It is estimated that there should be between 10 million and one billion stellar black holes in our galaxy that move quietly in the galaxy, completely silently. One problem arises when counting them: until some kind of matter enters their gravitational field, they are invisible.
However, invisibility does not mean that it is impossible to fix. For the first time in history, an international team of researchers spotted a black hole in a quiet state 5,200 light-years away.
How was it discovered? Since we do not currently have the tools to directly investigate a black hole, we need to observe its effects on the space around it. In the case of a black hole in the quiescent state, this effect is gravity. Since the gravity of a black hole is extremely extreme, It bends and twists any light coming in its vicinity.
Consequently, when something invisible from a distant distant star magnifies and makes it strangely bright, astronomers already know that the light must have passed through a gravitational field.
This phenomenon is called gravitational microlensing, and this method is used to detect such small and faint objects that our telescopes would otherwise be difficult to detect. However, a solitary black hole was first seen with this method.
“I inform you about the unambiguous fixation of an isolated, stellar black hole and the measurement of its mass. “We found that the lens does not emit fixed light and has a mass higher than that of a white dwarf or neutron star, which proves that it is a black hole,” said Kailash Sahu, a team of researchers led by astronomer at the Space Telescope Institute.
Gravitational microlensing occurs when an object with a gravitational field ends right in front of a distant star.
This gravitational field causes a space-time curvature; When light passes through this gravitational field, it also obeys this curvature and “bends” its path. This magnifies the light and slightly shifts the visible location of the distant star as well.
Through microlensing events, highly faint exoplanets and stars have already been discovered in the past. Ongoing experiments to monitor the sky detect thousands of microlensing events each year; Most of them are moving stars in front of other stars, which is not surprising given how many stars there are in the galaxy.
On June 2, 2011, two separate microlensing programs, the Optical Gravitational Lensing Experiment (OGLE) and the Microlensing Observations in Astrophysics (MOA), recorded an independent event that peaked on July 20.
This event, dubbed MOA-2011-BLG-191 / OGLE-2011-BLG-0462 (abbreviated MOA-11-191 / OGLE-11-0462), was outstanding. Not only did it last a long time, 270 days, but it also showed an unusually strong magnification. Since strong magnifications are susceptible to disturbances, such as the effects of a planet moving around a lensed object, the scientists decided to continue their observations and analyze them.
Observations of this region of the sky were made eight times by the Hubble Space Telescope, until 2017. Based on the data obtained, Sahu and his colleagues began to calculate the numbers and came to the conclusion that the data best corresponded to a black hole and not to a star.
Moreover, they were even able to take measurements on the black hole. Changes in the light of a distant star allowed the group to calculate its mass and motion. The black hole they discovered has a mass about 7.1 times that of the Sun. The width of its event horizon should be about 42 kilometers.
Just imagine and allow yourself to be surprised. Scientists have been able to detect an invisible object more than 5,000 light-years across, which is ten times shorter than the Grand Canyon; And this they were able to study by changing the light of a more distant star. It is an incredible achievement.
This is where even more amazing news begins. The team calculated the speed at which this object moves in a deer leap: 45 kilometers per second. As a result, it must be a wandering, fleeing black hole.
In space, it was probably destroyed by a supernova explosion of a precursor star. If such a supernova explosion is asymmetric, an unequal force can strike the nucleus of a collapsing star in space, which is called a birth shock. Two such cases have been discovered so far: the white dwarf named LP 40-365 and the pulsar named PSR J0002 + 6216.
A study conducted in 2019 showed that there must be millions of black holes moving so fast in a deer leap. Incredibly exciting story if MOA-11-191 / OGLE-11-0462 turns out to be one of them.
It is also possible that the object is moving in a very dense region of space. Researchers say it will then be examined with a sensitive X-ray telescope to determine if this black hole joins any matter from nearby interstellar space.
In addition, future instruments may detect even more such isolated black holes in stellar mass. Once we find and study such a population, we can learn even more about MOA-11-191 / OGLE-11-0462 and the black holes in Deer Leap in general.
The study will be published in The Astrophysical Journal, before it is available on the pre-review server arXiv.
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