What scientists have learned from the biggest ever collision of black holes

Scientists in the United States have discovered the biggest-known merger of two black holes using gravitational wave detectors.

The scientific findings from the collision, which was recorded in November 2023, were presented at this year’s International Conference on General Relativity and Gravitation in Glasgow, United Kingdom.

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What is a black hole?

Black holes are cosmic objects, or regions of space, which comprise a large concentration of matter packed into a relatively tiny space.

The enormous amount of mass packed into a small space creates a gravitational pull so strong that nothing, not even light, can escape it.

As no light is emitted from black holes, rendering them invisible, we do not know what, exactly, is inside them.

Black holes are believed to form when giant stars collapse at the end of their lives. The giant stars collapse when they run out of energy to continue fusion reactions, which keep them bright and hot.

Illustration of a giant star [Shutterstock]

When and how was this black hole collision observed?

The collision, which caused a gravitational wave, or sudden ripple in space-time, was observed on November 23, 2023, just before 13:00 GMT by two detectors simultaneously.

These detectors, in the US states of Washington State and Louisiana, are operated by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and are part of the LIGO-Virgo-KAGRA (LVK) network.

The LIGO comprises two large-scale laser interferometers, which act as antennae to detect gravitational waves.

The gravitational wave, which was detected for 0.1 seconds as a result of the collision, was named GW231123.

LIGO, which is funded by the US National Science Foundation, is a large-scale physics observatory that detects gravitational waves using highly sensitive laser interferometers. It was designed and built by scientists and engineers at the California Institute of Technology (Caltech) and the Massachusetts Institute of Technology (MIT).

Since black holes are completely dark – absorbing everything, including light around them – their collisions are invisible. This is why their mergers are detected by measuring the gravitational waves that they cause. About 300 black holes have been detected through gravitational waves.

Virgo, operated by the European Gravitational Observatory, and KAGRA, operated by the Ministry of Education, Culture, Sports, Science and Technology-Japan (MEXT), are similar interferometers.

What happens when black holes collide?

When black holes collide, they merge to form a larger black hole, which is what happened in this case.

The two black holes that collided were about 100 and 140 times the mass of the Sun individually. The collision produced a black hole more than 265 times the mass of the Sun.

This was much larger than the last largest black hole collision, GW190521, which was about 140 times the mass of the Sun. That collision was observed on May 21, 2019 and was detected 17 billion light years away from the Earth.

What have scientists learned from this?

The discovery has led to some revelations about black hole mergers.

“It increases our confidence that black holes can go through a series of successive mergers, to produce much more massive black holes,” Mark Hannam, a professor at Cardiff University and a member of the LIGO Scientific Collaboration, told Al Jazeera.

“We think it’s unlikely that black holes that massive form out of dying stars, so the previous-merger explanation is currently considered the most likely explanation,” Hannam said.

Will this have any impact on the Earth?

No, the black hole collision will not impact the Earth or the Milky Way galaxy.

Hannam said that the black hole merger that was detected is from an event that happened between a few million light years and 10 billion light years away.

This means that the merger took place millions of years ago, since a light year is how far light travels in one year, and gravitational waves travel at the speed of light.

Hannam explained that the distance of the merger can also be written as about 3 gigaparsecs.

“A parsec is about 31 trillion km, so converting the distance into kilometres produces numbers that don’t really have everyday names!”