Not only is the supermassive black hole at the heart of our galaxy spinning, it’s doing so at almost full speed, pulling anything near it along for the ride.
Physicists calculated the rotation speed of the Milky Way’s supermassive black hole, called Sagittarius A* (Sgr A*), using NASA’s Chandra X-ray Observatory to view X-rays and radio waves emitted by outflows of material.
Rotation speed a Black hole It is defined as “a” and is given a value from 0 to 1, where 1 represents the maximum rotational speed of a given black hole, which is a large fraction of the speed of light. Ruth A. DaliA Penn State physicist and his colleagues found that the rotation speed of Sagittarius A* ranges between 0.84 and 0.96, which is close to the upper limit set by the width of the black hole. The team described Sgr A*’s astonishing speed in a study published October 21 in the journal Monthly Notices of the Royal Astronomical Society.
“The discovery that Sagittarius A* is rotating at its maximum speed has far-reaching implications for our understanding Black hole “The formation and astrophysical processes associated with these magnificent cosmic objects.” Xavier CalmetteThe theoretical physicist at the University of Sussex, who was not involved in the research, told Live Science in an email.
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Black holes are an obstacle
The rotation of a black hole is different from the rotation of other cosmic objects. While planets, stars, and asteroids are solid bodies with physical surfaces, black holes are actually regions of spacetime bounded by a non-physical outer surface called the event horizon, beyond which light cannot escape.
“While the rotation of a planet or star is governed by the distribution of its mass, the rotation of a black hole is described by its angular momentum,” Calmette said. “Due to the intense gravitational forces near the black hole, the rotation causes space-time to become extremely curved and twisted, forming what is known as the ergosphere. This effect is unique to black holes and does not occur with solid objects such as planets or stars.”
This means that when they spin, black holes literally twist the fabric of space-time itself and pull anything within the atmosphere.
This phenomenon, called “frame drag” or the “lensing-and-thering effect,” means that to understand the way space behaves around a black hole, researchers need to know its rotation. Dragging the frame also causes strange visual effects around black holes.
“As light travels near a rotating black hole, the rotation of space-time causes the light’s path to be curved or twisted,” Calmette said. “This results in a phenomenon called gravitational lensing, where the path of light is bent due to the gravitational influence of the rotating black hole. The dragging effect of the frame can create light rings and even create the black hole’s shadow. These are manifestations of the effect of black holes’ gravity on light.”
The theoretical maximum speed of a black hole is determined by how it feeds on matter, and thus how it grows.
“When matter falls into the black hole, it increases the black hole’s rotation, but there is a limit to the amount of angular momentum it can have,” Calmette said. “Another factor is the mass of the black hole. Larger black holes have higher gravity, which makes it more difficult to increase their spin.
“In addition, interaction between the black hole and its surroundings, such as accretion disks, can transfer angular momentum and affect the black hole’s rotation,” he added.
This could explain why Sgr A*, which has a mass equivalent to about 4.5 million Suns, has a rotation speed of between 0.84 and 0.96, but the supermassive black hole that is rapidly feeding at the heart of the galaxy M87 – the first black hole ever imaged – is like that. It rotates at a speed between 0.89 and 0.91, even though it has a mass equivalent to 6.5 billion suns.
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