Accretion Disc.

Discovering the nature around the black hole.

    One of the most important parts of a black hole by which we can actually locate or see a black hole is the accretion disc. So, what is this disc? The answer to this question is very simple. It is a disc formed by diffused matter around a heavy, dense, or massive central body, such as a black hole. So, now it is clear that the disc contains only diffused material, but then why does it glow so much? The reason is that, due to friction, the diffused material is pulled inward towards the central body, and under this immense pressure and friction, it gets compressed and its temperature increases to a very high level, a level so high that the diffused material appears to glow and it emits electromagnetic radiation, and the frequency of the waves depends on the mass of the central body.

What physics says about it,

    The physical definition of a black hole is when matter accreted has enough rotational and angular momentum to prevent it from falling inward into its own accretor. As black holes take everything inside them once it is trapped, there is no possibility That light can also escape its grasp, so like its name, it is pitch black, so it is very difficult to detect. But once the black hole is fed by its vicinity, it becomes the brightest in the cosmos.  There are many ways for black holes to light up their cosmic surroundings. Some of the black holes require very special circumstances, but one that is universal is that whenever matter falls into a black hole, there is the production of thermal radiation. Matter falling towards a central object under the influence of gravity gets accelerated to higher and higher speeds and travels faster and faster, gaining more and more kinetic energy. But once a particle of falling matter plunges into an accretion disc – and possibly earlier – the particle’s motion is disturbed. So, due to these frequent collisions, there is no specified orbit of rotation.

 The entire motion is chaotic; none of the particles follow a definite path. However, this is typical of an accretion disc. As the particles fall inwards, motion becomes chaotic, and matter in the accretion disc is heated to very high temperatures, the temperature of which is far beyond our imagination. The maximum temperature in an accretion disc around a super massive black hole, which is about a hundred times the mass of our sun, will be around one million kelvin, and for the disc around a stellar black hole, it can be up to a factor of a hundred higher than the super massive one. By comparison, the temperature in the core of our sun amounts to about 15 million Kelvin, so by this we can get an idea of how high the temperature of the accretion disc can be. In physics, wherever there is a reference to heat, there is always a word about thermal electromagnetic radiation. Everyone emits thermal radiation in some way because, according to the law, the heat in a body cannot remain constant if it is to be released or exchanged with the environment over its entire lifetime. Only a body with an absolute zero temperature would not, but such bodies do not exist in this world. As the temperature of the body increases, so does the energy emitted in the form of radiation. The temperature of an accretion disc around a black hole is high enough for the disc matter to emit large amounts of highly energetic X-rays.

Concluding it with the help of quasars

    These accretion discs are also known as quasars. Quasars are the oldest known bodies in the universe and (with the exception of gamma ray bursts) the most distant objects we can see until now, as well as the brightest and most massive, outshining trillions of stars. So, all that we see in the accretion discs are small quasars which collide with each other, releasing an enormous amount of heat and energy. Therefore, the black holes would have been hard to detect and our research into them would not have been to its level where it is now if there had been no accretion disc around the black hole. They are the source of light or vision for us to see it.