Stars and Black Holes

By Beatrice A. Lopez
Below you will read research on stars and black holes. Black holes are stars whose core has been crushed by gravity. In the text to follow you will see how a star forms, read about its life and how it becomes a black hole.
Stars are composed of hydrogen gas and dust. Stars owe their existence to the force of gravity.

Stars are created from the thinly spread atoms of dust and gas that swirl throughout space. The atoms clump together into dense clouds that eventually collapse under their own gravity. Other forces counteract the gravity. The dust and cloud grows
steadily hotter until a nuclear furnace ignites creating a bright shining star. (Couper H. & Henbest N.

, 1996).
Stars are born when particles of hydrogen, helium and dust combine and collapse, shrinking and falling into itself making the cloud hotter. Tiny protons bump into each other and bounce away at high speeds stick together when it is hot enough. Four protons form a particle of helium gas. Two protons fuse together becoming neutrons. Matter that is released from this fusion turns into energy streaming outward from the core creating nuclear fusion.

Once the inward and outward forces are equal it reaches its final size and shines, becoming a star. The length of the hydrogen burning stage depends on the stars weight. A star with 15 times the weight of the sun uses up all its hydrogen in less than 10 million years. (Darling D., 1985)
The farthest star in the most distant galaxy is more than ten billion light years away.

The kind of star
a star becomes depends on how much gas and dust the protostar manages to pack into itself as it forms. The more mass a star collects the hotter and brighter it becomes. (Gallant R ., 2000).
Three major star types are red dwarfs, yellow dwarfs and blue giants. Red dwarfs are the dimmest and have the longest life span that is about a trillion years.

Red dwarfs become black dwarfs when they exhaust their hydrogen and fuel. Yellow dwarf stars have shorter life spans because they burn their hydrogen fuel faster. As fuel runs low they swell up into a red giant, then release planetary nebula, then shrink into white dwarfs and finally cool as black dwarfs. The massive blue giants have the shortest life span as they'll swell up into supergiants, explode as a supernova and end up as either a neutron star or black hole.

(Gallant R .,
2000).
A normal galaxy can contain more than 100 billion stars. When you multiply 100 billion stars times and infinite number of galaxies, the product is infinite. (Darling D., 1985)
A supernova is an explosion that marks the end of the life of a massive star.

A supernova has the mass three times the mass of the sun and explodes. Most black holes form after a supernova or explosion of a giant star. (Sipiera P., 1997).
Black holes are created when a star's very heavy core is squeezed hard enough to create matter into a tiny spot smaller than a pinhole from which nothing can escape including light. (Darling D.

, 1985).
The super strong gravity of a black hole pulls gases off nearby stars with such a force that the gases give off x-rays as they form an accretion disk of matter that spirals into the black hole. (Gallant R ., 2000).
Astronomers have theorized that there is a giant
black hole eating out the center of our own Milky Way galaxy. A supernova is an explosion that marks the end of the life of a massive star.

Most black holes form after a supernova or explosion of a giant star. Scientists theorize that a black hole looks like a black ball in space that is not very large. Inside you would see nothing. The surface of the ball is called the event horizon. The event horizon is the place where no light can escape. All things disappear from our universe in the black holes center.

It is called the singularity. The distance between the event horizon and singularity is called the schwartzchild radius that measures the actual size of the black hole. (Sipiera P., 1997)
Heavy weight stars can squeeze its core much harder. The inward pressure makes the core hotter.

It will use up all the hydrogen in its core within a few million years. The star turns into a red supergiant, shrinking the core smaller until it reaches the stage where it is filled with iron. Since iron cannot be fused to make energy the core will collapse under gravity causing an explosion. Enormous amounts of gas are shot into space at speeds up to 10,000 miles per second. The start then becomes a supernova.

It squeezes the core so
hard it becomes a neutron star. A neutron star is made of thick matter. Pulsars a type of neutron star that spin quickly making the star look like it turns on and off quickly. (Darling D., 1985).
The smallest stars are called white dwarfs and can be measured 1000 miles across with a diameter of 20 miles.

The dimmest, coldest and lightest stars are called red dwarfs and may weigh 10 times the planet Jupiter. The biggest stars are red supergiants and can have a diameter of about 450 million miles. The dim, red stars in globular clusters are the oldest stars and may have been born 10 to 15 billion years ago with the universe. The
youngest stars can be less than 100,000 years old. Wolf-Rayet stars are the hottest stars generating heat as high as 180,000 degrees fahrenheit and are located in the central planetary nebulae. (Darling D.

, 1985)
The Sun is a star. Like stars, the sun is a ball of gas. It is 8 and one third light years
away and 93 million miles away. The suns diameter is 865,000 miles. The sun is about 5 billion years old. (Darling D.

, 1985).
The sun appears as a large disk. At the top of the
sun you can see two huge gas eruptions called prominences. These prominences leap out hundreds of thousands of miles.

They have hair like spikes that are surges of hot gas called spicules. The mottled effect is caused by cells of hot gases welling up from beneath the surface, cooling and appearing darker than the surrounding gases. (Gallant R ., 2000).

Therefore, the sun, stars and black holes coexist with one another in the solar system
along with other matter in the galaxy. The sun is a star. Black holes are collapsed stars. Each does not exist without the other.

References
Couper H. & Henbest N. (1996). Black Holes. New York, NY: DK Publishing Inc.
Darling D.

(1985). The Stars from birth to black hole. Minneapolis, Minnesota: Dillon
Press Inc.
Gallant R .

(2000). The life stories of Stars. Tarrytown, New York: Benchmark Books
Sipiera P. (1997). Black Holes.

Canada: Children's Press, Grolier Publishing Co. Inc