Black holes are among the most impressive and mysterious objects in the known universe. These gravitational monsters are formed when massive stars at the end of their lives undergo gravitational collapse and shed their outer layers in a massive explosion (a supernova).
Meanwhile, the stellar remnant is becoming so dense that the curvature of space-time near it becomes infinite, and its gravity so strong that nothing (not even light) can escape its surface. This makes them impossible to observe with traditional optical telescopes that examine objects in visible light.
As a result, astronomers typically look for black holes at non-visible wavelengths or by observing their effect on nearby objects.
After consulting 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 giant black hole is about 12 times the mass of our Sun and is about 1,550 light-years from Earth.
Because of its mass and relative proximity, this black hole offers opportunities for astrophysicists.
The study was conducted by Dr. Sukanya Chakrabarti, Pei Ling Chan Endowed Chair at UAH Institute of Physics. She was joined by astronomers from 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 Observatories.
The paper describing their findings has recently appeared online and is being reviewed by the Astrophysical Journal.
Black holes are of particular interest to astronomers because they offer opportunities to study the laws of physics under the most extreme conditions. In some cases, such as the supermassive black holes (SMBH) found at the center of most massive galaxies, they also play critical roles in galaxy formation and evolution.
However, there are still unresolved questions regarding the role played by non-interacting black holes in galactic evolution. These binary systems consist of a black hole and a star, with the black hole not extracting any material from the companion star. 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. When they are numerous, they can influence the formation of our galaxy and its inner dynamics. We looked for objects reported to have large attendant masses but whose brightness could be attributed to a single visible star. Therefore, you have good reason to believe that the companion is dark.
To find the black hole, Dr. Chakrabarti and her team captured data from Gaia DR3 that contained information on nearly 200,000 binary stars observed by the European Space Agency’s (ESA) Gaia Observatory. The team followed up interesting sources by consulting 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 being subjected to a strong gravitational pull. like dr Chakrabari explained:
“The black hole’s gravitational pull 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. By analyzing the line-of-sight velocities of the visible star – and this visible star is similar to our own Sun – we can infer the mass of the black hole’s companion, as well as the rotation period and eccentricity of the orbit. These spectroscopic measurements independently confirmed the Gaia solution also shown 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 tighter orbits and stripping material from their stellar companions. This material forms a toroidal accretion disk around the black hole, which accelerates to relativistic velocities (close to the speed of light), becomes highly energetic, and emits X-rays.
Since non-interacting black holes have broader orbits and do not form these disks, their presence must be inferred from analysis of the motions of the visible star. said dr Chakrabarti:
“The majority of black holes in binary star systems are in X-ray binaries — in other words, they are bright in X-rays due to an interaction with the black hole, often due to the black hole consuming the other star. As the stuff falls down that deep gravitational potential when the other star, we can see x-rays. In this case we see a huge black hole, but it is in a long orbit of 185 days, or about half a year. It is quite far from the visible star and is not making any progress towards it.”
The one from Dr. Techniques used by Chakrabarti and her colleagues could lead to the discovery of many more non-interacting systems.
According to current estimates, there could be a million visible stars in our galaxy that have massive black holes as companions. While this represents only a tiny fraction of its stellar population (~100 billion stars), Gaia Observatory’s precise measurements have narrowed this search. To date, Gaia has received data on the positions and proper motions of over 1 billion astronomical objects – including stars, galaxies,
Further study of this population will allow astronomers to learn more about this population of binaries and how black holes form. like dr Chakrabarti summarized:
“There are currently several different routes proposed by theorists, but non-interacting black holes around luminous stars are a very new type of population. So it will likely take some time before we understand their demographics and how they form and how these channels differ – or if they are similar – to the more familiar population of interacting, merging black holes.
This article was originally published by Universe Today. Read the original article.