Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
White dwarf wikipedia , lookup
Cosmic distance ladder wikipedia , lookup
Astrophysical X-ray source wikipedia , lookup
Nucleosynthesis wikipedia , lookup
Hayashi track wikipedia , lookup
Main sequence wikipedia , lookup
Stellar evolution wikipedia , lookup
H II region wikipedia , lookup
Astronomical spectroscopy wikipedia , lookup
GALAXIES • Galaxies fall into (roughly) two different structural types. SPIRAL galaxies consist of a nucleus, a disk, a halo, and spiral arms. Interstellar material such as gas and dust are found in and near the spiral arm structure in the disk of the galaxy. The spiral arms are sites of star formation, which typically contain bright stars and OB associations, which make the spiral arm structure easily discernible. Our own Galaxy is a spiral. Spirals that are face-on towards us appear like giant pinwheels. • The other types of galaxies are ELLIPTICALS. As their name suggests, they have elliptical or spheroidal like shapes. The majority of their stars are old (K and M giants), and they have much less dust and gas than the spirals. – How are stars born? • When a heavy body passes near or through the nebula, its gravity causes swirls and ripples. It is no different in a nebula when a star passes by. The "piles" of matter continue to group together in the nebula until they are gigantic clumps of dust and gas. • At this stage, the star is called a protostar. As the clumps of gas and dust become larger, gravity squeezes them tighter, causing pressure and heat to build. Then, when the pressure in the center, the core, reaches a temperature of 18,000,000 degrees F (10,000,255 K), hydrogen fusion is initiated. • Now, the protostar has become a star. It shines with its own light. Its solar wind quickly pushes away the rest of the dust and gas in its vicinity (solar wind is explained in the comets section). SUPERNOVA • Main Sequence Star Death • After about ten billion years, a main sequence star has used up most of its hydrogen. The hydrogen core begins to contract, and the outer layers begin to expand. At that point, helium fusion begins. The star is now called a red giant. Life expectancy from here on is about one hundred million years. • After 100,000,000 years, the red giant tries to fuse its carbon into iron, but it does not possess enough outer pressure to do so. • The outer layers of the star drift off into space, and become what is called a planetary nebula. Its core collapses into a white dwarf star. • Supergiant Star Death • After about fifteen million years, a supergiant's core fuses into iron. Then, when it attempts to fuse the iron into heavier elements, it explodes in what is called a supernova. A supernova explosion is brighter than its parent galaxy. • One supernova explosion on A.D. July 4,1054, was so bright that it could be seen in broad daylight for twenty-three days. The nebula it created is called the Crab Nebula. • A supernova creates a nebula surrounding the now dead star. In the center, it leaves behind either a neutron star, a pulsar, or a blackhole. NEBULAE • Nebula is a vast cloud of dust and gas which stars are born. • Emission Nebulae • Emission Nebulae are the most colorful. They shine internally from young stars still in their stellar nursery. A large telescope (8+ inches) will reveal most of the colors. To see all of the colors a long-exposure photograph is required. – Reflection Nebulae • Reflection nebulae are nebulae which reflect stars' light. The Pleiades are a good example; the star Merope's light is reflected by a blue, wispy nebula near it. – Dark Nebulae • All nebulae in the truest sense are dark nebulae. They produce no light of their own; they either reflect light from stars, or stars illuminate them from their interior. • However, the only nebulae that are classified under "dark" are the ones that are dark. They have no stars near or within them with which to illuminate themselves. They are only seen when they omit light from background stars. – Inplanetary Nebulae • Planetary nebulae are the nebula which are created when a main sequence star grows into a red giant and casts off its outer layers. Some, though, are remnants from the Big Bang. • They came to be named "planetary" nebulae when nineteenth-century astronomers saw that they looked like the recently discovered Neptune and Uranus. The name has stuck ever since. – Supernova Remnants • These nebulae are the creations of ancient supernovas. The most famous example is the Crab Nebula, created by a supernova on July 4, 1054. BLACKHOLE • A black hole, in theory, is a type of dead star. After the supernova, if the remaining core is three solar masses (three times the sun), gravity will cause the core to collapse into a neutron star or a pulsar. If the core is nine or more solar masses, gravity causes it to collapse into an infinitely dense point, which makes such a large gravitational well that not even light can escape. Thus, since nothing ever comes out of it, it is called a hole. Since you can't see it because light can't escape, it is called a black hole. PULSAR – A pulsar is the same thing as a neutron star. The only difference is that a pulsar emits two very highenergy beams of radiation from its magnetic poles. Its magnetic field is one trillion times that of the Earth's. – A pulsar spins very rapidly. Most spin about once every second, but the fastest one has been clocked at 642 rotations per second. – The anatomy of a pulsar is very simple. The outside is a solid crust formed of neutrons. Inside is a liquid neutron "soup." In the very center is a solid core of neutrons. NEUTRON STAR – If a star has between 1.4 and 9 solar masses, it will become a neutron star. – A neutron star is a star made entirely of neutrons, as the name suggests. After a star goes supernova, the remaining core collapses. Gravity shrinks and condenses it into a sphere about the size of Manhattan (fifteen mile diameter) in a few seconds. However, to do this it has to break the barrier that keeps the electrons and protons separated. Because of the mass of the star, gravity can overcome this force. When that happens, the electrons and protons cancel each other out. All that is left are the neutrons. – This process creates such a dense star, that if you could somehow take a pinhead of material from it, it would weigh as much as a super tanker. • White Dwarfs DRAWF • A white dwarf is what remains of a dead main sequence star. A white dwarf has the approximate size of the Earth (7,500 mile diameter). Its maximum possible size is 1.4 solar masses. • It you were able to take a enough material from a white dwarf to fill a matchbox, it would have the weight of an elephant. • A white dwarf is made of carbon. It does not produce a fusion reaction. Therefore, it no longer produces heat. As it floats through space, it loses its heat over the course of