Civilization near a black hole

[anamiac]

So, I've played computer games where multiple races colonize and flight a 'galaxy' where a galaxy is a square map with dozens or hundreds of star systems.

Today I was reading about Sagittarius A*, which is the supermassive black hole at the center of our galaxy. Apparently it has 92 stars orbiting around it. So, I'm wondering how things would be different for one of these games if the setting was those 92 stars.

• Would the black hole prevent in any way prevent life on planets around these stars?
• The stars rotate around the black hole at different rates, based on distance from the black hole. One of the stars rotating around Sagittarius A* has made a full rotation in my lifetime, which in cosmos timelines, is very fast. So, the systems on your gamemap are rotating around the center of the map at different speeds, and systems that are close to each other (but at different elevations) at the start of the game may not be close to each other later on. This could mean that a civilization's territory would be more scattered.
• If we allow warp speed (as in warp 6, Star Trek universe), then there would be a second event horizon closer to singularity from which a spaceship could not leave the orbit of the blackhole under warp speed. This would make it possible, in theory, for civilizations to have stuff within the event horizon of the black hole - which would be very useful for your secret hidden bases and the like. Assuming that you can still be far enough from the black hole that your spacestation/planet/ship/whatever isn't ripped to shreds by tidal forces. This is also assuming that you don't have faster than light sensors. What would the universe look like from the deck of the USS Enterprise after it had crossed the event horizon of a black hole? Would you be able to see other things that were also inside the event horizon of the black hole, or would you be essentially blind?
• Without Warp speed, the rotation suddenly becomes very important. You know how when a plane flies from say, Denver to NY, if you looked on a regular map it wouldn't look like the plane was taking a straight line? Well, it'd be like that, I suppose, because dipping down into the lower orbits would cause you to rotate around the center faster, while going to the periphery would allow you to move back spin-ward in relation to the lower orbits.
• Solar systems could occasionally fall into lower orbits. Perhaps each system falls every 1000 years, which if your game lasts 100 years and has 100 planets, you'd expect to see 10% of the planets fall to a lower orbit over the course of a game. There would probably be a lowest possible orbit that could support life, so anything that was in that orbit and fell would be lost forever.

[Arioch]

The core of the galaxy is densely packed with very massive stars which have very short lifespans. I recall some speculation that the hard radiation given off by all these stars and the black hole might make this region totally uninhabitable. I don't know whether that's still accurate, but what's perhaps more relevant is that these massive stars only live for a few hundred million years, which is not long enough for life as we know it to evolve (which take billions of years). That and the possibility of frequent interactions with nearby stars, which could disrupt planetary orbits over large time scales.

Beyond those issues, I don't think the gravity of the black hole itself would have any effect on the planets themselves.

[anamiac]

Ah. So, if there isn't too much radiation then civilizations could colonize and expand INTO this region, but they couldn't start out there. It sounds like the stars around a black hole are bigger than the average star size in the galaxy? Why is that?

[icekatze]

hi hi

I suspect that there are other, smaller stars and planetary bodies in the core region that we just don't see because they're so dim in comparison to their neighbors, but the extreme radiation would still be a problem. On the other hand, a planet with a dense enough atmosphere and magnetosphere might not care as much about radiation, especially if there is room underground for life to hang out during a gamma ray burst or two. There are massive stars around the galaxy's center because there's much more mass in the form of gas and dust to draw from.

Warp speed kind of requires FTL sensors to avoid running into things. Also, if you can warp space-time, I don't think there is any really hard limit on how far into the black hole you could go, outside of being demolished by whatever forces and spinning debris is at work beyond the event horizon. Hiding a base beyond the event horizon would put it at a pretty severe time dilation disadvantage.

There's nothing really magic about the gravity around a black hole outside of the event horizon. If something is orbiting a black hole, there's no reason to assume that it would fall into the event horizon any more than we would assume the Earth is going to fall into the Sun. In fact, Sagittarius A* has an unusually small accretion rate. (Technically, Sagittarius A* has between 200 and 400 million stars orbiting it.)

[Arioch]

There's nothing really magic about the gravity around a black hole outside of the event horizon. If something is orbiting a black hole, there's no reason to assume that it would fall into the event horizon any more than we would assume the Earth is going to fall into the Sun. In fact, Sagittarius A* has an unusually small accretion rate. (Technically, Sagittarius A* has between 200 and 400 million stars orbiting it.)

Technically, Sagittarius A* has the entire galaxy orbiting around it.

A solar system orbiting very near to a black hole might be disrupted by gravitational tides if it got very, very close (the pull on the nearer planets being greater than the pull on the farther planets). But this probably isn't likely in the vicinity of Sgr A*, as the gravitational wells of supermassive back holes are ironically less steep than those of stellar mass black holes; I believe you can get fairly close to the event horizon of a supermassive black hole without being tidally ripped apart.

[Absalom]

So, I've played computer games where multiple races colonize and flight a 'galaxy' where a galaxy is a square map with dozens or hundreds of star systems.

Today I was reading about Sagittarius A*, which is the supermassive black hole at the center of our galaxy. Apparently it has 92 stars orbiting around it. So, I'm wondering how things would be different for one of these games if the setting was those 92 stars.

• Would the black hole prevent in any way prevent life on planets around these stars?

The radiation of the general area is very harsh. I think that for anything locally developed, you'd be looking at liquid-metal & similar biology, which is a few steps short of "swim in stars" heat. I'd be surprised if much (if any) research has been performed on the subject, though some limited portion of metallurgy might be relevant.

As the others pointed out, probably you couldn't have life that evolved on one of the planets. I'd go for "space whales" or something instead, under the hopes that with the right exotic biochemistry, and the presumable concentration of nova events, it could somehow work out.

Somehow (maybe an archilect gets bored?).

What would the universe look like from the deck of the USS Enterprise after it had crossed the event horizon of a black hole? Would you be able to see other things that were also inside the event horizon of the black hole, or would you be essentially blind?

Objects outside the black hole would appear blue-shifted as I best recall. I also suspect, but don't know, that the event horizon would appear to move. It's occasionally even questioned whether the conventional concept of a black hole really exists, or if instead the in-falling mass just causes it's own time to distort to a remarkably severe extent (effectively making black holes something of a "pause" button if you can survive the trip).

There's nothing really magic about the gravity around a black hole outside of the event horizon. If something is orbiting a black hole, there's no reason to assume that it would fall into the event horizon any more than we would assume the Earth is going to fall into the Sun. In fact, Sagittarius A* has an unusually small accretion rate. (Technically, Sagittarius A* has between 200 and 400 million stars orbiting it.)

Technically, Sagittarius A* has the entire galaxy orbiting around it.

That's similar to saying that the Moon orbits Mount Everest :p .

Also, we need a "tongue" smiley.

A solar system orbiting very near to a black hole might be disrupted by gravitational tides if it got very, very close (the pull on the nearer planets being greater than the pull on the farther planets). But this probably isn't likely in the vicinity of Sgr A*, as the gravitational wells of supermassive back holes are ironically less steep than those of stellar mass black holes; I believe you can get fairly close to the event horizon of a supermassive black hole without being tidally ripped apart.

As I recall, it's thought that in some cases you might be able to pass the event horizon without being frappéd (depending, you know, on how event horizons work, exactly. You could also be turned into a raw force-carrier field if they manifest as space-time domain walls or something).

[Arioch]

That's similar to saying that the Moon orbits Mount Everest .

It would be similar if Mount Everest was located at the center of Earth's core. But my point was that there's no clear dividing line between the stars that are orbiting the black hole and those that are just moving along with the rest of the galaxy, since they are all technically doing both.

Also, we need a "tongue" smiley.

There is one. Use capital P with your colon.

A solar system orbiting very near to a black hole might be disrupted by gravitational tides if it got very, very close (the pull on the nearer planets being greater than the pull on the farther planets). But this probably isn't likely in the vicinity of Sgr A*, as the gravitational wells of supermassive back holes are ironically less steep than those of stellar mass black holes; I believe you can get fairly close to the event horizon of a supermassive black hole without being tidally ripped apart.

As I recall, it's thought that in some cases you might be able to pass the event horizon without being frappéd (depending, you know, on how event horizons work, exactly. You could also be turned into a raw force-carrier field if they manifest as space-time domain walls or something).

Yes, I believe this is correct; if the black hole is massive enough (and therefore the event horizon is far enough away from the singularity), the location at which the tidal stress became dangerous would be inside the event horizon.

[icekatze]

hi hi

It is true that observations of the galactic center are hindered by a large number of troublesome factors, but as far as I can tell, it is generally hypothesized that the center of the galaxy's rotation is inside Sagittarius A, if not within the event horizon of Sagittarius A* itself. (To the point that it was set as the zero point for galactic latitude and longitude by the IAU in 1958.)

[anamiac]

(Technically, Sagittarius A* has between 200 and 400 million stars orbiting it.)

Ah, well yes, technically everything in the galaxy is in Galactocentric orbit around Sagittarius A*. I think what the article meant was that 92 stars have been discovered where their parent object - the closest thing they are orbiting - is Sagittarius A*. The moon's orbiting both the Sun, the Earth, the center of the local cluster, Sagittarius A*, the center of the local galaxy cluster, and possibly many other places including the center of the universe, but it's parent object is the earth.

Still, with 400,000,000 stars to choose from, it's hard to imagine that any of the 92 stars close to the black hole and subjected to all that radiation would be considered prime real estate.

Something I've wondered... Is it possible for light to orbit a black hole? Thus at some point when you're approaching the black hole you'd enter a region where you'd get illuminated from orbital light? I suppose that we don't constantly see things falling into black holes is a good counter-argument.