PHYSICS 1040 - ELEMENTARY ASTRONOMY - HOMEWORK #12
1. A __________ star is a very compact, dense ball of neutrons formed by the Type II _______________ explosion of an intermediate-mass star. The neutrons supply the neutron _______________ pressure that supports the star against its own gravity. However, 3 solar masses is the maximum possible mass for a __________ star. If the star has more than 3 solar masses, the neutron _______________ pressure fails, and the star undergoes total gravitational collapse to become a __________ __________.
2. A rapidly rotating magnetic neutron star is called a __________. This star rotates so fast because the law of conservation of _______________ _______________ says that, if the mass of an isolated object doesn't change, then its (size)2 x (rotation speed) remains constant. If a star the size of the Sun were to collapse down to the size of a neutron star (while keeping the same mass), it would become 50,000 times smaller. It would then rotate
( )2 = _______________
times faster than the Sun, which means that the collapsed star would rotate __________ times each second! This is about how fast the fastest __________ are observed to rotate.
3. If a white dwarf is a member of a binary star system, orbiting a normal companion star, the white dwarf=s gravity may pull gas (mostly _______________) from the other star. This hot gas will form a rotating _______________ disk around the white dwarf before spiraling down onto the white dwarf=s surface. As the _______________ gas builds up on the surface of the white dwarf, it is compressed and heated. Finally, when the temperature of the gas reaches about 10 million K, the _______________ gas on the white dwarf=s surface will explode in a violent nuclear __________ reaction. This is called a __________.
4. If a neutron star is a member of a binary system, orbiting a normal companion star, the neutron star's gravity may pull hot gas (mostly _______________) from the other star. This hot gas will form a rotating _______________ disk around the neutron star before spiraling down onto the neutron star's surface. As the _______________ gas settles onto the neutron star= s surface, it undergoes a fusion reaction into __________. As the _______________ gas builds up on the surface of the neutron star, it is compressed and heated. Finally, when the temperature of the gas reaches about 30 million K, the __________ gas on the neutron star=s surface will explode in a violent nuclear __________ reaction. This produces the sudden increase in x-rays called a __________.
5. Einstein=s special theory of relativity us based on two principles. a) The laws of physics which describe physical reality are the same regardless of the constant __________ with which you move. b) Regardless of your speed or direction of motion, you always measure the same value for the speed of __________. A speed is just a __________ divided by an elapsed __________, so these two principles predict that different observers in relative motion will disagree about their measurements of __________ and __________.
6. According to Einstein's general theory of relativity, gravity is the result of matter moving through _______________ space. Matter tells space how to _______________, and curved space tells matter how to _______________. As a star, planet, light beam, or baseball moves through this curved space, it experiences _______________. In addition, _______________ slows down in curved space, so that clocks actually run more slowly in stronger gravitational fields!
7. A pulsar in a binary system of two neutron stars was discovered by Joseph Taylor and Russell Hulse. As the two stars orbit each other every 7.75 hours, the distance between them slowly increases/decreases (circle one). The energy the stars lose as they spiral toward each other is carried away by _______________ waves, which are ripples in the structure of spacetime.
8. This drawing shows a rotating black hole. Identify a) the singularity (the point of infinite density); b) the event horizon (where the escape velocity equals the speed of light); c) the Schwarzschild radius; d) the ergosphere (where space and time are dragged around with the rotating black hole); and e) the static limit.
9. The Schwarzschild radius of a black hole of mass M (in solar units) is R
s = M x 3 km. For the Sun, M = 1 (by definition), so the Schwarzschild radius of a one solar mass black hole is _____ km. The Schwarzschild radius of a black hole with 10 solar masses (M = 10) is _____ km. The supermassive black hole at the center of our Milky Way galaxy has a mass of about 2.6 million solar masses (M = 2.6 million = 2.6 x 106). The Schwarzschild radius of the supermassive black hole at the center of our Milky Way galaxy is _______________ km.
10. Because a black hole does not give off any light of its own, astronomers search for black holes in __________ star systems. The black hole in a binary system may gravitationally pull gas from its companion star to form an _______________ disk around the black hole. As the gas spirals in toward the black hole, it is compressed and heated so it emits __________. Three such x-ray sources are Cygnus X-1, V404 Cygni, and A0620-00. Using Kepler= s third law, astronomers have concluded that each of these binary systems contains a __________ __________.