I’ve been arguing with a friend about this for a few days now.
Her original argument was that a black hole was just an imploded star with such high density that light could not escape (ie. a neutron star), which I disproved, but she still ascerts that a black hole is not actually a hole in the fabric of space, as I proposed it was.
However, after reseraching it, I’m starting to doubt myself. All the sites I’ve come across have definition the singularity as being a point in spacetime where mass becomes infinity, and both space, time and all matter within ‘cease to exist’, as least as far as we’re concerned.
Is it pointless to try and ascribe a black hole to the definition ‘hole’ or ‘non-hole’? If not, which is it generally theorized to be?
Depends on what you say a “hole” is. Is it a location in some n-dimenional space where you expect to find something and don’t? If that’s the case, then I’d have to say that it really isn’t a hole, per se. You find exactly what you expect, that is a set of points beyond the observable universe that culminates in a singularity. In that sense it “exists” just as much as a galaxy, a tree, or a “hole” in the ground exists.
Depends on what you say a “hole” is. Is it a location in some n-dimenional space where you expect to find something and don’t? If that’s the case, then I’d have to say that it really isn’t a hole, per se. You find exactly what you expect, that is a set of points beyond the observable universe that culminates in a singularity. In that sense it “exists” just as much as a galaxy, a tree, or a “hole” in the ground exists.
In conventional depictions of a black hole, it looks like something like a whirlpool in a bath tub. Some even show a flat accretion disk with jets blowing out the front (and back?).
But if a black hole is based around a singularity, wouldn’t the gravitational pull happen in a spherical / concentric form? i.e. wouldn’t things get pulled in from all directions equally? should a black hole look the same no matter which direction you look at it? the event horizon would be more like a 3-D bubble rather than a 2-D ring?
Or is there something about the spin of a black hole that imparts a plane to the structure?
Or is the math so complicated that 2-D or 3-D art just can’t capture it correctly?
Whether it’s ‘really a hole’ depends on how you define a ‘hole’; if you count a singularity as a ‘hole’ then it is, if not then it isn’t. The actual physics relies on the mathematical description of spacetime, and doesn’t casually fit into ordinary English. A lot of scientists suspect that quantum gravity will show that a black hole doesn’t actually collapse to a singularity, but that’s speculation not a solid theory.
The force of gravity from the black hole is symmetrical, but the accretion disk is matter that’s being pulled into the black hole that didn’t start off perfectly symmetrically, had some velocity not directly towards the black hole, and interacts with itself as it heads towards the black hole. The accretion disk is normal matter outside of the event horizon, often by a large distance, so while the horizon should be a sphere, the stuff near it doesn’t have to be, and usually isn’t.
The singularity isn’t a location in space where you expect to find something and don’t, because the singularity isn’t a location in space at all. What you expect to find but don’t is the location itself.
And not only is the accretion disk around a black hole not typically symmetric, neither, actually, is the hole itself. Black holes can have angular momentum, and it’s expected not only that most of them do, but that they have angular momentum very close (over 90%) to the maximum possible value. They do still attract in all directions, but the force is not the same in the direction of the poles as in the direction of the equator, and the force in the direction of the equator will depend on which direction the falling matter is moving.
But when OP’s friend points to aHubble photo or map, says," "OK, you told me “there’s the black hole named XDG3467, see, at the center of that galaxy.”
That we’re more or less sure it’s there–we see or can calculate the event horizon, mass, whatever–but what’s more accurate than that we can’t say. Imagine a large ink circle on a 2-D star map map of a certain scale marking the place, and then someone asks “OK, but where in that area encircled by the circumference is the center? Everything’s got a center if it has a periphery.”
And if the question is taken to means “where is the singularity, is it perhaps there?”–the answer might be “look, this is like asking where is “that particle” during a quantum tunneling event; the answer is there’s no there there, by definition.”
As planets or stars become larger, so does their gravitational force. A black hole is simply so large, and its gravitational force so strong, light can not escape. And it is theorized that any light or objects passing by would simply be sucked into it.
When researching this, be sure to read factual information from scientific astronomers, not science fiction fantasy stuff (of which there is plenty out there!)
It depends really what you mean by “a hole” - ultimately though, in the absence of an obvious definition of “a hole” that can be unambiguously applied to a black hole, I’d tend to agree more with it being pointless argument.
This is not at all theorized, in the sense that there is no scientific theory describing black holes which predicts this. A black hole’s gravity at any given distance is the same strength as the gravity of any object of the same mass at that same distance (thus, for instance, if you instantly turned the Sun into a black hole without changing its mass, the orbits of the planets would remain unchanged). Now, of course, if you approach too close to a black hole, you will get sucked in, but then, this too is true of every object. And in fact, it’s possible to approach a black hole more closely than for any other object of the same mass, for the simple reason that a black hole is smaller than any other object of the same mass.
I get what you’re going for, but the shallow black holes die first, the deep ones live the longest, and the well-fed black hole lives the longest of all.
This is due to Hawking radiation, which we’ve never seen but appear to expect to exist, and according to that theory, black holes evaporate at a rate proportional to the cube of their mass. Eventually, small black holes are radiating so fiercely their radiation pressure pushes away stuff they’d otherwise eat, so they get smaller, and radiate more intensely, in a feedback loop which continues until the black hole ceases to exist.
Nitpick: The evaporation rate is proportional to the inverse square of their mass, which makes the lifespan proportional to the cube of the mass.
Thermal radiation is proportional to temperature to the fourth power times area, temperature of a black hole is inversely proportional to mass, and area of a black hole is proportional to mass squared.
It’s also theorized that large enough black holes will end up with such a large accretion disc that infalling matter forms into stars orbiting the black hole instead of actually going into the black hole, so there might actually be a ‘full’ size.
An accretion disk forming stars doesn’t actually stop it from being an accretion disk. And black holes can also grow via mergers of smaller black holes.
It’s actually currently an open question just how the largest black holes get so big, whether it’s by continual accretion of ordinary matter, or by hierarchical mergers of smaller holes.
I was loosely paraphrasing something else that I read, here’s a paper on the theoretical maximum size of black holes. The limit is on how large they can grow via an accretion disc, while they could conceivably grow larger by mergers it seems unlikely you’d have two ultra-massive black holes that near each other, and detecting them would be difficult since they would not be luminous. https://arxiv.org/pdf/1511.08502v2.pdf