Stars have been studied and revered for thousands of
years by ancient scientists. With our technology, we are finding out more about
the amazing history of these firmamental wonders. In this section we will
explore the time-consuming creation and violent death of stars.
An interstellar cloud,
Henize 206
An interstellar cloud is the nursery of newborn stars,
or protostars. But these dark masses of gas and dust are
involved way before a star is a star. Interstellar clouds are located on the
spiral arms of a galaxy such as the Milky Way. Up to thousands of local
regions, called globules, are hidden deep in the cloud. The globules contract
under their own gravity, but the balance of pressure and gravity mostly keep
them from contracting or expanding too much. Effective cooling and compression
from outside eventually cause gravity to win. The globules collapse and many
end up as stars millions of years later. Three important events happen in the
collapse of a globule. It rotates
faster an the temperature and pressure increase inside
the globule. Centrifugal forces are brought in by the increase in rotation
speed. They shape the collapsing globule into central core surrounded by and
disk and this is called a protoplanetary disk. The
central core is what becomes a star. In the duration of the globule collapse, the temperature inside
gradually climbs to millions of degrees. As the temperature climbs, dust
particles break up into atoms. The atoms in turn break into atomic nuclei and
electrons. When the central temperature reaches ten million degrees, its
components, mostly hydrogen ignite. The nuclei of hydrogen collide and meld
into nuclei of helium. The globule collapses until it is a million times
smaller than its original size. This intense compression is combined with a
huge boost in pressure. The globule's rise in temperature augments this
pressure. The pressures build up and create a force to oppose the gravity. The
two become balanced again and the collapse stops. A star is born.
The Eagle Nebula,
a famous interstellar
cloud.
How long a star lives depends greatly on how big it
is. Larger stars die much quicker because they are hotter and they burn their nuclear
fuel faster. It is a lot like a cars and how it uses its fuel. The nuclear fuel
acts as the pressure that was involved in the making of the star. Once it is
exhausted, the outward forces (pressure) stop and gravity takes hold, pushing
the star inward. After all the fuel is used up, the core collapses, but there
are different categories for the way a star dies. When a star is smaller than
the sun, it is called a dwarf star. Theses simply grow dimmer and cooler until
they disappear from space. If the star is approximately the size of the sun, it
turns into a white dwarf. A white dwarf is a spherical diamond about the size
of Earth, and it's made up of carbon and oxygen. The white dwarf then fades
away slowly like the smaller stars until it is completely dead. If it is a
couple times larger than our sun, the death is a little more violent. A shock
goes through the entire star and it explodes as a supernova. The explosion is
as bright as a whole galaxy! A neutron star, a celestial body made mostly of tightly
packed neutrons, is left in the star's wake. When a star is more than twenty
times larger than the sun, it doesn't stop collapsing. It simply collapses into
itself until it implodes and bends the structure of space and time. This is
called a black hole.
The Cygnus
supernova remnant
Larger stars- a few million years
Stars about as large as the sun- approx. 10 billion years
Smaller Stars- 100+ billion years (some have been known to live a
trillion years!)