Why are quasars point sources?

[Airbrush]

If matter falling into a supermassive black hole (SBH) will form relativistic jets that may be thousands of light-years long, why are quasars point sources of light and EM radiation only a few light weeks or light months across?

 

My guess would be that quasars are the result of a relatively large amount of matter falling into a SBH, so there is more than just relativistic jets, but also unfathomable explosions going off continuously all around the inner edge of the accretion disk. Such explosive reactions require on the order of a solar mass per month.

[Klaynos]

They are not real point sources, but we are so far away that the wavefronts are flat to the greatest possible resolution (the rayleigh criterion shows that the two sides cannot be distinquisted) so they can be treated as point sources.

[Airbrush]

That is interesting info Klaynos. Then quasars may have the huge jets but they are so far away we can only see a point source. Is something going on with quasars that makes them so bright and appear "quasi-stellar" coming from a region as small as light weeks across? Or is that an illusion? Are quasars seen along a jet pointed directly at earth, like a gamma ray burst?

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Here is what I wiki'ed on "Rayleigh criterion":

 

"The resolving power of a lens is ultimately limited by diffraction (see Point Spread Function, Airy disc). The lens' aperture is analogous to a two-dimensional version of the single-slit experiment. Light passing through the lens interferes with itself creating a ring-shaped diffraction pattern, known as the Airy pattern, if the phase of the transmitted light is taken to be spherical over the exit aperture. The result is a blurring of the image. An empirical diffraction limit is given by the Rayleigh criterion invented by Lord Rayleigh"

 

So quasars may in reality have the shape of an active galaxy, but since it is so far away the jets blur into a spherical shape? But how does that translate to a region of brightness measured at only "solar system sized" or light weeks across because variations occur in weeks? Also the jets are exceptionally energetic and bright. But isn't there something extraordinary happening on the inner edge of the accretion disk?

Edited February 17, 2009 by Airbrush
Consecutive posts merged.

[Airbrush]

After some research into quasars I still cannot find answers to my questions about the mechanics of a quasar. How large are quasars? I assume the central supermassive black hole (SBH) that is probably at the center is on the order of Billions of solar masses. We already know that the extreme yet compact brightness of a quasar is not from the relativistic jets. If we were looking down a polar jet, then what we are looking at is called a blazar. But most quasars are not blazars, right? So the extreme brightness of a quasar does not come from the jets, but must be the result of massive amounts of gas and dust that are streaming into the SBH on the inner edge of the accretion disc. How can a quasar be the size of our solar system, if the diameter of the event horizon of a Billion-solar-mass black hole is probably not nearly as large as our solar system?

 

What is the Swartzchild Radius of a Billion-solar-mass black hole?

[Martin]

 

What is the Swartzchild Radius of a Billion-solar-mass black hole?

 

The Schwarz Schild radius of the sun is 3 kilometers.

 

Therefore the Schwarz Schild radius of a billionsolar mass is 3 billion kilometers

 

Do us a favor and learn how to spell the guy's name please: Schwarzschild.

[Airbrush]

Thanks for your help Martin. I just discovered info about OJ-287.

 

I assume the supermassive black holes (SBH), that are probably at the center of quasars, are on the order of Billions of solar masses. We already know that the extreme yet compact brightness of a quasar is not from the relativistic jets. If we were looking down a polar jet, then what we are looking at is called a blazar. But most quasars are not blazars, right? So the extreme brightness of a quasar does not come from the jets, but must be the result of massive amounts of gas and dust that are streaming into the SBH on the inner edge of the accretion disc.

 

I just discovered this article (below) about a binary SBH system, which is called OJ-287 over 3 Billion LY away, with a central black hole of 18 Billion solar masses (the largest known). It has a smaller SBH of "only" 100 Million solar masses in a 12-year orbit around it. They estimated the outer edge of the accretion disk of the bigger one as only about 10 light weeks in diameter.

 

Ten light weeks is about 0.19 light years, or over 1.1 Trillion miles if my math is correct (60 x 60 x 24 x 70days x 186,000mi/sec = 1.116 Trillion miles). Next I need to calculate the diameter of the event horizon for OJ-287. Using the data that Martin got from wikipedia, the Schwarzenegger (snicker, snicker, ok...."Schwarzschild") radius of an 18-Billion-solar-mass black hole is about 54 Billion meters or 54 Million kilometers or 33.5 Million miles, or about a third the distance from the earth to the sun.

 

Now I need some time to groke this in fullness.

 

http://www.caha.es/18-billions-of-suns-support-einstein.html

Edited February 19, 2009 by Airbrush
New info

[Martin]

Using the data that Martin got from wikipedia,

What data did I get from wikipedia?

Don't think I gave any info in this thread that was off the web.

 

If you mean the Schw. radius of the sun, I calculated that from scratch myself some ten+ years ago. They didn't have Wikipedia back then:D

[Airbrush]

I was trying to visualize the most massive known object in the universe, OJ-287, the 18 Billion solar mass supermassive blackhole (in binary with a 100 Million solar mass SBH) which has an accretion disk with a diameter of 0.19 light weeks. If superimposed over our solar system, with the singularity at the center of our sun, the event horizon would extend to within the orbit of Mercury by 3 million miles, at a radius of 33 Million miles, and the outer edge of the accretion disk would extend only one tenth the distance to the Oort cloud, which is at 50,000 au.

 

Out to what radius would the "ring zone" of the energetic reaction extend? How thick would the ring be? What would be the diameter of the ring of energetic reaction?

[Airbrush]

To answer my own questions. The region of energetic reaction is a disk shape and can be very wide or small, ranging from light hours, to light months across. They are really flattened ring shapes, but the supermassive black hole at the center is so small that it would be invisible.

 

http://en.wikipedia.org/wiki/Quasar

 

"Quasars are found to vary in luminosity on a variety of time scales. Some vary in brightness every few months, weeks, days, or hours. This means that quasars generate and emit their energy from a very small region, since each part of the quasar would have to be in contact with other parts on such a time scale to coordinate the luminosity variations. As such, a quasar varying on the time scale of a few weeks cannot be larger than a few light-weeks across. The emission of large amounts of power from a small region requires a power source far more efficient than the nuclear fusion which powers stars. The release of gravitational energy by matter falling towards a massive black hole is the only process known that can produce such high power continuously."