Black holes are incredibly dense stellar objects that form when dying stars collapse in on themselves. Nothing can escape their gravitational pull, including light and other black holes. Now, an unprecedented merger between two huge black holes has been reported by detectors based in Washington and Louisiana.
The two black holes, both located far beyond the outer limits of the Milky Way, began circling each other eons ago. Each was more than 100 times more massive than our sun.
Detecting Gravitational Waves
On November 23, 2023, twin observatories, collectively known as the Laser Interferometer Gravitational-Wave Observatory (LIGO), detected a gravitational wave — a form of radiation distinct from the electromagnetic radiation captured by other observatories.
LIGO consists of two concrete tubes, each exactly 4 km long (about 2.5 miles) and placed perpendicular to each other. A laser beam is split and travels along each tube, where a mirror reflects the laser. The light beams that make up the laser cancel each other out when they return to their source.
When a gravitational wave passes by, it literally distorts spacetime, causing the laser beams, the concrete tubes they are housed in, and the Earth itself to wobble very slightly. The distance shifted is a minuscule fraction of the size of a subatomic particle. Still, it alters the beams in a way that LIGO can use to record information about the source of the gravitational waves.
Read More: Here’s What Would Happen If You Walked Through a Black Hole
A Record-Breaking Black Hole
LIGO's analysis suggested the signals came from two objects around 10 billion light years away from Earth, rotating around 400,000 times faster than our planet. The waves recorded the ripples produced as the two huge objects merged to form an even larger black hole more than 225 times the size of our sun. These record-breaking features of the merger, which neared the limits permitted by Einstein's theory of relativity, made the signal hard to interpret. The results are now being publicly presented for the first time.
"This is the most massive black hole binary we've observed through gravitational waves, and it presents a real challenge to our understanding of black hole formation," said Mark Hannam, an astrophysicist from Cardiff University and a member of the LIGO Scientific Collaboration, in a press release.
The research team suspects that the two merging black holes were themselves products of other black hole unions, which would explain how they attained their universe-shaking size and speed. When black holes merge, they cause their offspring to spin even faster.
This is far from the first black hole merger to be detected. Over 300 such events have been previously recorded, although the largest such event until now produced a black hole that was a meager 140 times the size of the sun.
Making (Gravitational) Waves
Gravitational wave detectors have given stellar researchers a new tool with which to study the cosmos. LIGO, alongside the Italian detector Virgo, recorded the first direct detection of gravitational waves in 2015.
The data deluge resulting from LIGO's latest observation will occupy the project's researchers for some time.
"It will take years for the community to fully unravel this intricate signal pattern and all its implications," said Gregorio Carullo, an astrophysicist at the University of Birmingham, in a press release. "Despite the most likely explanation remaining a black hole merger, more complex scenarios could be the key to deciphering its unexpected features. Exciting times ahead!"
Read More: Black Hole Feast Sparks Brightest Cosmic Explosion Ever Recorded
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RJ Mackenzie is a freelance science reporter based in Glasgow, Scotland. He covers biological and biomedical science, with a focus on the complexities and curiosities of the brain. He has degrees in neuroscience from the University of Edinburgh and the University of Cambridge. He has written for National Geographic, Nature, and The Scientist, among other publications.
