1. Chapter 21- Stars Why will (or won’t) our sun become a black hole?

9. 2. A protostar is not hot enough to produce nuclear reactions yet, but as the process of collapse ( accumulation of more particles ) continues and the protostar becomes more and more dense, the temperature increases to approximately 10 million degrees Kelvin.

12. 3. When the temperature increases sufficiently, nuclear fusion can begin, forming heavier elements 4. Millions of years later, a star is born

16. b. The helium in the core begins to shrink, and the core heats up again c. Energy released by the heating of the helium core causes the outer hydrogen shell of the star to expand greatly d. As the outer shell expands, it cools and its color reddens; at this point the star is considered a red giant or supergiant

18. e. As the red giant ages, it continues to “ burn ” the hydrogen gas in its shell, and the helium core continues to get hotter and hotter f. At about 200,000,000 degrees Celsius, the helium atoms in the core fuse together to form carbon atoms and the last of the hydrogen gas surrounding the red giant begins to drift away

21. g. This drifting gas forms a shell around the central core of the star; this shell is called a planetary nebula

26. c. Gravity causes the last of the star’s matter to collapse inward ; matter is squeezed into an extremely dense white dwarf that still shines with a hot, white light d. At some point, the last of the white dwarf’s energy is gone and it becomes a dead star

28. It's the burned out corpse of a star named BPM 37093 only about 50 lightyears away from Earth in the region of the sky we refer to as the constellation Centaurus. The white dwarf star is a chunk of crystallized carbon that weighs 5 million trillion trillion pounds. That would equal a diamond of 10 billion trillion trillion carats

30. c. The core is squeezed so tightly that the heat given off reaches 600,000,000 degrees Celsius, and the carbon atoms begin to fuse together to form new and heavier elements such as oxygen and nitrogen, and eventually even iron

33. d. At these high temperatures, iron atoms in the core fuse to form new elements which explode into space e. The resulting clouds of dust and gases forms a new nebula

35. f. The remaining core of the star will become either a neutron star or a black hole, depending on its starting mass

41. Most massive star found, 114 times mass of Sun. 20,000 light years away in southern milky way galaxy.

42. b. Occurs when a massive core is swallowed up by its own gravity which becomes so strong that not even light can escape c. Black holes swallow cosmic matter and energy , which are probably squeezed out of existence within the black hole

52. Apparent magnitude

53. Absolute magnitude

54. 3. Nuclear fusion in the core of a star causes hydrogen atoms to fuse and form helium atoms, releasing heat and light energy and causing stars to shine

55. Nuclear fusion is the source of energy for stars.

60. 2. Main-sequence stars fall in an area from the upper left corner to the lower right corner and make up more than 90% of the stars in the sky

66. a. Apparent position of the star in June and December is noted b. A line is then drawn between the Earth’s position in these months and the center of the sun, this will become the base of a triangle whose length has already been carefully measured by astronomers

67. c. A diagonal line is drawn from each end of the base line to the apparent position of the star in June and December

68. d. The tip of the triangle that has been formed is the true position of the star; a vertical line is drawn from the true position to the base of the triangle, representing the actual distance to the star

70. 2. The distance to stars more than 100 light years away is measured by a complex mathematical formula using the brightness of the star 3. Spectroscopes may be used to measure the distance to galaxies by measuring the amount of red shift in a galaxy’s spectrum

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81. 2. Chromosphere – the middle layer of the sun’s atmosphere; temperatures average 27,800 degrees Celsius

85. 3. Photosphere – the innermost layer of the sun’s atmosphere; temperatures usually do not exceed 6000 degrees Celsius

87. 4. Core – center of the sun; temperatures up to 15 million degrees Celsius; where nuclear fusion takes place

93. 2. Another type of storm called a “ solar flare ” shows up as a bright burst of light on the sun’s surface

96. 3. A “ solar wind ” is a continuous stream of high-energy particles released into space in all directions