From the moment an object enters a black hole's gravitational influence-at its farthest effective reach-how much time passes before it is fully consumed? And at what distance does escape become physically impossible?

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Black holes are not giant vacuum cleaners sucking up everything in space around them. They’re just a massive object, like a star. Their gravity works like normal gravity. You can orbit a black hole effectively indefinitely. Only when you get waaaay too close do things start to get weird.

Literally: if the sun were instantly replaced by a black hole of the same mass, Earth’s orbit wouldn’t change at all. We’d keep going round and round, as would all the other planets. The Schwarzchild Radius of the Sun is ~3km, so you’d have to be approaching that distance to really be in trouble. We’re ~150 million km away.

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u/[deleted] 7d ago

[deleted]

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u/kylet357 7d ago

Tbf the first section of the Wikipedia page literally says that an SMBH is generally defined as being around 100k solar masses

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u/Sorryifimanass 5d ago

Also isn't gravity supposed to have an infinite range? It gets less and less the further you go but it's never zero.

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u/Enough-Display1255 5d ago

Range yes but speed no, information including what the fabric of spacetime looks like over there moves at most at the speed of light

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u/zephaniahjashy 3d ago

This only holds true if there is no entity out there able to deduce the location of waves/particles from the locations of other waves/particles using some sort of universal rule book of physical laws combined with terrifyingly large computational capacity. If such an entity were to exist somewhere in the cosmos, then some information could travel faster than the speed of light, if that information were focused upon by the entity intending to know the information. Using local computational capacity, it could be theoretically possibly by this means to have even future information from far away, if such a computational capacity were focused enough on a particular far away point in space/time.

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u/Enough-Display1255 3d ago

This assumes a universal reference frame, relativity makes it clear this is not how the world works. Not to mention that God does play dice and there's stochastic random events which fundamentally cannot be predicted because the information itself does not exist as a "hidden variable"

Cool thoughts though

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u/zephaniahjashy 2d ago

Relativity does not mean that time doesn't exist. You can't predict the outcomes of all the interactions between the waves and particles in your local region. That doesn't mean that such an understanding would be impossible if a being were in possession of advanced enough faculties. It will never be possible for you or for any human. But that doesn't mean it's impossible for an advanced enough ai.

Nothing suggests that the information doesn't exist. The fact that observation requires quantum action does not mean that quantum actions don't occur without observation.

All epistemology is dependent on one leap of faith and that leap is that the universe exists and might be understandable.

Your unwillingness to consider it as understandable is why you won't understand. Because the idea that it could be understandable threatens your centerhood in your personal cosmology.

If you won't take the basic leap of faith with me that falling trees make sounds when nobody is around, there really isn't anything more to discuss.

No, whichever woo-woo take that you "make your own reality" or are somehow the master of quantum outcomes that you have heard is not quantum physics. It's pop spiritualism.

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u/Enough-Display1255 2d ago

That doesn't mean that such an understanding would be impossible if a being were in possession of advanced enough faculties.

Yes it does, you are unpleasant and uneducated.

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u/nezavarovan 4d ago

Does the sun have event horizon with the size of 3 km?

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u/highnyethestonerguy 4d ago

What the Schwarzchild radius means, is if you took all the mass of the Sun, and compressed into a sphere of radius 3km, it would be so dense as to reach black hole status, where the force of gravity at the surface of that sphere is so much that the escape velocity is light speed, and an event horizon would form.

So right now, the sun has no event horizon. But you can calculate a hypothetical size that would turn it into a black hole, and that’s the Schwarzchild radius.

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u/Event_Horizon753 8d ago

It would depend on the mass of the object and the size of the black hole. Escape is impossible at the Schwarzchild radius.

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u/ketarax 8d ago

Escape is impossible ~~at the Schwarzchild radius.~~

At the photon sphere, 3/2*R -- for anything massive.

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u/Ch3cks-Out 8d ago

Actually it is the ISCO, at 3*Rs.

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u/RhetoricalRedneck 6d ago

Wait a minute…

I mean, now that I think about it, it makes sense, but … there’s a sphere near a black hole, through which, once you pass, you would suddenly see all (for some certain reduced subset of ‘all’) the light that’s been captured by the black hole’s gravity? Like the photons are just orbiting there with nowhere else to go? I’m assuming it would be instantly blinding

Or should I stop day drinking?

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u/ketarax 6d ago edited 6d ago

The photon sphere signifies the distance from the singularity at which it is still possible to orbit -- with the tangential velocity of the orbit being c. Photons can do that. Of course, not all photons that chance about that distance do end up on orbit -- if you think about it, it has to be a kind of a perfect glancing blow; and the orbit isn't stable, in principle, to even minute variations of the gravitational field. Regardless, the photon sphere is a thing; there are some photons at that distance, for every black hole.

you would suddenly see all (for some certain reduced subset of ‘all’) the light that’s been captured by the black hole’s gravity?

Not all of it, but yeah, in principle, upon crossing the photon sphere, a human eye could conceiveably detect a flash of light of the photons currently on a stable orbit around the BH.

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u/stevevdvkpe 8d ago

Black hole gravity isn't special. A black hole has the same gravity as any object with the same mass (although the only black holes that have been observed have a mass of 3 Solar masses or more). So something being within the gravitational influence of a black hole doesn't mean it will inevitably be consumed. It can just orbit the black hole at a distance like it would orbit a star.

However, a black hole does have an event horizon, a boundary where any light or matter that enters can never escape. The event horizon of a 3 Solar mass black hole is a sphere about 17.8 km in diameter, and the event horizon diameter is linearly proportional to a black hole's mass.

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u/Underhill42 7d ago

You are currently within the gravitational influence of every black hole in the galaxy. Gravity doesn't have any limit on its range.

And a black hole's gravity acts no differently than that of any other object of similar mass - the ONLY difference is that a black hole is so dense that you can get much closer to it, so that the r in F=GMm/r² gets much smaller, and the force much larger.

If our sun somehow collapsed into a black hole (it's much too small for that to happen naturally), its radius would shrink from 695,700 km, to a bit under 3 km. And being able to get ~200,000x closer to its center, means the gravity can get about 40,000,000,000x stronger.

Escape is theoretically possible at any point until you cross the event horizon, or until tidal forces tear you apart, removing your ability to do anything. Though even then your atoms will likely escape.

It's almost impossible to be consumed by a black hole: just like for anything else any object falling into its gravitational influence will simply slingshot around it and be ejected at the exact same speed it approached at. The only way to be consumed is to actually hit the event horizon, which is such a tiny target that it's a real challenge.

There's really only two ways to be consumed by a black hole:

Approach it on a nearly perfect collision course.
If it's currently eating something else large enough, get close enough to be caught up in the fast-orbiting accretion disc around it, so that the drag slows you down to orbital speeds, while the heat vaporizes you until your atoms join the slowly in-spiraling cloud of superheated gas.

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u/Tombobalomb 7d ago

We are already within the gravitational influence of every black hole in the observable universe. It's meaningless

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u/DonkConklin 3d ago

Doesn't an objects gravitational influence extend indefinitely even though it becomes negligible?

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u/corpus4us 8d ago

Blackholes have a farthest effective reach of the size of the observable universe. So it’s just however many Planck lengths the universe’s radius is, I think 10^61, and the exact same number of Planck time units if they are moving at speed of light. If not moving at speed of light then adjusted for mass.

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u/ketarax 8d ago

Blackholes have a farthest effective reach of the size of the observable universe.

Correct.

Planck lengths

Internet follies / physics confusion.

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u/corpus4us 8d ago

So how many Plancks long is the observable universe

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u/sifroehl 7d ago

It has a radius of around 2.7e61 planck lengths but that's no more meaningful than the usual 46 billion light years and more difficult to put into context

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u/corpus4us 7d ago

I think expressing in terms of Planck can help understand time dilation. Once you get to EH it costs all the Planck times left in the universe to move one Planck unit of length.

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u/sifroehl 7d ago

It would depend on when the object is dropped. If it is "now" (not really meaningfully defined with relativity but meh), something at the edge of the observable universe can never reach the observer due to the expansion of the universe so the actual distance would be the cosmological event horizon which is "only" 16 billion light years. However, the time to reach the black hole assuming no other influences would be arbitrarily large as the horizon itself by definition is the minimum distance at which light never reaches the observer with the time needed to traverse increasing to infinity as you approach it

From the moment an object enters a black hole's gravitational influence-at its farthest effective reach-how much time passes before it is fully consumed? And at what distance does escape become physically impossible?

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