Pink black holes

[haynewp]

Why are some black holes pink? Are pink holes pink on the inside?

[mathman]

Could you give a reference? I never heard of black holes being other than black. Are you talking about Hawking radiation?

[neutroncount]

Originally posted by haynewp
Why are some black holes pink? Are pink holes pink on the inside?

Are you sure you weren't reading a Cosmo article? Black holes get their name from the fact that you can see them. You can see the effects they have on their surroundings. An accretion disk can be found giving off all sorts of EM radiation around an event horizon of a black hole. Where did you get pink from?

[Ambitwistor]

Presumably the poster is referring to this:

http://msowww.anu.edu.au/~pfrancis/pink/
http://arXiv.org/abs/astro-ph/0107235

It refers to quasars that radiate in a way that would look pink to the naked eye. Of course, the radiation does not actually come from the black hole itself, but from outside of it. They theorize that this is due to particular properties of synchrotron radiation (produced by electrons outside the black hole accelerated by the hole's magnetic field).

[haynewp]

http://www.chron.com/content/interactive/space/astronomy/news/1999/ds/990507.html

[Phobos]

Welcome to Physics Forums, haynewp! [:)]

Originally posted by haynewp
http://www.chron.com/content/interactive/space/astronomy/news/1999/ds/990507.html

Gotta read your own link. It says..


We're pretty certain that it isn't the black holes themselves that are pink, the pink light is actually coming from gas just outside the black hole," Francis said.


A black hole is a singularity (point). No light escapes that. (Actually, no light escapes from the event horizon around the singularity...which is merely the distance from the singularity where the escape velocity is the speed of light.) So the singularity plus the volume within the event horizon is black. Now stuff falling into that region is being immensely accelerated (due to the extreme gravity). That creates lots of heat which therefore gives off light. Once that shining stuff hits the event horizon, it goes black. So "active" black holes can be imagined as a central black region with a spinning, glowing disk of material around it (stuff spiraling into the hole). An inactive black hole has no such "accretion disk" around it (no nearby matter to eat).

So, the question that remains is, why is the nearby stuff glowing pink?