BLACK HOLES

The winter is the best time to star gaze in the Bay area. The sky
clear and the constellations dramatic. One star group familiar to
nearly everyone is Orion. In the winter this magnificent warrior
guards the southwestern sky. Most people focus on the three
prominent stars in a perfect line that make up his belt. But
hanging directly below his belt is a fainter line of stars that
shape his sword. Grab your binoculars and look in the middle of the sword. The fuzzy area is not condensation on your lens but the famous Orion nebulae. It is an immense cloud of ionized hydrogen gas and is an area in our Milky Way galaxy where stars are being born.There are several other star nurseries that can be seen easily
now. The most obvious is the Pleiades also called the Seven
Sisters or the Seven Virgins. The Japanese call it Subaru and
named one of their automobiles manufacturers for it. Check out
the insignia on the front of a Subaru sometime.

Clouds of hydrogen gas swirl and eddy throughout space and
randomly converge. Under gravitational attraction the molecules
start falling in toward one another. As more and more gas is
attracted, the molecules become excited and give off visible
light (just like the Orion nebulae). As more and more hydrogen
atoms fall in together they become denser and denser and hotter
and hotter. When the temperature reaches 20 million degrees
Fahrenheit a nuclear reaction spontaneously begins.This nuclear reaction is called fusion; it is a simple process.

When hydrogen atoms are forced together they form helium and in
the process a tiny bit of energy is released. This energy comes
to our planet mainly in the form of sunshine and it is this force
that drives life. A star lives its life in a precarious balance‑‑
gravity pulling all of the atoms together and fusion driving them
all apart.

A moderately sized star like our sun has a life of ten billion
years or so (we are only half way through our sun’s life
expectancy so continue to make your mortgage payments). When the
nuclear fuel is used up, our sun will rapidly expand and cool.
The diameter will flare out past the Earth and our star will
become a red giant. After a brief moment (50,000 years or so) the
outer diameter of the sun drifts off and it collapses into a
white dwarf and fades slowly out of existence.

If the star is more than twice as big as the sun an entirely
different event occurs. As the nuclear fuel is exhausted the star
collapses violently on itself in a cataclysmic explosion known as
a supernova. Debris hurtles out into space at thousands of miles
per second and buried in the center is the remains of the star,
either a neutron star or a black hole.

In the first case all of the protons and electrons are driven off
leaving a ball of pure neutrons. The remaining star has a mass
comparable to our sun but has been squeezed to a diameter of ten
miles! A matchbox full of these pure neutrons weighs several
tons. The star spins rapidly on its axis and emits high frequency
pulses of radiation. Radio telescopes on earth regularly listen
to these bursts. They give rise to the other name for neutron
stars‑‑pulsars.

If the exploding star is three times larger than our sun a very
interesting event is predicted. The star should collapse to a
diameter of less than two miles; the gravitation force is so
immense that even light cannot escape its surface. The star
becomes a black hole.

Obviously we cannot see black holes, but the universe may be
littered with them. In 1971 astronomers found a star in the
constellation Cygnus that was behaving as if there was a massive
star rotating around it. This was the first evidence that a black
hole exists.Cygnus, the Swan also known as the Northern Cross can now be easily seen shortly after the sunsets in the western sky.

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Skills

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August 22, 2009