(ORDO NEWS) — Black holes are one of the most amazing and mysterious objects in the known universe. These gravitational giants form when massive stars undergo gravitational collapse at the end of their lives and shed their outer layers in a massive explosion (supernova explosion).
Meanwhile, the stellar remnant becomes so dense that the warp of space-time becomes infinite in its immediate vicinity, and its gravity is so strong that nothing (not even light) can escape its surface. This makes it impossible to observe them with conventional optical telescopes that study objects in visible light.
As a result, astronomers usually look for black holes at invisible wavelengths or observe their effects on nearby objects.
After examining Gaia Data Release 3 (DR3), a team of astronomers led by the University of Alabama at Huntsville (UAH) recently discovered a black hole in our cosmos’ backyard. As they describe in their study, this monstrous black hole is about twelve times the mass of our Sun and lies about 1,550 light-years from Earth.
Because of its mass and relative proximity, this black hole opens up possibilities for astrophysicists. The study was led by Dr. Sukanya Chakrabarty, Chair of Pei-Ling Chan at the UAH Department of Physics.
She was joined by astronomers from the observatories of the Carnegie Institute of Science, the Rochester Institute of Technology, the Carl Sagan Center of the SETI Institute, the University of California at Santa Cruz, the University of California at Berkeley, the University of Notre Dame, Wisconsin-Milwaukee, Hawaii, and Yale University.
A paper describing their findings has recently surfaced online and is under review in the Astrophysical Journal.
Black holes are of particular interest to astronomers because they offer the opportunity to study the laws of physics under the most extreme conditions. In some cases, like the supermassive black holes (SMBHs) that are at the center of most massive galaxies, they also play a vital role in the formation and evolution of galaxies.
However, questions concerning the role of noninteracting black holes in the evolution of galaxies still remain unresolved. These binary systems are composed of a black hole and a star, where the black hole does not pull material away from the stellar companion. Dr. Chakrabari said in a UAH press release:
“It is not yet clear how these non-interacting black holes affect the galactic dynamics in the Milky Way.
If there are many of them, they may well influence the formation of our galaxy and its internal dynamics.
We were looking for objects that are reported to have large companion masses but whose brightness can be attributed to the only visible star.
Thus, you have good reason to believe that the companion is dark.”
To find the black hole, Dr. Chakrabarti and her team analyzed the Gaia DR3 data, which included information on nearly 200,000 binary stars observed by the European Space Agency’s (ESA) Gaia observatory.
The team tracked the sources of interest by consulting spectrographic measurements from other telescopes, such as the Lick Observatory’s Automated Planet Finder, the Giant Magellanic Telescope (GMT) and the WM Telescope at the Keck Observatory in Hawaii.
These measurements showed that the main sequence star is subject to powerful gravitational influence. As Dr. Chakrabari explained:
“The attraction of a black hole to a visible star like the Sun can be determined using these spectroscopic measurements, which give us the radial velocity due to the Doppler shift.
By analyzing the radial velocities of a visible star – and this visible star is akin to our Sun – we can conclude that how massive the black hole’s companion is, as well as the period of rotation and the eccentricity of the orbit.
These spectroscopic measurements independently confirmed the Gaia solution, which also showed that this binary system consists of a visible star orbiting a very massive object.”
Interacting black holes are usually easier to observe in visible light because they are in narrower orbits and pull material from their stellar companions. This material forms a torus-shaped accretion disk around the black hole, which accelerates to relativistic speeds (close to the speed of light), becomes very energetic, and emits X-rays.
Because non-interacting black holes have wider orbits and do not form these disks, their presence must be inferred from an analysis of the movements of the visible star. Dr. Chakrabarti said:
“Most 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 another star.
When matter from another star falls into this deep gravitational well, we can see X-rays.
In this case, we’re looking at a monstrous black hole, but it’s on a long period orbit of 185 days, or about half a year.
It is quite far from the visible star and does not approach it.
The methods used by Dr. Chakrabarti and her colleagues may 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 massive black hole companions. Although this represents 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 1 billion astronomical objects, including stars, galaxies,
Further studies of this population will allow astronomers to learn more about this population of binary systems and the way black holes form. As Dr. Chakrabarti summarized:
“Currently, theorists have proposed several different routes, but non-interacting black holes around glowing stars represent an entirely new type of population.
It will take us some time to understand their demographics, how they form, and how these channels differ from or are they similar to the better-known population of interacting, merging black holes.”
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