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> An asteroid mass black hole would strike the Earth causing a massive amount of gamma radiation cooking everything on the surface

I'm ignorant on the matter, could you explain why this would happen? A black hole with a mount Everest mass would be a tiny fraction of a micrometer in diameter. Even assuming a huge asteroid we would be talking about micrometric objects so I don't understand how could they create such a dire scenario if traveling through Earth.

For comparison an Earth sized black hole would be ~9mm in diameter if my Google-fu is correct.

Really it depends on what you consider a mass of an asteroid to be.

If it's large enough, the black hole is going to be releasing xrays. If it's smaller, it's going to be releasing gamma rays.

The smaller the black hole, the faster it evaporates. The faster it evaporates, the more energy it puts out.

The black hole at this scale is still going to have too small a cross section to suck up any matter and the radiation might end up blowing away any matter before it gets to the black hole in the first place.

At these masses, there's no real danger in the black hole passing through the Earth itself. The only danger is how much radiation is going to be shot out as it passes through the atmosphere on either side of the planet.

"Google-fu" :)

Hawking radiation. A black hole emits hawking radiation at a wavelength about equal to its diameter, and with power (ie energy/time) inversely proportional to its diameter. So the smaller the black hole, the higher the energy of the photons it emits and also the more energy it emits per second. A black hole with the mass of Mount Everest (~10^14 kg) would, according to a hawking radiation calculator[0], have a schwarzschild radius of 10^-23m, and a proportional wavelength on the order of extremely intense gamma rays or cosmic rays, with a temperature of a billion degrees kelvin. Low-mass black holes aren't black at all.

[0] Online hawking radiation counter: https://www.vttoth.com/CMS/physics-notes/311-hawking-radiati...

It's important to note that Hawking Radiation is not a confirmed phenomenon, and unless we actually find such a small black hole, it will never be confirmed (stellar mass black holes are too cold compared to the microwave background to emit Hawking radiation, and will continue being so for an extraordinarily long time.

Excuse me if this is a silly questions, but you got my imagination going.

>A tennis ball mass black hole would go right through the Earth without too much fuss. The black hole's radius would be too small (smaller than an electron) to cause any damage.

Is it possible that tiny black holes of this size could be travelling through the earth at a regular basis? Do we have the means to reliably detect black holes that small?

Well there's two factors preventing that:

1. The smaller the black hole, the brighter and shorter lived it is. To get the black hole to live for any decent amount of time, it'd have to be travelling close to the speed of light for the effects of time dilation to extend it's life time from our perspective.

2. Detecting gravitational effects on a small scale is stupidly hard because of how weak gravity appears to be (compared to the other 3 forces: strong nuclear, weak nuclear, electromagnetic).

If you were to shine a laser and the tennis ball massed black hole travelled through the path of the laser, you wouldn't see any light missing because the wavelength of light would be larger than the black hole.

If you stopped the black hole (so it's not moving close to the speed of light), and tried to shine the laser at it for a greater effect: not only would you not see less light, you would actually see light shooting out of it so bright it'd be like putting your eye against many many atomic bombs because the Hawking Radiation would be so strong. (It'd also destroy itself in a blink of an eye)

You can increase the mass of the black hole to make it cooler and live longer. A 1,000 metric tonne black hole would live for around 46 seconds shedding radiation at an ever increasing amount before exploding into nothingness again. Assuming you could filter out the light coming from the black hole, you might see the phase of the laser light shift, but it'd all still end up at it's destination.

The greater problem would be trying to figure out how to shield the Earth from the amount of light shooting out of it.

Can we build a Black Hole Bomb?

Yeah we could shoot a black hole at the right mass (this is tunable) so that it evaporates on the target.

There's some other approaches too:

- Move a larger black hole into the target planet (this would require so much energy that other approaches would be better).

- Send a device to the target planet that generates a black hole massive enough to live long enough to oscillate through the planet back and forth, consuming the planet from the inside. It would take 600 quadrillion metric tonnes of mass to form a black hole 1 nanometer across, so this could be difficult to start.

- Create a black hole to power a ship's thrusters (Kugleblitz drive) to smash into a target at speeds approaching the speed of light.

Note that, without a consistent theory of quantum gravity, we don't know if black holes of such sizes can actually exist; and unless we happen to detect some, we don't actually know if Hawking radiation exists - it's not something that can be observed for a stellar-mass black hole in realistic time frames (a stellar mass black hole is predicted by the theory to evaporate after ~10^64 years - so the evaporation is far too slow to be observable; further, in the current age of the universe, the temperature of the cosmic microwave background is too high compared to the temperature of the Hawking radiation emitted by a stellar mass black hole for it to be observable, even theoretically).

> A tennis ball mass black hole going close to the speed of light would go right through the Earth without too much fuss. The black hole's radius would be too small (smaller than an electron) to cause any damage.

How would such black holes exist in the first place? I thought black holes are formed if the mass of the star is at least 3 times the mass of our Sun.

Primordial black holes are another possible way (besides star collapse) that BHs could form.

The theory is that during the immediate aftermath of the Big Bang, the distribution of mass-energy became chaotic, with local hotspots where mass-energy was more dense, and other spots where it was less dense.

GR says that if ANY amount of mass-energy comes to occupy a small enough area, then that is a black hole. Star collapse BHs have a lower mass limit because their own gravity is what forces their mass into a region small enough to become a BH.

So primordial BHs could have formed with arbitrarily small mass, because they didn't have to rely on their own gravity to attain BH density. The Big Bang did it, for them.

https://en.m.wikipedia.org/wiki/Primordial_black_hole#Theore...

Any primordial black holes of low mass that may have formed would have evaporated long ago through Hawking radiation. If you plug the mass of a tennis ball into the equations, it would evaporate in well under a second. (Btw, don't stand next to anything that radiates the entire mass-energy of a tennis ball in under a second. Small black holes shine really brightly)