Source: Sci News

Astronomers know that stellar-mass black holes — black holes ranging from 10 times to 100 times the Sun’s mass — are the remnants of dying stars, and that supermassive black holes, more than 1,000,000 times the mass of the Sun, inhabit the centers of most galaxies.

But scattered across the Universe are a few apparent black holes of a more mysterious type. Ranging from 100 to 10,000 solar masses, these intermediate-mass black holes are so hard to measure that even their existence is sometimes disputed.

The final 142-solar-mass black hole produced by the newly-discovered merger lies within this intermediate mass range between stellar-mass and supermassive black holes.

“Right from the beginning, this signal, which is only a tenth of a second long, challenged us in identifying its origin,” said Professor Alessandra Buonanno, a researcher at the University of Maryland and the Max Planck Institute for Gravitational Physics.

“But, despite its short duration, we were able to match the signal to one expected of black-hole mergers, as predicted by Einstein’s theory of general relativity, and we realized we had witnessed, for the first time, the birth of an intermediate-mass black hole from a black-hole parent that most probably was born from an earlier binary merger.”

Dubbed GW190521, the gravitational-wave signal was detected on May 21, 2019 at 03:02:29 UTC.

It came from two black holes weighing in at 85 and 66 times the mass of the Sun, respectively.

The larger of the two black holes is considered ‘impossible.’ Astronomers predict that stars between 65 and 130 solar masses undergo a process called pair instability, resulting in the star being blown apart, leaving nothing behind.

“The mass of the larger black hole in the pair puts it into the range where it’s unexpected from regular astrophysics processes,” said Professor Peter Shawhan, a scientist at the University of Maryland.

“It seems too massive to have been formed from a collapsed star, which is where black holes generally come from.”

“The ‘impossible’ black hole formed by the collision lies in the black hole desert between 100 and 1,000 times the mass of the Sun,” added Professor Susan Scott, a researcher in the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) at the Australian National University.

“We are very excited to have achieved the first direct observation of an intermediate-mass black hole in this mass range.”

“We also saw how it formed, confirming that intermediate-mass black holes can be produced through the merger of two smaller black holes.”

The GW190521 signal, resembling about four short wiggles, was extremely brief in duration, lasting less than one-tenth of a second.

From what the researchers can tell, it was generated by a source that is roughly 5 Gpc away, when the Universe was about half its current age, meaning that the signal traveled across space for 7 billion years before reaching Earth.

GW190521’s source is the most distant gravitational-wave source detected so far.

“This doesn’t look much like a chirp, which is what we typically detect,” said Dr. Nelson Christensen, a researcher at the French National Centre for Scientific Research.

“This is more like something that goes ‘bang,’ and it’s the most massive signal LIGO and Virgo have seen.”

Using the Zwicky Transient Facility, the astronomers may have spotted a light flare from the GW190521 collision. This is surprising, as black holes and their mergers are normally dark to telescopes.

One theory is the system may have been orbiting a supermassive black hole.

The newly-formed black hole may’ve received a kick from the collision, shooting off in a new direction and surging through the disk of gas surrounding the supermassive black hole, causing it to light up.

“There are a number of different environments in which this system of two black holes could have formed, and the disk of gas surrounding a supermassive black hole is certainly one of them,” said Dr. Vaishali Adya, a postdoctoral researcher in the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav) at the Australian National University.

“But it is also possible that this system consisted of two primordial black holes that formed in the early Universe.”

“Every observation we make of two black holes colliding gives us new and surprising information about the lives of black holes throughout the Universe.”

“We are beginning to populate the black hole mass gaps previously thought to exist, with ‘impossible’ black holes that have been revealed through our detections.”

The findings were published in two papers in the journal Physical Review Letters and the Astrophysical Journal Letters.

Source: Sci News