Stellar Evolution

Question 1

star formation

Answer 1

same as sun, nebula if its central mass less than 0.08 M.

go through pre main sequence (forming) phase

spend most of life cycle on main sequence fusing hydrogen

main sequence stars in equilibrium; outward thermal pressure balanced by inward gravitational force.

Question 2

star evolution after main sequence

Answer 2

when hydrogen in core is no longer fusing into helium, star cant fight gravity anymore.

enormous weight from stars outer layers compresses hydrogen in layers right outside core enough to trigger hydroge fusion in them.

extra internal heat causes the outer layers to expand into a red giant star.

for low mass stars (< 8 M), planetary nebulae formed and then white dward.

for high mass stars ( > 8 M) with much shorter, faster evolution, supernova forms (violent death explosion), then forming into either neutron star or black hole.

Question 3

end products of stars

Answer 3

white dwarf, neutron star, black hole

Question 4

white dwarf

Answer 4

radius of earth, temperature randing from 25000- 50000 K, 1 million density, very faint.

Question 5

neutron star

Answer 5

cores of massive stars after supernova, 1.4-3 solar M, 12 km radius, 10^14-10^15 density, gravity 10^7x stronger than earths, milli/submillisecond rotation, 10^12x earths magnetic field, pulsars.

Question 6

black holes

Answer 6

very dense, highly compact star, or star corpse.

since gravity depends on mass and radius, black holes have 3 km per solar mass radius so gravity is so strong even light doesnt escape.

Question 7

detecting black holes

Answer 7

gravitational force - matter falling in or stars revolving around black hole produce observable effects.

gravitational lensing - rays from faraway stars and galaxies bend.