# IF I threw the sun at a black hole

More specifically If I could throw the sun into a black hole and the black hole had the mass of earth

Firstly you’d need quite big hands, but my guess at the end product, is the black holer in a orbit around the sun possibly accreting matter from it.

Why would the black hole orbit the sun? Wouldn’t the sun orbit the black hole, which presumably has greater mass?

shea specified a BH of the mass of the earth, infact it would probably be too small to accrete much mass from the sun.

sorry, I missed that. :smack:

Never mind.

new question - how would you get a black hole with the mass of the Earth? I thought that black holes were generated from super-novas, so they would have star-like mass?

One way is to have one really big one, stop feeding it, wait a really long time for the hawkins radiation to cause it to shrink to the size you wnat.

Wouldn’t a black hole have more mass than the earth? I think it takes a very large sun to eventually reach black hole status, otherwise it turns into a neutron star or brown dwarf or white dwarf, etc. It would also depend on whether the observer is on the sun or outside of the range of the black hole’s pull.

Assuming you threw the sun directly at the black hole at a high velocity, it would eventually slow down until it actually just hung there and froze in time. But if you were on that sun time would remain constant and you’d eventually have part of it reach the event horizon and be sucked in.

I base this on something I once read that goes like this - you send a friend into a black hole, and he says he will send a flash of light your way from his flashlight every second. He does so, but as he got closer you notice that the flash occurs every 2 seconds, then every 30 seconds, then every hour…eventually the time between flashes is months and years. Yet from your friend’s point of view he keeps sending the flash of light every second. Why you would send your friend into a black hole I don’t know.

A black hole formed by the death of a star wouldn’t have enough time to lose very much mass at all (of course it wouldn’t losse any net mass, it would gain it) a primordial black hole fromed in the earlier stages of the universe possibly could have such a low mass.

Actually Bob, objects won’t stay frozen in time at the event horizon, as that assumes infite seperation between the observer and the object, though you’d see the pulses get further and furtehr apart until the object disappeared across the event horizon.

Black holes that exist in nature start at a few solar masses. However, there are theories of primordial black holes, black holes formed in the early universe, which can be of any size. I don’t know much about these theories, including how likely they are. But theoretically, there’s no reason you can’t have a black hole of any size, including the mass of the Earth, which would be about 0.9 cm in radius. Clearly, throwing the sun “into” something this small seems kind of odd.

I think that to first order, the black hole would have to orbit the sun lower than 870 meters before it would accrete solar material. Otherwise, it would orbit just like a planet, though causing some strong solar tidal waves, depending on how close it was.

If you aimed it right, the earth-mass black hole could orbit inside the sun;
a BH as big as the earth would be able to absorb all the material of the sun eventually.

It might take a long time (many years I expect)- but it will get faster as the black hole grows.

SF worldbuilding at
http://www.orionsarm.com/main.html

would the gravity of the sun somehow be able to pull whatever mass that was in a black hole out of a black hole? Strech the mass so that it became bigger then the event horizen

No.

what about one black hole pulling on another black hole? would the mass from one black hole strech past it’s event horizen into the other black hole or would the singularity of one black hole cross over as a singularity?

Pass.
http://www.aip.org/physnews/update/517-2.html
Quote;
**The mathematics that describe black hole interactions is so complex that no one is completely sure what the resulting gravitational waves will look like. Although computer simulations can help, many algorithms fail when they address regions near black hole singularities where the gravitational fields theoretically approach infinity. **
and;
In a recent simulation the researchers (Luis Lehner, University of British Columbia, 604-822-1383, luisl@sgi1.physics.ubc.ca) considered a grazing collision of two black holes. The holes merged into one, radiated energy in the form of gravity waves, and oscillated like a glob of gelatin…

So a lot of energy would escape in the form of gravity waves;
as all the mass of a black hole is effectively energy anyway I believe, the total mass will decrease.

(hey I am a worldbuilder not a physicist)

There’s a limit to how much energy you can lose in gravvitational waves. The simple rule is that the total area of the event horizon(s) can’t decrease (this is related to and probably caused by the Second Law of Thermodynamics: A black hole seems to have entropy proportional to its surface area). So if you take your two separate black holes and calculate their surface areas, then add those surface areas together and determine the mass of a single hole with that surface area, that’s the minimum mass of the hole that can be left over. As an example: Suppose we have two black holes, each with ten times the mass of the Sun. The surface area of a black hole is proportional to the square of its mass, so if we collided those two holes, we’d end up with a black hole with at least 14.1 solar masses, and at most 5.9 solar masses worth of energy would be radiated away as gravitational waves. In actual practice, the final black hole would probably be more than that and the radiation less, but that depends on the details of the collision. It’s very hard to model the details of such a collision, but these bounds on the final state are very strong and certain.