There’s A New Cosmic DNA Test For Black Holes That Can Help Trace Back Their Origins
Black holes do not have many defining characteristics that can help astronomers trace back their origins. Fortunately, new research has suggested a cosmic DNA test for black holes.
These tests analyze gravitational waves, which are tiny ripples in the fabric of spacetime, a concept that was proposed 110 years ago by Albert Einstein in his theory of general relativity.
A team of scientists led by researchers at the University of Cardiff has found that the ancestry of supermassive black holes could be revealed in their sizes and rotations. In addition, the spin patterns of these black holes could determine which region of space they were born in.
Facilities like the Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo Observatory detect gravitational waves, and they can be used to interpret the data that is collected.
“Our study gives us a powerful, data-driven way to identify the origins of a black hole’s formation history, showing that the way it spins is a strong indicator of it belonging to a group of high-mass black holes, which form in densely populated star clusters where small black holes repeatedly collide and merge with one another,” said Isobel Romero-Shaw, a researcher from the University of Cambridge.
When scientists discovered that some black holes were just too massive to have formed from a dying star, they became curious about the ancestry of all black holes.
Stellar-mass black holes with masses between 10 and 100 times that of the sun are born when giant stars die, collapsing under the force of their own gravity.
On the other hand, supermassive black holes have masses that are millions or billions of times greater than the sun.
There isn’t a collapsing star large enough to create such a massive black hole, leading to the theory that they develop due to mergers of smaller black holes.
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In 2015, LIGO and Virgo detected the first gravitational waves from merging black holes. The observation has helped confirm the merger theory.
Gravitational waves are only able to be detected when the objects involved are extremely gigantic. So, the waves are linked to the merger of black holes.
Once black holes are close enough together, they start to whirl around each other, emitting gravitational waves that create ripples in spacetime. The ripples carry angular momentum, which makes the black holes move closer and closer together.
As a result, the black holes continue releasing gravitational waves at an increasingly accelerated rate. They become even closer until they collide with one another and merge. This is how a supermassive black hole is formed.
“As we observe more black hole mergers with gravitational wave detectors like LIGO and Virgo, it becomes ever clearer that black holes exhibit diverse masses and spins, suggesting they may have formed in different ways,” said Fabio Antonini, the leader of the study from the University of Cardiff.
“However, identifying which of these formation scenarios is most common has been challenging.”
The team examined data on 69 gravitational wave events detected by LIGO and Virgo. They determined that the spin of a black hole changes when it reaches a specific mass, suggesting that black holes grow via repeated collisions in densely populated environments with millions of stars.
The study was published in Physical Review Letters.
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