4 The beginning . . .When a section of the nebula becomes more dense, its gravity pulls neighboring gas atoms toward it.It is not yet a star, but its increased heat is visible to infrared cameras – it is called a Protostar
5 Gravity keeps pulling matter into a tighter and tighter sphere
6 A star is bornThe third stage – and the first in which there really is a star – is called the Main Sequence stage.Main sequence stars, regardless of size or temperature are fusing Hydrogen into Helium in their cores.The sun is a Main Sequence Star
7 Middle Aged StarsWhen a Main Sequence Star starts to run low on Hydrogen fuel, it heats up in its core and expands to become a Giant or Super Giant.All Giant and Super Giant stars are fusing Helium into heavier elements in their cores.In the next stage of its life, the sunwill be a red giant. Hot in the center,cool on the surface.
9 Aging stars behave violently When a Giant or Super Giant star begins to run low on Helium fuel, it must change again.For small, medium and large stars it sheds mass in a spectacular display called a Planetary Nebula.Next, the remaining mass of the star collapses to become a white dwarf.
10 A planetary nebula is a bubble of hot, expanding gas around a white dwarf star. It’s beautiful to look at, but the white dwarf does not undergo fusion, so the star is dying.
11 The death of a small, medium or large star Eventually all the energy that can be released by the star is used up.What remains is a huge chunk of dark, cold charcoal. Its gravity remains, but it no longer gives heat or light to its solar system.
12 Extremely Large Stars Comparison of a blue star and the sun In nebulae where there is a lot of mass available, the stars that form are far larger than the sun.Big stars are hotter, brighter, and bluer that the sunThe hotter a star is the faster it uses up its fuel, so big stars are not main sequence stars for very long.Comparison of a blue star and the sun
13 When very large stars run out of fuel When a very large star enters its giant stage it becomes a SUPER GIANT, fusing He into C and O.
14 When the core of the super giant cools, gravity wins!
15 Super Nova the brightest event ever seen Like the collapse of a red giant, the star spews gas into space.Unlike the red giant, the collapse is so violent that matter is compressed beyond our comprehension.
16 Really big stars turn into neutron stars Atoms are crushed so completely that protons and electrons fuse, leaving only neutrons!The neutron star shown is only 19 miles in diameter even though it is twice as massive as the sun.It rotates on its axis 11 times every second.
17 And then there is the ultimate victory for gravity . . .
18 Really, really, really big stars If the star is among the very largest stars, its collapse is so complete that it becomes too dense for even light to escape.It is known as a Black Hole.We can’t really take a picture of a black hole, but we can record the behavior of the matter that surrounds one
19 So what happens next?The gasses that are shed during the collapse of giants and super giants form new nebula and are recycled as new stars form.Our solar system appears to be made of recycled materials. Perhaps the atoms that make up you were once in a star!