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Download Astronomy Homework - Life
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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.