Gravitational-wave sleuths look for more cosmic crashes

After three years of upgrading and waiting, due in part to the coronavirus pandemic, the Laser Interferometer Gravitational-wave Observatory has officially resumed its hunt for the signatures of crashing black holes and neutron stars.

“Our LIGO teams have worked through hardship during the past two-plus years to be ready for this moment, and we are indeed ready,” Caltech physicist Albert Lazzarini, the deputy director of the LIGO Laboratory, said in a news release.

Lazzarini said the engineering tests leading up to today’s official start of Observing Run 4, or O4, have already revealed a number of candidate events that have been shared with the astronomical community.

“Most of these involve black hole binary systems, although one may include a neutron star,” he said. “The rates appear to be consistent with expectations.”

One such event, called S230518h, was detected last week. Researchers say that if they can confirm the data, the event was most likely caused by the merger of a faraway black hole and a neutron star.

The twin LIGO gravitational-wave detectors at Hanford, Wash., and Livingston, La., will be joined for O4 by the Virgo detector in Italy as well as the KAGRA observatory in Japan. Virgo is scheduled to take part in the run starting later this year. KAGRA will parallel LIGO’s observations for the next month, take a break for some upgrades, and then rejoin the run.


Student wins top prize for gravitational wave work

Christine Ye, a senior at Eastlake High School in Sammamish, Wash., has won the top award in the nation’s oldest and most prestigious competitions for science students, thanks to her research into the mysteries of black holes and neutron stars.

“I’m totally in shock,” the 17-year-old told me after winning the $250,000 first-place award in the 2022 Regeneron Science Talent Search. “It feels amazing.”

Ye was among 40 finalists honored on March 15 in Washington, D.C., during a live-streamed ceremony that was emceed by “Saturday Night Live” cast member Melissa Villaseñor. More than $1.8 million in all was awarded to the finalists, who were evaluated on the basis of their projects’ scientific rigor and their potential to become scientific leaders.

Ye’s award-winning research is based on an analysis of readings from the Laser Interferometer Gravitational-wave Observatory, and addresses one of LIGO’s most puzzling observations.

In 2019, researchers at LIGO and at Europe’s Virgo gravitational-wave observatory detected ripples in spacetime that were caused by the collision of a black hole and a mystery object that was 2.6 times as massive as our sun. The object’s size fell into a “mass gap” between the heaviest known neutron star and the lightest known black hole.

The analysis conducted by Ye and her co-author, Northwestern University postdoctoral fellow Maya Fishbach, determined that rapidly spinning neutron stars could get as massive as the mystery object. Their study will be the subject of a presentation next month in New York at a meeting of the American Physical Society.

Cosmic Space

Confirmed! Black holes and neutron stars collide

Gravitational-wave astronomers are confident that they’ve filled out their repertoire of cataclysmic collisions, thanks to the detection of two cosmic crashes that each involved a black hole and a neutron star.

Over the past five years, astronomers have used the twin LIGO gravitational-wave detectors in Washington state and Louisiana, plus the Virgo detector in Italy, to pick up signals from more than 50 violent mergers of black holes with black holes, or neutron stars with neutron stars.

In 2019, the astronomers picked up readings from two events that might have been caused by hot black-hole-on-neutron-star action. But one of those detections, on April 26, 2019, could plausibly have been nothing more than noise in the detectors. The other event, on Aug. 14, 2019, involved a crash between a black hole and an object that was either the heaviest known neutron star or the lightest known black hole. The gravitational-wave hunters couldn’t say definitively which.

In contrast, astronomers leave little doubt that the gravitational waves sparked by two separate events in January 2020 were thrown off by the merger of a black hole and a neutron star. They lay out their evidence in a paper published today by The Astrophysical Journal Letters.

“With this new discovery of neutron star-black hole mergers outside our galaxy, we have found the missing type of binary. We can finally begin to understand how many of these systems exist, how often they merge, and why we have not yet seen examples in the Milky Way,” Astrid Lamberts, a member of the Virgo collaboration who works at the Observatoire de la Côte d’Azur in France, said in a news release.

There’s still some mystery surrounding the detections.

Cosmic Space

Fast radio bursts linked to a prime suspect

For years, astronomers have puzzled over the origins of phenomena known as fast radio bursts — cosmic emissions that last only a fraction of a second but blast out more than 100 million times more power than our sun. Some even wondered whether the bursts, known as FRBs, might serve as signals from extraterrestrial civilizations.

Now they’ve tracked down the source of the first fast radio burst detected in our own Milky Way galaxy — and it’s not aliens. Instead, it’s a magnetar, a type of neutron star with a powerful magnetic field.

Scientists have long suspected that fast radio bursts had something to do with magnetars. But the newly reported case, described in three studies published today by the journal Nature, serves as the astronomical equivalent of a smoking gun.

“There’s this great mystery as to what would produce these great outbursts of energy, which until now we’ve seen coming from halfway across the universe,” Kiyoshi Masui, a physicist at the Massachusetts Institute of Technology, said today in a news release. “This is the first time we’ve been able to tie one of these exotic fast radio bursts to a single astrophysical object.”

Masui is part of the team that picked up the first clues to the source, a magnetar 30,000 light-years from Earth that’s known as SGR 1935+2154. The team includes researchers from MIT, the University of British Columbia, McGill University, the University of Toronto and the Perimeter Institute for Theoretical Physics.

They made use of a radio telescope array called the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, which began science operations in 2018 at the Dominion Radio Astrophysical Observatory in British Columbia’s Okanagan Valley.

In April, astronomers detected bursts of X-ray and gamma-ray activity from SGR 1935 — which led the CHIME team to turn their attention to that part of the sky, around the center of the Milky Way. Shortly after an X-ray burst on April 28, CHIME registered two sharp peaks in radio emissions, within a few milliseconds of each other.

That fit the pattern for a fast radio burst, emanating from a point in the vicinity of SGR 1935. “If it was coming from any other object close to the magnetar, it would be a very big coincidence,” Masui said.

The source was near the edge of CHIME’s field of view, which made it difficult to determine the radio burst’s brightness. So the team put out the word for other astronomers to check their records.

By a stroke of luck, another radio astronomy project —  known as the Survey for Transient Astronomical Radio Emission 2, or STARE2 — had a wide-field view of the same blast.

“When I saw the data, I was basically paralyzed,” Caltech graduate student Christopher Bochenek said in a news release. “At the radio frequencies we observe with STARE2, the signal was much stronger than what CHIME reported. We had caught the FRB head-on.”

STARE2 isn’t your typical radio telescope array: The heart of the Caltech-led, NASA-funded project is a handmade radio receiver that’s about the size of a large bucket. “It’s a piece of 6-inch metal pipe with two literal cake pans around it,” Bochenek told The Associated Press.

Three of the receivers are placed at widely separated locations in California and Utah, which makes it possible to triangulate on the source of cosmic radio emissions. They’re not as sensitive as the more traditional big-dish telescopes, but they can take in the whole sky.

The readings from STARE2, combined with data from other instruments, suggested that the April 28 burst was 3,000 times brighter than any previously observed magnetar radio signal.

Among the other instruments participating in the observational campaign was China’s Five-Hundred-Meter Aperture Spherical Radio Telescope, also known as FAST. Astronomers on the FAST team missed out on detecting FRB 200428, but they kept an eye on SGR 1935 as it emitted a series of 29 gamma-ray bursts. None of those bursts coincided with a blast of high-energy radio waves.

“The weak correlation could be explained by special geometry and/or limited bandwidth of FRBs,” study co-author Zhang Bing of the University of Nevada at Las Vegas said in a news release. “The observations of SGR J1935 start to reveal the magnetar origin of FRBs, although other possibilities still exist.”

Astrophysicists haven’t yet figured out the mechanism for producing fast radio bursts, but one hypothesis is that they can occur when a magnetar throws off a flare of charged particles that interact with debris surrounding the star. The resulting shock wave could set electrons gyrating wildly, throwing off radio waves as well as X-rays.

To unravel that part of the mystery, the CHIME team and other astronomers are keeping a close watch on SGR 1935.

“We’ve got our eyes open for other magnetars,” Masui said, “but the big thing now is to study this one source and really drill down to see what it tells us about how FRBs are made.”

The CHIME/FRB Collaboration’s study, described in a Nature paper titled “A Bright Millisecond-Duration Radio Burst From a Galactic Magnetar,” was funded by the Canada Foundation for Innovation and other supporting institutions. The second Nature study, “A Fast Radio Burst Associated With a Galactic Magnetar” counts Bochenek as well as V. Ravi, K.V. Belov, G. Hallinan, J. Kocz, S.R. Kulkarni and D.L. McKenna among its authors. Zhang is among 48 authors of the third Nature paper, titled “No Pulsed Radio Emission During a Bursting Phase of a Galactic Magnetar.”


Gravitational waves point to cosmic conundrum

Telltale ripples in the fabric of spacetime have revealed the existence of a cosmic object that scientists can’t definitively classify.

Whatever it is, the object was engulfed suddenly by a black hole weighing 23.2 times the mass of our sun, 800 million light-years away. The gravitational waves thrown off by that violent merger were picked up last August by the twin detectors of the Laser Interferometer Gravitational-Wave Observatory, or LIGO, and by the Virgo gravitational-wave detector in Italy.

The gravitational-wave patterns revealed that the smaller object was 2.6 times as massive as our sun. And that’s where the classification problem arises.

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Did a black hole just gobble up a neutron star?

Neutron star and black hole illustration
An artist’s conception shows a neutron star swirling around a black hole. (OzGrav ARC Centre of Excellence Illustration via Australian National University / Carl Knox)

The Laser Interferometer Gravitational-Wave Observatory, or LIGO,  has detected mergers of black holes, and even a couple of neutron star smash-ups. But it hasn’t yet confirmed the signature of a black hole gobbling a neutron star.

That could soon change.

Over the past week, physicists have been buzzing over an Aug. 14 detection made by the twin LIGO detectors in Hanford, Wash., and Livingston, La., as well as by the European Virgo gravitational-wave detector in Italy. Those L-shaped facilities monitor ever-so-slight fluctuations in laser beams to look for wobbles in spacetime caused by passing gravitational waves.

The types of waves that LIGO and Virgo detect are given off only by violent cosmic events such as supernova explosions and cataclysmic collisions. LIGO’s first black hole detection, made in 2015, earned the Nobel Prize in physics two years later. More such detections have been made since then.

Detecting the first neutron star merger, and matching that event up with multispectral observations from a wide array of telescopes, marked another milestone in 2017. Neutron stars are the super-dense stellar cores that are left behind when stars bigger than our sun burn out and collapse.

Picking up on the collision of a neutron star and a black hole would complete a gravitational-wave trifecta. LIGO’s team thought they might have detected such a smash-up back in April, but the signal was weak and couldn’t be confirmed.

Astronomers say the Aug. 14 detection, known as S190814bv and traced to a source roughly 900 million light-years away, could be the one.

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Readings hint at black hole eating neutron star

Scientists work in the LIGO Hanford control room. (Caltech / MIT / LIGO Lab Photo / C. Gray)

The science teams for the Laser Interferometer Gravitational-Wave Observatory, or LIGO, and Europe’s Virgo detector today laid out the details of their recent detections, including a crash between neutron stars, three black hole mergers and what may be the first observed collision of a neutron star and a black hole.

Astronomers and their fans have been talking about the detections for days, thanks to the fact that LIGO and Virgo are quickly sharing the raw results from their current observing run. But today’s statements provided the most authoritative views from researchers running the two gravitational-wave detectors.

The April 26 detection of a cosmic collision known as S190426c is the most intriguing event. The subtle signal of a far-off disturbance in the gravitational force was picked up by LIGO’s twin detectors at Hanford in Eastern Washington and at Livingston in Louisiana. The Virgo detector in Italy also detected the signal.

The signal is consistent with what might be expected if a black hole were to swallow a neutron star, roughly 1.2 billion light-years from Earth. Such an event has never been observed before.

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LIGO and Virgo gear up for gravitational waves

LIGO upgrade
Detector engineers Hugh Radkins (foreground) and Betsy Weaver (background) take up positions inside the vacuum system of the detector at LIGO Hanford Observatory to perform the hardware upgrades required for Advanced LIGO’s third observing run. (LIGO / Caltech / MIT Photo / Jeff Kissel)

Physicists won’t be fooling around on April 1 at the Laser Interferometer Gravitational-Wave Observatory in Washington state and Louisiana, or at the Virgo gravitational-wave detector in Italy.

Instead, they’ll all be bearing down for the most serious search ever conducted for signs of merging black holes, colliding neutron stars — and perhaps the first detection of a mashup involving both those exotic phenomena.

Both experiments have been upgraded significantly since their last observational runs, resulting in a combined increase of about 40 percent in sensitivity. That means even more cosmic smashups should be detected, at distances farther out. There’s also a better chance of determining precisely where cosmic collisions occur, increasing the chances of following up with other types of observations.

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Year in Science: Neutron star smashup leads the list

Neutron star merger
An artist’s conception shows the “cocoon” that is thought to have formed around the smashup of two neutron stars. (NRAO / AUI / NSF Image / D. Berry)

For the second year in a row, the journal Science is hailing a discovery sparked by the Laser Interferometer Gravitational-Wave Observatory as the Breakthrough of the Year.

Last year, the breakthrough was LIGO’s first-ever detection of a gravitational-wave burst thrown off by the merger of two black holes. This time, the prize goes to the studies spawned by the first observed collision of two neutron stars.

More than 70 observatories analyzed the data from the Aug. 17 event, which came in the form of gravitational waves as well as electromagnetic emissions going all the way from radio waves to gamma rays.

“The amount of information we have been able to extract with one event blows my mind,” Georgia Tech physicist Laura Cadonati, deputy spokesperson for the LIGO team, told Science.

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Scientists spot neutron stars as they clash and flash

Neutron star merger
An artist’s conception shows two neutron stars merging, and sending out radiation as well as gravitational waves in the process. (NSF / LIGO / Sonoma State University Illustration / A. Simonnet)

For the first time ever, researchers have recorded the cataclysmic smash-up of two neutron stars by virtue of their gravitational waves as well as their electromagnetic emissions, producing data that could unlock cosmic secrets galore.

The findings from the Aug. 17 event, detailed today in more than a dozen research papers, represent the best example of “multi-messenger astronomy.”

More than 70 observatories and thousands of scientists contributed to the findings, headed by the Laser Interferometer Gravitational-wave Observatory, or LIGO.

“We did it again — but this time, we all did it,” David Reitze, executive director of the LIGO Laboratory, said at today’s news briefing announcing the results.

By combining the gravitational-wave readings with observations in wavelengths ranging from radio signals to gamma rays, scientists are gaining new insights into how neutron stars evolve, and how gold and other heavy elements are forged in their furnaces.

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