The first clearly detected medium-mass black hole: the strongest gravitational wave signal to date.

Using gravitational wave detectors, astronomers have discovered a black hole 142 times the mass of the sun, the largest black hole merger ever observed. Astrophysicists are very concerned about this gravitational wave event because it challenges the current theory of black hole formation. The universe is full of echoes of space-time ripples, gravitational waves, and now, in the “cosmic symphony” we hear, a new sound has been added.

The first clearly detected medium-mass black hole: the strongest gravitational wave signal to date.

An imaginary image of two black holes colliding.

Since 2015, astrophysicists have been using gravitational wave detectors to “listen” to the universe’s ripple-like signals and analyze the large-scale collision events that send them by decoding the tiny ripples produced in space-time. Now, according to a new study by the Laser Interferon Gravitational Wave Observatory (LIGO) and the European Virgo interferometer, scientists have detected a new gravitational wave signal from a fast and violent “explosion” event. Studying the event may help us solve more cosmic puzzles.

“This is another discovery,” said Gabriela Gonzalez, a physicist at Louisiana State University and a member of the new study. “After more than a year of research, this strange signal, called GW190521, has led scientists to believe that they have discovered the largest black hole merger to date, resulting in 142 times the mass of the sun and the first clearly detected medium-mass black hole (i.e., a black hole with a mass 100 to 1,000 times the mass of the sun).

A huge explosion in the universe.

The first clearly detected medium-mass black hole: the strongest gravitational wave signal to date.

Based on a gravitational wave signal detected on May 21, 2019, astronomers speculated that the signal was generated when a medium-mass black hole 85 times the mass of the sun collided with a star black hole 66 times the mass of the sun, resulting in a medium-mass black hole 142 times the mass of the sun.

The unique signal was quickly discovered when scientists combed through the observations of the gravitational wave detector. The study’s co-author, 筎 Zsuzsanna Marka, an astronomer at Columbia University, clearly remembers that the probe received the signal on May 21, 2019. She is one of the few astrophysicists who connects cell phones to cosmic exploration in real time, and is alerted whenever gravitational wave detectors “listen” to possible signals in the universe.

After receiving the reminder, Marca began checking for neutrino outbreaks associated with these events. That night, however, she realized that it might be a very special probe. “I noticed the huge quality involuntarily, ” says Marca. She remembers thinking, “It’s great, it means a lot.” This is indeed one of the large-scale events we would like to see, which is incredible, but it is not clear whether such a massive black hole really exists. “

Black holes vary in size. According to NASA, stellar black holes, a type of black hole formed by the collapse of the gravitational gravity of large-mass stars, are 10 to 25 times the mass of the sun; Astronomers speculate that there may be some kind of black hole somewhere in between, a medium-mass black hole. It is estimated that the mass of a medium-mass black hole is about 100 to 1,000 times that of the sun.

The first clearly detected medium-mass black hole: the strongest gravitational wave signal to date.

This image shows the black hole collisions and meso-star collisions detected so far. The event that produced GW190521 is located at the top of the center and is the largest black hole mass of any collision.

Medium-mass black holes are not formed by dying star eruptions, as most small black holes do. The mass of a medium-mass black hole is obviously too large compared to a stellar black hole formed by the collapse of a single star’s gravity; a star always loses some matter during an eruption, but when a star reaches a certain volume, no matter how large it becomes, it erupts to form a black hole with a mass of about 65 times that of the sun. According to the LIGO team, larger stars lose more matter when they erupt, eventually forming black holes the same size.

This process could explain how stars 130 times the mass of the sun form black holes up to 65 times the mass of the sun, while for larger stars (130 to 250 times the mass of the sun), instability is more likely to occur against supernovae, and stars will be completely destroyed, leaving no black holes or any other debris. Astronomers therefore believe that star collapse does not produce black holes with a mass between 65 and 120 times the mass of the sun, a range known as “the gap in instability.”

Until recently, medium-mass black holes were mysterious objects that existed in theory, even by black hole standards. Using LIGO’s early detection results, astronomers observed stellar black holes, while the Event Vision Telescope captured images of supermassive black holes at the center of the M87 galaxy, but it was not easy to detect medium-mass black holes.

The new explosion is evidence of the first detection of a medium-mass black hole. Astronomers have calculated that the gravitational wave signal was generated when a medium-mass black hole 85 times the mass of the sun collided with a stellar black hole 66 times the mass of the sun. Pedro Marronetti, director of the Gravitational Physics Program at the National Science Foundation, said in a statement: “LIGO has once again surprised us by detecting not only black holes of unsealable size, but also using techniques that are not specifically designed for star-merger events. “The LIGO project is funded by the National Science Foundation of the United States.

“This is very important because it demonstrates the capabilities of the LIGO detector, which detects signals from completely unpredictable astrophysical events,” Maronetti said. “

Is it a new black hole or something more exotic?

The first clearly detected medium-mass black hole: the strongest gravitational wave signal to date.

A numerical model of the black hole collision detected on May 21, 2019.

As usual, when it comes to gravitational waves, astronomers have to make assumptions around a small amount of information deciphered in the results. They named the gravitational wave signal GW190521 and found that its duration was much shorter than other signals previously detected by LIGO, at only one-tenth of a second, and its frequency was much lower than that generated by previous black hole merger events. Astronomers can also track the signal to specific sky regions.

Based on this information, astrophysicists calculated the distance at which the collision occurred — about 7 billion light-years away. They were also able to calculate the mass of the two colliding objects, 85 times and 66 times the mass of the sun, respectively, and the mass of the object after the collision was about 142 times that of the sun (some mass was lost in the form of gravitational wave energy during the collision).

Because of the limits on the size of black holes produced by dying stars, these initial mass suggests that at least one of the larger black holes — or possibly smaller ones — may itself be the result of a collision between two black holes. “The two black holes merge to form a new black hole… And then they merge again,” Marca said. “

Marca hopes the collision will take place near the nuclei of an active galaxy, which can anchor other objects because of the strong gravitational force of the active galactic nuclei. The nucleo of an active galaxy is a dense region at the center of a galaxy, and the radiation emitted by it is thought to be generated by the accumulation of supermassive black hole matter in the center of the galaxy. However, using current data, astronomers have yet to determine the exact mechanism behind GW190521.

In the longer term, if more meso-mass black holes are discovered, a major mystery about supermassive black holes, their origins, could be solved.

“They’re like elephants in a room, with millions of sun mass,” Christopher Berry, an astrophysicist at Northwestern University and a LIGO researcher, said in a separate statement. For a long time, we have been looking for a medium-mass black hole to fill the gap between a stellar black hole and a supermassive black hole. Now, we have evidence that medium-mass black holes do exist. “

While astronomers are excited about the gravitational wave signal and the possibility of finding a medium-mass black hole, they are not sure the current hypothesis is correct. Of course, the merger of two black holes 85 times and 66 times the mass of the sun is the most data-compliant, but astrophysicists are also considering other, more bizarre explanations.

“What if something new happens that produces these gravitational waves?” “It’s an attractive prospect,” said Vicky Kalogera, a physicist at Northwestern University and an expert on the LIGO team. She added that current assumptions about the cause of the signal include the collapse of a Star of the Milky Way and some kind of ancient cosmic string.

After the first discovery.

The first clearly detected medium-mass black hole: the strongest gravitational wave signal to date.

Gravitational waves diffuse from the merger of two black holes.

Currently, both the LIGO and Virgo detectors are offline. They were forced to close at the end of March due to the new crown pneumonia pandemic. However, astrophysicists are planning to upgrade the two probes and their algorithms to continue to probe space-time in the universe.

Upgrades to the detector and its algorithms are critical to tracking more signals like the GW190521. If the detectors themselves were more sensitive, scientists would be able to capture more distant signals, and fine-tuning data processing algorithms would make it easier for them to identify more text message numbers like this.

Mr Gonzalez said the detection of collisions between two black holes, and the fact that one of the black holes itself was formed by merger, suggested that there were many signals to be observed in the universe. “I hope this means more black holes — probably clusters of black holes, because they come together, so they merge more frequently,” she said. “

Of course, all this must also depend on future detection results. “Nature does what it has to do, and we can’t tell it what to do,” Gonzalez said. “

The LIGO and Virgo teams published the results of the study in the September 2 issue of Physical Review Letters and The Astrophysical Journal Letters, a previous article detailing the discovery of gravitational wave signals and the latest discussing the physical properties and astrophysical significance of the signal.