An object roughly the size of the solar system not only contains hundreds of billions of stars around it, but also twists the invisible “fabric” of space-time itself.
Overnight in Chile’s famous Atacama Desert – the driest desert on the planet, where the weather is completely cloudless and the nights are clear almost all year round. That is why the entire radio telescope complex is located there. So, in the photo above the antenna, the Milky Way extends to the very center of the galaxy, located in the constellation Sagittarius. Unfortunately, in Russia it is very difficult to see it, except perhaps in summer somewhere in the south, just above the horizon.
When the Sagittarius A* object was photographed, the resulting images finally confirmed what scientists had long understood: there is a supermassive black hole. According to current ideas, its diameter roughly corresponds to the diameter of Pluto’s orbit, that is, it roughly corresponds to the size of the solar system or, in any case, to its main part. But in fact, the mass of more than four million Suns is contained in these dimensions. This monster is located about 27 thousand light years away from us.
Scientists are trying to find out what is happening to him there. And they discovered that this black hole, probably like everything or almost everything in the Universe, rotates around its axis. This can be seen in how this rotation affects the behavior of nearby stars. The fact is that Einstein, as you know, discovered that any mass is bent, twisting the fabric of space-time, creating in it something like a funnel in which everything is attracted to it, and this is the gravitational force. But in addition, he also realized that this spatial structure is also affected by the rotation of a massive object. It seemed to drag on space-time. And this can be seen through the behavior of an object flying around it. For example, astronomers recently discovered that the orbit of one of the stars closest to the center of the galaxy is constantly shifting, a phenomenon called precession. It describes its ellipse around the center of gravity, but each new ellipse it creates is slightly offset in the direction of the black hole’s rotation.
The question is: how fast does the black hole at the center of our galaxy rotate and, in general, what is the maximum possible limit to this speed? The fact is that rotation creates centrifugal force, that is, it makes things fly in different directions and thus oppose the force of gravity. And for example, if our Earth begins to rotate too quickly around its own axis, it will cease to exist as a planet: all its matter will fly away. It is true that this cannot happen with a black hole: there is no matter in it at all. Inside there is such crushing that the particles cannot exist in their physical form.
And yet, the current laws of physics do not allow it to rotate as fast as desired. However, scientists have never observed it spinning faster than the speed of light, or 300,000 kilometers per second. Despite being so close, at up to 99% the speed of light, some still spin. For example, scientists have calculated the rotation speeds of nearly two dozen black holes ranging in mass from a few million to hundreds of millions of suns, and it turns out that more than half of them have a “spin” (spin rate) of 80 to 99 % speed of light. Additionally, for each black hole – based mainly on its mass – it is possible to calculate its maximum possible magnitude of rotation between 0 and 1, where 0 means no rotation at all and 1 is the maximum level. Astrophysicists recently calculated that for Sagittarius A* the number is between 0.84 and 0.96, much higher than previously thought. It turns out the supermassive black hole at the center of the Milky Way is spinning almost to the limit of its capabilities. Scientists say that when the galactic center rotates very quickly, this could mean that the galaxy has survived a collision with a neighboring large galaxy, i.e. its current behavior allows us we understand something about its past.