Re: Effect of Black Hole Impact Against a Planet?

On Mar 15, 1:52 pm, mike3 <mike4...@xxxxxxxxx> wrote:
On Mar 14, 7:07 pm, alien8er <Alien8...@xxxxxxxxx> wrote:



On Mar 14, 12:43 pm, mike3 <mike4...@xxxxxxxxx> wrote:

On Mar 13, 2:31 pm, Sam Wormley <sworml...@xxxxxxxxx> wrote:

mike3 wrote:
Hi.

I'm wondering: what would the effects be if a "small"blackholewere
toimpacta planet? I've heard of huge objects the size of Mars
hitting planets as they are formed (this is one possible explanation
for how we got the Moon), but what would happen if a similar Mars-mass
object were to strike a planet _as ablackhole_ instead? It would
seem theblackholecould potentially be more lethal, if it is slow
enough to get trapped in the gravity well, thereby eventually
collapsing the entire planet. But what if it was going a lot faster,
so fast that it exits the other end of the planet and doesn't come
back? Such animpactas an uncollapsed object would probably disrupt
the planet completely, but what about as ablackhole? Now I don't
know if such "tiny"blackholes exist, but this is a hypothetical
scenario.

   A blackho,e the size of a marble has the same mass (and therefore
   gravitation) as the earth. Define the mass and velocity of the BH
   impactor for your question.

As mentioned, I was thinking of something the size of a good planet
(oid),
perhaps as "large" (massive) as Mars, with a velocity much faster
than the escape velocity from the earth, say around 50 km/s or more.

And what about one with even smaller mass, say that of Ceres or other
planetoid of ~500 km diameter uncollapsed, also with a similar
velocity?

  Basically either would drill a small (couple inches wide, tops)hole
pretty much straight through the Earth. On approach and departure (at
50 km/s) it would excite air atoms into extreme ionization producing
plenty of visible recombination radiation- it might resemble a linear
lightning bolt. If it passed through/near enough to some particularly
unstable geology the rocks might re-settle enough to tweak
seismometers. If not, and there was nobody near either point, we might
not notice it at all.

Wouldn't there be some sort of horrendous tidal force though? And what
about the hyperheating of all the matter it accretes?

The tidal forces would be "horrendous" out to a radius of a couple
inches from the event horizon; remember the hole is _tiny_. I had a
chart bookmarked that seems to have gone away- a hole the mass of the
Moon is a couple millimeters across and its one-gee radius is about
two inches (from memory). Your Mars or planetoid-sized hole will be
not much larger; mass and radius scale linearly for BHs.

At 50 km/s it won't be able to accrete much of anything because your
typical accretion disk extends out many multiples of the distance at
which the gravitational field of the hole is equal to one gee; it will
all be more strongly attracted to the Earth than to the hole. That's
_after_ it exits the body of the planet; any matter the hole tries to
accrete on the way through will be stripped off by the Earth itself.

The Earth is roughly 12750 km through; at 50 km/s that's 254
seconds, about 4 1/4 minutes for it to completely pass through the
planet. I don't think that's slow enough to make it change its "orbit"
enough to hit the Earth again.

(I put orbit in quotes above because I think you're being too
conservative here; 50 km/s is a reasonable impact velocity for a comet
bound to the Sun, but I don't see as reasonable any miniBH's being so
bound to the Sun. They'd more reasonably be orbiting the Galactic
center, or be complete rogues, with much greater velocities.)

Any "hyperheating" of any accreted matter will be through such
processes as Xray absorption, from Xrays generated by infalling
matter. A hole with the Sun's mass will be at a blackbody temperature
of nanoKelvins, so a Mars or smaller mass hole will be much colder to
start with.


Mark L. Fergerson
.

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