Black holes are among the most impressive and mysterious objects in the known universe. These gravitational behemoths form when massive stars undergo gravitational collapse at the end of their lifespan and lose their outer layers in a massive explosion (a supernova).
Meanwhile, the stellar remnant becomes so dense that the curvature of spacetime becomes infinite around it and its gravity so intense that nothing (not even light) can escape from its surface. This makes them impossible to observe using conventional optical telescopes that study objects in visible light.
As a result, astronomers typically search for black holes in non-visible wavelengths or by observing their effect on nearby objects.
After reviewing Gaia Data Release 3 (DR3), a team of astronomers led by the University of Alabama Huntsville (UAH) recently observed a black hole in our cosmic backyard. As they describe in their study, this monstrous black hole is about twelve times the mass of our Sun and is located about 1,550 light-years from Earth.
Due to its mass and relative proximity, this black hole presents opportunities for astrophysicists.
The study was led by Dr. Sukanya Chakrabarti, holder of the Pei-Ling Chan Chair in the Department of Physics at UAH. She was joined by astronomers from observatories at the Carnegie Institution for Science, Rochester Institute of Technology, SETI Institute Carl Sagan Center, UC Santa Cruz, UC Berkeley, University of Notre Dame, Wisconsin-Milwaukee, Hawaii and Yale.
The document outlining their findings was recently posted online and is being reviewed by the Astrophysical Journal.
Black holes are of particular interest to astronomers because they offer the possibility of studying the laws of physics under the most extreme conditions. In some cases, such as supermassive black holes (SMBHs) that reside at the center of most massive galaxies, they also play a vital role in galaxy formation and evolution.
However, there remain unresolved questions regarding the role non-interacting black holes play in galactic evolution. These binary systems consist of a black hole and a star, where the black hole does not pull material from the stellar companion. Said Dr. Chakrabari in a UAH press release:
“It is not yet clear how these non-interacting black holes affect galactic dynamics in the Milky Way. If there are many of them, they may well affect the formation of our galaxy and its internal dynamics. We have been looking for objects that would have large companion masses, but whose brightness could be attributed to a single visible star, so you have good reason to think the companion is dim.
To find the black hole, Dr. Chakrabarti and his team analyzed data from the Gaia DR3, which included information on nearly 200,000 binary stars observed by the European Space Agency’s (ESA) Gaia Observatory. The team tracked sources of interest by looking at spectrographic measurements from other telescopes, such as the Lick Observatory’s automated planet finder, the Giant Magellan Telescope (GMT), and the WM Keck Observatory in Hawaii.
These measurements showed a main-sequence star under strong gravitational force. As Dr. Chakrabari explained:
“The attraction of the black hole to 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. By analyzing the line-of-sight velocities of the visible star – and this visible star is similar to our own Sun – we can deduce the mass of the black hole’s companion, as well as the rotation period and the eccentricity of the orbit. These spectroscopic measurements have independently confirmed Gaia’s solution which also indicated that this binary system is composed of a visible star orbiting a very massive object.”
Interacting black holes are generally easier to observe in visible light because they are in tighter orbits and draw material from their stellar companions. This material forms a torus-shaped accretion disk around the black hole which is accelerated to relativistic speeds (near the speed of light), becoming highly energetic and emitting X-rays.
Because non-interacting black holes have larger orbits and do not form these disks, their presence must be inferred from analysis of the motions of the visible star. Says Dr. Chakrabarti:
“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 hole black devours the other star. As the other star’s stuff falls into this deep gravitational potential well, we can see x-rays. In this case, we’re looking at a monster black hole, but it’s in a long orbit period of 185 days, or about six months. It is quite far from the visible star and makes no advance towards it.”
The techniques employed by Dr. Chakrabarti and his colleagues could lead to the discovery of many other non-interacting systems.
According to current estimates, there could be a million visible stars in our galaxy that have huge black hole companions. Although this is only a tiny fraction of its stellar population (~100 billion stars), precise measurements from the Gaia Observatory have narrowed this search. To date, Gaia has obtained data on the positions and proper motions of over a billion astronomical objects, including stars, galaxies,
Further studies of this population will allow astronomers to learn more about this population of binary systems and how black holes form. As Dr. Chakrabarti summarizes:
“There are currently several different routes that have been proposed by theorists, but non-interacting black holes around bright stars are a whole new type of population, so it will probably take us some time to understand their demographics, and how they fit together. form, and how these channels are different – or if similar – from the better-known population of interacting, merging black holes.”
This article was originally published by Universe Today. Read the original article.
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