Download Astronomy Homework - Life

Name: _______________________________________
Astronomy Homework - Life-Cycle of Stars
Date: _____
1. Most of the life of a star is spent on the (red giant/main sequence) of the H-R
diagram.
2. All stars on the main sequence are in hydrostatic equilibrium which means the pressure
produced by fusion (exceeds/equals) the inward pull of gravity.
3. As a star uses up its hydrogen fuel, a core of (helium/oxygen) builds.
4. When there is no more hydrogen to fuse in the core, (fusion/fission) stops and gravity
takes over.
5. As the helium core contracts, temperatures and pressures (increase/decrease).
6. Stars leave the main sequence when (they fuse hydrogen in their cores/they run out
of hydrogen to fuse in their cores).
7. Hydrogen begins to fuse in a (shell/core) around the contracting helium core.
8. As the core of a star contracts, the outer layers of the star (contract/expand).
9. Stars leave the main sequence and reach the (red giant/white dwarf) stage.
10. When a star leaves the main sequence, the luminosity of the star
(increases/decreases).
11. Fusion of helium occurs in the core when temperatures reach (1 million/100 million)
degrees Kelvin.
12. Helium will fuse into (oxygen/carbon).
13. Helium fusion lasts for a few (tens of millions/tens of billions) of years.
14. When there is no more helium to fuse in the core, the core will (expand/contract).
15. Surrounding the contracting carbon core of a star are, in order out from the core,
fusion burning shells of (hydrogen then helium/helium then hydrogen).
16. The red giant will next become a (supergiant/white dwarf).
17. The eventual fate of all stars depends upon the (mass/composition) of the star when
it first formed.
18. Low mass stars (can/cannot) fuse carbon in their cores because they (do/do not)
have enough mass to allow temperatures high enough for carbon fusion.
19. The temperature at which carbon will fuse is (100,000,000°°K/600,000,000°°K).
20. The carbon core of a star becomes degenerate which means (it cannot be squeezed
any further/its about to do a bad thing).
20. Stars that begin to fluctuate in size and luminosity are known as (pulsating
variable/white dwarf) stars.
21. Eventually, stars eject their outer envelopes of gas into space as shells of gas known
as (supernova/planetary nebula).
22. The exposed carbon core is now a (white dwarf star/pulsar).
23. White dwarfs cool over time and become (brown dwarfs/black dwarfs).
24. High mass stars have at least (2/8) solar masses when the carbon core forms.
25. High mass stars evolve (faster/slower) than low mass stars.
26. High mass stars (do/do not) go through a red giant phase of evolution.
27. High mass stars (can/cannot) generate temperatures high enough to fuse carbon into
heavier elements.
28. The final stage of evolution produces a core made of (oxygen/iron).
29. Iron (can/cannot) fuse into heavier elements.
30. When an iron core contracts, protons and electrons combine and produce a tiny core
made of (neutrons/dark matter).
31. Neutrons cannot be crushed further and the core rebounds out producing a shock
wave called a (nova/supernova).
32. Supernova can shine as bright as (a thousand stars/an entire galaxy).
33. Type Ia supernova are produced by (core collapse/matter accumulating and
exceeding the Chandrasekhar limit of a white dwarf).
34. Type II supernova are produced by (core collapse/matter accumulating and
exceeding the Chandrasekhar limit of a white dwarf).
35. An example of a supernova remnant is the (Ring Nebula/Crab Nebula).
36. If the remnant of a supernova has less than 3 solar masses, the remnant is called a
(neutron star/black hole).
37. Neutrons stars haves sizes of about (ten/ten thousand) kilometers.
38. A pulsar is a rapidly rotating neutron star that emits (a beam of light towards the
Earth/radio signals at irregular intervals).
39. Neutron stars are often found in binary systems where they accumulate gas from their
companion and produce (x-rays/gamma rays).
40. The mass of a neutron star cannot exceed (1/3) solar masses.
41. If the neutron degeneracy pressure is exceeded, the core will collapse and produce
(another supernova/a black hole).
42. Light (can/cannot) escape a black hole.
43. The event horizon is the (time at which a black hole forms/radius at which the
escape velocity is greater than the speed of light).
44. Very massive objects will cause space itself to (expand/warp).
45. Time dilation means as you approach a black hole, time (speeds up/slows down)
from a distant observer's point of view.