Tag: gravitational waves

Using pulsars scientists detect background signal of the universe’s gravitational waves

10:07 am

The uncertainty of science: Using the variations in the precise radio pulses sent out by many pulsars over a fifteen year year astronomers think they have detected the background signal produced by many gravitational waves over time throughout the universe.

Astrophysicists using large radio telescopes to observe a collection of cosmic clocks in our Galaxy have found evidence for gravitational waves that oscillate with periods of years to decades, according to a set of papers published today in The Astrophysical Journal Letters. The gravitational-wave signal was observed in 15 years of data acquired by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) Physics Frontiers Center (PFC), a collaboration of more than 190 scientists from the US and Canada who use pulsars to search for gravitational waves. International collaborations using telescopes in Europe, India, Australia and China have independently reported similar results.

Imagine that each wave is a single wave on the ocean. This detection is the rough equivalent of looking at the ocean’s overall surface and measuring the general roughness of all the waves.

The press is making a big deal about this discovery. It is good science, and will over time provide valuable insights into evolution and merger of black holes, but it is not that big a deal, especially because this research carries with it many assumptions and uncertainties that good scientists recognize. They thus remain somewhat skeptical about the data. Mainstream journalists however consider gravitational waves cool, and so they hype any press release about them, sometimes to the point of absurdity.

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New catalog of 90 gravitational wave detections published

9:24 am

The scientists operating the world’s three gravitational wave detectors today released a new catalog of all their detections, totaling 90 with 35 never before published.

All signals come from merging black holes and neutron stars. The new catalog contains some surprises, such as an unusual neutron-star–black-hole merger, a massive black hole merger, and binary black holes revealing information about their spins.

…The researchers have also published two papers accompanying their new catalog today. One looks at what the events can tell us about the population of compact objects in our Universe, how often they merge, and how their masses are distributed. In the other paper the researchers employed the gravitational waves to better understand the expansion history of the cosmos by measuring the Hubble constant.

Because of the tiny sample so far detected, these generalized results cannot be taken too seriously, though they do give hints at the larger context.

All three observatories are now undergoing upgrades, and will resume operations in a few weeks.

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Gravitational wave detectors see two different black holes as they swallowed a neutron star

9:41 am

Astronomers using three different gravitational wave detectors have seen the gravity ripples caused when two different black holes swallowed a nearby neutron star.

The two gravitational-wave events, dubbed GW200105 and GW200115, rippled through detectors only 10 days apart, on January 5, 2020, and January 15, 2020, respectively.

Each merger involved a fairly small black hole (less than 10 Suns in heft) paired with an object between 1½ and 2 solar masses — right in the expected range for neutron stars. Observers caught no glow from the collisions, but given that both crashes happened roughly 900 million light-years away, spotting a flash was improbable, even if one happened — and it likely didn’t: The black holes are large enough that they would have gobbled the neutron stars whole instead of ripping them into bite-size pieces.

Note the time between the detection, in early 2020, and its announcement now, in mid-2021. The data is very complex and filled with a lot of noise, requiring many months of analysis to determine if a detection was made. For example, in a third case one detector was thought to have seen another such merger but scientists remain unsure. It might simply be noise in the system. I point this out to emphasize that thought they are much more confident in these new detections, there remains some uncertainty.

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Scientists confirm another 44 black hole mergers detected by gravitational waves

12:16 pm

Scientists have now confirmed that since the first detection of a gravitational wave five years ago they have detected another 44 black hole mergers in the same manner.

A global network of scientists has completed the first major analysis of gravitational wave data, providing exciting insights into some of the most exotic objects in the Universe. “We are announcing the discovery of 44 confirmed black hole mergers, which is a more than a four-fold increase in the number of previously known gravitational-wave signals,” says Shanika Galaudage from Australia’s Monash University, who was part of the research team.

…Their results are described in a trio of papers on the pre-print server arXiv. The first paper describes 39 new detections from the first half of the observing run, primarily of binary black hole systems. This brings the total number of gravitational wave events detected to 47, of which 44 are confidently double black holes, two are confidently double neutron stars, and one is still uncertain.

They think they are detecting more black hole mergers because they are heavier and thus emit bigger and more easily detected waves. They are also finding that the black hole mergers fall into two classes, two holes spinning in the same direction and two holes spinning in opposite or randomly different directions. The former formed together as a binary star system. The latter formed independently and somehow ended up linked up and merging.

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Biggest black hole merger yet detected by gravitational waves

3:30 pm

The uncertainty of science: In May 2020 scientists using the LIGO and VIGO gravitational waves telescopes detected evidence of a merger from two giant black holes, one of which was of a size that according to all theories had been considered “impossible.”

The short gravitational wave signal, GW190521, captured by the LIGO and Virgo gravitational wave observatories in the United States and Europe on 21 May last year, came from two highly spinning, mammoth black holes weighing in at a massive 85 times and 66 times the mass of the Sun, respectively.

But that is not the only reason this system is very special. The larger of the two black holes is considered `impossible’. Astronomers predict that stars between 65 – 130 times the mass of the Sun undergo a process called pair instability, resulting in the star being blown apart, leaving nothing behind.

With a mass of 85 solar masses, the larger black hole falls squarely in that forbidden range, referred to as the upper black hole mass gap, and should be `impossible’.

The explanation the scientists propose is that this black hole initially formed with a mass smaller than 65 solar masses, and then sucked in matter, including a possible additional black hole merger, that raised its weight to 85 solar masses.

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More gravitational waves detected

9:47 am

Using the LIGO and Virgo gravitational wave telescopes astronomers have detected two more gravitational waves.

On April 25, 2019, one of the twin LIGO instruments and the Virgo detector observed a candidate signal which – if confirmed – would be the first binary neutron star merger during the third observation run, which began on April 1. A second candidate signal was seen on April 26, which – if confirmed – could be a never-observed-before collision of a neutron star with a black hole. The latter candidate was observed by both LIGO instruments and the Virgo detector. Dozens of telescopes on the Earth and in space are searching for electromagnetic or astro-particle counterparts. No identification with an electromagnetic transient signal nor a host galaxy has been made to date for either candidate.

The resolution of LIGO and VIRGO are somewhat limited, so other telescopes have to scan a very large part of the sky to spot a counterpart. It is therefore likely that it will be years before the first counterpart event is identified. When it is however it will tell us how far away the event was and confirm what kind of event it was. Right now, they are only making educated guesses.

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Four more gravitational wave detections

9:16 am

The uncertainty of science: The scientists running the LIGO gravitational wave detector have announced the detection of four more gravitational waves, bringing to eleven the total number so far observed.

During the first observing run O1, from September 12, 2015 to January 19, 2016, gravitational waves from three BBH mergers were detected. The second observing run, which lasted from November 30, 2016, to August 25, 2017, yielded a 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 based on the dates on which they were detected. With the detection of four additional BBH mergers the scientists learn more about the population of these binary systems in the universe and about the event rate for these types of coalescences.

The observed BBHs span a wide range of component masses, from 7.6 to 50.6 solar masses. The new event GW170729 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.

In two BBHs (GW151226 and GW170729) it is very likely that at least one of the merging black holes is spinning. One of the new events, GW170818, detected by the LIGO and Virgo observatories, was very precisely pinpointed in the sky. It is the best localized BBH to date: its position has been identified with a precision of 39 square degrees (195 times the apparent size of the full moon) in the northern celestial hemisphere. [emphasis mine]

The highlighted quote above illustrates the amount of uncertainty here. Though these appear to be gravitational waves, and have been confirmed in multiple ways, the data is very coarse, providing only a limited amount of basic information about each event. This limited information is still very valuable, and certainly advances our understanding of black holes and their formation, but it is important to recognize the limitations of that data.

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Neutron star merger caused gravitational wave?

10:17 am

The uncertainty of science: Astronomers now believe that one of the half dozen or so gravitational waves detected by LIGO was likely caused by the merger of two neutron stars.

One of these, GW170817, resulted from the merger of two stellar remnants known as neutron stars. These objects form after stars much more massive than the Sun explode as supernovae, leaving behind a core of material packed to extraordinary densities.

At the same time as the burst of gravitational waves from the merger, observatories detected emission in gamma rays, X-rays, ultraviolet, visible light, infrared and radio waves – an unprecedented observing campaign that confirmed the location and nature of the source.

The initial observations of GW170817 suggested that the two neutron stars merged into a black hole, an object with a gravitational field so powerful that not even light can travel quickly enough to escape its grasp.

While intriguing, this result is uncertain, and based on many assumptions.

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Danish astronomers question gravitational wave detection

9:23 am

The uncertainty of science: A team of Danish astronomers have questioned the gravitational wave detection achieved in the past few years by the LIGO gravitational wave telescopes.

The details are complex and very much in dispute, and the position of these Danish astronomers is very much in the minority, but their doubts have not been dismissed, and illustrate well the best aspects science. The article also outlines how the physics community and the LIGO scientists have welcomed the skepticism, even as they have doubts about the claims of the Danish astronomers. This is the hallmark of good science, and lends weight to the work at LIGO.

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Another LIGO black hole merger detected

8:47 am

Astronomers have announced another black hole merger detected by the LIGO gravitational wave observatory.

Dubbed GW170608, the latest discovery was produced by the merger of two relatively light black holes, 7 and 12 times the mass of the sun, at a distance of about a billion light-years from Earth. The merger left behind a final black hole 18 times the mass of the sun, meaning that energy equivalent to about 1 solar mass was emitted as gravitational waves during the collision.

This event, detected by the two NSF-supported LIGO detectors at 02:01:16 UTC on June 8, 2017 (or 10:01:16 pm on June 7 in US Eastern Daylight time), was actually the second binary black hole merger observed during LIGO’s second observation run since being upgraded in a program called Advanced LIGO. But its announcement was delayed due to the time required to understand two other discoveries: a LIGO-Virgo three-detector observation of gravitational waves from another binary black hole merger (GW170814) on August 14, and the first-ever detection of a binary neutron star merger (GW170817) in light and gravitational waves on August 17.

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Astronomers detect neutron star merger in both light and gravitational waves

9:00 am

Big news! Astronomers from dozens of telescopes on the ground and in space have observed for the first time the light burst caused by the merger of two neutron stars because earlier observations of the merger’s gravitational wave and gamma ray burst told them where to look in the sky.

On 17 August 2017 the NSF’s Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States, working with the Virgo Interferometer in Italy, detected gravitational waves passing the Earth. This event, the fifth ever detected, was named GW170817. About two seconds later, two space observatories, NASA’s Fermi Gamma-ray Space Telescope and ESA’s INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL), detected a short gamma-ray burst from the same area of the sky.

The LIGO–Virgo observatory network positioned the source within a large region of the southern sky, the size of several hundred full Moons and containing millions of stars. As night fell in Chile many telescopes peered at this patch of sky, searching for new sources. These included ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA) and VLT Survey Telescope (VST) at the Paranal Observatory, the Italian Rapid Eye Mount (REM) telescope at ESO’s La Silla Observatory, the LCO 0.4-meter telescope at Las Cumbres Observatory, and the American DECam at Cerro Tololo Inter-American Observatory. The Swope 1-metre telescope was the first to announce a new point of light. It appeared very close to NGC 4993, a lenticular galaxy in the constellation of Hydra, and VISTA observations pinpointed this source at infrared wavelengths almost at the same time. As night marched west across the globe, the Hawaiian island telescopes Pan-STARRS and Subaru also picked it up and watched it evolve rapidly.

Press releases today from numerous other observatories are too numerous to link here, and most essentially say the same thing. The key facts so far gleaned however are intriguing:

Distance estimates from both the gravitational wave data and other observations agree that GW170817 was at the same distance as NGC 4993, about 130 million light-years from Earth. This makes the source both the closest gravitational wave event detected so far and also one of the closest gamma-ray burst sources ever seen

This event also highlights the advantages of observing the universe in as many ways as possible. Some phenomenon get to us sooner, and thus provide us clues on where to look with other tools. Without the gravitational wave and gamma ray burst detectors, on Earth and in space, the other optical and infrared telescopes would have almost certainly not have recorded this merger.

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Nobel Prize for Physics awarded to three LIGO scientists

10:20 am

The 2017 Nobel Prize for Physics has been awarded to three scientists involved in the development of the Laser Interferometer Gravitational-wave Observatory (LIGO), which detected the first gravitational waves in 2015.

While some of the recent Nobel Prizes have been absurd (such as the Peace award to Obama), this award is absolutely deserved and appropriate. Until LIGO detected that gravitational wave they were merely a theory. The detection proved the theory to be real.

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Gravitational waves from black hole collision detected

10:47 am

Three Earth gravitational wave observatories have detected the waves coming from the same collision of two black holes.

The collision was observed Aug. 14 at 10:30:43 a.m. Coordinated Universal Time (UTC) using the two National Science Foundation (NSF)-funded Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors located in Livingston, Louisiana, and Hanford, Washington, and the Virgo detector, funded by CNRS and INFN and located near Pisa, Italy.

The detection by the LIGO Scientific Collaboration (LSC) and the Virgo collaboration is the first confirmed gravitational wave signal recorded by the Virgo detector.

Based on the data obtained, they estimate that the two black holes 25 and 31 times the mass of the Sun and are about 1.8 billion light years away.

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LISA Pathfinder switched off

8:17 am

After a successful mission proving the technology for a full scale orbiting gravitational wave detector, LISA Pathfinder was shut off yesterday.

After 16 months of science measurements an international team deactivated the LISA Pathfinder satellite on the evening of the 18th of July 2017. The gravitational-wave laboratory in space powered down after receiving the last commands in the evening and circles the Sun on a safe parking orbit. LISA Pathfinder has tested key technologies for LISA, the future gravitational-wave observatory in space, and has demonstrated their operative readiness. LISA is scheduled to launch into space in 2034 as an ESA mission and will “listen” to the entire Universe by measuring low-frequency gravitational waves.

The idea is laudable, but for Europe to need another seventeen years to build and launch the full scale telescope is absurd. They now know what needs to be done. It should be relatively easy and quick to get it into orbit. And even if it isn’t easy, seventeen more years? Give me a break.

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Success of test mission paves way for orbiting gravitational wave detector

9:57 am

The success of LISA Pathfinder during the past year to test the technology for building an orbiting gravitational wave detector has now made it possible for Europe to approve construction of the full scale telescope, set to launch in the 2030s.

The LISA Pathfinder mission, launched in late 2015, beat its precision target by a factor of 1,000 and quieted critics who have doubted its potential, says project scientist Paul McNamara, an astrophysicist at ESA in Noordwijk, the Netherlands. “This is not the impossible task that some people believed it was.”

Currently set to fly in 2034, the full-scale Laser Interferometer Space Antenna (LISA) will be the space analogue of the Laser Interfero-meter Gravitational-Wave Observatory (LIGO), two machines in the United States — each with a pair of 4-kilometre-long arms — that first detected the ripples by ‘hearing’ the merger of two black holes. LISA’s three probes will fly in a triangle, millions of kilometres apart, making the mission sensitive to much longer gravitational waves, such as the ripples produced by the collisions of even larger black holes.

The article also notes that the European Space Agency also approved two other large missions, one to launch in 2022 and go the moons of Jupiter, another an X-ray observatory that will launch in 2028.

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Another gravity wave detected by LIGO

1:12 pm

The LIGO gravitational wave detector has detected its second gravitational wave, thought to come from the merger of two black holes.

The new observation came at 3:38.53 Coordinated Universal Time on 26 December 2015—late on Christmas day at LIGO’s detectors in Livingston, Louisiana, and Hanford, Washington. As in the first event, the detectors sensed an oscillating stretching of space-time, the signal, according to Einstein’s 
general theory of relativity, of massive objects in violent motion. Computer modeling indicated that its source was two black holes spiraling together about 1.4 billion light-years away. (LIGO researchers had seen a weaker signal on 12 October 2015 that may be a third black hole merger.)

Note the last sentence in the quote above. They might have had a third detection, but are uncertain enough to have not claimed it as one.

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LISA Pathfinder proves space-based gravity wave detection technology

8:43 am

Engineers have announced that the gravity wave detection technology being tested in orbit by Europe’s LISA Pathfinder works.

To show that the necessary sensitivity is possible, LISA Pathfinder measures the distance between two masses, both of which are inside the spacecraft. “We’ve shrunk the arm of a large gravitational wave antenna to 35 centimeters so we could show it works properly,” Paul McNamara, LISA Pathfinder project scientist, told the press conference.

LISA Pathfinder was launched in December 2015 to a spot 1.5 million kilometers from Earth. When its test masses where first released to float free in February, “the relief was unbelievable,” McNamara says. Science operations began on 1 March and on that first day the team was able to measure distance variations between the masses much smaller than LISA Pathfinder’s mission requirements, Stefano Vitale, the mission’s principle investigator, told reporters. After a month, the variations were even smaller, “very close to [eLISA] requirements,” he says.

They now hope to launch an array of at least three such spacecraft by the mid-2030s.

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Want to discover gravitational waves? You can!

9:04 am

The citizen science project, Einstein@home, will begin providing its participants data from the upgraded LIGO gravitational wave detector beginning March 9.

Rather than looking for dramatic sources of gravitational waves, such as the black-hole merger that LIGO detected on 14 September, Einstein@home looks for quieter, slow-burn signals that might be emitted by fast-spinning objects such as some neutron stars. These remnants of supernova explosions are some of the least well understood objects in astrophysics: such searches could help to reveal their nature.

Because they produce a weaker signal than mergers, rotating sources require more computational power to detect. This makes them well-suited to a distributed search. “Einstein@home is used for the deepest searches, the ones that are computationally most demanding,” Papa says. The hope is to extract the weak signals from the background noise by observing for long stretches of time. “The beauty of a continuous signal is that the signal is always there,” she says.

To participate all you have to do is let their software become your screensaver, doing its work whenever you walk away from your computer.

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LISA Pathfinder cubes in freefall

8:38 pm

After a week of testing scientists have now completely released LISA Pathfinder’s two gold-platinum cubes so that they are floating free within the spacecraft.

With the cubes released, the spacecraft is now measuring the position of each cube and using thrusters to adjust its position and keep the cubes floating within it. This success has essentially proven that the technology works, though they now have to see if the technology can be maintained in orbit for a long enough period of time to be worthwhile. If so, this mission will be followed by multiple similar spacecraft, flying in formation while also measuring their positions precisely relative to each other. If a gravitational wave rolls past, they will detect it by the tiny differences of each cube’s position, kind of like beach balls floating on the ocean as a wave rolls past.

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India okays its own LIGO detector

4:32 pm

The Indian government today approved construction of LIGO-India, using some duplicate components already available from the American LIGO gravitational wave detector.

“We have built an exact copy of that instrument that can be used in the LIGO-India Observatory,” says David Shoemaker, leader of the Advanced LIGO Project and director of the MIT LIGO Lab, “ensuring that the new detector can both quickly come up to speed and match the U.S. detector performance.” LIGO will provide Indian researchers with the components and training to build and run the new Advanced LIGO detector, which will then be operated by the Indian team.

What this new instrument will accomplish is to give astronomers more information when a gravitational wave rolls past the Earth. By having detectors half a world apart, they will be able to better triangulate the direction the wave came from, which in turn will help astronomers eventually pinpoint its source event.

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LISA Pathfinder’s cubes floating free

9:21 am

More gravitational wave news: LISA Pathfinder’s two gold-platinum 46mm cubes have been released and are now floating free inside their spacecraft.

After a week of further testing, they will stop controlling the cube’s positions with electrostatic force. They will then watch them very precisely with lasers to test whether the equipment is capable of detecting distance shifts small enough for a future version, made up of three such spacecraft, to detect gravitational waves. The idea is that, as a wave rolls by, the cubes will shift positions at slightly different times, just as different beach balls will do so on ocean waves.

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First direct detection of a gravitational wave

9:45 am

The science team from the Laser Interferometer Gravitational-wave Observatory (LIGO) announced today that on September 14, 2015 they made the first direct detection of a gravitational wave, produced by the merging of two distant black holes.

Based on the observed signals, LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the sun, and the event took place 1.3 billion years ago. About three times the mass of the sun was converted into gravitational waves in a fraction of a second — with a peak power output about 50 times that of the whole visible universe. By looking at the time of arrival of the signals — the detector in Livingston recorded the event 7 milliseconds before the detector in Hanford — scientists can say that the source was located in the Southern Hemisphere.

According to general relativity, a pair of black holes orbiting around each other lose energy through the emission of gravitational waves, causing them to gradually approach each other over billions of years, and then much more quickly in the final minutes. During the final fraction of a second, the two black holes collide at nearly half the speed of light and form a single more massive black hole, converting a portion of the combined black holes’ mass to energy, according to Einstein’s formula E=mc2. This energy is emitted as a final strong burst of gravitational waves. These are the gravitational waves that LIGO observed.

Because of the faintness of the wave signal, I suspect that the scientists involved have spent the last four months reviewing their data and the instrument very carefully, to make sure this was not a false detection. That they feel confident enough to make this announcement tells us that they think the detection was real.

Recently ESA launched Lisa Pathfinder, a prototype space-based gravitational wave detector designed to test the technology for building a larger in-space observatory that would be far more sensitive that LIGO. Funding for that larger detector has dried up, Today’s announcement will likely help re-energize that funding effort.

More information here.

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The elusive effort to detect gravitational waves.

9:19 am

After spending more than half a billion dollars and eight years of looking without a single detection, the Laser Interferometer Gravitational-Wave Observatory (LIGO) has gotten a major upgrade.

If commissioning continues to go relatively smoothly, plans call for the first Advanced LIGO observing run to start in late 2015. A second run, with a decent shot of finding a gravitational wave, would occur in the winter of 2016–17. (Weiss likes to point out that a 2016 discovery would be a nice 100th-anniversary commemoration of Einstein’s paper describing gravitational waves.) By the third science run, planned for 2017–18, the machine should be getting sensitive enough to almost certainly nail a detection, says Reitze.

It is hoped that the increased sensitivity, ten times better than before. will allow LIGO to finally make the first detection of a gravitational wave.

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Astronomers think they have discovered a distant supermassive black hole that is being ejected from its galaxy at a speed of several million miles per hour.

4:48 pm

Astronomers think they have discovered a distant supermassive black hole that is being ejected from its galaxy at a speed of several million miles per hour.

Although the ejection of a supermassive black hole from a galaxy by recoil because more gravitational waves are being emitted in one direction than another is likely to be rare, it nevertheless could mean that there are many giant black holes roaming undetected out in the vast spaces between galaxies. “These black holes would be invisible to us,” said co-author Laura Blecha, also of CfA, “because they have consumed all of the gas surrounding them after being thrown out of their home galaxy.”

This conclusion however is not final. The data could also be explained by the spiraling in of two supermassive black holes.

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