To travel all the way around it without actually going into it?
Should be, so long as you maintain a sufficient distance.
I’ll let somebody else figure out what that distance is.
The distance would depend on mass… for a super-super-super-duper black hole, you could theoretically travel just around the rim of the event horizon. Or so says Kip thorne…
Man, two black hole questions and I can’t find that book to save my life
It wouldn’t be a problem. In fact, if our Sun imploded and turned into a black hole tomorrow, the Earth would continue orbiting around it on the exact same path. (Same goes for Mercury.) Of course, we would all be dead, and the Earth would get a bit cold…
Our sun doesn’t have enough mass to become a black hole (poor little sun). If a planatary system was orbiting a star that had enough mass to become a black hole and did so (without an explosion that would push out the planets) the planets would still happily orbit the black hole but get a little cold.
A black hole is just a mass that has a gravitational field.
The earth does circumnavigate a black hole, every time the galaxy rotates. Our galactic core is one huge black hole.
Qadgop’s post reminds me of a question I once had, so this is a slight hijack…
Can the earth really be said to orbit the center of the galaxy? Isn’t it more appropriate to say our Solar System orbits the center of the galaxy? It’s kind of like saying that the moon orbits the sun. That seems inappropriate to me, but IANA astronomer.
Diver
Are we sure that the earth’s orbit wouldn’t change? I vaguely remember that for a swarzschild black hole orbited by a massive object, there’s one stable circular orbit for a given velocity, but I don’t remember for sure that it’s the same orbit as you’d get from the sun. Seems like it ought to be, but I’m not positive it is.
Oh, and a black hole is NOT just a mass that has a gravitational field. I have a gravitational field, and I’m not a black hole (so far as I know). A black hole is a singularity, so it must be a point mass.
The moon does follow some kind of path around the sun. Since it’s not an elliptical path, we don’t usually say that it orbits the sun.
I would think the orbit would have to change, even if there was a 100% efficient conversion (no mass thrown off in an explosion, which there wouldn’t be since the sun can’t be a black hole anyway).
I think that though the center of mass for the sun might coincide with the center of mass for the black hole, the sun is still not as dense and so wouldn’t warp spacetime the same way as a black hole would.
You can circumnavigate a black hole, as long as you stay outside the Schwartzchild radius. Outside that radius, a black hole acts like a sun or planet having the same mass, so you can hav the same sorts of orbits as around a star or planet. For a given velocity there’s only one circular orbit, just as around an ordinary star, but there is an infinite number of elliptical orbits that have the same total energy. (The velocity of an object in an elliptical orbit varies with position, unlike a circular orbit.)Of course, if you dip inside the Schwartzchild radius in the course of such an elliptical orbit, you’re a goner.
This isn’t to sa that unusual things can’t happen in an orbit around a black hole. There was an article in Scientific American between 5 and 10 years ago about peculiar effects of light bending in orbits around a black hole, even if yoy keep away from the Event Horizon.
USCdiver,
Yep. Semantics, but the correct thing to say would be that the center of gravity of the earth-moon system orbits the sun. Also, the moon doesn’t exactly orbit the earth, but the earth and moon orbit a common center of gravity. That point lies within the surface of the earth though, so the earth “elliptically wobbles” more than it really “orbits” 
I have a page about what would happen if the Sun turned into a black hole:
http://www.badastronomy.com/bad/misc/black_hole_sun.html
We would orbit just the same, as others have pointed out. There is a subtle effect, called frame dragging, whereby the rotating black hole would kinda sorta drag the fabric of spacetime around it. The effect is not terribly big, even near the hole, but over a zillion years (pardon the exactness of my estimate) it might affect the Earth, changing the orbit a bit. I doubt it would be a whole lot though.
The black hole in the center of the Milky Way is about 2.6 million times the mass of the Sun. The orbiting observatory Chandra recently detected a big ole x-ray flare from it, which can be used to determine the size of the hole, and they got a number pretty close to what you’d expect for a hole with that mass, given the uncertainties. Pretty cool.
You can say the Earth orbits the Milky Way’s black hole, but it’s more accurate to say the Sun does. Even more accurate would be to say the Sun orbits the mass inside the Sun’s orbital radius. The BH is only a tiny fraction of the total mass of the Galaxy.
The statement “A is just a B” does not imply that anything that is “just a B” must be an A. For example:
An elephant is just a mammal. I’m a mammal, and I’m not an elephant (so far as I know.)
You’re right, it’s also a delicious crumb cake. With whipped frosting.
And at the risk of hijacking the thread (hey, it’s about black holes… their space/time distortions counteract any hijack activity! So there!)… Mr. Bad Astronomer, genius, sir, I recall an old TV news story about how a big ol’ stream of anti-matter was detected pouring out of the center of the Milky Way (which was used as evidence that there was a black hole there).
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Is this accurate, or is it just a case of an astronomer saying, “I see something…” and a news anchor immediately shouted, “Anti-matter! Black holes! Woohoo!”
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If it is true, is this whole “anti-matter stream” thing a commonplace feature of black holes, or is it more or less unique?
Not to pre-empt the Bad Astronomer, but:
Are you sure that the news report said antimatter? My reasons for asking are twofold. One, I don’t know of any way that we can detect antimatter at the sort of distances you’re talking about. Second, I think you might be misremembering when they actually said X-rays. X-rays spew out of rotating black holes along the axis of rotation, IIRC, and it’s one of our primary means of detecting them.
I also remember hearing about an antimatter stream at the heart of our galaxy.
I hope to see The B.A.'s response to SPOOFE’s question too, but let me stick my neck out and give this one a try…
I think that particle jets (containing some anti-matter) are not uncommon for large “active” black holes (i.e., ones with substantial accretion disks). Also, I don’t think it’s possible to directly detect anti-matter (since it otherwise behaves as ordinary matter…e.g., a spectrograph could not tell the difference) but its presence can be inferred from x-rays, gamma-rays or whatever that can be detected.
Bad Astronomer, I have a question. Angular momentum is conserved in star–>black hole phenomenon, so even if a rotating star was roughly spherical, wouldn’t the resultant black hole be far more ellispoidal than spherical? As such, wouldn’t the resultant means of orbit need to be adjusted for the same mass?
Pardon me while I step in and make a fool of myself.
Black Holes aren’t spherical – they aren’t anything, as far as I know. A black hole results when your gravitational attraction is strong enough to overcome all of the forces that try to keep your particles apart – electrostatic interactions, electron degeneracy pressure, neutron degeneracy pressure. It really is – as one clever button has it – “where God is dividing by zero”. Maybe we’ll find some other source of pressure that keeps black holes from condensing into a dimensionless singularity one day. But even if we do, the shape of that tiny dot at the center of the Schwartzchild radius won’t have an effect on the shape of your Event Horizon, which will be spherical.
The “spin” of a black hole is an important quantity, nonetheless, and determines some of its properties. Have they figured out what happens to it when a black hole “evaporates” as Hawking predicts? It shouldn’t spontaneously go to zero. They probably hashed this out a while ago, but I haven’t been paying attention.