Definition- a cloud of interstellar gas and/or dust.
Due to some unknown force the nebula begins to contract untill it has a gravitational force.
When the nebula has a gravitational force it continues to condense.
The gravitational energy (potential), converts to energy of motion or heat energy(kenetic).
Definition- a collapsing cloud of gas and dust destined to become a star.
Protostars form when contracting nebulas produce enough energy to emit long, red wave lengths of light.
Protostars however do not have enough energy for nuclear fusion to occur.
Eventually the core of the protostar will be hot enough to fuse 4 hydrogen atoms into a helium atom and energy. To do this however, the temperature of the core must reach at least 10 million degrees K.
Definition- a sequence of stars on the Hertzsprung-Russell diagram, containing the majority of stars, that runs diagonally from the upper left to the lower right.
When a protostar begins to have nuclear fusion, gas pressure becomes an outward force working against the gravitational force of the star.
When these forces are balanced, the star becomes a stable main-sequence star.
The main sequence star phase of a star is the longest lasting phase in a star's life, (up to 90% of star's life).
When the hydrogen core is depleated, the star quickly evolves and dies.
Definition- a large, cool, star of high luminosity; a star occupying the upper right portion of the Hertzspung-Russell diagram.
Red giants form when the hydrogen core of a yellow main sequence star is depleated.
When this happens the core contracts and produces enough heat to fuse helium into heavier elements. Outside the core are shells that are still fusing hydrogen.
With the extra nuclear fusion taking place there is no longer enough gravity to balance the star's opposing forces allowing the star to expand.
As the star's shells are expanding the surface temperature of the star decreases turning the once yellow star red.
Definition- a red giant but with more mass and luminosity.
What happens to form a red giant is the same as a red supergiant except only large blue main sequence stars can form red supergiants and red supergiants fuse even heavier elements than red giants.
Definition- a shell of incandescent gas expanding from a star.
Definition- an exploding star that increases in brightness many thousands of times.
Supernovae are extreamly rare, (none have been veiwed since the begining of the telescope).
Supernovae are millions of times brighter than the star before the explosion.
Definition- a star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size; believed to be near its final stage of evolution.
White dwarfs are very dense.
Fun Fact! Matter in a white dwarf is more dense than water. A spoonfull of this matter weighs several tons!
Definition- a star of extremely high density composed entirely of neutrons.
Neutron stars are remnants of supernovae.
Fun Fact! If the Earth were to collapse to the density of a neutron star, it would have a diameter about the length of a football field. A pea-sized amount of this matter would weigh 100 million tons!
Definition- a massive star that has collapsed to such a small volume that its gravity prevents the escape of all radiation (including light).
Fun Theory! One scientific theory is that matter that is sucked into a black hole is heated and emits a series x-rays before it is engulfed.