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9 Cards in this Set
- Front
- Back
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What is a quazar?
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Comes from the word Quasi Stellar Object. They look like stars when you just see an image of them, but with very un-starlike spectra. They are very far away and very luminous! They are like black holes in the center of galaxies but are surrounded by a secretion disk. As matter surrounding the quazar falls into it, it strikes the secretion disk and heats it up, causing it to radiate a lot of light.
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How do we know that quazars are so far away from us?
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They have a lot of emission lines with very strong redshifts. We use this redshift with Hubble's law to find the distance to them. We also know that they are very far away because they experience gravitational lensing which happens when a galaxy passes between us and the Quazar, so they must be at least as far away as the galaxy. Also, there were a lot of quazars in the same part of the sky as lots of clusters of galaxies, and both the quazars and the galaxy clusters had the same red shift. Also, new technology has let us photograph the quazar in its galaxy and we can see that it is the nucleus, meaning it really is that far away!
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What observations tell us that the energy of a quazar must come from a volume of space about the size of our galaxy?
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The long distances between us and quazars tell us their luminocities must be huge appear as bright to us as they do. They are also variable and, over the course of a few days, can turn on and off the brightness of a few thousand of our galaxies. We know that their extreme brightness comes from a relatively small volume of matter because of the very small amount of time over which a quazar varies. This is because they can't vary on a timescale shorter than it would take light to cross them.
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How could black holes be responsible for this emission of energy even if no light could escape them?
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The energy being emitted from these quazars (black hole nuclei of galaxies, as was said above) is being emitted from outside the event horizon (where light can no longer escape) of the quazar. The secretion disk surrounds the quazar and as matter falls into the black hole it hits the secretion disk with a great deal of force, heating it up to produce huge amounts of energy. This is really the convertion of gravitational potential energy to radiation and it's pretty efficient.
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There are no nearby quazars to us, and yet we claim we are in no special part of the galaxy. How is this possible?
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We are in a special time, though! The farther away we look in distance the farther back in time we can see. So if all the quazars are far away from us, that means all the quazars existed a very long time ago. This is because, in order for them to emit this great volume of energy, they needed to have a lot of matter falling into them. So now adays (and this is what we see in nearby aka recent galaxies) we have massive black holes at the centers of galaxies that just don't have that much matter falling into them, so they do not have luminocities like the quazars of yore. Creatures far away looking at us, however, might see these black holes as quazars because the light from them is still reaching the far away planet.
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What are Seyfert galaxies?
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These are things like intermediaries between regular spiral galaxies like ours and quazars. They are spiral galaxies with particularly bright, point-like nulclei. For whatever reason, the particular black hole in the middle of them is being fed now.
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What is a radio galaxy?
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These are galaxies that show levels of radio emission above that of regular galaxies. Most of these have coming out from them jets. The material in these jets can make huge radio lobes extending to either side of the galaxy, a much greater expanse than the optical size of the galaxy that we see. We think this is because the black hole in the center's disk is confined largely to the equitorial regions of the black hole's spin. Any material coming out from the black hole can't then get out the sides because the disk is blocking it, so it has to go out the poles. We don't know why the material comes rushing out.
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What is the evidence for the existence of black holes at the centers of galaxies?
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This has to do with kepler's law again so we can measure how much matter is contained between an object and the center of mass. We can look at objects very close to the center of the galaxy that are moving very very fast. When we calculate the mass between them and the center of the galaxy we see that it must be more than 1 million solar masses worth of matter crammed into a few 10s of A.U.s in the center of the galaxy, so there must be a black hole there!
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How can we study the early phases of galaxy evolution?
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by looking far far away in distance, which lets you look far far back in time. This lets you see what galaxies were like in the past. They were littler, bluer, and having lots of collisions (since bluer means star formation was happening more in our galaxy than it is now). The really huge ellipticals we see are built up by them gobbling up other smaller galaxies in their vicinity.
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