what is black hole? detail of black hole. interesting topic for presentation.

1. BLACK HOLE

2. INTRODUCTION
• A black hole is a great amount of matter packed in a very small area. It is a place in space
which has such s big gravitational field, that nothing , not even light can escape.
• Scientists can not directly observe black holes, and the only way to perceive them is by
detecting their effect on other matter nearby. As the attracted matter accelerates and heats up, it
emits x-rays that radiate into space, emitting powerful gamma rays bursts, which devour
nearby stars.

3. HISTORICAL BACKGROUND
• The first time the idea of a black hole was suggested in the late 1790’s by John Michell of
England and Pierre- Simon Laplace of France. The both proposed the idea of the existence of
an “invisible star” by applying Newton law of gravity. They calculated its mass and size,
which is now called the “event horizon” that an object would need to be faster than even the
speed of light in an order to escape.
• Later in 1915, Einstein predicted the existence of black holes with his general relativity theory.
After that, in 1967, John Wheeler, an American theoretical physicist, applied the term of black
holes to what it means now.

4. PARTS OF BLACK HOLE
• Singularity
The point where whole mass of a black hole is concentrated
• Photon sphere
The outer edge where light bends but is still escapable
• Event horizon
It is a “point of no return” around a black hole
• Accretion disk
It is a disk of gases, dust , stars and planets that fall into the
orbit of black hole.

5. • The Ergo sphere
If a black hole is rotating, as it spins, its mass causes the space
and time to rotate around it
• The Schwarzschild radius
This is the event horizon radius. It is a radius at which the
escape velocity is equal to the speed of light

6. • Jets of gas
In some black holes, there is such high intensity that
magnetic fields are emitted perpendicular to the accretion
disk. Due to this, some charged particles have to go around
the black hole, because it is in a magnetic field

7. TYPES OF BLACK HOLES
• Stellar- mass black holes
Stellar mass black holes are created when massive stars explode, leaving behind a black hole with the
mass of just the few suns.
• Intermediate black holes
Such bodies could form when stars collide in a chain reactions and usually contain the mass equivalent
to hundreds and thousands of suns
• Supermassive black holes
Supermassive black holes exits in the heart of galaxies and usually contain the mass equivalent to
millions and billions of suns.

8. ACCORDING TO ITS PHYSICAL
PROPERTIES
• The Schwarzschild black hole, which has no charge, or rotation, the simplest type of black
hole that exist
• The Reisner- Nordstrom black hole, which does not rotate, but which does have electrical
charge
• The Kerr- Newman black hole, which has charge and rotates
• The Kerr black hole, which rotates and does not have charge inside

10. FORMATION AND GROWTH OF BLACK
HOLES

11. HOW WE DETECT BLACK HOLES
• Black holes do not give off light so, ae cannot just look for them.
• However astronomers can find black holes by observing the gravitational effects on other
objects nearby.
• X-rays
• Rotating stars
• Gravity lenses

12. X-RAYS
• Astronomers can discover some black holes because they are sources of x-rays
• The intense gravity from black hole will pull in dust particles from a surrounding cloud of dust
or a nearby star.
• As the particles speeds up and heat up, they emit x-rays so the x-rays don’t come directly from
the black hole, but from its effect on the dust around it.
• Astronomers use satellites to observe x-ray sources in the sky

13. ROTATING STARS
• Many stars rotate around each other, much as the planets orbit our sun. whether astronomers
see a star circling around something, but they cannot see what that something is, they suspect a
black hole.

14. GRAVITY LENSES
• Astronomers use a technique called gravity lensing to search for black holes.
• When a very massive object passes between a star and a earth, the object acts like a lens and focusses light
rays from the star on the earth. This causes the star to brighten

16. FIRST PICTURE OF M87 BLACK HOLE