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.