Dark matter is it 'pie in the sky?'

[Cunjo Carl]

Just a couple followups.

@sh1pman, so I went and asked the astrophysicists at work about dark matter falling into black holes, and they agreed that it's assumed it'll increase the black hole's mass just like normal matter. For the more in depth study though, none of them knew of any! The general consensus was that there wouldn't be much we'd actually be able to see in a simulation- we've recently observationally ruled out large range dark matter to dark matter interactions, and really have no idea about the short range interactions (though most theories indicate very little or no interaction). So, dark matter would be able to fall into the black hole if it was heading straight for it, but the dark matter wouldn't (to our guessing) have any crazy accretion-disk-like interactions to help it collide, drag and spin down into the center. Because of this, one of the cosmologists said they'd be surprised if more than 5-10% of a typical black hole originated as dark matter.

For the evaporation, from the article I put up the red region on the left should be the region of black holes excluded because we'd be able to observe their hawking radiation

Most black holes, even tiny ones, really shouldn't evaporate much. I remember calculating it for something a while back, and found that a moon-mass black hole would be roughly indistinguishable energy-wise from the faint glow of the cosmic microwave background. The lighter the black hole, the 'hotter' the particles it can emit, so at a few thousand times smaller a black hole will appear with the intensity of the sun! But this black hole would only have the area of a tiny dust speck, so it'll ultimately be less bright than a light bulb. The line on the chart suggests evaporating black holes would just be too faint to notice until it's finally small/hot enough to pump out (apparently) a few watts of gammas each. At this intensity, it would still be bajillions of years before we'd see the exciting final 'Vwip!' as it explodes into some kilotons of exotic matter (which would in turn become a massive burst of Gammas and neutrinos for us to witness.)

 

Edited May 15, 2019 by Cunjo Carl

[Starstruck69]

11 hours ago, Cunjo Carl said:

Just a couple followups.

@sh1pman, so I went and asked the astrophysicists at work about dark matter falling into black holes, and they agreed that it's assumed it'll increase the black hole's mass just like normal matter. For the more in depth study though, none of them knew of any! The general consensus was that there wouldn't be much we'd actually be able to see in a simulation- we've recently observationally ruled out large range dark matter to dark matter interactions, and really have no idea about the short range interactions (though most theories indicate very little or no interaction). So, dark matter would be able to fall into the black hole if it was heading straight for it, but the dark matter wouldn't (to our guessing) have any crazy accretion-disk-like interactions to help it collide, drag and spin down into the center. Because of this, one of the cosmologists said they'd be surprised if more than 5-10% of a typical black hole originated as dark matter.

For the evaporation, from the article I put up the red region on the left should be the region of black holes excluded because we'd be able to observe their hawking radiation

Most black holes, even tiny ones, really shouldn't evaporate much. I remember calculating it for something a while back, and found that a moon-mass black hole would be roughly indistinguishable energy-wise from the faint glow of the cosmic microwave background. The lighter the black hole, the 'hotter' the particles it can emit, so at a few thousand times smaller a black hole will appear with the intensity of the sun! But this black hole would only have the area of a tiny dust speck, so it'll ultimately be less bright than a light bulb. The line on the chart suggests evaporating black holes would just be too faint to notice until it's finally small/hot enough to pump out (apparently) a few watts of gammas each. At this intensity, it would still be bajillions of years before we'd see the exciting final 'Vwip!' as it explodes into some kilotons of exotic matter (which would in turn become a massive burst of Gammas and neutrinos for us to witness.)

 

Thanks for this carl very interesting. Great post.

You know an area of slight confusion for me is that even if a black hole is that of a small one(the highlighted red area on your diagram) and therefore is able to emit 'hawking radiation'. Why can it not also emit light?

[Starstruck69]

Just to be clear when i say 'light' i don't just mean in the visible spectrum.

'Hawking radiation' is in the upper region of the scale below. 

Do we know why it is predominantly this region?

[RocketSquid]

Black holes are one of the major proposed explanations for dark matter, falling under the category of Massive Astronomical Compact Halo Objects (MACHOs). Studies have ruled out any objects between 0.3 lunar masses and 100 solar masses as candidates, but black holes are still a theoretical possibility.

As for the statement that dark matter and dark energy are distinct, that isn't necessarily the case; the dark fluid theory accounts for both with the existence of a negative-mass fluid spread throughout the universe and interacting gravitationally with objects.