Black Holes

Cece WilliamsWesley Trocchio

Hunter FloraA Period

Cece WilliamsWesley Trocchio

Hunter FloraA Period

What Are Black Holes?

A black hole is a super dense celestial object that has such an intense gravitational pull that it

attracts everything near it, and in some instances, prevents everything,

including light, from escaping.

Formation • There are many theories to the formation of a

black hole.• The most common theory is where a colossal star

with a mass of more than 3 times the Sun’s reaches the end of its life, gets crushed under its own gravity, and leaves behind a compact black hole.

• Another theory is when a massive star runs out of nuclear fuel, an unstable situation develops. Gravity gets the upper hand. The outer layers explode in a supernova, and the center region implodes. If the central core of the star is massive enough, such as ten times the mass of the Sun, then nothing can stop its collapse, and a black hole forms.

• Some scientists believe trillions of black holes were produced in the Big Bang.

Growth

Black holes grow by accreting matter that falls into them. Stellar-mass black holes

(black holes with the sun's mass or perhaps up to 50 times as much) can

double their mass by accreting material from a companion star. Supermassive

black holes may grow by absorbing millions of stars over the course of

billions of years.

Types of Black Holes

• Stellar Black Holes- Formed from the gravitational collapse of a massive star.

• Supermassive Black Holes- The largest black hole in a galaxy and is believed to be present in every galaxy’s center. They can have a mass as big as a million to a billion suns compressed into a tiny region.

• Miniature Black Holes- Tiny black holes.

How to Detect Black Holes• Black holes don't give off light, so we can't just

look for them. However, astronomers can find black holes by observing the gravitational effects on other objects nearby.

• Astronomers can discover some black holes because they are sources of x-rays. The intense gravity from a black hole will pull in dust particles from a surrounding cloud of dust or a nearby star. As the particles speed 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. Although x-rays don't penetrate our atmosphere, astronomers use satellites to observe x-ray sources in the sky.

Where Black Holes are Located• One possibility is at the centers of galaxies, where the concentration of

stars makes it very likely that the some of the larger ones had burned off their fuel and imploded, forming black holes which swallowed each other until there was only one big black hole left. Quasars, the bright regions at the centers of galaxies emitting humongous amounts of energy, could easily contain black holes.

• Andromeda Stars at the center of this galaxy are orbiting an object that is extremely massive, yet that cannot be seen through telescopes.

• M87 Jets of plasma shoot out of opposite sides of this galaxy. In 1994, a study conducted using the Hubble Space Telescope indicated that it may very well be the location of a black hole.

• NGC 4261 An image of the center of this galaxy, taken from the Hubble Space Telescope, shows what may be the accretion disk of a black hole and jets of plasma shooting out of it.

• Another possible location for a black hole is a binary star system where only one star is visible. The second star might be a black hole. One example of such a system is Cygnus X-1. It is also the source of X-rays, and by observing the orbit of the visible star, scientists have determined that the second star is far too massive to be a white dwarf or a neutron star. It is almost certain to be a black hole.

Parts of a Black Hole

• Event Horizon- the black hole's surface is known as the event horizon. Behind this horizon, the inward pull of gravity is overwhelming and no information about the black hole's interior can escape to the outer universe.

• Singularity- At the center of a black hole lies the singularity, where matter is crushed to infinite density, the pull of gravity is infinitely strong, and spacetime has infinite curvature.

How Matter is Pulled into Black Holes

To be "sucked" into a black hole, one has to cross inside the

Schwarzschild radius. At this radius, the escape speed is

equal to the speed of light, and once light passes through, even

it cannot escape.

Who Discovered Black Holes?

German physicist Karl Schwarzschild, English geologist John Michell, and

American physicist John Wheeler all made valuable contributions to our

understanding of black holes today.

Interesting Theories• Time does not exist in black holes.• “What would happen if you were to fall into a black

hole? As you approach the black hole, your watch would begin to run slower than the watch of your colleagues on the spaceship. Also, your comrades notice that you begin to take on a reddish color. This is due to the warping of space in the vicinity of the hole. Then, just before you "enter" the hole (pass through the outer event horizon), your friends would see you apparently "frozen" there, just outside the event horizon and to them, your watch would have stopped (if they could observe it). They would never see you enter the hole, because at that distance from the singularity, an object must travel at the speed of light to maintain its distance. Thus your dim, red image would stay frozen in their eyes for as long as the hole exists.”

Picture Credits(In order of Slide)

• http://legerdemain.wordpress.com/2008/09/13/the-upper-mass-limit-for-black-holes/

• http://scienceblogs.com/startswithabang/2009/11/believe_it_or_not_a_black_hole.php

• http://uiforum.uaeforum.org/showthread.php?7230-Black-Holes• http://uiforum.uaeforum.org/showthread.php?7230-Black-Holes• http://dsc.discovery.com/space/top-10/strange-universe/space-10-

weirdest-things-universe-02.html• http://www.nonequilibrium.net/page/46/• http://ya.astroleague.org/?p=198• http://www.lancs.ac.uk/ug/heysm/• http://reference.findtarget.com/search/black%20hole

%20thermodynamics/• http://www.le.ac.uk/ph/faulkes/web/stars/r_st_overview.html• http://obs.carnegiescience.edu/news/newsimages/m31.jpg• http://blogs.discovermagazine.com/badastronomy/files/2007/

galaxytail_stars.jpg

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