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### Course: Cosmology and astronomy>Unit 2

Lesson 2: Quasars and galactic collisions

# Quasar correction

Quasar Correction. Created by Sal Khan.

## Want to join the conversation?

• Isn't the event horizon really a sphere? If so, isn't the accretion disk really an accretion sphere?
• You must also keep in mind the theory that the event horizon, and singularity somewhat hold 4-Dimensional properties. Take light for example, traveling into the the event horizon. Once touching the surface it is absorbed, and in theory takes on a 4-Dimensional geodesic path, leading back to the same point. You travel from point A to point B and realize that you are at point A again, then continue on traveling in that manner trying to find an impossible escape route. You must understand though, that what I just explained is horribly simplified. In terms of the 3rd Dimension, we have a Y-Axis, an X-Axis, and a Z-Axis. Up and down, left and right, forwards and backwards. So a 3-Dimensional geodesic path ending at the same point, would be a straight walk around the Earth. If you start at a point on a sphere and move in a perfectly straight line across the surface of that sphere, you will end up back where you started. So then you add another dimension (in theory), and make a similar path along a 3-Dimentional surface (which we commonly know as something that is 2-Dimentional, but that is not the limit of what a surface can be), of a 4-Dimensional object. It is something that should definitely be accounted for. The event horizon and singularity of a black hole is still very mysterious to us, and a lot of what we know so far is in fact far from adequate compared to what we will know in the distant future with the advancement of technology. But this theory is supposed to be fairly close to the truth, and the problem is that we haven't been able to closely observe a black hole. The only way we have observed visual evidence of a hole itself, is seeing light bent by the ridiculously powerful gravitational force around it. Other than that, we haven't even been able to observe if the event horizon is in fact just spherical, or if it is composed of more than what we are accustomed to when it comes to modern physics. There are many theories that conflict with each other, and it's something that is best studied on your own so you can form your own ideas and opinions. Until further scientific advances, we are partially in the dark when it comes to a lot of this stuff.
• - .. How could you explain the concept of "red-shifted" to say an 8th grader studying earth and space science?
• Do the black holes expand with the universe?
• Wouldn't the escaping light very near to the event horizon be redshifted so much as it fought against the black hole's gravity that it wouldn't even be detectable?

Sorry if this seems unspecific.
• That is correct, light escaping from a black hole is red shifted because of gravity. Even the light escaping from earth is red shifted but by a very small amount.
• What can emit energy that is SO HIGH that when it reaches us, and after being red-shifted, we see gamma-rays.
• Gamma rays themselves, depending on how much they are redshifted, could still be gamma rays when they reach us.
• is their a classification of quasars?
• Is there a force that acts on quasars like the Hawkins radiation on a black hole?
• Quasars are the side effect of supermassive black holes actively consuming matter.
• What if the supermassive black hole in Sagittarius A constellation becomes a quasar? Will it consume the whole galaxy?
• Quasars don't consume the galaxy they are a part of, they are simply supermassive black holes that are actively feeding on a lot of matter.