The ground-breaking measurement reveals a black hole rotating at a quarter of the speed of light

A team of astronomers has managed to calculate the speed of rotation of distant supermassive black holes thanks to the chance meeting of objects with a star, which it immediately destroyed.

All black holes have spin, which they develop through their interactions with other matter in space. When black holes grow by accreting matter, they can spin at higher speeds; when they grow through mergers with other massive objects, they tend to slow down. In their latest work, the team was able to infer the spin of a supermassive black hole by measuring the wobble of its accretion disk after a star is disrupted, a polite word for tearing from the giant object. They found that the spin of black holes was less than 25% of the speed of light, at least for a black hole. The teams research was published today in nature.

The rotation of a black hole is related to its evolution. For example, a black hole that grew from the steady accretion of gas over billions of years tends to be high-spinning, while a black hole that grew from mergers with other black holes should spin slowly, said Dheeraj Pasham, an astronomer at MIT and director. author of the new paper, in an email to Gizmodo.

Black holes are regions of space-time with gravitational fields so intense that not even the light can escape them beyond a certain point, called the event horizon. But black holes also pull a lot of material into their vicinity, which is great, allowing researchers to study the physics of these shadow giants. The material accumulation of rocky debris, dust and gas in the black hole’s accretion disk and its bright glow is what makes it possible for the Event Horizon Telescope to direct image of black hole shadows.

There are other ways in which supermassive black holes and therefore their host galaxies can grow over time, and each mode has a specific prediction for the spin distribution, Pasham added. Thus, if we can measure the spin disruption of supermassive black holes, we can constrain how they (and their host galaxies) grew over cosmic time.

Occasionally, unlucky stars that pass too close to a black hole are trapped by its tidal force and torn apart; part of the star may be ejected into space, while part of it lies in an abundance of superheated stellar material that becomes part of the black hole’s accretion disk.

The spinning giant was discovered in February 2020, when the Zwicky transient detected a flash of light from an object 1 billion light-years from Earth. The team studied the light source, which they believed to be a tidal disruption event, for more than 200 days using NASA’s NICER telescope, which surveys the cosmos at X-ray wavelengths.

The group found that X-ray emissions from the source peaked every 15 days. This led the team to conclude that these peaks occurred when the accretion disk was directly aligned with the telescope. Working backwards from this apparent wobble of the accretion disk, the team estimated the black hole’s approximate mass, as well as that of the star from which it had taken material. They arrived at an estimate for the rotation of the black hole itself.

It is not the first time that a rotation of black holes has been calculated; in 2019, a team that included Pasham found a signal which they linked to a black hole spinning at about half the speed of light. However, as Pasham told Gizmodo, the nature of that signal is still a mystery, while the new measurement corresponds to the rotation of black holes in accordance with relevant theories. While a black hole spinning at a quarter of the speed of light (167,654,156 miles per hour, or 74,948,114 meters per second) is still very fast in our simple human terms, we must remember that these are some of the most extreme objects in the universe.

Pasham added that a black hole cannot spin faster than 94% of the speed of light, or 630,379,631.62 mph (281,804,910.52 m/s). Kip Thorne calculated in 1974. This maximum is due to the amount of torque on the black hole created by radiation emitted by the accretion disk and absorbed by the black hole. MIT also produced a helpful video to walk people through the new findings, which you can watch below:

X-ray flares from distant objects in space are often a sign of black holes to their usual mess. In 2021, a team including Pasham determined that a strange object in space known as Lopa may have been a black hole is being born; in 2022, another flash from an object 8.5 billion light years away turned out to be the most distant tidal disruption event yet observedand which saw its black hole blasting a jet of superheated material directly at Earth.

The team will continue to catalog tidal disruption events, with the goal of understanding the spin distribution of supermassive black holes. The arc toward understanding the universe of black holes is long, but deciphering their physics can help us unravel some of the universes greatest mysteries.

More: Astronomers discover the most massive stellar black hole in the Milky Way