A Presentation on( 16-01-10)

8/6/2019 A Presentation on( 16-01-10)

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A PRESENTATION ON BLACK HOLE

THE MYSTRY OF UNIVERSE

PREPARED BY

MD.JUNAYED STD NO :0902059



BLACK HOLES: WHAT ARE THEY?

Black holes are the evolutionary endpoints of stars at least 10 to 15 times asmassive as the Sun. If a star that massive or larger undergoes a supernova

explosion, it may leave behind a fairly massive burned out stellar remnant. Withno outward forces to oppose gravitational forces, the remnant will collapse in onitself. The star eventually collapses to the point of zero volume and infinitedensity

, creating what is known as a " singularity ". Around the singularity is aregion where the force of gravity is so strong that not even light can escape.Thus, no information can reach us from this region. It is therefore called a black

hole, and its surface is called the " event horizon ".



WHEN WERE BLACK HOLES FIRST

THEORIZED?

Using Newton's Laws in the late 1790s, John Michell of England and Pierre

LaPlace of France independently suggested the existence of an "invisiblestar." Michell and LaPlace calculated the mass and size which is nowcalled the "event horizon" that an object needs in order to have anescape velocity greater than the speed of light. In 1967 John Wheeler, anAmerican theoretical physicist, applied the term "black hole" to these

collapsed objects.



IF WE CAN'T SEE THEM, HOW DO

WE KNOW THEY'RE THERE?

X-raysX-raysX-rays

X-rays experimentAstronomers can discover some black holes and neutron stars because they

are sources of x-rays. The intense gravity from a black hole or a neutron starwill pull in dust particles from a surrounding cloud of dust or a nearby star. Asthe particles speed up and heat up, they emit x-rays. So the x-rays don't comedirectly from the black hole or neutron star, but from its effect on the dustaround it. Although x-rays don't penetrate our atmosphere, astronomers use

satellites to observe x-ray sources in the sky.



ROTATING STARS

Many stars rotate around each other, much as the planets orbit ourSun. When astronomers see a star circling around something, butthey cannot see what that something is, they suspect a black hole or a

neutron star.



HOW MANY TYPES OF BLACK HOLES ARE

THERE?

STELLAR

To create a massive core a progenitor (ancestral) star would need to be atleast 20 times more massive than our Sun. If the core is very massive(approximately 2.5 times more massive than the Sun), no known repulsiveforce inside a star can push back hard enough to prevent gravity fromcompletely collapsing the core into a black hole. Then the core compacts intoa mathematical point with virtually zero volume, where it is said to haveinfinite density.Anything, including light, that passes across the event horizon toward theblack hole is forever trapped .



SUPERMASSIVE

Supermassive black holes likely exist in the centers of most galaxies,including our own galaxy, the Milky Way galaxies, including our own galaxy.Supermassive black holes are awesome phenomena that are believed toexist at the centre of most, if not all, galaxies.



MINIATURE

The exact mechanisms that result in what are known as miniature blackholes have not been precisely identified, but a number of hypotheses havebeen prproposed. The basic idea is that miniature black holes might havebeen formed shortly after the "Big Bang," proposed.



SINCE LIGHT HAS NO MASS HOW CAN

IT BE TRAPPED BY THE

GRAVITATIONAL PULL OF A BLACK

HOLE?

It is a hypothetical consideration as this effect of gravity is to imagine a piece

of rubber sheeting stretched out.



THE BLACK HOLE AT THE CENTER OF OUR

GALAXY

Astronomers are still not sure but have long suspected that a very massive blackhole existed at the center of our galaxy, created early in the history of theuniverse. Their suspicion focused on a compact radio source, also found to emitx-rays, hidden behind dust clouds in the constellation of Sagittarius, the archer.





SOME PICTURES OF BLACK HOLE



THIS IS ALL ABOUT MY

PRESENTATIONu..

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A Presentation on( 16-01-10)

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