Black hole | Definition , Equation , Structure and Types .

A Black hole is a place in space where gravity pulls so much strong that neither a particle nor electromagnetic waves like light can escape from it .

Black holes are invisible because no light can escape from black hole . However , space telescopes with special instruments helps to find black holes .They can observe the behavior of material and stars that are very close to black holes .

Fig. 1 Black hole

Few years ago black holes were just an imagination , but On 11 February 2016 , the LIGO scientific collaboration and the virga say about the first direct detection of gravitational waves , which also represented the first of black hole merger . On 10 April 2019 , the first direct image of a black hole and its vicinity was published .

Equation and Conditions for black hole 

For more better understanding , Consider a spherical body of mass M and radius R . suppose due to some reason the volume goes on decreasing while , the mass remains the same . Then there will be a time when object will be start to behave like a black hole . 

V = ( GM/R )1/2 

The escape velocity ( V )  from such a dense material will be very high . suppose the radius is so small that the value of escape velocity ( Formally , escape velocity is the speed an object must attain to ” break free ” of gravitational attraction of another body  )  is more then or equal to speed of light , then that spherical body will  behave like a black hole . 

eg- We know that , radius of earth is nearly  6400 km and escape velocity from earth surface is nearly 11.2 km/s . but if we if we compress the radius of earth till nearly 8.77 mm and mass of earth will be same as before , then value of escape velocity from earth surface will be equal to speed of light means earth will start behaving like a black hole .

Structure of Black hole

There are two basic parts of a black hole  the Singularity  and the Event horizon .

The event horizon is the boundary  in space time that makes where the escape velocity from the mass is the speed of light . It is not a physical surface , but a sphere surrounding the black hole through which matter and light can pass only inward toward the mass of the black hole . Its radius is known as Schwarzschild radius . 

As predicted by theory of general relativity , the presence of mass deforms space-time in such a way that the path taken by the particles or electromagnetic waves ( eg . light ) bend towards the mass . 
If an event occurs inside the boundary ( event horizon ) , outside observers can not get any information of event because neither electromagnetic waves or particles can reach  out side from event horizon , that why we are unable to determine what’s going on inside the boundary . 

The singularity is at the center and where the mass resides  and space -time curvature becomes infinite  . Once any matter comes inside the horizon then that matter will fall to the center ( singularity ) with such strong gravity , the matter converts to just a point – a tiny , tiny volume with a crazy – big density . It’s likely that the laws of physics break down at the singularity . Scientists are actively engaged in research to know about the singularities and what happens at these singularities  as well as  they are trying to give a full theory that better describes what happens at the singularities  ( center of black holes ) .

Types of Black hole 

Stellar , Intermediate , Supermassive and Miniature are basically four types of black hole .

( 1 ) Stellar black hole 

It is formed by the gravitational collapse of a star . This collapse also causes an exploding star or a supernova , that blasts part of the star into space . Stellar black holes have masses ranging from about 5 to around 50 of solar masses .The closest stellar black hole to earth is V616 mono cerotis which is 3000 light year away and 9 to 13 times the mass of the sun .

Fig. 2 Stellar black hole

( 2 ) Intermediate black hole 

It’s estimated that the intermediate mass black hole have a mass between 100 to 1000 solar masses and located roughly 290 million year from earth . Intermediate black hole is such large in size , no single star could ever form such a heavy black hole . Cosmology experts think that such black holes could form is for a single black hole to devour lots and lots of material to get up to the required heft , or for individual black holes to merge together . At that time we have not proper answer regarding the origin of intermediate black holes . 

( 3 ) Supermassive black hole

The Supermassive black holes are largest black holes . These black holes have masses more than 1 million suns together . Cosmology experts have found proof that at the center of every large galaxy , a supermassive black hole exist . Mass of supermassive black holes are nearly 4 million sun . Cosmology experts think that supermassive black holes were made at the same time as the galaxy they are in .

Fig. 3 Supermassive black hole

( 4 ) Miniature black hole

Miniature black holes are also known as quantum mechanical black holes or micro black holes . These black holes are hypothetical tiny black holes and for which quantum mechanics effects play an important role .

Miniature black holes are hypothetical tiny black holes predicted in 1971 by the great scientist Stephen Hawking , according to him they are not that black evaporate with time . A body of very small mass can also behave like a black hole , just it’s mass should be above the Planck mass (about 22 micrograms) . To make a black hole , mass of body must be concentrated such a way that the value of escape velocity from the bod exceeds the speed of light .

Evaporation of black hole is inversely proportional to the size of black hole due to that micro black holes are highly unstable .

Fig. 16.4 Miniature black hole

Leave a Comment

Your email address will not be published.