Реферат: How A Star Is Born Essay Research

How A Star Is Born Essay, Research Paper

Birth of Stars

Since my entire thesis for this paper is about how a star is born, I guess the first thing I should start out with is by telling you exactly what a star is. Stars are self-luminous gaseous spheres. They shine by generating their own energy and radiating it off into space. The stars’ fuel for energy generation is the stuff they are made of — hydrogen, helium, carbon, etc. — which they burn by converting these

elements into heavier elements. Nuclear fusion occurs, which

is when the nuclei of atoms fuse into nuclei of heavier atoms.

The energy given off by a star through nuclear burning heats

its interior to many millions and, even in some cases to Pleiades Star Cluster

hundreds of millions to billions of degrees Fahrenheit. It causes heat to flow from the interior toward the surface, where it is released out into space and makes the star shine. Because stars are only so big, they will eventually use up their nuclear fuel and run out of energy. (University of Oregon, Unknown)

The first step in making new stars is to compress

a cloud in order to strengthen gravity’s effect so that

the cloud material can contract and break-up into

smaller units that eventually collapse to form stars.

The clouds in the inter-stellar space are called

Inter-stellar Medium, which are mainly made up Rho Ophiuchi

of hydrogen and helium. The cloud itself is very cold, somewhere around a hundred degrees Kelvin, which is far below -150?C. All particles in the cloud attract each other by gravitational force. According to calculations of scientists, a cloud having the mass comparable to the mass of our Sun will be able to hold itself together due to the gravity pushing against it. As traveling compression waves move

past a cool molecular cloud, it compresses the cloud, driving

the particles closer together. If the compressed cloud has no

way to stop the contraction, it?ll continue to collapse and

raise the gas pressure sufficiently to resist further contraction. Supernova 1994D

Another possible explanation for the contraction that is occurring at this time is due to shockwaves from surround supernovas. (Kippenhahn, 1994)

At this point the contracted interstellar clouds are called Bok globules. Globules are usually a few light years in size and they are made up of hydrogen and dust. ?At some point, however, a significant amount of energy goes into dissociating molecular hydrogen to form atomic hydrogen; later more energy is needed to ionize all chemical species.? Basically after this the cloud doesn?t have a

whole lot of energy left and it starts to contract even

more. During this time around the particles that make

up the cloud have been getting even hotter and have

been giving off more visible light and less infrared Dark Bok Globules in IC 2944

radiation. Because it is cooler dust in the

surrounding stellar nebula out of which the star is

forming, it absorbs photons, heats up, and gives off

energy as infrared radiation. As the star cools it also

starts to spin much more rapidly. So, the stellar

nebula hides the baby star until most of the

surrounding gas and dust in the nebula is either

attracted to it or blown away by it.(Goldberg, 1982) Eagle Nebula?formed by forming stars

During the next step of star formation the spin, pressure, and temperature inside the interstellar cloud continue to increase. Due to these increases the Bok Globules will split into the protoplanetary disk and the central core. The protoplanetary disk has the potential to actually change form and become planets. On the other hand, the central core will go on to become one of those loveable pin pricks of light in the sky that we call stars. (Strobel, Unknown)

During the next step of stellar birth, the core continues to increase in temperature and whenthe forming star has stabilized itself, then it

has become a protostar. The temperature of a

protostar’s surface is about 4000 K, and energy in its

deep interior is transported to the surface entirely by

convection. Eventually, temperature and luminosity Artistic Depiction of Protostar

rise to the highest level that they can reach on the H-R diagram and the protostar becomes a pre-main sequence star. At this point its radius is about the same as the Earth’s distance from our Sun. Gravity eventually raises the temperature in a protostar’s core to 1 million K and past, which is hot enough to even melt some of the lighter metals on the periodic table. Eventually when the core reaches a temperature of a few million degrees or more, the burning of Hydrogen begins. When that happens, it ignites for the first time and shines as an adult star. The ignition blows off the remaining rocks and dust that, before this point in time, covered the protostar from our spying eyes. After a certain amount of time, the core reaches a critical point where it begins to resist the force of gravity and its compression slows. Astronomers define the zero-age main sequence as the point when a protostar stops contracting, becomes stable, and they get all their luminosity by burning hydrogen. To give you an idea of how long it takes for a star to go from the stage of being a protostar to the point where hydrogen burning begins and the star becomes stable, it took our Sun about 30 million years to bridge that gap. Stars that are larger than our Sun?s mass bridge this gap quite quickly, while for the smaller stars, the protostar period is much longer than that for the Sun. (Hansen, 1994)

Our star has now formed and it has finally reached it?s adult stage of life. The adult star is not very interesting at all. It contains mostly hydrogen and it will burn for much longer than you or I could even possibly

begin to imagine. The hydrogen inside the star is

converted into helium by the means of nuclear

fusion. Stars that start their lives with masses less

than about eight solar masses stop their nuclear

burning trip with helium burning at the core. Stars

that start their lives with masses greater than about Model of Star?s internal process

eight solar masses continue their nuclear burning

and go on to produce such products as neon,

magnesium, silicon, and sulfur. Eventually, silicon

and sulfur ignite in the star’s core to form iron and

nickel. (Hansen, 1994)

Various info about star at mature stage

In conclusion, before I wrote this paper I would have to say that even though every night when I happen to glance upwards I see a whole bunch of stars, I never even had the slightest idea of where they came from

until now. Stars come from these cosmic

nurseries that scientists and astronomers refer

to as nebulas in one of the oddest ways

imaginable. I learned quite a bit about where stars

come from and I hope to continue to learn even

more about stars in the not so distant future. M-29 Butterfly Nebula


еще рефераты
Еще работы по иностранному языку