Cosmology and astronomy
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?(28 votes)
- 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.(9 votes)
- What can emit energy that is SO HIGH that when it reaches us, and after being red-shifted, we see gamma-rays.(3 votes)
- Gamma rays themselves, depending on how much they are redshifted, could still be gamma rays when they reach us.(3 votes)
- 1:13-1:38.. How could you explain the concept of "red-shifted" to say an 8th grader studying earth and space science?(1 vote)
- First teach them about the doppler effect: https://www.khanacademy.org/science/physics/mechanical-waves-and-sound/doppler-effect/v/introduction-to-the-doppler-effect
Red and blue shift are simply applying the doppler effect to light waves.(6 votes)
- Do the black holes expand with the universe?(4 votes)
- is their a classification of quasars?(3 votes)
- how can it be emitting waves and light if nothing can escape a black hole(2 votes)
- The black hole is not emitting waves; the accretion disk (mass yet to enter the event horizon) is emitting waves. The waves are of sufficient velocity to escape the gravitational pull of the black hole.(3 votes)
- Is there a force that acts on quasars like the Hawkins radiation on a black hole?(1 vote)
- Quasars are the side effect of supermassive black holes actively consuming matter.(4 votes)
- so if quasar rays are devouring solar masses then whats stopping them from destroying earth?(1 vote)
- The closest quasar is some billion light years away. Even with its immense mass, it would have to be far closer to us to effect Earth at all.(3 votes)
- is a quasar biger than the milky way? or any other galaxies(2 votes)
- I'm not sure if you're talking about the supermassive black hole or the radiation emitted, which is the quasar. The supermassive black hole itself wouldn't be larger than a galaxy since it sits within the galaxy, but the light emitted from it (the quasar) would extend beyond the galaxy.(1 vote)
- 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.(1 vote)
- 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.(2 votes)
I want to make a quick correction to the video on quasars. In that video I said, and I mistakenly said that the creation disk that's really releasing the energy of the quasar, that it's releasing energy predominately in the x-ray part of the electromagnetic spectrum. And that was incorrect. Most quasars are actually emitting electromagnetic radiation across the spectrum, all the way from x-rays, as high frequency as x-rays, all the way down to infrared. And some quasars even release super high frequency gamma rays, and they'll release low frequency electromagnetic waves all the way down to radio waves. So I just wanted to make that correction. It's not predominately in the x-ray part of the spectrum. It's across the spectrum right over here. It's this entire range of the spectrum, and sometimes even a wider range. Now, the other thing I want to clarify is this is the range of the spectrum that's being emitted. But we have to remember that most, or actually all of these quasars are quite far away. The closest is 780 million light years away. Many of them are many, many billions of light years away. And so they're moving away from us at a very fast speed, or they're getting redshifted because the universe is expanding so fast relative to us at that point, or that coordinate is moving so fast away from our coordinate. And so even though this is the spectrum that's being emitted, it's all going to be redshifted. It's all going to be redshifted down, and so we are going to observe things at a much lower frequency, maybe around the radio part of the frequency. So everything will be redshifted down. And that's why these were originally called quasi stellar radio sources. Anyway, hopefully that clears things up a little bit.