TAT Blog interesting astrophysics stories

What Sonic Black Holes Say About the Real Deal

 

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Can a fluid analogue of a black hole point physicists toward the theory of quantum gravity, or is it a red herring?

NATALIE WOLCHOVER  --  SCIENCE

IN A 1972 lecture at the University of Oxford, a young physicist named William Unruh asked the audience to imagine a fish screaming as it plunges over a waterfall. The water falls so fast in this fictitious cascade that it exceeds the speed of sound at a certain point along the way. After the fish tumbles past this point, the water sweeps its screams downward faster than the sound waves can travel up, and the fish can no longer be heard by its friends in the river above.

Something similar happens, Unruh explained, when you fall into a black hole. As you approach one of these super-dense objects, the fabric of space and time becomes increasingly curved—equivalent to strengthening gravity, according to Albert Einstein’s general theory of relativity. At a point of no return known as the “event horizon,” the space-time curvature becomes so steep that signals can no longer climb to the outside world. Within the event horizon, even light is held captive by the black hole’s gravity, rendering black holes invisible.

 

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Here’s what the next 10 years of space science could look like

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In the new decadal survey, researchers recommend building a planet-hunting space telescope that takes inspiration from a previously proposed mission called HabEx (illustrated). IMAGE COURTESY OF SCOTT GAUDI

By Maria Temming
4 HOURS AGO

The Astronomy and Astrophysics Decadal Survey is basically a sneak preview of the next 10 years of U.S. space science. Every decade, experts assembled by the National Academies of Sciences, Engineering and Medicine collect input from astronomers nationwide to recommend a prioritized list of projects to policy makers and federal agencies. Past to-do lists have been topped by specific big-ticket items, such as the James Webb Space Telescope and the Nancy Grace Roman Space Telescope (SN: 10/6/21; SN: 8/13/10). But this year, astronomers are shaking things up.

The latest decadal survey, which charts the course for U.S. astronomy and astrophysics from 2022 to 2032, recommends that NASA create a new program to develop several major space telescopes at a time. Investing early in multiple mission concepts could curb the risk of individual missions becoming too unwieldy and expensive, according to the report released November 4.

 

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A rush to watch a supernova exposed its last gasp before exploding

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Scientists spotted an exploding star in one of a pair of galaxies known as the Butterfly galaxies (shown). Observations of that supernova (bright spot in the zoomed-in view) in the hours and days after it went off showed details of the star’s life just before death. NASA, ESA, RYAN FOLEY/UCSC, JOSEPH DEPASQUALE/STSCI

 

By Emily Conover
NOVEMBER 2, 2021 

A mad scramble to observe the moments after a star’s death is helping scientists understand how the star lived out its last year.

Astronomers reported the exploding star just 18 hours after it flared up on March 31, 2020, in a galaxy about 60 million light-years away from Earth in the Virgo cluster. The supernova occurred in part of the sky already watched by NASA’s Transiting Exoplanet Survey Satellite, which images large portions of the sky every 30 minutes (SN: 1/8/19). And a team of scientists quickly realized that data would track precisely how the eruption brightened over time, making it ideal for further study.

To learn even more, the team leapt into action, viewing the supernova with a variety of telescopes in the hours and days that followed, even orchestrating a last-minute change of plans for the Hubble Space Telescope. That provided the supernova’s spectrum, an accounting of its light broken up by wavelength, at various moments after the blast.

All that data revealed that in the last year of its life, the star had spewed some of its outer layers into space, researchers report October 26 in Monthly Notices of the Royal Astronomical Society. The amount of material ejected was about 0.23 times the mass of the sun, the team estimates. When the supernova went off, it launched a shock wave that plowed through that material shortly after the explosion, generating light picked up by the telescopes.

 

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When a nearby star goes supernova, scientists will be ready

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STELLAR SWOON A simulation of a supernova tracks the turmoil in the center of a dying star in the moments after its core collapses. The collapse creates a shock wave (blue line) that travels outward, blasting the star apart. Red colors represent material hurtling outward, blues represent inward motion. The surfaces of the lumpy shapes have equal entropy, which is related to temperature. T. MELSON, H.-T. JANKA AND A. MAREK/ASTROPHYS. J. LETT. 2015

By Emily Conover
FEBRUARY 8, 2017

 

Almost every night that the constellation Orion is visible, physicist Mark Vagins steps outside to peer at a reddish star at the right shoulder of the mythical figure. “You can see the color of Betelgeuse with the naked eye. It’s very striking, this red, red star,” he says. “It may not be in my lifetime, but one of these days, that star is going to explode.”

With a radius about 900 times that of the sun, Betelgeuse is a monstrous star that is nearing its end. Eventually, it will no longer be able to support its own weight, and its core will collapse. A shock wave from that collapse will speed outward, violently expelling the star’s outer layers in a massive explosion known as a supernova. When Betelgeuse detonates, its cosmic kaboom will create a light show brighter than the full moon, visible even during the daytime. It could happen tomorrow, or a million years from now.

 

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Neutron star collisions probably make more gold than other cosmic smashups

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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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Gravitational waves reveal the first known mergers of a black hole and neutron star

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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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An atomic clock measured how general relativity warps time across a millimeter

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Clocks at different heights tick at different rates. An atomic clock has now revealed this key feature of the general theory of relativity on a scale of a millimeter. HIROSHI WATANABE/GETTY IMAGES PLUS

By Emily Conover -- OCTOBER 18, 2021

The record-breaking result reveals the incredible precision achievable by atomic clocks

A millimeter might not seem like much. But even a distance that small can alter the flow of time.

According to Einstein’s theory of gravity, general relativity, clocks tick faster the farther they are from Earth or another massive object (SN: 10/4/15). Theoretically, that should hold true even for very small differences in the heights of clocks. Now an incredibly sensitive atomic clock has spotted that speedup across a millimeter-sized sample of atoms, revealing the effect over a smaller height difference than ever before. Time moved slightly faster at the top of that sample than at the bottom, researchers report September 24 at arXiv.org.

“This is fantastic,” says theoretical physicist Marianna Safronova of the University of Delaware in Newark, who was not involved with the research. “I thought it would take much longer to get to this point.” The extreme precision of the atomic clock’s measurement suggests the potential to use the sensitive timepieces to test other fundamental concepts in physics.

An inherent property of atoms allows scientists to use them as timepieces. Atoms exist at different energy levels, and a specific frequency of light makes them jump from one level to another. That frequency — the rate of wiggling of the light’s waves — serves the same purpose as a clock’s regularly ticking second hand. For atoms farther from the ground, time runs faster, so a greater frequency of light will be needed to make the energy jump. Previously, scientists have measured this frequency shift, known as gravitational redshift, across a height difference of 33 centimeters (SN: 9/23/10).

 

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Growing Anomalies at the Large Hadron Collider Raise Hopes

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Computer reconstruction of a collision event in the Large Hadron Collider beauty experiment. The collision produces a B meson, which subsequently decays into other particles that strike LHCb’s detectors.  CERN/LHCb

Charlie Wood -- May 26, 2020

 

Amid the chaotic chains of events that ensue when protons smash together at the Large Hadron Collider in Europe, one particle has popped up that appears to go to pieces in a peculiar way.

All eyes are on the B meson, a yoked pair of quark particles. Having caught whiffs of unexpected B meson behavior before, researchers with the Large Hadron Collider beauty experiment (LHCb) have spent years documenting rare collision events featuring the particles, in hopes of conclusively proving that some novel fundamental particle or effect is meddling with them.

In their latest analysis, first presented at a seminar in March, the LHCb physicists found that several measurements involving the decay of B mesons conflict slightly with the predictions of the Standard Model of particle physics — the reigning set of equations describing the subatomic world. Taken alone, each oddity looks like a statistical fluctuation, and they may all evaporate with additional data, as has happened before. But their collective drift suggests that the aberrations may be breadcrumbs leading beyond the Standard Model to a more complete theory.

“For the first time in certainly my working life, there are a confluence of different decays that are showing anomalies that match up,” said Mitesh Patel, a particle physicist at Imperial College London who is part of LHCb.

 

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A Hint of Dark Matter Sends Physicists Looking to the Skies

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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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Event Horizon Telescope (EHT) tests of the strong-field regime of General Relativity

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Credit: EHT Collaboration, [CC BY 4.0]

Written by Sebastian H. Völkel and Nicola Franchini

The name “black hole” describes the incredible phenomena that light cannot escape away from it. Here, the gravitational pull is beyond any measure, meaning that there is no emission at all. The boundary of this region is called the event horizon. On the other hand, the light that only approaches but never passes the event horizon is strongly deflected and eventually follows highly bent orbits around the black hole, until some of it can be observed on Earth.

Albert Einstein’s general theory of relativity predicts the existence of black holes. The mass of these objects can span from tens to millions or even billions of times the mass of the Sun. The latter is referred to by astrophysicists as supermassive black holes. These monsters have a lot of astrophysical relevance since they dwell in the centers of most galaxies, including the Milky Way.

According to scientists, black holes are surrounded by very hot gas in the shape of disks that are constantly rotating around the black hole. While some gas spirals inwards from far-out regions of the disk, other gas of the inner region falls into the black hole. These mechanisms produce light, which either fall in the black hole or escape from the system. The closest thing to a picture of a black hole (which itself does not emit light) is a detailed measurement of the shining gas being swallowed by it. Ongoing developments in radio astronomy, computer simulations, and data analysis techniques make it possible to take images of supermassive black holes, as demonstrated by the Event Horizon Telescope Collaboration in the last few years.

 

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When James Webb launches, it will have a bigger to-do list than 1980s researchers suspected

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Engineers work on the James Webb Space Telescope’s primary mirror. The 18 hexagonal mirror segments are made of lightweight yet tough beryllium and coated with a thin layer of gold to boost reflectivity. DESIREE STOVER/NASA

Lisa Grossman
OCTOBER 6, 2021

Delays for the space telescope mean there’ll be more cool science to do

The James Webb Space Telescope has been a long time coming. When it launches later this year, the observatory will be the largest and most complex telescope ever sent into orbit. Scientists have been drafting and redrafting their dreams and plans for this unique tool since 1989.

The mission was originally scheduled to launch between 2007 and 2011, but a series of budget and technical issues pushed its start date back more than a decade. Remarkably, the core design of the telescope hasn’t changed much. But the science that it can dig into has. In the years of waiting for Webb to be ready, big scientific questions have emerged. When Webb was an early glimmer in astronomers’ eyes, cosmological revolutions like the discoveries of dark energy and planets orbiting stars outside our solar system hadn’t yet happened.

“It’s been over 25 years,” says cosmologist Wendy Freedman of the University of Chicago. “But I think it was really worth the wait.”

An audacious plan
Webb has a distinctive design. Most space telescopes house a single lens or mirror within a tube that blocks sunlight from swamping the dim lights of the cosmos. But Webb’s massive 6.5-meter-wide mirror and its scientific instruments are exposed to the vacuum of space. A multilayered shield the size of a tennis court will block light from the sun, Earth and moon.

For the awkward shape to fit on a rocket, Webb will launch folded up, then unfurl itself in space (see below, What could go wrong?).

 

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Breathtaking 'Einstein Ring' Reveals Views of a Galaxy 9.4 Billion Light-Years Away

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The Molten Ring. (Saurabh Jha/Rutgers, The State University of New Jersey)

MICHELLE STARR

24 SEPTEMBER 2021


One of the most spectacular Einstein rings ever seen in space is enabling us to see what's happening in a galaxy almost at the dawn of time.

The smears of light called the Molten Ring, stretched out and warped by gravitational fields, are magnifications and duplications of a galaxy whose light has traveled a whopping 9.4 billion light-years. This magnification has given us a rare insight into the stellar 'baby boom' when the Universe was still in its infancy.

The early evolution of the Universe is a difficult time to understand. It blinked into existence as we understand it roughly 13.8 billion years ago, with the first light emerging (we think) around 1 billion years later. Light traveling for that amount of time is faint, the sources of it small, and dust obscures much of it.

Even the most intrinsically luminous objects are extraordinarily hard to see across that gulf of space-time, so there are large gaps in our understanding of how the Universe assembled itself from primordial soup.

 

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Hunting Season for Primordial Gravitational Waves

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October 30, 2020• Physics 13, 164


The BICEP Array radio telescope, which searches for signatures of gravitational waves in the early Universe, has started an observing run that will break new ground in detection sensitivity.

In 2020, the raging pandemic halted many scientific endeavors around the globe. But after the last flights of the season left the Amundsen-Scott South Pole Station in February, the complex remained “frozen” in a pre-COVID era. There, a few dozen researchers can still mingle without face masks while managing physics, astronomy, and geoscience experiments that run during the six-month-long winter night. The latest experiment to kick off at the South Pole is the BICEP Array telescope, an instrument designed to probe the faint microwave light coming from the infant Universe. After a team assembled the new telescope in the brief austral summer, a lone engineer stayed to tend to the instrument (see Q&A: Searching for Light in the Darkness of Winter).

Focusing on a small patch of the South Pole’s dark winter sky, the BICEP Array will characterize with unprecedented accuracy the polarization of the cosmic microwave background (CMB). From these measurements, cosmologists hope to learn about inflation, the Universe’s extremely rapid expansion that occurred in the first 10−32
seconds after the big bang, before a more leisurely expansion began. They will examine subtle polarization patterns, called B modes, that theorists predict were produced by gravitational waves that arose during the inflation epoch.

 

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Squeezing down the Theory Space for Cosmic Inflation

 

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Daniel Meerburg  October 4, 2021• Physics 14, 135

An updated search for primordial gravitational waves has not found a signal, which implies that some popular early Universe models are becoming less viable.

Remarkably, the large-scale Universe can be adequately described by a model involving only a handful of parameters. This lambda cold dark matter (LCDM) model postulates that the expansion of the Universe is driven by the presence of two dark components—dark energy and dark matter—and that the galactic structure we observe today was sourced by small density variations in the very early Universe. However, cosmologists expect that these primordial density fluctuations were accompanied by fluctuations in the fabric of spacetime itself. These gravitational waves could be observed through a predicted signal in the cosmic microwave background (CMB). The BICEP/Keck Collaboration, which has been a frontrunner in the search for this illustrious signal, reports on its latest data set, finding no evidence of gravitational waves [1]. The resulting limits push up against model predictions, which suggests that we are either quickly closing in on a detection or that we may soon witness a paradigm shift. In addition, the analysis shows that researchers properly understand the astrophysical contaminants that obscure the search for this relic signature. By reducing uncertainties about this contamination, we should have greater confidence in any future claims of a detection.

 

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Extending LIGO's Reach Into the Cosmos

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New mirror coatings will increase the volume of space LIGO can probe in its next run

 

Since LIGO's groundbreaking detection, in 2015, of gravitational waves produced by a pair of colliding black holes, the observatory, together with its European partner facility Virgo, has detected dozens of similar cosmic rumblings that send ripples through space and time.

In the future, as more and more upgrades are made to the National Science Foundation-funded LIGO observatories—one in Hanford, Washington, and the other in Livingston, Louisiana—the facilities are expected to detect increasingly large numbers of these extreme cosmic events. These observations will help solve fundamental mysteries about our universe, such as how black holes form and how the ingredients of our universe are manufactured.

One important factor in increasing the sensitivity of the observatories involves the coatings on the glass mirrors that lie at the heart of the instruments. Each 40-kilogram (88-pound) mirror (there are four in each detector at the two LIGO observatories) is coated with reflective materials that essentially turn the glass into mirrors. The mirrors reflect laser beams that are sensitive to passing gravitational waves.

Generally, the more reflective the mirrors the more sensitive the instrument, but there is a catch: The coatings that make the mirrors reflective also can lead to background noise in the instrument—noise that masks gravitational-wave signals of interest.

 

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