The word comet derives from the Greek word kome, meaning “hair.” The name describes the blurry, diaphanous appearance of a comet’s long tail. most comets (called long-period comets) travel even beyond Pluto and might take millions of years to complete a single orbit. So-called “short-period” comets don’t venture beyond Pluto and, therefore, have much shorter orbital periods.
direction of motion of the comet.
The light, radiation and radio waves from these galaxies and stars being absorbed into a black hole travel billions of light years through space. When we look at quasars which are 10-15 billion light years away, we are looking 10-15 billion years into the past. Pretty amazing, right?Many astronomers believe that quasars are the most distant objects yet detected in the universe. Quasars give off enormous amounts of energy – they can be a trillion times brighter than the Sun! Quasars are believed to produce their energy from massive black holes in the center of the galaxies in which the quasars are located. Because quasars are so bright, they drown out the light from all the other stars in the same galaxy.
Despite their brightness, due to their great distance from Earth, no quasars can be seen with an unaided eye. Energy from quasars takes billions of years to reach the Earth’s atmosphere. For this reason, the study of quasars can provide astronomers with information about the early stages of the universe.
If a supermassive black hole is the source of a quasar’s power, then about 10 Sunlike stars per year falling into the black hole could produce its enormous luminosity. Quasars might be the ancestors of all galaxies, the violent beginnings of us all.
Red Dwarf Stars :
Red Dwarf stars are smaller than our sun. And since they are smaller, they also have less mass. Because of their small size, these stars burn their fuel very slowly, which allows them to live a very long time. This also causes these stars to not shine as brightly as others. Some red dwarf stars will live trillions of years before they run out of fuel.
Yellow Stars :
White Dwarfs :
Red Giants :
Blue Giant Stars :
Giant and Super Giant Stars :
Neutron Star :
If the core mass is between 1.4 and 3.2 solar masses, the compression from the star’s gravity will be so great the protons fuse with the electrons to form neutrons. The core becomes a super-dense ball of neutrons. Only the rare, massive stars will form these remnants in a supernova explosion. Neutrons can be packed much closer together than electrons so even though a neutron star is more massive than a white dwarf, it is only about the size of a city. The neutrons are degenerate and their pressure (called neutron degeneracy pressure) prevents further collapse.If the core remnant has a mass greater than 3 solar masses, then not even the super-compressed degenerate neutrons can hold the core up against its own gravity. Gravity finally wins and compresses everything to a mathematical point at the center. The point mass is a Black Hole. Only the most massive, very rare stars (greater than 10 solar masses) will form a black hole when they die.
In general, compact stars of less than 1.44 solar masses – the Chandrasekhar limit – are white dwarfs, and above 2 to 3 solar masses (the Tolman–Oppenheimer–Volkoff limit), a quark star might be created; however, this is uncertain.Gravitational collapse will usually occur on any compact star between 10 and 25 solar masses and produce a black hole. Some neutron stars rotate very rapidly and emit beams of electromagnetic radiation as pulsars.