Earlier this year, astronomers spotted an object that they thought must have been a black hole in our galaxy; This time, this finding is almost confirmed.
The second group of scientists, who conducted a separate, independent analysis of them, came to almost the same conclusion, which further reinforces the idea that we could potentially detect a black hole wandering in the galaxy.
Astronomers at the University of California, Berkeley, Casey Lamy and Jessica Lou came to a slightly different conclusion in a new study. Depending on the mass range of the object, it may be more of a neutron star than a black hole.
In any case, this means that we may have a new device in our galaxy to search for “dark”, compact objects that can not be detected otherwise; This method involves measuring the curvature of their gravitational fields and the distortion of light from distant stars when that light passes in front of them; This phenomenon is called gravitational microlensing.
“This is the first free-floating black hole or neutron star we have discovered through gravitational microlensing. Through microlensing, we can study and evaluate these compact objects. “I think we have opened a new window to these dark, invisible objects,” said Lou.
Black holes are the collapsed nuclei of massive stars; Their collapse occurs after the end of life, they remove the outer layers of matter and explode into space. The parent stars of such black holes are about 30 times more massive than the sun and live relatively short.
Accordingly, according to the best estimates, from 10 million to one billion stellar black holes should swim silently, peacefully in our galaxy.
However, black holes are called black for some reason. They do not emit any light that we could detect, but when they begin to absorb matter, X-rays are emitted into the cosmos around them. Therefore, if a black hole does nothing and is just hanging in space, there is almost no way to fix it.
Almost. The black hole generates an extreme gravitational field, so strong that it distorts any light passing in front of it. For us as observers, this means that at this time a distant star will appear brighter and in a different place than it actually is.
That is exactly what happened on June 2, 2011. Two different microleasing programs – OGLE and MOA – independently recorded an event that peaked on July 20th.
This event was called MOA-2011-BLG-191 / OGLE-2011-BLG-0462 (abbreviated OB110462) and because it was unusually long and dazzling, scientists decided to study it in detail.
“The duration of the dazzling event indicates how massive the front lens is, which distorts the light of the star in the background. Prolonged events are mainly caused by black holes. However, this is not a guarantee, because the duration of the flash episode depends not only on the mass of the front lens, but also on how fast the front lens and the rear star move relative to each other, ”explains Lamy.
According to him, by measuring the visible position of the background star, it is possible to confirm whether the front background lens is really a black hole.
In this case, the region was observed eight times with the Hubble Space Telescope, until 2017.
In an in-depth analysis of this data, a team of astronomers led by Kailash Sahu, a researcher at the Space Telescope Institute, concluded that the culprit was a micro-lensing black hole about 5,153 light-years away that is 7.1 times the mass of the Sun.
New analyzes by Luce and Lama have added more Hubble data collected through 2021. Their group found that the object is somewhat small, about 1.6 – 4.4 solar masses.
This means that an object can also be a neutron star. It is also the collapsed core of a massive star, a star with a mass of about 8 to 30 solar masses.
Such an object is supported by something called neutron degeneration pressure, which is why neutrons do not want to occupy the same space; This protects them from collapsing into a completely black hole. Such objects have a mass of about 2.4 solar masses.
Interestingly, no black hole of less than 5 solar masses has been recorded so far. This is called the lower edge crack of the mass. If the research of Lama and his colleagues is correct, it means that we may already have the object of fixing the lowest mass crack object, which is very fascinating.
The two groups obtained different masses of the lens object because their analyzes yielded different results for the relative motion of the compact object and the lenticular star.
Sahum and his team found that a compact object travels at a relatively high speed, 45 kilometers per second, the cause of which is the impulse given at birth: the explosion of a skewed supernova could cause a collapsed nucleus to explode into space.
Lam and his colleagues traveled 30 kilometers per second. They say such results indicate that a supernova explosion may not be necessary for the birth of a black hole.
At this point it is impossible to say with certainty which estimate is correct for this object, but astronomers hope to find more such objects in the future and learn much more about them.
“Whatever the object, it is the first dark stellar debris ever discovered that will erupt into the galaxy without another companion star,” Lamy said.
The study will be published in The Astrophysical Journal, before it is available on the arXiv server.
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