Stars Essay, Research Paper
Star Birth
Our lives are intimately linked to the stars, but in ways much more down to
earth than the romantic views of them. As we all know, our sun is a star and the
thermonuclear reactions that are continuously taking place inside it are what
provide and sustain life on our planet. What do we get from the sun? We get
carbon, oxygen, calcium and iron, courtesy of stars that disappeared billions of
years ago (Naeye, 1998). Star formation is a study in contradictions because the
formation of a star begins with atoms and molecules floating freely through space
that are brought together through gravity to form masses that become stars. Stars
go through three major stages of development in their transformation from infancy
to adult stars: a collection of dust and gases, protostar, full-blown star. Pictures of
these various stages are mind-boggling in their beauty and bring one to an
immense sense of awe at the machinations of the universe. Scientists believe that
stars begin as a collection of interstellar dust and gases (Frank, 1996). This mass of
dust and gases forms a cloud that begins shrinking and rotating until it eventually
develops into what is called a protostar. Once the protostar reaches sufficient
mass, it then begins the process of converting hydrogen to helium through a series
of nuclear reactions, or nuclear fusion until it becomes a full-blown star
(Astronomy, 1995). Those protostars that are too small to complete the nuclear
fusion die out to become what are known as brown dwarfs (refer to photo at right).
Thanks to an image from the Mt. Palomar observatory, astronomers have obtained
the first image of a brown dwarf, named Gliese 229B (or GL229B). It is a small
companion to the red star, Gliese 229, which is approximately 19 light-years from
Earth in the constellation Lepus. GL229B is too hot and massive to be classified as
a planet, yet at the same time it is too small and cool to be able to shine like a
typical star ?in fact, it is actually at least 100,000 times dimmer than our own sun
and is the faintest object ever to be discovered orbiting another star.
As a star forms, it is this ?fusion-powered heat and radiation? emanating from the
core of the star which keeps the star whole (Watery Nurseries, 1997). If it weren?t
for this, the star would actually collapse under the stress of its own weight.
However there is a balancing act that takes place within the star between radiation
and gravity (which provides fuel for the star) that prevents this and makes it
possible for star to have a life span of billions of years. The big question, though,
is how does this whole process get started and what actually makes it
possible for these masses meld together to form a star, instead of just exploding
back into cosmic particles? What actually happens is that the clouds of gas and
dust are actually drawn into compaction through self-created gravitational collapse.
As the picture at left (from the Hubble Telescope) shows, these clouds go through
continuous implosion to become solid masses. Scientifically speaking, it is logical
to assume that this implosion should actually generate so much heat that the gas
and dust expand, rather than come together and yet this is not the case.
The reason why, scientists believe, is due to water molecules that are formed
during this process. It is the addition of these charged molecules, called
hydronium, that they believe provide the ingredient necessary to prevent further
expansion of the gasses and dust, thereby allowing the continuance of implosion
until the star finally forms a solid mass. Hydronium is made up of three hydrogen
atoms and one oxygen ion. In theory, it has the ability to transform into water
(H2O) plus one independent hydrogen atom, as long as it is able to capture a free-
floating electron from somewhere. It takes hundreds of millions of years for the
particles of dust and gas to come together into these gigantic clouds that can span
hundreds of light-years in size. The clouds are dominated by their two prime
elements of hydrogen and helium while particles of dust make up about one
percent of a cloud?s mass. In addition, there are other molecules present that
contribute to the molecular structure of the cloud, such as ammonia and other
carbon-based elements. Each cloud contains enough elements to create
approximately ten thousand new stars. It takes many millennia for a collapsing gas
cloud to fragment into thousands of dense, rotating clumps of gas that will
eventually become newborn stars. The cores of these gaseous clumps are
continuously compacting more and more as their rotation becomes faster and faster
and, over time, the cores become elongated. Some of these elongated cores are
hypothesized to eventually become binary and multiple star systems by virtue of
the fact that the cloud is stretched out so much. Over time, stars naturally change.
Once the star enters its maturity, a stage where nuclear reactions begin to stabilize,
it will spend the majority of its existence there. As they age and enter the late
evolution stage, they often swell and become red giants which can evolve into
novas, planetary nebulas, or supernovas. By the end of its life, a star will change
into a white dwarf, black dwarf, or neutron star depending upon the composition of
its original stellar mass. Thanks to NASA’s Hubble Space Telescope we have
gained new insight into how stars might have formed many billions of years ago in
the early universe. This picture from the Hubble shows a pair of star clusters,
which might be linked through stellar evolution processes. There are actually a
pair of star clusters in this picture which are located approximately 166,000 light-
years from the Large Magellanic Cloud (LMC) in the southern constellation
Doradus. According to astronomers, the clusters, for being so distinctly separate,
are unusually close together. In the past, observations such as this were restricted
to clusters within our own Milky Way galaxy. Because of the fact that the stars in
the Large Magellaniv Cloud do not have many heavy elements in their
composition, they are considered to be much more primordial than other newly
forming stars and, therefore, more like scientists speculate stars were like in the
early universe. There is an ongoing debate among astronomers as to the
importance of disks in the formation process. Many astronomers believe that most
of the matter that makes up the star actually starts off inside a disk which spirals
inward until it coheres into a star. There have actually been observations of
massive disks as they orbit infant stars and it is these observations which have
led scientists to believe that disk accretion is very important to the process of star
formation. The key to understanding star formation is the correlation between
young stars and clouds of gas and dust. Usually the youngest group of stars have
large clouds of gas illuminated by the hottest and brightest of the new stars. The
old theory of gravity predicts that the combined gravitational attraction of the
atoms in a cloud of gas will squeeze the cloud, pulling every atom toward the
center. Then, we might expect that every cloud would eventually collapse and
become a star; however, the heat in the cloud resists collapse. Most clouds do not
appear to be gravitationally unstable, but such a cloud colliding with a shock wave
can be compressed disrupted into fragments. Theoretical calculations show that
some of these fragments can become dense enough to collapse and form stars.
Astronomers have found a number of giant molecular clouds where stars are
forming in a repeating cycle. Both high-mass and low -mass stars form in such a
cloud, but when the massive stars form, their intense radiation or eventual
supernova explosion push back the surrounding gas and compressive period. This
compression in turn can trigger the formation of more stars, some of which will be
massive. Thus a few massive stars can drive a continuing cycle a star formation
in a giant molecular cloud. While low-mass stars do form in such clouds along
with massive stars, low-mass stars also form in smaller clouds of gas and dust.
Because lower mass stars have lower luminosities and do not develop quickly into
supernova explosions, low-mass stars alone can not drive a continuing cycle a star
formation. Collapsing clouds of gases do not form a single object; because of
instabilities, it fragments producing an association of ten to a thousand stars. The
association drifts apart within a few million years. The sun probably formed in
such a cluster about five billion years ago. Stars are supported by the outward flow
Of energy generated by nuclear fusion in their interiors. The energy generated
Keeps each layer of the star hot enough so that the gas pressure can support the
weight of the layers above. Each layer in the star must be in hydrostatic
equilibrium; that is, the inward weight is balanced by outward pressure. Stars are
elegant in their simplicity. Nothing more than a cloud of gas held together by
gravity and warmed by nuclear fusion, a star can achieve stability balancing its
weight generating nuclear energy.
Astronomy: The Stars: The New York Public Library Science Desk
Reference, 01-01-1995.
Frank, Adam, In the nursery of the stars: infant stars are anything but quiet. They
kick, they scream, they spew forth a thousand suns’ worth of hot gas many light-
years into space.(Cover Story)., Vol. 17, Discover Magazine, 02-01-1996, pp 38.
Naeye, Robert, The story of starbirth. (origins of the universe)., Astronomy, Feb
1998 v26 n2 p50.
Watery stellar nurseries.(water may help stars form from gas clouds)., Vol. 18,
Discover Magazine, 07-01-1997, pp 14.