Astronomers were able to take the first direct image of a black hole in 2019, thanks to the glow of material in its presence, but it is natural that many black holes are impossible to detect.
Now it appears that another team using the Hubble Space Telescope has finally found something no one has seen before, a completely invisible black hole, and it was announced in The Astrophysical Journal.
Black holes are what remain after large stars die and their cores collapse. They are incredibly dense, with gravity so strong that nothing can move fast enough to escape them, including light.
Astronomers are keen to study black holes because they can tell us a lot about the ways stars die, and by measuring the masses of black holes, we can tell what was happening in the stars’ last moments, when the cores were collapsing and their outer layers were expelled.
It may seem that black holes are by definition invisible, they earned their name after all by their ability to trap light, but we can still detect them by the way they interact with other things thanks to their strong gravitational pull, and hundreds of tiny black holes have been discovered from Through the way it interacts with other stars.
There are two different methods for such a discovery. In X-ray binary stars, where a star and a black hole orbit a common center while producing X-rays, the black hole’s gravitational field can pull material from its companion.
Matter revolves around the black hole, heating up due to friction as it does so, and hot matter glows brightly in X-ray light, making the black hole visible, and pairs of black holes can also be detected when they merge together, spiraling inward and emitting a short flash of gravitational waves , which are ripples in space-time.
There are many rogue black holes that drift through space without interacting with anything, which makes them difficult to detect, and this is a problem, because if we cannot detect isolated black holes, we cannot know how they formed and the stars that came from them died.
To discover such an invisible black hole, the team of scientists had to combine two types of observations over several years.
Einstein’s general theory of relativity predicts that massive objects will bend light as it passes through them, meaning that any light that passes near an invisible black hole, but not close enough to end up inside it, will bend in a similar way to light passing through a lens. This is called With a gravitational lens, it can be observed when a foreground object aligns with a background object, bending its light, and this method has already been used to study everything from galaxy clusters to planets around other stars.
The authors of this new research combined two types of gravitational lensing observations in their search for black holes, and it began with their observations of light from a distant star that suddenly magnified, making it appear brighter for a brief period before returning to normal.
And they couldn’t see any object in the foreground that was zoomed in via a gravitational lensing process. This suggested that the object might be a single black hole, something that hadn’t been seen before, and the problem was that it could just be a faint star.
Detecting whether it is a black hole or a faint star requires a lot of work, and here came the second type of gravitational lensing observations, as the authors took pictures with Hubble repeatedly for six years, and this allowed them to calculate the mass and distance of the object that caused the effect of the lens, and found that it It’s seven times the mass of our sun, and it’s located about 5,000 light-years away, which seems far away but is actually relatively close, and the star should be that big and that close to us, and since we can’t see it, they concluded that it must be an invisible black hole. .
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