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Black hole crash creates LIGO’s biggest ‘bang’

Scientists say the merger of two black holes that occurred when the universe was half its current age has created the most massive source of gravitational waves ever observed.

After traveling billions of light-years, the disturbance in spacetime was picked up on May 21, 2019, by the Laser Interferometer Gravitational-Wave Observatory, also known as LIGO, and the Virgo gravitational-wave detector in Italy. The unusual event and its implications are described in papers published today by Physical Review Letters and the Astrophysical Journal Letters.

“This doesn’t look much like a chirp, which is what we typically detect,” Nelson Christensen, an astrophysicist at the French National Center for Scientific Research, said in a news release. “This is more like something that goes ‘bang,’ and it’s the most massive signal LIGO and Virgo have seen.”

Christensen and his colleagues say the signal, known as GW190521, appears to have come from the violent collision of two spinning black holes that were about 85 and 66 times as massive as our sun.

The merger created an even bigger black hole that’s about 142 times as massive as the sun. It also released the equivalent of eight solar masses in the form of gravitational-wave energy, in accordance with Albert Einstein’s E=mc2 formula, the scientists said.

GW190521 not only ranks as the biggest bang recorded since LIGO made its initial, Nobel-winning gravitational-wave detection in 2015. It also counts as LIGO’s first detection of a mysterious object known as an intermediate-mass black hole.

For decades, physicists have been fleshing out their theories regarding the nature and origin of black holes — concentrations of matter so massive and compact that nothing, not even light, can escape their gravitational grip.

Some black holes are thought to be created when stars up to 130 times as massive as our sun run out of their fusion fuel and collapse inward, producing black holes as big as 65 solar masses. There are also scenarios in which stars that weigh more than 200 solar masses can collapse into black holes in the range of 120 solar masses.

A completely different process leads to the creation of monster black holes at the centers of galaxies (including our own galaxy). Such supermassive black holes are at least 1,000 times as massive as the sun.

Not that long ago, scientists thought the physics behind gravitational collapse ruled out the creation of black holes between 65 and 120 solar masses. Instead, the collapse of midsize stars was thought to produce instability through the creation of electron-antielectron pairs — and as a result, the stars were supposed to blow themselves completely apart.

Now, the fact that one of the black holes involved in last year’s smashup was measured at 85 solar masses is complicating claims for the existence of a pair instability mass gap.

“The fact that we’re seeing a black hole in this mass gap will make a lot of astrophysicists scratch their heads and try to figure out how these black holes are made,” said Christensen, who is the director of the Artemis Laboratory at the Nice Observatory in France.

The authors of the paper published in the Astrophysical Journal Letters have already come up with one possibility: Perhaps the midsize black hole was not directly produced by a stellar collapse, but instead by an earlier merger of smaller black holes — just the sort of merger that LIGO and Virgo have been detecting over the past five years.

“This event opens more questions than in provides answers,” said Caltech physicist Alan Weinstein, a member of the LIGO collaboration. “From the perspective of discovery and physics, it’s a very exciting thing.”

Weinstein cautioned that there’s still some uncertainty about the current explanation for GW190521.

“Since we first turned on LIGO, everything we’ve observed with confidence has been a collision of black holes or neutron stars,” he said. “This is the one event where our analysis allows the possibility that this event is not such a collision.  Although this event is consistent with being from an exceptionally massive binary black hole merger, and alternative explanations are disfavored, it is pushing the boundaries of our confidence. And that potentially makes it extremely exciting.”

Further observations from LIGO and Virgo could turn up something completely new in the gravitational-wave menagerie — for example, evidence for the creation of primordial cosmic strings.

The LIGO project is funded by the National Science Foundation and operated by Caltech and MIT. It relies on two gravitational-wave detectors that have been built at Hanford, Wash., and at Livingston, La., with about 2,000 miles of separation to provide a double-check on the detectors’ results.

Each detector consists of an L-shaped network of tunnels, measuring 2.5 miles on a side, with laser beams reflected back and forth within the tunnels. Gravitational waves from far-off cataclysms disturb the fabric of spacetime ever so slightly — but the detectors are sensitive enough to pick up such disturbances to within the width of a proton.

Europe’s Virgo detector, designed according to a similar scheme, provides further verification for LIGO’s gravitational-wave data and makes it easier to triangulate on the sources of the waves.

In the case of GW190521, the waves are thought to have been thrown off by a source that’s now roughly 17 billion light-years (5 gigaparsecs) away from us — at a time when the universe was about half its current age of 13.8 billion years. That makes it one of the most distant gravitational-wave sources detected so far.

Because light travels at a finite speed, it may seem counterintuitive for a signal that was sent out 7 billion years ago to be received from an object that’s 17 billion light-years away.

But in an email exchange, Weinstein told me there’s a relatively simple explanation for the seeming mismatch. “The universe has been expanding since the gravitational waves were emitted,” he wrote. “So physical distances are tricky to interpret in an expanding universe, and must be treated with care.”

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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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Japan joins the global gravitational wave hunt

KAGRA detector
An illustration provides a cutaway view of the underground KAGRA gravitational-wave detector in Japan. (ICRR / Univ. of Tokyo Illustration)

Japan’s Kamioka Gravitational-Wave Detector, or KAGRA, is due to start teaming up with similar detectors in Washington state, Louisiana and Italy in December, boosting scientists’ ability to triangulate on the origins of cataclysmic cosmic events such as black hole smash-ups.

Representatives of KAGRA, the U.S.-based Laser Interferometer Gravitational-Wave Observatory (LIGO) and Europe’s Virgo detector signed a memorandum of agreement today in Toyama, Japan, to confirm their collaboration. The agreement includes plans for joint observations and data sharing.

“This is a great example of international scientific cooperation,” Caltech’s David Reitze, executive director of the LIGO Laboratory, said in a news release. “Having KAGRA join our network of gravitational-wave observatories will significantly enhance the science in the coming decade.”

Nobel-winning physicist Takaaki Kajita, principal investigator of the KAGRA project, said “we are looking forward to joining the network of gravitational-wave observations later this year.”

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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 a smallish black hole smashup

Black hole merger
An artist’s conception shows two black holes in the process of merging. (LIGO / Caltech / MIT Illustration)

It took months to figure it out, but the scientists in charge of the Laser Interferometer Gravitational-wave Observatory, or LIGO, have confirmed their observations of the most lightweight black hole merger yet.

The latest detection provides further confirmation of Einstein’s general theory of relativity — and will help physicists hone their routine for combining observations from different types of scientific instruments, an approach known as “multi-messenger astronomy.”

Scientists say the spike in gravitational waves known as GW170608, detected on June 8, was set off by the smashup of two black holes weighing seven and 12 times as much as our sun.

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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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Hubbub hints at smash-up of neutron stars

Neutron star merger
An artist’s conception visualizes the gravitational waves given off by a neutron star collision. (LIGO / MIT / Caltech Illustration)

Another big announcement about gravitational waves is coming up, and this time the hints point to  observations in electromagnetic wavelengths as well — emissions of light that may have come from a collision of neutron stars, or a supernova.

That would be a biggie for astronomers: So far, the scientists behind the Laser Interferometer Gravitational-wave Observatory, or LIGO, have detected three confirmed collisions of black holes, but no neutron star smash-ups or stellar explosions.

All will be revealed at 7 a.m. PT on Oct. 16, when representatives from LIGO, Europe’s Virgo gravitational-wave observatory, and a sampling of researchers from 70 other observatories are to share new findings during a briefing at the National Press Club in Washington, D.C.

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