In fact, the phenomenon of black holes devouring celestial bodies is common in the universe, but once scientists discovered that the "black hole preys on the whole" process is different. On November 22, 2014, ASASSN detected a set of X-rays, which ASASSN refers to as the "all-day automated search for supernova projects."
But this isn't a supernova, this time from the center of a galaxy 290 million light-years away, which we now think is the signal from a constant very close supermassive black hole.
This black hole has millions of times the mass of our Sun, the stars are disintegrated by the black hole, the black hole engulfs the star, yes, this is indeed what astrophysicists say when explaining this phenomenon.
We think events like this are rare, and in a galaxy it may occur only once every 100,000-100,000 years, and such events are called "tidal (force) disintegration events" .
When the star approaches the black hole, the black hole is more attractive to one side of the star than the other, which tears the star into pieces, and then the material that spirals into the black hole forms an accretion disk.
It is a ring of gas and dust with acceleration, which heats up and shines, and the light emitted reaches the earth in the form of visible light, ultraviolet light, and X-rays.
What's special about this is that it turns a resting, dormant black hole into one we can use
The black hole that is being swallowed up is observed, and this is what it looks like. Well, if that seems boring, you should look at some of the artist's work on this event, but cynical people might ask, "How do we know this is really happening?"
Could it be that scientists want more research funding? Or do you want to encourage people to "go to science"? I'll explain later how we know this is actually happening. But first of all, the evolution of this event has become strange .
In the years after the event, the scientists looked for three X-ray telescopes to observe this part of the sky, and they found strong and regular X-ray pulses that brightened and dimmed every 131 seconds, a pattern that could be seen in the data from all three telescopes, and they observed for 450 days. But this law maintains this rhythm and does not weaken.
Over time, the relative intensity of the pulses has become stronger, and the X-ray signal has increased by about 40%, so what causes this X-ray pulse? What information can it provide us about black holes?
We have to start from the basics, black holes are one of the simplest objects in the universe, they have only two properties, mass and spin, there should be electricity prices, but because black holes are basically neutral, mass and spin are the focus of discussion.
Mass is relatively easy to determine, far from black holes You can even use Newtonian physics to estimate the mass of black holes after measuring their effects on other celestial bodies.
After measuring black holes in this way, scientists found black holes with unequal masses: small masses only a few times that of the sun These are called stellar black holes; large masses up to billions of times the mass of the sun, these are supermassive black holes.
It is widely believed that there is a supermassive black hole at the center of most galaxies, how is the spin of the black hole measured?
Since black holes are formed from collapsing stars, and we know that stars rotate, all black holes should rotate as well, I mean to ask how small is the probability that a pile of matter is just compressed into a point without any rotation?
This is really impossible, and in addition, foreign objects that fall into the black hole will transfer their angular momentum to the black hole, which is like a figure skater, if you can shrink your arm into a small point, you should be able to imagine that the black hole spins very quickly.
But spin is more difficult to measure, it's not like mass, spin only affects objects around the black hole, but we have a way.
There are three ways to measure, and to grasp all three of them you have to understand ISCO.
In Newtonian physics , you can make a steady circular motion around an object at any radius , no matter how close you are to the center object , but this is not the case in general relativity.
Under general relativity there is an innermost stable circular orbit called ISCO. If the radius of circular motion is within ISCO , then this orbit is not stable, it falls into a black hole, and when it sees a black hole that is devouring stars, the inner edge of the accretion disk is ISCO, and the size of ISCO depends on the spin of the black hole.
The faster the spin, the smaller the ISCO, which is in the case of the black hole spinning and accretion disk, the rotation direction is the same, the particles will go closer when the black hole spins, compared to the black hole when it does not spin the particles will go farther, that is to say, you can think of the black hole's spin as an effect on the gravity of the black hole.
Black hole spin is generally measured in the physics world by a parameter without units, which is 0 when the black hole has no spin And the maximum spin is 1. This number can also drop to -1 when the black hole spins in the opposite direction of rotation of the accretion disk.
As the spin increases, the RADIUS of isCO decreases by up to a factor of 6 until it is equal to the event horizon, and when the two are equal, many scientists believe that the black hole cannot rotate any faster. Because if there is an object that can make a circular motion within the event horizon, then light can escape from the black hole, so that we can see the singularity of the black hole, which is called a "naked singularity", which many scientists think is quite awkward.