Meg Urry is describing the NuStar telescope in an article she wrote for CNN. In it she says
What type of acceleration is necessary to make something glow in a vacuum?
Thanks,
Rob
Hoo, boy, where to start. First of all, a dropped object does not gain energy. It gains kinetic energy, but at the cost of potential energy, so the total energy remains constant.
Second of all, you won’t glow at all from falling in a vacuum. Things falling into a black hole glow because they’re not in a vacuum: They’re bumping into all of the other junk in the vicinity that’s also falling into the hole.
Third, things bumping into each other at any speed will cause a glow. It’s just that at low energies, the glow will be too faint and too low-frequency to notice. How fast does it have to be to be noticed? Well, that depends on what instruments you’re using to try to detect it.
Fourth, what matters is the speed at collision. The acceleration you used to build up that speed doesn’t matter.
Interesting. According to the article, the matter in the accretion can gain temperatures in the millions of degrees. Does significant fusion occur in matter falling into a black hole?
Thanks,
Rob
Does it glow because it’s red (blue/white/uv) - hot? Blackbody radiation?
Would acceleration of charged particles also produce radiation, similar to synchrotron radiation?
Yes to both, plus a few more. Different sources of radiation predominate in different parts of a black hole’s accretion disk and environs. And at the temperatures we’re talking here, we’re beyond even UV, and into the X-ray range.
here’s a night-vision video of a helicopter landing in kuwait at night. Sand striking the leading edges of the rotor blades causes luminous emissions; probably not visible with the unaided eye, but the night-vision system on the camera makes it obvious.
Sometimes in my sandblasting cabinet, blasting aluminum oxide grit at hard surfaces can cause a glow bright enough to be seen when I turn the room lights off. Even when not blasting at hard work surfaces, the tungsten carbide nozzle on the blasting gun causes visible luminous emissions from the alox grit blasting out of it; with the lights off, it looks like a very,very dim afterburner.
are these the same sort of phenomenon that result in luminumous emissions from debris falling into black holes? If I increased the supply pressure on my sandblaster to several thousand psi (resulting in very high grit velocities), would I see the wavelength of the emitted photons decrease into blue, violet, ultraviolet, and possibly even X-rays?
Broadly speaking, yes, it’s the same sort of phenomenon, but in practice, I highly doubt you could crank up your sandblaster enough to get even blue.
With sand, couldn’t that be piezo-electric discharge?
Don’t know about aluminum-oxide and piezo electric, but maybe static discharge?
I don’t know - thus, my question as to whether it was the same phenomenon as the one causing X-ray emissions from black holes.
Seems unlikely. Electrical arcs in air - spark plug sparks, lightining, static dishcarge events - are bluish-white in color; the light coming from my sandblaster is yellowish-orange.