# Would a possible accretion disk around a primordial black hole 500 au from the Sun be visible in present telescopes?

If the hypothetical two-inch black hole 500 au from the Sun had an accretion disk, might current telescopes detect it already or do we have to wait till the Vera Rubin Observatory starts work?

• Related question by OP: astronomy.stackexchange.com/q/44269 Commented Jun 10, 2021 at 9:34
• According to vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator a 5 Earth mass Schwarzschild BH has a Schwarzschild radius of 4.4347 cm. I don't know how to estimate the size or luminosity of the accretion disk of such a BH. And of course an accreting BH is likely to be spinning. Commented Jun 10, 2021 at 9:53
• @PM2Ring So that would be 8.8 cm diameter, a bit more than 3 inches. I dunno if it's appropriate to consider a singularity "spinning", rather the accretion disk itself would.
– John
Commented Jun 10, 2021 at 10:05
• A spinning BH, aka a Kerr BH, causes the surrounding spacetime to spin. We don't need to worry about the singularity (if it even exists) because we can never observe it. Matter orbiting a BH is moving close to the speed of light, so it has a lot of angular momentum, and when the matter falls into the BH that angular momentum gets transferred to the BH. Commented Jun 10, 2021 at 10:18
• I would love to see an answer that attempted to describe the accretion disk physics for a hypothetical BH of 5 Earth masses, and assuming (let's say) the gas density of the ISM. Would there even be sufficient infalling matter to create the viscosity and turbulence in the inner portion of the disk that we could observe as radiated gravitational energy? At what distance from the miniscule event horizon would that be? Commented Jun 15, 2021 at 3:58