Black Holes

Presented by-Jyotsana SharmaBtech (hons.) CSERA1803A10

Black HolesContents---

• History.• Formation of black holes.• Gravity deforms space time.• Gravity bends path of light.• Event horizon• Falling into black holes.• Rotating black holes.• Techniques• References

History--

The idea of preventing light from escaping as described by general theory of relativity was given by John Michelle. Even the British astronomer Pierre -Simon Laplace came with the same conclusion.

The intense gravitational field left when a giant star collapses.It is called a black hole because not even light can escape.Objects too heavy to be neutron stars collapse to black holes.

Formation-

As the mass increases, so does the gravitational pull. If the gravitational pull is such that even light can escape , then a black hole is formed.

Formation Continued…

Gravity deforms space time

Diagrammatical representation

Gravity bends the path of light

Event horizon

The point at which no light can escape.

A nonrotating black hole has only a “center” and a “surface”.

• The black hole is surrounded by an event horizon which is the sphere from which light cannot escape

• The distance between the black hole and its event horizon is the Schwarzschild radius (RSch= 2GM/c2)

• The center of the black hole is a point of infinite density and zero volume, called a singularity

Falling into a black hole

Falling into a black hole gravitational tidal forces pull spacetime in such a way that time becomes infinitely long (as viewed by distant observer). The falling observer sees ordinary free fall in a finite time.

Falling into a black hole• Signals sent from the freely falling observer would be

time dilated and red shifted.• Once inside the event horizon, no communication with

the universe outside the event horizon is possible.• But incoming signals from external world can enter.• A black hole of mass M has exactly the same

gravitational field as an ordinary mass M at large distances.

Seeing black holes

Rotating black holes

• A rotating black hole (one with angular momentum) has an ergo sphere around the outside of the event horizon

• In the ergo sphere, space and time themselves are dragged along with the rotation of the black hole

1-Accertion disks and gas jets.

2-Strong Radiation emissions

3-Gravitational lensing

Techniques for finding black holes

Types of Black Holes--

1-Supermassive Black holes.

2-Stellar- mass black holes.

3-Intermediate mass black holes.

Advantages and Disadvantages--

They can be significant in this way:1-Individual modes may dominate the time evolution of some perturbation, and a whole set of them could be used to completely describe this time evolution.

The disadvantages are that –1-when a black hole evaporates information is really gone.2-Due to this there is trouble in energy conservation.3-Invariance in time predictability.

References---

1-www.google.com.2-www.wikipedia.com.3-Anatony on Black holes.

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