Black holes are born when big stars die, according to NASA. Typically, it is a violent death that involves an intense burst of energy that destroys or pushes away close items. That means it is almost impossible to form two black holes close enough together that will merge during the age of the Universe.
But pushing them together in densely populated areas, such as the cores of star clusters, is one approach to encourage them to merge. The LIGO-Virgo-KAGRA Collaboration observed around 85 pairs of black holes colliding since 2015, which allowed scientists to identify gravitational waves that came from them as Albert Einstein theorized.
Black Holes Crashing Into Each Other Generate Gravitational Waves, Distorting Space-Time
How Do Black Holes Collide?
Observations from the LIGO-Virgo-KAGRA Collaboration also showed that these cosmic collisions happen frequently. As detector sensitivity increases, it is also expected that scientists would be able to catch more of these events on a near-daily basis during the next observation period, starting this year. But what scientists do not know is how these collisions happen.
Two factors can bring black holes that are initially extremely far apart together in star clusters, SciTech Daily reports. For starters, mass segregation causes the most massive things to sink to the center of the gravitational potential well. That means any black holes scattered across the cluster will eventually end up at the center, forming an unseen "dark core."
There are also dynamic interactions, wherein the gravitational impact of neighboring objects can alter the interactions of two black holes in the cluster. These factors might cause the binary to lose orbital energy and drift closer together.
These two things that might occur in star clusters can leave traces on the parameters of merging binaries. The geometry of the binary's orbit shortly before it joined is an important characteristic. The orbital configurations can be rather extended or less like the peaceful, sedate circle that the Earth traces about the Sun, and more like the squashed ellipse that Halley's Comet rushes along in its travels in and out of the Solar System because star cluster mergers may occur fast.
The gravitational wave signal of black holes includes distinct modulations that may be investigated to determine where the two objects collided, especially when they are in such an elongated orbit.
The team discovered that some of the binaries recorded by the LIGO-Virgo-KAGRA collaboration indeed had elongated orbits, implying that they collided in a densely populated star cluster. Their findings suggest that at least 35% of the recorded binary black hole collisions might have occurred in star clusters.
What Happens When Black holes Collide?
As per the Black Hole Encyclopedia of Space Telescope Science Institute (STScI), black holes merging can become one bigger black hole but it will be an extremely violent event that even computer simulations could not exactly show it. But scientists know that it would produce tremendous energy and send massive ripples, called gravitational waves, through the space-time fabric of the cosmos.
No one has ever witnessed black holes merging yet, although it has been detected many times. There are even galaxies with two supermassive black holes that move dangerously close to each other. Theoretical models suggest that these black holes spiral toward each other until they eventually collide.
Gravitational waves have been a fundamental prediction of Einstein's theory of general relativity and detecting them would provide an understanding of gravity, as well as give new insights into the physics of black holes. Powerful instruments are currently under construction to detect these waves from outer space.
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