Detecting Black Holes: Is It Possible?

[RebelRiver]

Hello, this is my first topic. but i was thinking,

Theoretically if you have a way to detect radiation from far distances, couldn't you detect the radiation from black holes?

 

[Matterwave]

We do have a way to detect radiation from far distances...they are called telescopes. The (theoretical) Hawking radiation given off by astronomical black holes is far far far far far far far too faint for us to detect though. The temperature of such a black body would be far less than the temperature of the CMBR...and therefore any signals from these objects would be covered by the CMBR.

 

[RebelRiver]

We do have a way to detect radiation from far distances...they are called telescopes. The (theoretical) Hawking radiation given off by astronomical black holes is far far far far far far far too faint for us to detect though. The temperature of such a black body would be far less than the temperature of the CMBR...and therefore any signals from these objects would be covered by the CMBR.

So your saying that the way we use to find radiation is by sight with a telescope?

 

[Nabeshin]

So your saying that the way we use to find radiation is by sight with a telescope?

Yes. Note that you should not think of telescope in the scrict optical sense, as the term generally encompasses any object which aids in detecting any wavelength of electromagnetic radiation.

As the above post mentions, the only EM radiation emitted by a lonely black hole is hawking radiation, and is much much too weak to detect. If, however there is matter falling into the black hole it will emit lots of x-ray radiation and we see this all the time.

 

[Chronos]

Agreed with Nabeshin, Hawking radiation is fainter that the CMB background, hence undetectable.

 

[physalpha]

About black hole.
What is important factor to be a black hole?
Total mass, mass density(mass/ volume) or any step to be a black hole, which one is the important factor to be a black hole?
I've heard supernova explosion makes a black hole.
And then, which size or density black hole is minimum?

 

[Nabeshin]

Well you get a black hole when a mass M is compressed into a volume with characteristic size 2M, so roughly the criterion is (units where c=G=1):
$$\rho \gtrsim \frac{1}{8M^2}$$
So the deciding parameter is the density, but the density scales like the inverse square of the mass.