The discovery of a so-called monster black hole that has about 12 times the Sun’s mass is detailed in a new Astrophysical Journal research submission, the lead author of which is Dr. Sukanya Chakrabarti, a physics professor at The University of Alabama in Huntsville (UAH). Dr. Chakrabarti, the Pei-Ling Chan Endowed Chair in the Department of Physics at UAH, a part of the University of Alabama System, said:
“It is closer to the sun than any other known black hole, at a distance of 1,550 light years. So, it’s practically in our backyard.”
Black holes are seen as exotic because, although their gravitational force is felt by stars and other objects in their vicinity, no light can escape them, so they can’t be seen in the same way as visible stars. Dr. Chakrabarti said:
“In some cases, like for supermassive black holes at the centers of galaxies, they can drive galaxy formation and evolution. It is unclear how these noninteracting black holes affect galactic dynamics in the Milky Way. If they are numerous, they may well affect the formation of our galaxy and its internal dynamics.”
Finding the black hole
To find it, Dr. Chakrabarti and a national team of scientists analyzed data from nearly 200,000 binary stars released over the summer from the European Space Agency’s Gaia satellite mission. She said:
“We searched for objects reported to have large companion masses but whose brightness could be attributed to a single visible star. Thus, you have a good reason to think that the companion is dark.”
Interesting sources were followed up with spectrographic measurements from various telescopes, including the Automated Planet Finder in California, Chile’s Giant Magellan Telescope, and the W.M. Keck Observatory in Hawaii. Dr. Chakrabarti said:
“The pull of the black hole on the visible sun-like star can be determined from these spectroscopic measurements, which give us a line-of-sight velocity due to a Doppler shift.”
A Doppler shift is a change in frequency of a wave about an observer, like how the pitch of a siren’s sound changes as an emergency vehicle passes. She explained:
“By analyzing the line-of-sight velocities of the visible star — and this visible star is akin to our sun — we can infer how massive the black hole companion is, as well as the period of rotation and how eccentric the orbit is. These spectroscopic measurements confirmed the Gaia solution, indicating that this binary system is composed of a visible star orbiting a massive object.”
The black hole has to be inferred from analyzing the visible star’s motions because it does not interact with the luminous star. Noninteracting black holes don’t typically have a doughnut-shaped ring of accretion dust and material that accompanies them that interact with another object. Accretion makes the interacting type relatively easier to observe optically, which is why far more of that type have been found. Dr. Chakrabarti said:
“The majority of black holes in binary systems are in X-ray binaries — in other words, they are bright in X-rays due to some interaction with the black hole, often due to the black hole devouring the other star. So as the stuff from the other star falls down this deep gravitational potential well, we can see X-rays.”
These interacting systems tend to be on short-period orbits, she says, adding:
“In this case, we’re looking at a monster black hole, but it’s on a long-period orbit of 185 days, or about half a year. So it’s far from the visible star and not making any advances toward it.”
The techniques the scientists employed should also apply to finding other noninteracting systems. Peter Craig, a doctoral candidate at the Rochester Institute of Technology who is advised on his thesis by Dr. Chakrabarti, said:
“This is a new population that we’re just starting to learn about and will tell us about the formation channel of black holes, so it’s been very exciting to work on this.”
Dr. Chakrabarti said:
“Simple estimates suggest that about a million visible stars have massive black hole companions in our galaxy. But there are a hundred billion stars in our galaxy, so it is like looking for a needle in a haystack. The Gaia mission, with its incredibly precise measurements, made it easier by narrowing down our search.”
Scientists are trying to understand the formation pathways of noninteracting black holes. Dr. Chakrabarti concluded:
“There are currently several different routes that theorists have proposed, but noninteracting black holes around luminous stars are a new type of population. So, it will likely take some time to understand their demographics, how they form, and how these channels are different — or if they’re similar — to the more well-known interacting population, merging black holes.”
Provided by the University of Alabama in Huntsville [Note: Materials may be edited for content and length.]
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