Accretion disk around galaxy NGC 4261

[JeffOCA]

Hello,

When you look at the accretion disk around NGC 4261 (see here), you can read that the dark, dusty disk represents a cold outer region which extends inwards to an ultra-hot accretion disk with a few hundred million miles from the suspected black hole.
So, from the outside, you have successively a bright ring, then a dark dusty ring and "an ultra-hot accretion disk" very close to the center black hole itself.

My question : due to the ultra-hot temperature in the accretion disk, the dark material (dust) is extremely heated and, so, should radiate in a very bright way (UV and/or X-rays). Why not ?

Regards
JF

 

[Chronos]

Here is an X ray image of NGC 4261 http://chandra.harvard.edu/photo/2003/ngc4261/

 

[JeffOCA]

Ok, the picture link I posted is taken at visible wavelengths that why dust material is not bright. Am I right ?

Regards
JF

 

[Chronos]

Yes. Dust tends to radiate at the frequency of light it receives.

 

[pmacias]

Hello JF,

Thank you for your question about the accretion disk around NGC 4261. The reason why the dark material in the accretion disk does not appear to radiate in a bright way is due to a process called self-shadowing. This occurs when the dense material in the accretion disk blocks the light from the inner, hotter regions, creating a shadow effect. This is similar to how a tree can cast a shadow on the ground, blocking the sunlight from reaching certain areas.

In the case of the accretion disk, the dust and gas are so dense that they effectively block the light from the inner, hotter regions, making them appear dark. However, this does not mean that they are not emitting any radiation at all. In fact, they are still emitting infrared radiation, which can be detected by instruments such as infrared telescopes. Additionally, the outer, cooler regions of the accretion disk can also emit radiation in the form of radio waves.

It is also important to note that the accretion disk is not a uniform structure, and there may be regions where the dust and gas are less dense, allowing some of the inner, hotter radiation to escape. Overall, the appearance of the accretion disk can vary depending on the viewing angle and the density of the material in different regions.

I hope this helps to clarify your question. Thank you for your interest in the fascinating world of galactic accretion disks.

Best regards,