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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Science and Nature  7.2.2021

You don’t have to know a whole lot about science to know that black holes normally suck things in, not spew things out. But NASA detected something mighty bizarre at the supermassive black hole Markarian 335. Two of NASA’s space telescopes, including the Nuclear Spectroscopic Telescope Array (NuSTAR), amazingly observed a black hole’s corona “launched” away from the supermassive black hole.

Then an enormous pulse of X-ray energy spewed out. This kind of phenomena has never been observed before.
“This is the first time we have been able to link the launching of the corona to a flare. This will help us comprehend how supermassive black holes power some of the brightest objects in the cosmos.” Dan Wilkins, of Saint Mary’s University, said. This is one of the most important discoveries so far.

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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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The Andromeda nebula, photographed at the Yerkes Observatory around 1900. To modern eyes, this object is clearly a galaxy. At the time, though, it was described as "a mass of glowing gas," its true identity unknown. (From the book Astronomy of To-Day, 1909)

Thanks to Edwin Hubble, we now can better comprehend the true scale of the universe.

By Corey S. Powell  January 2, 2017 

What’s in a date? Strictly speaking, New Year’s Day is just an arbitrary flip of the calendar, but it can also be a cathartic time of reflection and renewal. So it is with one of the most extraordinary dates in the history of science, January 1, 1925. You could describe it as a day when nothing remarkable happened, just the routine reading of a paper at a scientific conference. Or you could recognize it as the birthday of modern cosmology–the moment when humankind discovered the universe as it truly is.

Until then, astronomers had a myopic and blinkered view of reality. As happens so often to even the most brilliant minds, they could see great things but they could not comprehend what they were looking at. The crucial piece of evidence was staring them right in the face. All across the sky, observers had documented intriguing spiral nebulae, swirls of light that resembled ghostly pinwheels in space. The most famous one, the Andromeda nebula, was so prominent that it was easily visible to the naked eye on a dark night. The significance of those ubiquitous objects was a mystery, however.

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MICHELLE STARR 18 DECEMBER 2020

The Universe is full of galaxy clusters, but Abell 2261 is in a class of its own. In the galaxy in the centre of the cluster, where there should be one of the biggest supermassive black holes in the Universe, astronomers have been able to find no trace of such an object.

And a new search has only made the absence more puzzling: if the supermassive black hole got yeeted out into space, it should have left evidence of its passage. But there's no sign of it in the material surrounding the galactic centre, either.

But this means that constraints can be placed on what the supermassive black hole - if it is there, evading detection - is doing.

Galaxy clusters are the largest known gravitationally bound structures in the Universe. Typically, they're groups of hundreds to thousands of galaxies that are bound together, with one huge, abnormally bright galaxy at or close the centre, known as the brightest cluster galaxy (BCG).

But even among BCGs, Abell 2261's BCG (named, in fact, A2261-BCG, and located about 2.7 billion light-years away) stands out. It's about a million light-years across - up to to 10 times the size of the Milky Way galaxy - and it has a huge, puffy core 10,000 light-years across, the largest galactic core ever seen.

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Samuel Velasco/Quanta Magazine

The Gaia telescope gauges the distances to stars by measuring their parallax, or apparent shift over the course of a year. Closer stars have a larger parallax.

Natalie Wolchover - December 17, 2020

On December 3, humanity suddenly had information at its fingertips that people have wanted for, well, forever: the precise distances to the stars.

“You type in the name of a star or its position, and in less than a second you will have the answer,” Barry Madore, a cosmologist at the University of Chicago and Carnegie Observatories, said on a Zoom call last week. “I mean …” He trailed off.

“We’re drinking from a firehose right now,” said Wendy Freedman, also a cosmologist at Chicago and Carnegie and Madore’s wife and collaborator.

“I can’t overstate how excited I am,” Adam Riess of Johns Hopkins University, who won the 2011 Nobel Prize in Physics for co-discovering dark energy, said in a phone call. “Can I show you visually what I’m so excited about?” We switched to Zoom so he could screen-share pretty plots of the new star data.

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See also a recent article on the debate about the Hubble constant

NASA image

By Ashley Strickland, CNN | Posted - Dec. 7, 2020

The two largest planets in our solar system are coming closer together than they have been since the Middle Ages, and it's happening just in time for Christmas.

So, there are some things to look forward to in the final month of 2020.

On the night of Dec. 21, the winter solstice, Jupiter and Saturn will appear so closely aligned in our sky that they will look like a double planet. This close approach is called a conjunction.

"Alignments between these two planets are rather rare, occurring once every 20 years or so, but this conjunction is exceptionally rare because of how close the planets will appear to one another," said Rice University astronomer and professor of physics and astronomy Patrick Hartigan in a statement.

"You'd have to go all the way back to just before dawn on March 4, 1226, to see a closer alignment between these objects visible in the night sky."

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See also a beautiful webpage from University of Exeter

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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The canonical Einstein Cross, the quadruply lensed quasar Q2237+030, is seen in this Hubble image. A new study has found two additional Einstein Crosses created by the lensing of compact galaxies. [NASA, ESA, and STScI]

By Susanna Kohler on 9 December 2020

Seeing quadruple? In a rare phenomenon, some distant objects can appear as four copies arranged in an “Einstein cross”. A new study has found two more of these unusual sights — with an unexpected twist.

Searching for Rare Crosses

Gravitational lensing — the bending of light by the gravity of massive astronomical objects — can do some pretty strange things. One of lensing’s more striking creations is the Einstein cross, a configuration of four images of a distant, compact source created by the gravitational pull of a foreground object (which is usually visible in the center of the four images).

 The canonical example of this phenomenon is the Einstein Cross, a gravitationally lensed object called QSO 2237+0305, seen in the cover image above. In this case, as with the majority of known Einstein crosses, the background source is a distant quasar — the small and incredibly bright nucleus of an active galaxy. But other sources can be lensed into Einstein crosses as well, under the right circumstances.

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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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This illustration generated by a computer model shows multiple black holes found within the heart of a dense globular star cluster. Credit: Aaron M. Geller, Northwestern University/CIERA

New analysis of gravitational-wave data leads to wealth of discoveries.

An international research collaboration including Northwestern University astronomers has produced the most detailed family portrait of black holes to date, offering new clues as to how black holes form. An intense analysis of the most recent gravitational-wave data available led to the rich portrait as well as multiple tests of Einstein’s theory of general relativity. (The theory passed each test.)

The team of scientists who make up the LIGO Scientific Collaboration (LSC) and the Virgo Collaboration is now sharing the full details of its discoveries. This includes new gravitational-wave detection candidates which held up to scrutiny — a whopping total of 39, representing a variety of black holes and neutron stars — and new discoveries as a result of combining all the observations. The 39 events averaged more than one per week of observing.

The observations could be a key piece in solving the many mysteries of exactly how binary stars interact. A better understanding of how binary stars evolve has consequences across astronomy, from exoplanets to galaxy formation.

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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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This year's Nobel Prize in Physics was awarded to Roger Penrose, Reinhard Genzel and Andrea Ghez.

By Emma Reynolds and Katie Hunt, CNN, October 6, 2020

(CNN)The 2020 Nobel Prize in Physics has been awarded to scientists Roger Penrose, Reinhard Genzel and Andrea Ghez for their discoveries about black holes.

Göran K. Hansson, secretary for the Royal Swedish Academy of Sciences, said at Tuesday's ceremony in Stockholm that this year's prize was about "the darkest secrets of universe."

Penrose, a professor at the University of Oxford who worked with Stephen Hawking, was awarded half of the prize "for the discovery that black hole formation is a robust prediction of the general theory of relativity." The other half was awarded jointly to Genzel and Ghez "for the discovery of a supermassive compact object at the center of our galaxy."

"Penrose, Genzel and Ghez together showed us that black holes are awe-inspiring, mathematically sublime, and actually exist," Tom McLeish, professor of natural philosophy at the University of York, told the Science Media Centre in London.

Ghez, born in New York City and a professor at the University of California, Los Angeles, is only the fourth woman to win a Nobel physics prize. It was awarded to a woman for the first time in 55 years in 2018, when Donna Strickland won for groundbreaking inventions in the field of laser physics.

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From the Royal Swedish Academy of Sciences

1  Original announcement

2  Scientific Background

3  Popular Science  Background

A view of the center of the Milky Way galaxy. Theories of modified gravity have had a hard time describing the universe from relatively small scales like this all the way up to the scale of the universe as a whole. NASA/JPL-Caltech/ESA/CXC/STScI

Modified gravity theories have never been able to describe the universe’s first light. A new formulation does.

Charlie Wood July 28, 2020

For decades, a band of rebel theorists has waged war with one of cosmology’s core concepts — the idea that an invisible, intangible form of matter forms the universe’s primary structure. This dark matter, which seems to outweigh the stuff we’re made of 5-to-1, accounts for a host of observations: the tight cohesion of galaxies and packs of galaxies, the way light from faraway galaxies will bend on its way to terrestrial telescopes, and the mottled structure of the early universe, to name a few.

The would-be revolutionaries seek an alternative cosmic recipe. In place of dark matter, they substitute a subtly modified force of gravity. But attempts to translate their rough idea into precise mathematical language have always run afoul of at least one key observation. Some formulations get galaxies right, some get the contortion of light rays right, but none have pierced dark matter’s most bulletproof piece of evidence: precise maps of ancient light, known as the cosmic microwave background (CMB). “A theory must do really well to agree with this data,” said Ruth Durrer, a cosmologist at the University of Geneva. “This is the bottleneck.”

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Snapshots of the appearance of M87 *, obtained with images and geometrical models and the EHT array between 2009 and 2017. The diameter of the rings is the same, but the location of the bright side varies. - (Image Credit: M. Wielgus, D. Pesce & the EHT Collaboration)

September 23, 2020

The Event Horizon Telescope is an array of telescopes that uses a technique called Very Long Baseline Interferometry (VLBI) to form a virtual radio telescope with a dish diameter similar to the size of Earth.

In the period between 2009-2013, M87* (the supermassive black hole in the galaxy M87) was observed with prototype EHT telescopes, at four different sites. Eventually, the entire EHT array came into operation in 2017, with seven telescopes located in five locations around the Earth.

Although the observations from 2009-2013 contained much less data than those from 2017 (lacking the capacity to provide a picture of the black hole at that point in time), the EHT team was able to identify changes in the appearance of M87* between 2009 and 2017 using statistical models.

The researchers concluded that the diameter of the black hole's shadow remains consistent with the predictions of Einstein's general theory of relativity for black holes of 6.5 billion solar masses. But they also found something unexpected: the crescent-shaped ring of hot plasma around M87* wobbles! It is the first time astronomers have glimpsed the dynamic accretion structure so close to the event horizon of a black hole, where gravity is extreme.

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Link to the publication 

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