BLACK HOLE                      DARK MATTER      

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What is Black  hole

Black hole is an extremely dense  celestial body whose intensity of gravitational field is so high that not even electromagnetic radiations could escape .It is an extremely high density matter of very low volume due to its abnormally strong cohesive force of contraction .It shape and size are generally undefined ,but mostly it takes the shape which will ensure its least volume. Any object or even wave having energy will always have a tendency to get sucked up due to its tremendous tidal divergence. It is said that in every galaxy the black hole always orient itself in the vortex surrounded by the other celestial objects. Its also have the funnel like curvilinear shape or tunnel having a vortex whose end cannot be detected. The centre of the black hole where the gravitational tide is maximal is called singularity. No object could theoretically survive there due to its extreme pressure and density ,before reaching there the object collapses.

 How are they formed 

Black holes are formed generally from supernova explosion .It is the explosion of a massive star by a sharp increase in brightness followed by the redshift. Gradually all the fuels of the star gets utilized after the star explodes to a giant red ball then contracts moderately to reduce its volume and increase its density to a dwarf star and finally to black hole it may leave behind a fairly massive burned out stellar remnant. With no outward forces to oppose gravitational forces, the remnant will collapse in on itself. The star eventually collapses to the point of zero volume and infinite density. Black holes has the tendency to move the object to its schwarzchild radius. To get sucked up in the black hole one has to cross the event horizon of the schwarzchild radius. At this point the escape speed of the body equals the speed of light and not even light could escape. 

The Schwarzchild radius is    vesc = (2GM/R)1/2


Did you know
If the Sun was replaced with a black hole that had the same mass as the Sun, the Schwarzschild radius would be 3 km (compared to the Sun's radius of nearly 700,000 km). Hence the Earth would have to get very close to get sucked into a black hole.This shows  the effect of its tidal divegent force .

How are they detected 

 If a black hole passes through a cloud of interstellar matter, or is close to another "normal" star, the black hole can accrete matter into itself. As the matter sucked up towards the black hole, it gains kinetic energy, heats up and is squeezed by inward forces. The heating ionizes the atoms, and when the atoms reach a few million degrees Kelvin, they emit X-rays. The X-rays are sent off into space before the matter crosses the Schwarzchild radius and crashes into the singularity. Thus there is a random variation of emitted X-rays. The infalling matter that emits X-rays does not fall into the black hole at a steady rate, but rather more sporadically, which causes an observable variation in X-ray intensity. Additionally, if the X-ray source is in a binary system, the X-rays will be periodically cut off as the source is eclipsed by the companion stars which are perfect source of in falling material for a black hole.

Cygnus X-1 is the longest known black hole which is a highly variable and irregular source with X-ray emission that flickers in hundredths of a second. Its companion star is HDE 226868.



Recently dark matter have been detected by scientists. These mysterious substance covers about 85% of the universe .

They have discovered  a surge of these particles from the innermost zone of the Milky way whose radiations closely match with that of dark matter .Dark matters are said to have been holding the mystery of the formation of the universe . These are extremely high energetic particles ,astronomers had realized that these flowing dark matters holds the galaxies and generates the extra gravity to create a balance of  forces .Without it the  motion of the galaxies in this dynamic universe is high enough to make the galaxies fly apart .Scientist feels that these dark matter is made up of particles called neutralinos .These are basically transparent and can pass through any body. Trillions of such dark matter are also present in earths atmosphere  and passes through our body every second .These do not interact with ordinary matter.

Dark matter was also been detected by a surge of positron ,a form of antimatter. The observation fitted predictions that dark matter would be much dense in the galactic core where the particle would collide and smash emitting positron .




Prepared   by

Rajkrishna Paul




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