A team of astronomers has managed to calculate the rotation speed of a distant supermassive black hole because the object accidentally collided with a star, which it promptly destroyed.
All black holes have a spin that they develop through their interactions with other matter in space. As black holes grow through the accumulation of matter, they can spin faster; As they grow by merging with other massive objects, they tend to slow down. In their most recent work, the team managed to infer the spin of a supermassive black hole by measuring the wobble of its accretion disk after a star was disturbed – a polite word for torn – by the gigantic object. They found that the black hole’s spin was less than 25% of the speed of light – slow, at least for a black hole. The team’s research was published today in nature.
“The rotation of a black hole is related to its evolution. “For example, a black hole that grew through steady accumulation of gas over billions of years tends to spin strongly, while a black hole that grew through mergers with other black holes should spin slowly,” Dheeraj said Pasham, an astronomer at MIT lead author of the new paper, in an email to Gizmodo.
Black holes are regions of space-time with gravitational fields that are so intense that not even light can escape them beyond a certain point called the event horizon. But black holes also attract a lot of material near them, which is brilliant and allows researchers to study the physics of these shadowy giants. The material – a collection of rocky debris, dust and gas – is the black hole’s accretion disk, and its bright glow allows the Event Horizon Telescope to Directly image shadows of black holes.
“There are other modes in which supermassive black holes – and therefore their parent galaxies – can grow over time, and each mode has a specific spin distribution prediction,” Pasham added. “So if we can measure the spin perturbation of supermassive black holes, we can determine how they (and their host galaxies) have grown over cosmic time.”
Occasionally, unfortunate stars that get too close to a black hole are caught by its tidal force and torn to pieces; Part of the star may be ejected into space, while another part will be stretched into a mass of superheated stellar matter that will become part of the black hole’s accretion disk.
The rotating giant was discovered in February 2020 when the Zwicky Transient Facility detected a flash of light from an object 1 billion light-years from Earth. The team studied the light source, which they thought was a tidal event, for over 200 days using NASA’s NICER telescope, which observes the cosmos at X-ray wavelengths.
The group found that the source’s X-ray emissions peaked every 15 days. This led the team to conclude that these spikes occurred when the accretion disk was aimed directly at the telescope. Based on this apparent wobble of the accretion disk, the team looked at the approximate mass of the black hole as well as that of the star from which it had scooped material. They came up with an estimate for the spin of the black hole itself.
This is not the first time the spin of a black hole has been calculated; in 2019, a team that included Pasham a signal found that they were associated with a black hole rotating at about half the speed of light. However, as Pasham told Gizmodo, the nature of this signal is “still a mystery,” whereas the new measurement corresponds to the black hole’s spin, in agreement 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 it is 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 miles per hour (281,804,910.52 m/s). Kip Thorne did the math in 1974. This maximum is due to the torque acting on the black hole, generated by the radiation emitted by the accretion disk and swallowed by the black hole. MIT also produced a helpful video to walk people through the new findings, which you can watch below:
X-ray flashes from distant objects in space are often a sign that black holes are up to their usual mischief. In 2021, a team that included Pasham discovered that a strange object in space known as “the cow” may a black hole is created; In 2022, another flash was found to have originated from an object 8.5 billion light years away the most distant tidal disruption event observed to dateand whose black hole shot a jet of superheated matter directly at Earth.
The team will continue to catalogue tidal disruption events, with the goal of figuring out the spin distribution of supermassive black holes. The road to understanding the universe of black holes is long, but deciphering their physics could help us unravel some of the universe’s greatest mysteries.
More: Astronomers discover the heaviest stellar black hole in the Milky Way