Accretion disc and infrared emission

Question

Recently I have been reading on accretion disc and came across a web site talking about methods of detecting the disc around young form stars and one of the methods is by the infrared excess that is being emitted by the formation of the young star.

But how is this infrared emission being created itself? I was thinking that, it was due to the circumstellar dust, which is causing extinction, which is reducing the light that actually being formed, is this correct?

Also is the accretion disc itself how stars are formed, or are there other use to accretion disc, for example are the around a black hole, and is there a situation where a accretion disc fails to form a star.

Answer 1

The infrared light is primarily blackbody emission from the dust in the accretion disk. The dust is heated by light from the protostar, but since most of the dust is relatively far away, it doesn't get very hot.

Dust is effective at extincting optical light, but at the wavelengths we're talking about (e.g., 10 microns or even longer wavelengths), dust is essentially transparent.

Accretion disks are very common: they can form around young stars, around compact objects (white dwarfs, neutron stars, black holes) in binary systems, and around supermassive black holes in galaxy centers. Around young stars, the accretion disk is material that hasn't made its way into the young star, but is orbiting it: you can't really have an accretion disk without a central object for the disk material to orbit around.