Was not sure what to call the thread, and this was the best I could come up with.

Ok. I admit that this is very very far fetched, but I would like to know your opinion on my thoughts, whether possible.... never etc....

The scenario is two seperate black holes with a distance between them that remains constant.
These two black holes are at such a distance that the space between them is in constant pull, but given that the pull from each direction is equal there is an equalibrium (sp?).

First would you be able to shoot a beam of light and have it pass straight through unhindered.

Secondly could a star (although unlikely a system) be held whereby you could see black holes `feeding` in the skies.

As I say far fetched in many ways including not being able to support life on a star, a planet oribitting a star would come to different pulls, but...

As with any masses there will be an equilibrium point on the line connecting them where the gravitational force vanishes; this is called the first Lagrange point. But it's not particularly stable, though it's possible to get something with a comparatively small mass (i.e. much smaller than your black holes) in a periodic orbit around that point. So light could pass by without being deflected either way at that point, though the gravitational forces won't cancel around that point. It'd be very, very tough to keep something like a star in place around there.

Stratraveler has answered very concisely on two matters-

Stars in orbit near a black hole, for this thread.

And, an accretion disc around a black hole, as a means of feeding a black hole.

If only I could be as direct...

What I could say is plain, dull, and tedious. But, here goes, because I thought to answer
the light beam question.

Sorry to complicate things, but consider five scenarios.

The first is a few hundred million years after the Big Bang. The first generation of stars produced few black holes. They were super massive, but very pure material (no metals). When they went supernova, they made metals.

The second would be not long after that, when the "next generation" of stars contained by-products, collected from the first. They did implode, and make black holes if they were ~more than 8 times solar mass (Sun). Leading up to the process, supermassive pre-black hole stars would eject lots of nearby orbiting material, through gravity and stellar wind. In other words, they would kick out smaller stars, and blow away nearby gas and dust. If they imploded, the field around would have less material to orbit the new black hole, then there was to begin with. But, that era was more crowded than later times, so multiple black holes could merge more easily.

The third scenario would be about five billion years, after the Big Bang. Things were less crowded. Black holes candidates would still form in stellar nurseries. But, numbers of nurseries make clusters. Those need the action of (for instance) a rotating spiral galaxy, to thin them out. At some point, they become black holes on the move. They might cross paths, eventually.

The fourth scenario is the collision and merger of galaxies. I imagine that strips away a lot of gas and dust. There are areas that can undergo starbursts, and eventually create black holes. But, those conditions would have less remaining gas and dust (because of the stripping action of the collision). Black holes that orbit each other perhaps would have less
material between them.

The fifth scenario is in a region where previous supernovae have cleared away an area, leaving less material, nearby.

So, if we choose a scenario where things are less crowded, it might go like this.

1. First, a supernova removes alot of local gas and dust, but not other stars. Two black holes eventually enter the area. They get within a few light years. This could be comparable to the extreme orbital influence for our solar system- the Oort Cloud, which is from about .1 light years (6300 AU), to about .237 light years (15,000 AU).

2. The orbits would perhaps be eccentric, and by virtue of their dense gravitational influence, any stars coming within a certain obital appraoch, would be ejected from the system (slingshot effect). Doing this would dissipate the orbits of the black holes. They would then lose some momentum, and move into a smaller orbit.

3. Once they got to within a proximity, perhaps equal to our inner Oort cloud (for comparison), they would have a stable orbit for a billion years, with few stars left in their local system. Yet, they would be orbiting each other.

4. So, lets say one of the ejected stars had a flare, and sent light streaming toward the black holes. By the time it gets there, it is in an alignment to go right between them. No problem. As long as nothing deflects it, a photon at that point keeps going.

5. Over the course of a billion years, the black holes lose orbital energy (which is wasted away in the form of gravity waves). The critical distance is about three kilometers for each solar mass (Sun). That is the black hole no-escape boundary. If something comes to within 1.3 times that distance, it will be detoured into an orbit around the black hole- only to face an eventual passing over the last threshold, the Schwarzschild radius.


I guess the answer to your question is if the black holes have entered non-eccentric orbits, so that we can talk about a stable distance between them, we can estimate the scenario where a photon, would, or would not pass unaffected between them.

Of course, the mass of the black holes may not be the same, and they could have many values. But, given a case where they were similar, and given a least case scenario of around eight solar masses, then-

Using 3 kilometers for each solar mass, to arrive at a rough estimate of the Schwarzschild radius, that would make the black hole region for each one about 25 kilometers (very roughly). In addition, the cusp of orbital capture would be at 1.3 times that radius. So, a defelction zone would be encountered out to ~33 kilometers.

Bottom line, if 8 solar mass black holes were co-orbiting in a high vacuum region, and a series of photons passed between, they are safe as along as the black holes were more than 66 kilometers apart (4.4088^10-7 AU or .00000044088 AU).


For scale comparison, there are a couple of "scale bar images" to click on

And, you asked if we can see black holes pulling in material. Since there are none, really close to image, we have to settle on the effects they generate. Hubble Telescope took a nice image of a black hole region, on one of its earliest assignments. It could have been better, because that was one year before the wide-field camera was replaced.

It shows material being ejected at .5 C (half the speed of light). Two large jets form. The top one is slightly pointing toward us; the bottom one, away from us. There is a large accretion area, around 400 light years in diameter. I don't know the mass of the black hole, but it might be upwards of a million solar masses.

Images-

NGC 4621 Composite, With A Small (real color) HST Optical Image

NGC 4621 Central Region, And BH Accretion Disk

Larger scale bar (vertical), FWIW.

Many thanks for the excellent explanations and images.

I had never thought of the points raised, and am certainly going to have to take some of the jargon to google to get a better understanding.

Never considered that a black hole could just merely replace the space occupied by a star.
Always had the impression (wrongly it appears) that anything and everything is 'sucked' in.

regards

Quasars

Hmmmm......, so.........

Would I be right in saying that there is little to no difference in a threat to Earth between a galaxy colliding or a black hole engulfing.

Just to assure you that I am not in the least bit worried about this, but after lamens terms...... May worry once I have sorted ,y credit card bill mind

so-o-o-o-o-o..... How close is the nearest Quasar or are we talking the extreme of the galaxy, and if this is the case...... How come so much material so far out?

regards

The closest known quasar is 3C 273...They are about 13 billion lys away, so they were in the past...

Correct, in that they both present no threat. The next time a galaxy collides with the Milky Way will be in about three billion years when we meet the Andromeda galaxy; there'll be some gravitational limboing but it's not as if a star is likely to collide with the sun or anything like that. And there aren't any black holes anywhere near us so we're in no danger there.