrated in black) and a neutron star (white) spiral inward before merging, producing ripples in spacetime (dark gray). MARK MYERS/OZGRAV/SWINBURNE UNIVERSITY

An elusive source of ripples in spacetime has finally been found

By Emily Conover JUNE 29, 2021

Caught in a fatal inward spiral, a neutron star met its end when a black hole swallowed it whole. Gravitational ripples from that collision spread outward through the cosmos, eventually reaching Earth. The detection of those waves marks the first reported sighting of a black hole engulfing the dense remnant of dead star. And in a surprise twist, scientists spotted a second such merger just days after the first.

Until now, all identified sources of gravitational waves were twos of a kind: either two black holes or two neutron stars, spiraling around one another before colliding and coalescing (SN: 1/21/21). The violent cosmic collisions create waves that stretch and squeeze the fabric of spacetime, undulations that can be sussed out by sensitive detectors.

The mismatched pairing of a black hole and neutron star was the final type of merger that scientists expected to find with current gravitational wave observatories. By pure coincidence, researchers spotted two of these events within 10 days of one another, the LIGO, Virgo and KAGRA collaborations report in the July 1 Astrophysical Journal Letters.

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The NuSTAR telescope is sensitive to the high-energy X-rays that would provide stronger evidence for the existence of axions.
NASA/JPL-Caltech

Jonathan O'Callaghan  -  October 19, 2021

Approximately 85% of the mass in the universe is missing — we can infer its existence, we just can’t see it. Over the years, a number of different explanations for this “dark matter” have been proposed, from undiscovered particles to black holes. One idea in particular, however, is drawing renewed attention: the axion. And researchers are turning to the skies to track it down.

Axions are hypothetical lightweight particles whose existence would resolve two major problems. The first, fussed over since the 1960s, is the strong charge-parity (CP) problem, which asks why the quarks and gluons that make up protons and neutrons obey a certain symmetry. Axions would show that an unseen field is responsible.

The second is dark matter. Axions “are excellent dark matter candidates,” said Asimina Arvanitaki, a theoretical physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada. Axions would clump together in exactly the ways we expect dark matter to, and they have just the right properties to explain why they’re so hard to find — namely, they’re extremely light and reluctant to interact with regular matter.

Earlier this year, a group of scientists reported that they might have spotted evidence of axions being produced by neutron stars — collapsed stars that are so dense, a tiny sample little bigger than a grain of sand would weigh as much as an aircraft carrier. Ever since the 1980s, physicists have thought that if axions do exist, they should be produced inside the hot cores of neutron stars, where neutrons and protons smash together at high energies.

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Image from a MAYA collaboration numerical relativity simulation of a neutron star-black hole (NSBH) binary merger, showing the disruption of the neutron star. Credit: Deborah Ferguson (UT Ausitn), Bhavesh Khamesra (Georgia Tech), and Karan Jani (Vanderbilt University).

News Release • June 29, 2021

For the first time, researchers have confirmed the detection of a collision between a black hole and a neutron star. In fact, the scientists detected not one but two such events occurring just 10 days apart in January 2020. The extreme events made splashes in space that sent gravitational waves rippling across at least 900 million light-years to reach Earth. In each case, the neutron star was likely swallowed whole by its black hole partner.

Gravitational waves are disturbances in the curvature of space-time created by massive objects in motion. During the five years since the waves were first measured, a finding that led to the 2017 Nobel Prize in Physics, researchers have identified more than 50 gravitational-wave signals from the merging of pairs of black holes and of pairs of neutron stars. Both black holes and neutron stars are the corpses of massive stars, with black holes being even more massive than neutron stars.

Now, in a new study, scientists have announced the detection of gravitational waves from two rare events, each involving the collision of a black hole and a neutron star. The gravitational waves were detected by the National Science Foundation's (NSF's) Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States and by the Virgo detector in Italy. The KAGRA detector in Japan, joined the LIGO-Virgo network in 2020, but was not online during these detections.

The first merger, detected on January 5, 2020, involved a black hole about 9 times the mass of our sun, or 9 solar masses, and a 1.9-solar-mass neutron star. The second merger was detected on January 15, and involved a 6-solar-mass black hole and a 1.5-solar-mass neutron star. The results were published today, June 29, in The Astrophysical Journal Letters.

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A Hubble Space Telescope image (left) of a galaxy known to host a ‘fast radio burst’ helps ID where in the galaxy the blast originated (oval). After image processing (right), the burst’s origin appears centered on one of the galaxy’s spiral arms. NASA, ESA, ALEXANDRA MANNINGS/UNIVERSITY OF CALIFORNIA SANTA CRUZ, WEN-FAI FONG/NORTHWESTERN UNIVERSITY, ALYSSA PAGAN/STSCI

Locating the bursts’ homes suggests a connection to ordinary, young stars

By Lisa Grossman  JUNE 1, 2021 

Five brief, bright blasts of radio waves from deep space now have precise addresses.

The fast radio bursts, or FRBs, come from the spiral arms of their host galaxies, researchers report in a study to appear in the Astrophysical Journal. The proximity of the FRBs to sites of star formation bolsters the case for run-of-the-mill young stars as the origin of these elusive, energetic eruptions.

“This is the first such population study of its kind and provides a unique piece to the puzzle of FRB origins,” says Wen-fai Fong, an astronomer at Northwestern University in Evanston, Ill.

FRBs typically last a few milliseconds and are never seen again. Because the bursts are so brief, it’s difficult to nail down their precise origins on the sky. Although astronomers have detected about 1,000 FRBs since the first was reported in 2007, only 15 or so have been traced to a specific galaxy.

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Researchers bombarded lead nuclei electrons at the Thomas Jefferson National Accelerator Facility. DOE JEFFERSON LAB

By Adrian Cho Apr. 27, 2021

Say what you want about lead, it’s got a surprisingly thick skin—of neutrons, that is. In fact, the layer of neutrons on the outside of a lead nucleus is twice as thick as physicists thought, according to a new study. The seemingly abstruse result could have out-of-this-world implications: Neutron stars, the ultradense spheres left behind when stars explode in supernova explosions, could be stiffer and bigger than theory generally predicts.

“It’s a fantastic experimental achievement,” says Anna Watts, an astrophysicist at the University of Amsterdam who studies neutron stars. “It’s been talked about for years and years and years, and it’s so cool to finally see it done.”

An atom’s nucleus consists of protons and neutrons stuck together by the so-called strong nuclear force. Neutrons generally outnumber protons. Not by too much, however, as a large imbalance in the number of protons and neutrons increases a nucleus’ internal energy and can make it unstable. Theory generally predicts a large nucleus consists of a nearly equal mixture of proton and neutrons surrounded by a skin of pure neutrons.

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Scientists think neutron stars are layered. As shown in this illustration, the state of matter in their inner cores remains mysterious.
Credits: NASA’s Goddard Space Flight Center/Conceptual Image Lab

Apr 17, 2021

Matter in the hearts of neutron stars ­– dense remnants of exploded massive stars – takes the most extreme form we can measure. Now, thanks to data from NASA’s Neutron star Interior Composition Explorer (NICER), an X-ray telescope on the International Space Station, scientists have discovered that this mysterious matter is less squeezable than some physicists predicted.

The finding is based on NICER’s observations of PSR J0740+6620 (J0740 for short), the most massive known neutron star, which lies over 3,600 light-years away in the northern constellation Camelopardalis. J0740 is in a binary star system with a white dwarf, the cooling remnant of a Sun-like star, and rotates 346 times per second. Previous observations place the neutron star’s mass at about 2.1 times the Sun’s.

"We're surrounded by normal matter, the stuff of our everyday experience, but there’s much we don’t know about how matter behaves, and how it is transformed, under extreme conditions,” said Zaven Arzoumanian, the NICER science lead at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “By measuring the sizes and masses of neutron stars with NICER, we are exploring matter on the verge of imploding into a black hole. Once that happens, we can no longer study matter because it’s hidden by the black hole’s event horizon."

Arzoumanian and members of the NICER team presented their findings on Saturday, April 17, at a virtual meeting of the American Physical Society, and papers describing the findings and their implications are now undergoing scientific review.

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Neutron stars (one illustrated) squash the mass equivalent of the sun into the size of a city. CASEY REED/PENN STATE

By Elizabeth Quill FEBRUARY 3, 2021

The predictions were right about black holes, gravitational waves and universe expansion

Albert Einstein’s mind reinvented space and time, foretelling a universe so bizarre and grand that it has challenged the limits of human imagination. An idea born in a Swiss patent office that evolved into a mature theory in Berlin set forth a radical new picture of the cosmos, rooted in a new, deeper understanding of gravity.

Out was Newton’s idea, which had reigned for nearly two centuries, of masses that appeared to tug on one another. Instead, Einstein presented space and time as a unified fabric distorted by mass and energy. Objects warp the fabric of spacetime like a weight resting on a trampoline, and the fabric’s curvature guides their movements. With this insight, gravity was explained.

Einstein presented his general theory of relativity at the end of 1915 in a series of lectures in Berlin. But it wasn’t until a solar eclipse in 1919 that everyone took notice. His theory predicted that a massive object — say, the sun — could distort spacetime nearby enough to bend light from its straight-line course. Distant stars would thus appear not exactly where expected. Photographs taken during the eclipse verified that the position shift matched Einstein’s prediction. “Lights all askew in the heavens; men of science more or less agog,” declared a New York Times headline.

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Gravitational waves, produced when behemoths like black holes and neutron stars spiral inward and merge, have been spotted 50 times (each event represented with a large circle above). NADIEH BREMER/VISUALCINNAMON.COM

By Emily Conover and Nadieh Bremer

Fifty events reveal the similarities and differences in these cosmic smashups

Throughout the universe, violent collisions of cosmic beasts such as black holes wrench the fabric of spacetime, producing ripples called gravitational waves. For most of history, humans have been oblivious to those celestial rumbles. Today, we’ve detected scores of them.

The first came in 2015, when scientists with the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, spotted gravitational waves spawned from the merger of two black holes. That event rattled the bones of the cosmos — shaking the underlying structure of space and time. The detection also stirred up astronomy, providing a new way to observe the universe, and verified a prediction of Albert Einstein’s general theory of relativity (SN: 2/11/16).

The first came in 2015, when scientists with the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, spotted gravitational waves spawned from the merger of two black holes. That event rattled the bones of the cosmos — shaking the underlying structure of space and time. The detection also stirred up astronomy, providing a new way to observe the universe, and verified a prediction of Albert Einstein’s general theory of relativity (SN: 2/11/16).

But like a lone ripple in a vast sea, a single detection can tell scientists only so much. Now, LIGO and its partner observatory Advanced Virgo have collected 50 sets of gravitational waves. Most of these spacetime ripples resulted from two black holes spiraling inward before colliding. Some arose from collisions of dense stellar corpses called neutron stars. Two collisions involve celestial bodies that can’t be confidently identified, hinting that scientists may have spotted the first merger of a neutron star with a black hole (SN: 6/23/20).

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When neutron stars collide, the shell of expanding ejecta can interact with the surrounding interstellar medium, producing long-lived radio flaring. [NASA's Goddard Space Flight Center/CI Lab]

By Susanna Kohler on 11 December 2020

When a pair of neutron stars collide, they emit a fireworks show. Could some of the low-energy light produced in these mergers be detectable years later? A team of scientists thinks so — and they’re pretty sure they’ve found an example.

A Rainbow of Signals

In addition to gravitational waves, a slew of electromagnetic radiation is produced in the merger of two neutron stars, spanning the spectrum from gamma rays to radio waves.

In 2017, the now-famous neutron star collision GW170817 gave us a first look at this expected emission: it revealed a short gamma-ray burst, infrared and optical light from ejecta in a kilonova, and relatively short-lived X-ray and radio afterglows caused by high-speed outflows.

But there’s one expected type of emission that was missing from GW170817, and it’s never before been spotted in any neutron star collision: radio flaring.

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A burst of gamma-ray light in another galaxy (shown in an artist’s illustration) hints that colliding neutron stars produced a magnetar. NASA, ESA, D. PLAYER/STSCI

 A recent stellar flash may have signaled the birth of a highly magnetic, spinning stellar corpse

By Lisa Grossman (ScienceNews)
DECEMBER 1, 2020

A surprisingly bright cosmic blast might have marked the birth of a magnetar. If so, it would be the first time that astronomers have witnessed the formation of this kind of rapidly spinning, extremely magnetized stellar corpse.

That dazzling flash of light was made when two neutron stars collided and merged into one massive object, astronomers report in an upcoming issue of the Astrophysical Journal. Though the especially bright light could mean that a magnetar was produced, other explanations are possible, the researchers say.

Astrophysicist Wen-fai Fong of Northwestern University in Evanston, Ill., and colleagues first spotted the site of the neutron star crash as a burst of gamma-ray light detected with NASA’s orbiting Neil Gehrels Swift Observatory on May 22. Follow-up observations in X-ray, visible and infrared wavelengths of light showed that the gamma rays were accompanied by a characteristic glow called a kilonova.

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Scientists have now detected 50 sets of gravitational waves, many produced when two black holes (illustrated) spiral around one another before colliding and merging into one.
© N. FISCHER, S. OSSOKINE, H. PFEIFFER, A. BUONANNO/MAX PLANCK INSTITUTE FOR GRAVITATIONAL PHYSICS, SIMULATING EXTREME SPACETIMES (SXS) COLLABORATION

By Emily Conover OCTOBER 28, 2020 

Earth is awash in gravitational waves.

Over a six-month period, scientists captured a bounty of 39 sets of gravitational waves. The waves, which stretch and squeeze the fabric of spacetime, were caused by violent events such as the melding of two black holes into one.

The haul was reported by scientists with the LIGO and Virgo experiments in several studies posted October 28 on a collaboration website and at arXiv.org. The addition brings the tally of known gravitational wave events to 50.

The bevy of data, which includes sightings from April to October 2019, suggests that scientists’ gravitational wave–spotting skills have leveled up. Before this round of searching, only 11 events had been detected in the years since the effort began in 2015. Improvements to the detectors — two that make up the Advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, in the United States, and another, Virgo, in Italy — have dramatically boosted the rate of gravitational wave sightings.

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Magnetars, highly magnetized stellar corpses like the one illustrated here, could be the source of two different cosmic enigmas: fast radio bursts and high-energy neutrinos, a new study suggests. DRACO-ZLAT/ISTOCK/GETTY IMAGES PLUS

The elusive particles would be hard to catch, but they’d be a smoking gun, researchers say

By Lisa Grossman, SEPTEMBER 16, 2020 

For over a decade, astronomers have puzzled over the origins of fast radio bursts, brief blasts of radio waves that come mostly from distant galaxies. During that same period, scientists have also detected high-energy neutrinos, ghostly particles from outside the Milky Way whose origins are also unknown.

A new theory suggests that the two enigmatic signals could come from a single cosmic source: highly active and magnetized neutron stars called magnetars. If true, that could fill in the details of how fast radio bursts, or FRBs, occur. However, finding the “smoking gun” — catching a simultaneous neutrino and radio burst from the same magnetar — will be challenging because such neutrinos would be rare and hard to find, says astrophysicist Brian Metzger of Columbia University. He and his colleagues described the idea in a study posted September 1 at arXiv.org.

Even so, “this paper gives a possible link between what I think are two of the most exciting mysteries in astrophysics,” says astrophysicist Justin Vandenbroucke of the University of Wisconsin–Madison, who hunts for neutrinos but was not involved in the new work.

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© Carl Knox, ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav)

23 June 2020

Scientists puzzle over the mysterious astrophysical object: have they discovered the heaviest neutron star or the lightest black hole ever observed?

An international team of scientists including Lancaster University have discovered a compact object lying between neutron stars and black holes in terms of mass.

When the most massive stars die, they collapse under their own gravity and leave behind black holes; when stars that are a bit less massive die, they explode in a supernova and leave behind dense, dead remnants of stars called neutron stars.

For decades, astronomers have been puzzled by a gap that lies between neutron stars and black holes: the heaviest known neutron star is no more than 2.5 times the mass of our sun, or 2.5 solar masses, and the lightest known black hole is about 5 solar masses.

The question remained: does anything lie in this so-called mass gap?

Now, in a new study from the National Science Foundation's Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo detector in Europe, scientists have announced the discovery of an object of 2.6 solar masses, placing it firmly in the mass gap.

The object was found on August 14, 2019, as it merged with a black hole of 23 solar masses, generating a splash of gravitational waves detected back on Earth by LIGO and Virgo. A paper about the detection has been accepted for publication in The Astrophysical Journal Letters.

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See the same news from Virgo website

See the same news from LIGO website

A bright radio burst generated by a magnetar (one illustrated) in our galaxy hints that similar objects are responsible for at least some of the fast radio bursts in other galaxies, which have puzzled astronomers for over a decade. L. CALÇADA/ESO

High-energy event nearby could help explain mystery signals from distant galaxies

By Maria Temming

Astronomers think they’ve spotted the first example of a superbright blast of radio waves, called a fast radio burst, originating within the Milky Way.

Dozens of these bursts have been sighted in other galaxies — all too far away to see the celestial engines that power them (SN: 2/7/20). But the outburst in our own galaxy, detected simultaneously by two radio arrays on April 28, was close enough to see that it was generated by a highly magnetic neutron star called a magnetar.

That observation is a smoking gun that magnetars are behind at least some of the extragalactic fast radio bursts, or FRBs, that have defied explanation for over a decade (SN: 7/25/14). Researchers describe the magnetar’s radio burst online at arXiv.org on May 20 and May 21.

“When I first heard about it, I thought, ‘No way. Too good to be true,’” says Ben Margalit, an astrophysicist at the University of California, Berkeley, who wasn’t involved in the observations. “Just, wow. It’s really an incredible discovery.”

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You may have a look also in a recent TAT paper  

This simulation shows the radiation emitted from a binary black hole system. In principle, we should have neutron star binaries, black hole binaries, and neutron star-black hole systems, covering the entire allowable mass range. In practice, we saw a longstanding 'gap' in such binaries between about 2.5 and 5 solar masses. With the newest LIGO data, that gap seems to disappear.NASA'S GODDARD SPACE FLIGHT CENTER

Ethan Siegel

Mar 20, 2020

On Monday, March 16, 2020, astrophysicist Carl Rodriguez expressed a sentiment echoed by gravitational wave physicists all across the world: NOT NOW LIGO! Just minutes earlier, the LIGO collaboration sent out an alert suggesting that it had just detected another gravitational wave event, the 56th candidate detection since starting up its latest data-taking run in April of 2019. This one appears to indicate the merger of two black holes, like so many others before it.

Unlike most of the others, however, this one might be the nail-in-the-coffin of the idea of a "mass gap" between neutron stars and black holes. Before LIGO turned back on last April, all of its events, combined with otherwise-known neutron stars and black holes, showed two distinct populations: low-mass neutron stars (below 2.5 solar masses) and high-mass black holes (5 solar masses and up). This latest event, however, falls right into the mass gap range, and could demolish the idea once and for all.

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Powerful magnetic and electric fields whip charged particles around, in a computer simulation of a spinning neutron star. Credit: NASA's Goddard Space Flight Center

These stellar remnants are some of the Universe’s most enigmatic objects — and they are finally starting to give up their secrets.

Adam Mann

NATURE NEWS FEATURE 04 MARCH 2020

When a massive star dies in a supernova, the explosion is only the beginning of the end. Most of the stellar matter is thrown far and wide, but the star’s iron-filled heart remains behind. This core packs as much mass as two Suns and quickly shrinks to a sphere that would span the length of Manhattan. Crushing internal pressure — enough to squeeze Mount Everest to the size of a sugar cube — fuses subatomic protons and electrons into neutrons.

Astronomers know that much about how neutron stars are born. Yet exactly what happens afterwards, inside these ultra-dense cores, remains a mystery. Some researchers theorize that neutrons might dominate all the way down to the centre. Others hypothesize that the incredible pressure compacts the material into more exotic particles or states that squish and deform in unusual ways.

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NASA’S GODDARD SPACE FLIGHT CENTER/CI LAB

Astronomers still hope to catch a star going supernova and a bumpy neutron star, among others
BY LISA GROSSMAN 1:14PM, MAY 6, 2019

BANG, CRASH Physicists using the LIGO and Virgo observatories are catching all sorts of cosmic collisions, including of pairs of neutron stars (illustrated). But scientists hope to bag even more exotic quarry.

Seekers of gravitational waves are on a cosmic scavenger hunt.

Since the Advanced Laser Interferometer Gravitational-wave Observatory turned on in 2015, physicists have caught these ripples in spacetime from several exotic gravitational beasts — and scientists want more.

This week, LIGO and its partner observatory Virgo announced five new possible gravitational wave detections in a single month, making what was once a decades-long goal almost commonplace (SN Online: 5/2/19).

“We’re just beginning to see the field of gravitational wave astronomy open,” LIGO spokesperson Patrick Brady from the University of Wisconsin–Milwaukee said May 2 in a news conference. “Opening up a new window on the universe like this will hopefully bring us a whole new perspective on what’s out there.”

The speed and pitch of gravitational wave signals allow astronomers to make out what’s stirring up the waves. Here are the sources of gravitational waves that scientists that already have in their nets, and what they’re still hoping to find.

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The observatories are also releasing their first catalog of gravitational-wave events

On Saturday, December 1, scientists attending the Gravitational Wave Physics and Astronomy Workshop in College Park, Maryland, presented new results from the National Science Foundation's LIGO (Laser Interferometer Gravitational-Wave Observatory) and the European- based VIRGO gravitational-wave detector regarding their searches for coalescing cosmic objects, such as pairs of black holes and pairs of neutron stars. The LIGO and Virgo collaborations have now confidently detected gravitational waves from a total of 10 stellar-mass binary black hole mergers and one merger of neutron stars, which are the dense, spherical remains of stellar explosions. Six of the black hole merger events had been reported before, while four are newly announced.

From September 12, 2015, to January 19, 2016, during the first LIGO observing run since undergoing upgrades in a program called Advanced LIGO, gravitational waves from three binary black hole mergers were detected. The second observing run, which lasted from November 30, 2016, to August 25, 2017, yielded one binary neutron star merger and seven additional binary black hole mergers, including the four new gravitational-wave events being reported now. The new events are known as GW170729, GW170809, GW170818, and GW170823, in reference to the dates they were detected.

All of the events are included in a new catalog, also released Saturday, with some of the events breaking records. For instance, the new event GW170729, detected in the second observing run on July 29, 2017, is the most massive and distant gravitational-wave source ever observed. In this coalescence, which happened roughly 5 billion years ago, an equivalent energy of almost five solar masses was converted into gravitational radiation.

GW170814 was the first binary black hole merger measured by the three-detector network, and allowed for the first tests of gravitational-wave polarization (analogous to light polarization).

The event GW170817, detected three days after GW170814, represented the first time that gravitational waves were ever observed from the merger of a binary neutron star system. What's more, this collision was seen in gravitational waves and light, marking an exciting new chapter in multi-messenger astronomy, in which cosmic objects are observed simultaneously in different forms of radiation.

One of the new events, GW170818, which was detected by the global network formed by the LIGO and Virgo observatories, was very precisely pinpointed in the sky. The position of the binary black holes, located 2.5 billion light-years from Earth, was identified in the sky with a precision of 39 square degrees. That makes it the next best localized gravitational-wave source after the GW170817 neutron star merger.

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A still image of a visualization of the merging black holes that LIGO and Virgo have observed so far. As the horizons of the black holes spiral together and merge, the emitted gravitational waves become louder (larger amplitude) and higher pitched (higher in frequency). The black holes that merge range from 7.6 solar masses up to 50.6 solar masses, with about 5% of the total mass lost during each merger.TERESITA RAMIREZ/GEOFFREY LOVELACE/SXS COLLABORATION/LIGO-VIRGO COLLABORATION

Dec 4, 2018,
Ethan Siegel Senior Contributor
Science

On September 14th, 2015, just days after LIGO first turned on at its new-and-improved sensitivity, a gravitational wave passed through Earth. Like the billions of similar waves that had passed through Earth over the course of its history, this one was generated by an inspiral, merger, and collision of two massive, ultra-distant objects from far beyond our own galaxy. From over a billion light years away, two massive black holes had coalesced, and the signal — moving at the speed of light — finally reached Earth.

But this time, we were ready. The twin LIGO detectors saw their arms expand-and-contract by a subatomic amount, but that was enough for the laser light to shift and produce a telltale change in an interference pattern. For the first time, we had detected a gravitational wave. Three years later, we've detected 11 of them, with 10 coming from black holes. Here's what we've learned.

There have been two "runs" of LIGO data: a first one from September 12, 2015 to January 19, 2016 and then a second one, at somewhat improved sensitivity, from November 30, 2016 to August 25, 2017. That latter run was, partway through, joined by the VIRGO detector in Italy, which added not only a third detector, but significantly improved our ability to pinpoint the location of where these gravitational waves occurred. LIGO is currently shut down right now, as it's undergoing upgrades that will make it even more sensitive, as it prepares to begin a new data-taking observing run in the spring of 2019.

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CASEY REED/PENN STATE UNIVERSITY, WIKIMEDIA COMMONS

TOUGH STUFF An exotic substance thought to exist within a type of collapsed star called a neutron star (illustrated) may be stronger than any other known material.

A strand of spaghetti snaps easily, but an exotic substance known as nuclear pasta is an entirely different story.

Predicted to exist in ultradense dead stars called neutron stars, nuclear pasta may be the strongest material in the universe. Breaking the stuff requires 10 billion times the force needed to crack steel, for example, researchers report in a study accepted in Physical Review Letters.

“This is a crazy-big figure, but the material is also very, very dense, so that helps make it stronger,” says study coauthor and physicist Charles Horowitz of Indiana University Bloomington.

Neutron stars form when a dying star explodes, leaving behind a neutron-rich remnant that is squished to extreme pressures by powerful gravitational forces, resulting in materials with bizarre properties (SN: 12/23/17, p. 7).

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Artist's impression of a neutron-star merger (Courtesy: NASA)

Physics World

05 Sep 2018

A jet of charged particles moving at nearly the speed of light smashed its way out of debris left behind in the aftermath of the neutron-star merger that produced the gravitational waves detected by the LIGO–Virgo collaboration on 17 August 2017.

The event, catalogued as GW170817, has been a Rosetta Stone for astronomers because it allowed them for to observe the same event using gravitational waves and electromagnetic radiation ranging from a gamma ray burst (GRB) to a radio afterglow. This was a first for the new and exciting field of multimessenger astronomy.

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[Credit: NSF/LIGO/Sonoma State University/A. Simonnet]

B. F. Schutz
Posted on August 20, 2018

Last Friday we celebrated the one-year anniversary of an event that those of us who were involved will never forget. The Virgo gravitational-wave detector had joined the two LIGO instruments on August 1, 2017, and the three detectors had since then been patiently listening out together for gravitational wave sounds coming from anywhere in the Universe. On August 17, the deep quiet was interrupted by a squeal, a chirp lasting much longer and going to a much higher pitch than the GW150914 chirp that had launched the field of gravitational wave observational astronomy two years earlier. We named it, prosaically, GW170817.

This one-minute-long squeal was followed by an incredible explosion that radiated intense gamma-rays, X-rays, light, radio waves — right across the whole electromagnetic spectrum. What came first was a burst of gamma-rays, just 2 seconds after the end of the squeal. Then it began brightening up at other wavelengths. The explosion itself did not register in LIGO and Virgo, because as it rushed out in all directions it was too smooth to generate gravitational waves. But astronomers at their telescopes saw it: a kilonova, a new type of cosmic explosion.

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Artist’s illustration of two merging neutron stars. Astronomers witnessed such a merger in August 2017, and we're now trying to interpret these observations. [University of Warwick/Mark Garlick]

By Susanna Kohler on 13 April 2018

Now that the hubbub of GW170817 — the first coincident detection of gravitational waves and an electromagnetic signature — has died down, scientists are left with the task of taking the spectrum-spanning observations and piecing them together into a coherent picture. Researcher Iair Arcavi examines one particular question: what caused the blue color in the early hours of the neutron-star merger?

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Artist’s animation of a pair of neutron stars locked in a binary orbit. [NASA/Dana Berry, Sky Works Digital ]

 More than forty years after the first discovery of a double neutron star, we still haven’t found many others — but a new survey is working to change that.

The Hunt for Pairs

In 1974, Russell Hulse and Joseph Taylor discovered the first double neutron star: two compact objects locked in a close orbit about each other. Hulse and Taylor’s measurements of this binary’s decaying orbit over subsequent years led to a Nobel prize — and the first clear evidence of gravitational waves carrying energy and angular momentum away from massive binaries.
Forty years later, we have since confirmed the existence of gravitational waves directly with the Laser Interferometer Gravitational-Wave Observatory (LIGO). Nonetheless, finding and studying pre-merger neutron-star binaries remains a top priority. Observing such systems before they merge reveals crucial information about late-stage stellar evolution, binary interactions, and the types of gravitational-wave signals we expect to find with current and future observatories.

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Read also

Rapid-response program to explore a double neutron star merger

A simulation of a neutron star merger. NASA GODDARD SPACE FLIGHT CENTER

BY KATHERINE HIGNETT ON 1/19/18 AT 8:47 AM

Update | Last August, astronomers detected the massive collision of two neutron stars. This neutron star merger sent gravitational waves surging through space. It also unleashed a gamma ray burst—the world’s most powerful laser.

Normally gamma ray bursts glow brightly for a short time, then fizzle out and lose energy. New electromagnetic observations from NASA’s Chandra X-ray observatory show the burst brightening, baffling astronomers.

An exploding cocoon
A more complex explanation is needed for the bizarre brightening, the authors wrote. They propose that a "cocoon"-shaped explosion might do the job. In this model, a jet from the collision shock-heats the surrounding gas and debris, creating a boiling cocoon of matter.

The new X-ray observations support recent discoveries from radio emissions. Last month, another team of researchers reported the strengthening of radio emissions from the neutron star merger. They produced a digital reconstruction, seen in the video below, of a similar "cocoon" model.

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Credits: ESO

IN BRIEF

• Vacuum birefringence has been observed by a team of scientists for the first time ever using the European Southern Observatory's (ESO) Very Large Telescope (VLT).
• The team observed neutron star RX J1856.5-375, which is about 400 light-years from Earth, with just visible light, pushing the limits of existing telescope technology.

A LITTLE LESS STRANGE

Vacuum birefringence is a weird quantum phenomenon that has only ever been observed on an atomic scale. It occurs when a neutron star is surrounded by a magnetic field so intense, it’s given rise to a region in empty space where matter randomly appears and vanishes.

This polarization of light in a vacuum due to strong magnetic fields was first thought to be possible in the 1930s by physicists Werner Heisenberg and Hans Heinrich Euler as a product of the theory of quantum electrodynamics (QED). The theory describes how light and matter interact.

Now, for the first time ever, this strange quantum effect has been observed by a team of scientists from INAF Milan (Italy) and from the University of Zielona Gora (Poland).

Using the European Southern Observatory’s (ESO) Very Large Telescope (VLT), a research team led by Roberto Mignani observed neutron star RX J1856.5-375, which is about 400 light-years from Earth.

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NSF, LIGO, SONOMA STATE UNIV., A. SIMONNET

CRASH AND WAVE In a galaxy 130 million light-years away, two neutron stars collided. This year, in the first detection of its kind, observatories caught the resulting gravitational waves and light show (illustrated).

Discovery offers clues to heavy element formation, universe’s expansion and more
BY EMILY CONOVER 8:31AM, DECEMBER 13, 2017

Thousands of astronomers and physicists. Hundreds of hours of telescope observations. Dozens of scientific papers. Two dead stars uniting into one.

In 2017, scientists went all in on a never-before-seen astronomical event of astounding proportions: a head-on collision between two neutron stars, the ultradense remnants of exploded stars.

The smashup sent shivers of gravitational waves through Earth, and the light show that followed sent shivers of excitement down astronomers’ spines. A real-life scientific drama quickly unfolded as night after night, astronomers around the world raced the sunrise, capturing every possible bit of data before day broke at their observatories.

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Natalie Wolchoverm --  October 25, 2017 

Newly discovered “standard sirens” provide an independent, clean way to measure how fast the universe is expanding.

To many cosmologists, the best thing about neutron-star mergers is that these events scream into space an otherwise close-kept secret of the universe. Scientists combined the gravitational and electromagnetic signals from the recently detected collision of two of these stars to determine, in a cleaner way than with other approaches, how fast the fabric of the universe is expanding — a much-contested number called the Hubble constant.

In the days since the neutron-star collision was announced, Hubble experts have been surprised to find themselves discussing not whether events like it could settle the controversy, but how soon they might do so.

Scientists have hotly debated the cosmic expansion rate ever since 1929, when the American astronomer Edwin Hubble first established that the universe is expanding - and that it therefore had a beginning. How fast it expands reflects what’s in it (since matter, dark energy and radiation push and pull in different ways) and how old it is, making the value of the Hubble constant crucial for understanding the rest of cosmology.

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The core of a neutron star is such an extreme environment that physicists can’t agree on what happens inside. But a new space-based experiment — and a few more colliding neutron stars — should reveal whether neutrons themselves break down.

Joshua Sokol - Contributing Writer - October 30, 2017

The alerts started in the early morning of Aug. 17. Gravitational waves produced by the wreck of two neutron stars — dense cores of dead stars — had washed over Earth. The thousand-plus physicists of the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) rushed to decode the space-time vibrations that rolled across the detectors like a drawn-out peal of thunder. Thousands of astronomers scrambled to witness the afterglow. But officially, all this activity was kept secret. The data had to be collected and analyzed, the papers written. The outside world wouldn’t know for two more months.

The strict ban put Jocelyn Read and Katerina Chatziioannou, two members of the LIGO collaboration, in a bit of an awkward situation. In the afternoon on the 17th, the two were scheduled to lead a panel at a conference dedicated to the question of what happens under the almost unfathomable conditions in a neutron star’s interior. Their panel’s topic? What a neutron-star merger would look like. “We sort of went off at the coffee break and sat around just staring at each other,” said Read, a professor at California State University, Fullerton. “OK, how are we going to do this?”

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BANG, FLASH Light waves and gravitational waves from a pair of colliding neutron stars reached Earth at almost the same time, ruling out theories about the universe based on predictions that the two kinds of waves might travel at different speeds

Speed of spacetime ripples rules out some alternatives to dark energy
BY LISA GROSSMAN 5:34PM, OCTOBER 24, 2017

Ripples in spacetime travel at the speed of light. That fact, confirmed by the recent detection of a pair of colliding stellar corpses, kills a whole category of theories that mess with the laws of gravity to explain why the universe is expanding as fast as it is.

On October 16, physicists announced that the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, had detected gravitational waves from a neutron star merger (SN Online: 10/16/17). Also, the neutron stars emitted high-energy light shortly after merging. The Fermi space telescope spotted that light coming from the same region of the sky 1.7 seconds after the gravitational wave detection. That observation showed for the first time that gravitational waves, the shivers in spacetime set off when massive bodies move, travel at the speed of light to within a tenth of a trillionth of a percent.

Within a day, five papers were posted at arXiv.org mourning hundreds of expanding universe theories that predicted gravitational waves should travel faster than light — an impossibility without changes to Einstein’s laws of gravity. These theories “are very, very dead,” says the coauthor of one of the papers, cosmologist Miguel Zumalacárregui of the Nordic Institute for Theoretical Physics, or NORDITA, in Stockholm. “We need to go back to our blackboards and start thinking of other alternatives.”

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A cloud of debris ejected into space as two neutron stars merge. (Credit: NASA Goddard Space Flight Center/CI Lab)

By Nathaniel Scharping | October 16, 2017

The first gravitational wave observed from a neutron star merger offers the potential for a whole raft of new discoveries. Among them is a more precise measurement of the Hubble constant, which captures how fast our universe is expanding.

Ever since the Big Bang, everything in the universe has been spreading apart. It also turns out that this is happening faster and faster — the rate of expansion is increasing.

We’ve known this for a century, but astronomers haven’t been able to get precise measurements of the increase in rate, due mostly to the fact that they’ve had to cobble together a range of data to estimate how far away things in the universe are. Gravitational wave observations offer a direct means of measuring distances in the universe. The LIGO collaboration is constantly monitoring the universe for the subtle stretching of space-time that huge astronomical collisions can create, and measurements of the amplitude and frequency of the waves it catches hold valuable information for astronomers.

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Artist’s impression of two neutron stars – the compact remnants of what were once massive stars – spiralling towards each other just before merging.

The collision of these dense, compact objects produced gravitational waves – fluctuations in the fabric of spacetime – that were detected by the LIGO/Virgo collaboration on 17 August 2017. A couple of seconds after that, ESA's Integral and NASA’s Fermi satellites detected a burst of gamma rays, the luminous counterpart to the gravitational waves emitted by the cosmic clash.

This is the first discovery of gravitational waves and light coming from the same source.

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Zwei Neutronensterne verschmelzen und explodieren. Erstmals fingen Forscher ein solches Ereignis direkt ein. Und lösen Grundfragen der Astronomie. © ESO/L. Calçada/M. Kornmesser

Gerade den Nobelpreis eingesackt und nun das: Die Gravitationswellenjäger fangen das Echo einer Sternenexplosion ein und katapultieren die Astronomie in eine neue Ära.

Von Ulrich Schnabel  -- 16. Oktober 2017

Das Leben schreibt bekanntlich die besten Geschichten, und die Erforschung der Gravitationswellen gehört sicher zu den schönsten Storys der modernen Wissenschaft: Rund 100 Jahre lang blieben sie verborgen, wie Dornröschen hinter der Märchenhecke, und alle Nachweisversuche scheiterten. Dann wurden sie endlich entdeckt, verkündet fast auf den Tag genau 100 Jahre, nachdem Einstein sie postuliert hatte. Und seither geht es Schlag auf Schlag: Immer neue Gravitationswellenfunde wurden in den vergangenen Monaten vermeldet, gerade wurde ihr Nachweis mit dem Nobelpreis geehrt und nun das nächste große Ding: Weltweit jubeln Astronomen über einen ganz besonderen Fund, der gleich mehrere kosmische Rätsel auf einmal löst.

"Es kommt nur selten vor, dass ein Wissenschaftler Zeuge des Beginns einer neuen Ära werden kann", sagt die italienische Astronomin Elena Pian, eine der Entdeckerinnen. Doch der heute vorgestellte Fund sei genau ein solch historischer Moment. Ähnlich euphorisch klingen ihre Kollegen. "Wir befinden uns jetzt im Zeitalter der Multi-Messenger-Astronomie!" So triumphierend formuliert es der britische Astrophysiker Andrew Levan, Autor eines von insgesamt sieben (!) Fachartikeln, in denen die Entdeckung in den Zeitschriften Nature und Nature Astronomy ausgebreitet wird.

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By Ashley Strickland, CNN
Updated 2325 GMT (0725 HKT) October 16, 2017

(CNN)For the first time, two neutron stars in a nearby galaxy have been observed engaging in a spiral death dance around one another until they collided. What resulted from that collision is being called an "unprecedented" discovery that is ushering in a new era of astronomy, scientists announced Monday.

"We can now fill in a few more tiles in the jigsaw puzzle that is the story of our universe," said Laura Cadonati, deputy spokeswoman for the LIGO Scientific Collaboration and professor in the school of physics at Georgia Tech.
The collision created the first observed instance of a single source emitting ripples in space-time, known as gravitational waves, as well as light, which was released in the form of a two-second gamma ray burst. The collision also created heavy elements such as gold, platinum and lead, scattering them across the universe in a kilonova -- similar to a supernova -- after the initial fireball.

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An illustration of two neutron stars colliding. NASA

• For the first time, astronomers have detected a neutron-star collision.
• Gravitational waves heard by two detectors pinpointed the source to a galaxy 130 million light-years away.
• The collision produced a radioactive "kilonova" that forged hundreds of Earths' worth of platinum, gold, silver, and other atoms.
• The discovery solves a longstanding mystery about the origins of heavy elements.

Platinum and gold are among the most precious substances on Earth, each fetching roughly $1,000 an ounce.

However, their allure may grow stronger — and weirder — thanks to a groundbreaking new finding about their violent, radioactive, and cosmic origins.

On Monday, scientists who won a Nobel Prize for their discovery of gravitational waves, or ripples in the fabric of space, announced the first detection of the collision of two neutron stars.

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The fifth observation of gravitational waves (GW) marks the beginning of a new era in astronomy. On August 17, 2017, the LIGO and VIRGO collaborations detected neutron stars merging for the first time and immediately alerted observatories around the world. In a matter of hours the event had been located, another first for GW astronomy, and telescopes around the world begun studying it almost immediately.

The event observed, called GW170817, was produced in galaxy NGC 4993, located 130 million light-years from Earth. The gravitational signal was the strongest ever observed, lasting over 100 seconds, and it emitted a gamma-ray burst (GRBs), providing the first piece of evidence that GRBs are produced by neutron star collisions. It also provided the strongest evidence yet that neutron star mergers are responsible for the creation of the heaviest elements in the universe, like gold and platinum.

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For decades, researchers believed that violent supernovas forged gold and other heavy elements. But many now argue for a different cosmic quarry.

Across history and folklore, the question of where Earth’s gold came from — and maybe how to get more of it — has invited fantastical explanation. The Inca believed gold fell from the sky as either the tears or the sweat of the sun god Inti. Aristotle held that gold was hardened water, transformed when the sun’s rays penetrated deep underground. Isaac Newton transcribed a recipe for making it with a philosopher’s stone. Rumpelstiltskin, of course, could spin it from straw.

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 An artist’s rendering of the merger of two neutron stars from Aug. 17. Credit Robin Dienel/The Carnegie Institution for Science

Astronomers announced on Monday that they had seen and heard a pair of dead stars collide, giving them their first glimpse of the violent process by which most of the gold and silver in the universe was created.

The collision, known as a kilonova, rattled the galaxy in which it happened 130 million light-years from here in the southern constellation of Hydra, and sent fireworks across the universe. On Aug. 17, the event set off sensors in space and on Earth, as well as producing a loud chirp in antennas designed to study ripples in the cosmic fabric. It sent astronomers stampeding to their telescopes, in hopes of answering one of the long-sought mysteries of the universe.

LIGO Detects Fierce Collision of Neutron Stars for the First Time

By Nicolas Arnaud  -- October 11, 2017

*** MEDIA ADVISORY ***
Issued jointly by the LIGO Laboratory, LIGO Scientific Collaboration, National Science Foundation, and Virgo Collaboration

Scientists representing LIGO, Virgo, and some 70 observatories will reveal new details and discoveries made in the ongoing search for gravitational waves.

WHAT: Journalists are invited to join the National Science Foundation as it brings together scientists from the LIGO and Virgo collaborations, as well as representatives for some 70 observatories, on Monday, October 16, at 16:00 CEST at the National Press Club in Washington, D.C.

The gathering will begin with an overview of new findings from LIGO, Virgo, and partners that span the globe, followed by details from telescopes that work with the LIGO and Virgo Collaboration to study extreme events in the cosmos.

The first detection of gravitational waves, made on September 14, 2015 and announced on February 11, 2016, was a milestone in physics and astronomy; it confirmed a major prediction of Albert Einstein’s 1915 general theory of relativity, and marked the beginning of the new field of gravitational-wave astronomy. Since then, there have been three more confirmed detections, one of which (and the most recently announced) was the first confirmed detection seen jointly by both the LIGO and Virgo detectors.

The published articles announcing LIGO-Virgo’s first, second, and third confirmed detections have been cited more than 1,700 times (total), according to the Web of Science citation counts. A fourth paper on the three-detector observation was published on October 6; a manuscript was made publicly available on September 27.

WHEN: Monday, October 16, 2017  16:00 CEST

** Panels to begin at 16:00 and 17:15, with a 15-minute break in between. Event expected to conclude by 18:30.

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ESO will hold a press conference on 16 October 2017 at 16:00 CEST, at its Headquarters in Garching, Germany, to present groundbreaking observations of an astronomical phenomenon that has never been witnessed before.

The event will be introduced from ESO’s Paranal Observatory in Chile by the Director General, Xavier Barcons, and will feature talks by representatives of many research groups around Europe.

This invitation is addressed exclusively at media representatives. To participate in the conference, bona fide members of the media must register by completing an online form. Please indicate whether you wish to come in person to the press conference or if you will participate online only.

By registering for the conference, journalists agree to honour an embargo, details of which will be provided after registration, and not to publish or discuss any of the material presented before the start of the conference on 16 October 2017 at 16:00 CEST.

On site journalists will have a question and answer session with panelists during the conference. We will also take questions from journalists participating online. In-person individual interviews right after the conference are also possible.

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Are we about to make a breakthrough to go beyond black holes? Here’s what it means if we do!

If there’s one major difference between General Relativity and Newtonian gravity, it’s this: in Einstein’s theory, nothing lasts forever. Even if you had two perfectly stable masses in orbit around one another — masses that never burned out, lost material, or otherwise changed — their orbits would eventually decay. Whereas in Newtonian gravity, two masses would orbit their mutual center of gravity for an eternity, relativity tells us that a tiny amount of energy gets lost with every moment that one mass is accelerated by the gravitational field it passes through. That energy doesn’t disappear, but gets carried away in the form of gravitational waves. Over long enough time periods, enough energy is radiated away that those two orbiting masses will touch and merge together. Three times, now, LIGO has seen this happen for black holes. But it may be about to take the next step, and see neutron stars merge for the first time.

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Sept. 5, 2017

By following up on mysterious high-energy sources mapped out by NASA's Fermi Gamma-ray Space Telescope, the Netherlands-based Low Frequency Array (LOFAR) radio telescope has identified a pulsar spinning at more than 42,000 revolutions per minute, making it the second-fastest known.

A pulsar is the core of a massive star that exploded as a supernova. In this stellar remnant, also called a neutron star, the equivalent mass of half a million Earths is crushed into a magnetized, spinning ball no larger than Washington, D.C. The rotating magnetic field powers beams of radio waves, visible light, X-rays and gamma rays. If a beam happens to sweep across Earth, astronomers observe regular pulses of emission and classify the object as a pulsar.

"Roughly a third of the gamma-ray sources found by Fermi have not been detected at other wavelengths," said Elizabeth Ferrara, a member of the discovery team at NASA's Goddard Space Center in Greenbelt, Maryland. "Many of these unassociated sources may be pulsars, but we often need follow-up from radio observatories to detect the pulses and prove it. There's a real synergy across the extreme ends of the electromagnetic spectrum in hunting for them."

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A still from a computer simulation of merging neutron stars, which are thought to power short gamma-ray bursts. Rumors are swirling that gravitational-wave observatories as well as electromagnetic ground- and space-based telescopes have all spied such a merger in the distant galaxy NGC 4993. Credit: NASA/AEI/ZIB/M. Koppitz and L. Rezzolla

Astrophysicists may have detected gravitational waves last week from the collision of two neutron stars in a distant galaxy—and telescopes trained on the same region might also have spotted the event.

Rumours to that effect are spreading fast online, much to researchers’ excitement. Such a detection could mark a new era of astronomy: one in which phenomena are both seen by traditional telescopes and ‘heard’ as vibrations in the fabric of space-time. “It would be an incredible advance in our understanding,” says Stuart Shapiro, an astrophysicist at the University of Illinois at Urbana-Champaign.

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A fundamental challenge
Bill Saxton/NRAO/AUI/NSF

By Joshua Sokol

Imagine you’re an astronomer with bright ideas about the hidden laws of the cosmos. Like any good scientist, you craft an experiment to test your hypothesis.

Then comes bad news – there’s no way to carry it out, except maybe in a computer simulation. For cosmic objects are way too unwieldy for us to grow them in Petri dishes or smash them together as we do with subatomic particles.

Thankfully, though, there are rare places in space where nature has thrown together experiments of its own – like PSR J0337+1715. First observed in 2012 and announced in 2014, this triple system is 4200 light years away in the constellation Taurus.

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July 17, 2017

NASA’s new Neutron star Interior Composition Explorer (NICER) mission to study the densest observable objects in the universe has begun science operations.

Launched June 3 on an 18-month baseline mission, NICER will help scientists understand the nature of the densest stable form of matter located deep in the cores of neutron stars using X-ray measurements.

NICER operates around the clock on the International Space Station (ISS). In the two weeks following launch, NICER underwent extraction from the SpaceX Dragon spacecraft, robotic installation on ExPRESS Logistics Carrier 2 on board ISS and initial deployment. Commissioning efforts began June 14, as NICER deployed from its stowed launch configuration. All systems are functioning as expected.

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This image shows the configuration of NICER's 56 X-ray mirrors that will gather scientific observations and play an instrumental role in demonstration X-ray navigation. Credit: NASA

Nearly 50 years after British astrophysicist Jocelyn Bell discovered the existence of rapidly spinning neutron stars, NASA will launch the world's first mission devoted to studying these unusual objects.

The agency also will use the same platform to carry out the world's first demonstration of X-ray navigation in space.
The agency plans to launch the two-in-one Neutron Star Interior Composition Explorer, or NICER, aboard SpaceX CRS-11, a cargo resupply mission to the International Space Station to be launched aboard a Falcon 9 rocket.
About a week after its installation as an external attached payload, this one-of-a-kind investigation will begin observing neutron stars, the densest objects in the universe. The mission will focus especially on pulsars—those neutron stars that appear to wink on and off because their spin sweeps beams of radiation past us, like a cosmic lighthouse.

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May 26, 2017

A new NASA mission is headed for the International Space Station next month to observe one of the strangest observable objects in the universe.

Launching June 1, the Neutron Star Interior Composition Explorer (NICER) will be installed aboard the space station as the first mission dedicated to studying neutron stars, a type of collapsed star that is so dense scientists are unsure how matter behaves deep inside it.

A neutron star begins its life as a star between about seven and 20 times the mass of our sun. When this type of star runs out of fuel, it collapses under its own weight, crushing its core and triggering a supernova explosion. What remains is an ultra-dense sphere only about 12 miles (20 kilometers) across, the size of a city, but with up to twice the mass of our sun squeezed inside. On Earth, one teaspoon of neutron star matter would weigh a billion tons.

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The dishes of the Karl G. Jansky Very Large Array are seen making thefirst-ever precision localization of a Fast Radio Burst, and therebypointing the way to the host galaxy of FRB121102. Credit: Danielle Futselaar (artsource.nl)

One of the rare and brief bursts of cosmic radio waves that have puzzled astronomers since they were first detected nearly 10 years ago has finally been tied to a source: an older dwarf galaxy more than 3 billion light years from Earth.

Fast radio bursts, which flash for just a few milliseconds, created a stir among astronomers because they seemed to be coming from outside our galaxy, which means they would have to be very powerful to be seen from Earth, and because none of those first observed were ever seen again.

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Colour composite photo of the sky field around the lonely neutron star RX J1856.5-3754 in the constellation of Corona Australis and the related cone-shaped nebula. It is based on a series of exposures obtained with the multi-mode FORS2 instrument at VLT KUEYEN through three different optical filters. The trail of an asteroid is seen in the field with intermittent blue, green and red colours. RX J1856.5-3754 is exactly in the centre of the image. Image credit: ESO.

By studying the light emitted from an extraordinarily dense and strongly magnetised neutron star using ESO’s Very Large Telescope, astronomers may have found the first observational indications of a strange quantum effect, first predicted in the 1930s. The polarisation of the observed light suggests that the empty space around the neutron star is subject to a quantum effect known as vacuum birefringence.
A team led by Roberto Mignani from INAF Milan (Italy) and from the University of Zielona Gora (Poland), used ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile to observe the neutron star RX J1856.5-3754, about 400 light-years from Earth.

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Andromeda's pulsing neutron star. Credit: Andromeda: ESA/Herschel/PACS/SPIRE/J. Fritz, U. Gent/XMM-Newton/EPIC/W. Pietsch, MPE; data: P. Esposito et al. (2016)

Decades of searching in the Milky Way's nearby 'twin' galaxy Andromeda have finally paid off, with the discovery of an elusive breed of stellar corpse, a neutron star, by ESA's XMM-Newton space telescope.

Andromeda, or M31, is a popular target among astronomers. Under clear, dark skies it is even visible to the naked eye. Its proximity and similarity in structure to our own spiral galaxy, the Milky Way, make it an important natural laboratory for astronomers. It has been extensively studied for decades by telescopes covering the whole electromagnetic spectrum.
Despite being extremely well studied, one particular class of object had never been detected: spinning neutron stars.
Neutron stars are the small and extraordinarily dense remains of a once-massive star that exploded as a powerful supernova at the end of its natural life. They often spin very rapidly and can sweep regular pulses of radiation towards Earth, like a lighthouse beacon appearing to flash on and off as it rotates.

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Louie Psihoyos / Corbis

The Arecibo Observatory in Puerto Rico, which has spotted the first example of a repeating fast radio burst.

One paper suggests that fast radio bursts can repeat, but a finding on the origin of another burst is in doubt.

Mark Zastrow
02 March 2016

Three reports within a week have astronomers aflutter about the puzzling origins of short, bright pulses of radio waves called fast radio bursts (FRBs).

Last week, astronomers said that they had1 identified the origins of an FRB for the first time — pinpointing the signal to a distant galaxy. And a paper published today3 offers a different clue to the origins of FRBs, which have baffled astronomers since they were first observed nine years ago. It reports the discovery of a repeating signal: a surprise because all 17 known bursts so far have been one-off blips.

But sceptics have questioned the first work, recording telescope observations within days of the announcement that cast doubt on the finding2.

Origin story

On 24 February, astronomers announced that they had identified the origin of an FRB in a galaxy 1.9 billion parsecs (6 billion light years) away, probably produced by a collision between two neutron stars1. A network of telescopes had scanned the area of sky in which an FRB had been picked up by the Parkes radio telescope in New South Wales, Australia, and had discovered a fading afterglow of radio waves in an elliptical galaxy. The odds of finding such a radio signal by chance were just one or two in a thousand, wrote the team led by Evan Keane of the Square Kilometre Array Organisation, which is headquartered at the Jodrell Bank Observatory outside Manchester, UK.

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L. G. Spitler, P. Scholz, J. W. T. Hessels, S. Bogdanov, A. Brazier, F. Camilo, S. Chatterjee, J. M. Cordes, F. Crawford, J. Deneva, R. D. Ferdman, P. C. C. Freire, V. M. Kaspi, P. Lazarus, R. Lynch, E. C. Madsen, M. A. McLaughlin, C. Patel, S. M. Ransom, A. Seymour, I. H. Stairs, B. W. Stappers, J. van Leeuwen & W. W. Zhu

Nature (2016) doi:10.1038/nature17168

Fast radio bursts are millisecond-duration astronomical radio pulses of unknown physical origin that appear to come from extragalactic distances. Previous follow-up observations have failed to find additional bursts at the same dispersion measure (that is, the integrated column density of free electrons between source and telescope) and sky position as the original detections9. The apparent non-repeating nature of these bursts has led to the suggestion that they originate in cataclysmic events10. Here we report observations of ten additional bursts from the direction of the fast radio burst FRB 121102. These bursts have dispersion measures and sky positions consistent with the original burst4. This unambiguously identifies FRB 121102 as repeating and demonstrates that its source survives the energetic events that cause the bursts. Additionally, the bursts from FRB 121102 show a wide range of spectral shapes that appear to be predominantly intrinsic to the source and which vary on timescales of minutes or less. Although there may be multiple physical origins for the population of fast radio bursts, these repeat bursts with high dispersion measure and variable spectra specifically seen from the direction of FRB 121102 support an origin in a young, highly magnetized, extragalactic neutron star.

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The Australia Telescope Compact Array, in New South Wales, which helped to identify the location of a fast radio burst.

For the first time, astronomers have traced an enigmatic blast of radio waves to its source.

Mark Zastrow
24 February 2016 Corrected: 25 February 2016

Since 2007, astronomers have detected curious bright blasts of radio waves from the cosmos, each lasting no more than a few milliseconds. Now scientists have been able to pinpoint the source of one of these pulses: a galaxy 1.9 billion parsecs (6 billion light years) away. It probably came from two colliding neutron stars, says astronomer Evan Keane, a project scientist for the Square Kilometre Array (SKA). Keane, who works at the SKA Organization's headquarters at Jodrell Bank Observatory outside Manchester, UK, led the team that reports the detection in Nature1.

The discovery is the “measurement the field has been waiting for”, says astronomer Kiyoshi Masui of the University of British Columbia in Vancouver, Canada. By finding more such fast radio bursts (FRBs) and measuring the distance to their source, astronomers hope to use the signals as beacons to shed light on the evolution of the Universe.

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                     Jim West/Alamy
The Green Bank Telescope in West Virginia is the third facility to have detected a fast radio burst.

American telescope detects clue to source of fast radio bursts.

Elizabeth Gibney
02 December 2015

For the past eight years, astronomers have been mystified by sudden, very short blasts of radio waves that defy explanation.

Now the most detailed study so far1 has furnished a clue to the origin of at least one of these strange pulses, or 'fast radio bursts' (FRBs). It came from a dense, magnetized region of space, and was probably emitted by a young neutron star (a compact core left in the aftermath of a supernova), says study author Kiyoshi Masui at the University of British Columbia in Canada.

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Gamma ray picture of the Milky Way, as seen by the NASA Fermi satellite. Inserts: two independent statistical analyses showed that the distribution of photons is clumpy rather than smooth, indicating that the excess gamma rays from the center of our galaxy are unlikely to be caused by dark matter annihilation.
Image courtesy of Christoph Weniger, UvA , © UvA/Princeton

The excess of gamma rays from the center of the Milky Way probably originates from rapidly rotating neutron stars and not from dark matter annihilation as previously claimed.

he puzzling excess of gamma rays from the center of the Milky Way probably originates from rapidly rotating neutron stars, or millisecond pulsars, and not from dark matter annihilation, as previously claimed. This is the conclusion of new data analyses by two independent research teams from the University of Amsterdam (UvA), Netherlands, and Princeton University/Massachusetts Institute of Technology (MIT).

In 2009, observations with the Fermi Large Area Telescope revealed an excess of high-energy photons, or gamma rays, at the center of our galaxy. It was long speculated that this gamma ray excess could be a signal of dark matter annihilation. If true, it would constitute a breakthrough in fundamental physics and a major step forward in our understanding of the matter constituents of the universe.

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Artist's concept of a millisecond pulsar. Credit: NASA

January 26, 2016 by Tomasz Nowakowski

(Phys.org)—NASA's Fermi Gamma-ray Space Telescope has once again proven that it is an excellent tool to search for rotating neutron stars emitting beams of electromagnetic radiation, known as pulsars. A team of astronomers, led by H. Thankful Cromartie of the University of Virginia, has recently used the 305-meter Arecibo radio telescope in Puerto Rico to observe unidentified sources of gamma rays detected by the Large Area Telescope (LAT) onboard the Fermi spacecraft. As it turns out, six of these objects indicated by LAT are rapidly rotating neutron stars, with periods of a few thousandths of a second, called millisecond pulsars (MSPs). The scientists published their results online on Jan. 20 on the arXiv pre-print server.

The objects of the study were chosen from the LAT's 4-year point source catalog. The astronomers chose 34 from over 1,000 unidentified sources of gamma rays to observe them in detail with the Arecibo telescope. The catalog provided crucial spectral data that helped distinguish possible MSPs from other gamma-ray-emitting objects, like active galactic nuclei (AGNs).

"Overall, the search for MSPs in the galactic disk has been made extremely efficient by employing Fermi-LAT data in selecting radio search targets," the researchers noted in their paper posted on arXiv.

Arecibo observations were conducted from June to September 2013. The telescope's raw sensitivity and its large gain makes it a very efficient tool for finding millisecond pulsars. Thanks to Arecibo, the researchers were able to detect six MSPs with rotation periods ranging between 1.99 and 4.66 ms. One of the newly detected pulsars is a typical neutron star, a white dwarf binary with an 83-day orbital period. According to the research, the other MSPs are in interacting compact binaries wit orbital period less than eight hours.

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An image of the Vela pulsar (which lies at the heart of the Vela supernova remnant) in which glitching has been observed. The pulsar itself is the bright white spot at the centre of the hot gas, and a jet powered by its rotational pole is also observed in this Chandra X-ray Observatory image. (Courtesy: NASA/CXC/PSU/G Pavlov et al.)

Pulsars are known to be the most precise cosmic timekeepers, but occasional "glitches" or a sudden increase in their spin rate disrupts the stars' otherwise regular behaviour. A new study of the glitching process by an international team of researchers suggests that superfluid matter in the core of a pulsar may cause the poorly understood effect. The work combines radio and X-ray data to determine pulsar masses, and successfully explains glitches that are documented in 45 years' worth of observational data.

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Fermi-LAT sky map with the celestial neighborhood of the newly discovered pulsar PSR J1906+0722. The color scale shows the gamma-ray intensity. [Knispel/AEI/NASA/DOE/Fermi LAT Collaboration]

Since the release of the second Fermi-LAT catalog in 2012, astronomers have been hunting for 3FGL J1906.6+0720, a gamma-ray source whose association couldn’t be identified. Now, personal-computer time volunteered through the Einstein@Home project has resulted in the discovery of a pulsar that has been hiding from observers for years.

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• A clump of material has been jettisoned from a double star system at incredibly high speeds.
• X-rays from Chandra reveal that a pulsar in orbit around a massive star punched through a circumstellar disk of material.
• Three Chandra observations of the system were taken between December 2011 and February 2014.
• The data suggest the clump may even be accelerating due to the pulsar's powerful winds.

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Some long-duration gamma-ray bursts are driven by magnetars
8 July 2015

Observations from ESO’s La Silla and Paranal Observatories in Chile have for the first time demonstrated a link between a very long-lasting burst of gamma rays and an unusually bright supernova explosion. The results show that the supernova was not driven by radioactive decay, as expected, but was instead powered by the decaying super-strong magnetic fields around an exotic object called a magnetar. The results will appear in the journal Nature on 9 July 2015.

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Artist's impression of a pulsar, including the extreme magnetic field surrounding the dense stellar object. Credit: NASA

For the first time, the mass of a binary pulsar pair has been precisely measured, but it was a race against time before the extreme gravitational warping of spacetime caused one of the dense objects to blip out of view.

Pulsars are rapidly-spinning neutron stars that generate powerful beams of radiation from their poles. Neutron stars are the stellar husks of long-dead stars that ran out of hydrogen fuel and collapsed under gravity to create a mass of degenerate matter.

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An artist's impression of a neutron star. The cosmic object's 'nuclear pasta' would be located between the crust and the outer core of the neutron star. Credit: NASA/Dana Berry

The crusts of neutron stars — cosmic cousins of black holes — possess a weird form of matter known as "nuclear pasta."

Now, scientists have found that nuclear pasta may be even stranger than previously thought, forming defects that bond pieces together into complex, disorderly shapes. This complex nuclear pasta could ultimately doom the powerful magnetic fields seen from neutron stars, researchers say.

A neutron star, like a black hole, is a remnant of a star that died in a catastrophic explosion known as a supernova. Neutron stars are typically small, with diameters of about 12 miles (19 kilometers) or so, but they are so dense that a neutron star's massmay be about the same as that of the sun. A chunk of a neutron star the size of a sugar cube can weigh as much as 100 million tons, making neutron stars the densest objects in the universe besides black holes.

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