Types of Stars

1. Types of Stars

2. Size of the Star Determines its Fate

3. Gas Nebula • A gas nebula is a cloud of gas or dust, and is considered to be the birthplace of a new star.

4. Protostar A protostar is what you have before a star forms. A protostar is a collection of gas and dustthat has collapsed down from a giant molecular cloud. The protostar phase lasts about 100,000 years. All of the energy in a protostar comes from heating caused by gravity– nuclear fusion reactions have not started yet.

5. Main Sequence Star • Most of the stars in our galaxy are main sequence stars. Our Sun is a medium-smallmain sequence star. So are our nearest neighbors, Sirius and Alpha Centauri A. Main sequence stars can vary in size, mass and brightness, but they're all doing the same thing: converting hydrogeninto heliumin their cores, releasing a tremendous amount of energy.

6. A.C and Sirius

7. Main Sequence Star • Small main sequence stars – red, cool (3000oC ­- 4000oC) • Medium main sequence stars - yellow– white, fairly hot (6000oC – 10,000oC) • Large main sequence stars – blue, very hot (30, 000oC)

8. Main Sequence A star in the main sequence is in a state of equilibrium. Gravity is pulling the star inward, and the light pressure from all the fusion reactions in the star is pushingoutward. The inward and outward forces balance each other out, and the star maintains a spherical (round) shape. The size of main sequence depends on their mass, which determines the force of gravitypulling them inward.

9. Yellow Dwarf (Sun-Sized) Stars • Stars like our sun are medium-small main sequence stars called yellow dwarfs. They are yellow hot (about 6000oC) at the surface. Our sun will become a red giantin another 5 billion years; later it will become a white dwarf. Our sun is not massiveenough to ever become a supernova.

10. Red Giant Star • When a small to medium (Sun-sized) main sequencestar has used up most of the hydrogenin its core, fusionstops and the star no longer generates an outward pressure to counteract the force of gravitypulling it together. The inner core contracts, but this causes the core to heat up again

11. Red Giant Star • Heat from the core causes the outer shell of hydrogen to ignite. The outer shell balloons out dramatically, growing bigger,but cooling down to 3,500 K. The aging star has become a red giant star, and can be 100times larger than it was in its main sequence phase. The red giant phase of a star's life will only last a few hundred million years before it becomes a white dwarf.

12. White Dwarf Star • When a medium-size main sequence(Sun) / red giant star has completely run out of hydrogenfuel in its core and it lacks the mass to force higher elements into fusion reaction, it becomes a white dwarf star. The outward light pressure from the fusion reaction stops and the star collapsesinward under its own gravity.

13. White Dwarfs!

14. White Dwarf Star • A white dwarf is only about the size of Earth, but with most of the massof the sun. The collapse causes the core temperatures to soar to 200 million oC and the heliumin the core starts to fuseto make carbon.

15. White Dwarf Star • The high temperatures are what make a white dwarf white-hot. • The burning gases of the red giant will spread & cool down to form a planetary nebula surrounding the core. A white dwarf will just keep cooling down until it reaches the background temperature of the Universe (-270 oC). This process will take hundreds of billionsof years, so no white dwarfs have actually cooled down that far yet.

16. Black Dwarf Star • When a whitedwarf has turned most of its helium core into carbon, it cools off to the point that it is no longer giving off much light, it becomes a cold, dark carbon cinder called a black dwarf. Some think that the collapsing pressure caused by the force of gravity would be great enough to turn the carbon star into a big black diamond.

17. Large Size Stars

18. Blue Giants • A blue giant is a huge, very hot, (blue hot) star. It burns through its fuel quickly and has a short lifespan. (Ex: Alnitakin Orion)

19. Blue Giants • The largeststars in the universe are supergiant stars. These monsters form when large, blue main sequencestars run out of fuel and start to collapse (just like red giants). Supergiants have dozensof times the mass of the Sun.

20. Blue Supergiants • Unlike a relatively stable star like the Sun, supergiants are consuming hydrogen fuel at an enormous rate and will consume all the hydrogen fuel in their cores within just a few millionyears. Supergiant stars live fast and die young, detonating as supernovas; completely disintegrating themselves in the process.

21. Supernovas • When the blue main-sequence/supergiantruns out of fuel, gravity causes a final collapse that creates such huge pressures and temperatures (8 billion oC) that the star explodes, forming a supernova. Shock waves from the supernova disrupt or destroy much of the surrounding galaxy. Vast clouds of rare elementsblast out into space, forming a supernova remnant remnant(SRN).

22. Neutron Stars • A star with 1.4 to 3times the mass of the Sun does notform a white dwarf when it dies. Instead, the star dies in a catastrophic supernova explosion, and the remaining core becomes a neutron star. A neutron star is only 10 kilometers(6 miles) in diameter and has the mass of about 1.4 times that of our sun.

23. Neutron Stars • A neutron star is so dense that on Earth, one teaspoonful would weigh a billion tonsBecause of its small size and high density, a neutron star possesses a surface gravity about 2 x 1011(200 billion) times that of Earth. As its name implies, a neutron star is an exotic type of star that is composed entirely of neutrons. This is because the intense gravityof the neutron star crushes protonsand electronstogether to form neutrons. If stars are even more massive, they will become black holesinstead of neutron stars after the supernova goes off.

28. Black Holes • For supermassive blue main-sequence stars 3-30xthe mass of the sun, the pull of gravity is so great during the final collapse that no lightcan escape. A supernova explosion occurs, but the remnantcloud, shock wave and even the starlightall get pulled back into the blackhole.