[HN Gopher] Signatures of gravitational atoms from black hole me...
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Signatures of gravitational atoms from black hole mergers
Author : thunderbong
Score : 90 points
Date : 2024-09-17 10:45 UTC (12 hours ago)
(HTM) web link (physics.aps.org)
(TXT) w3m dump (physics.aps.org)
| perihelions wrote:
| Is the reason these are coherent quantum states that the
| postulated ultralight axions don't strongly interact with
| anything except gravity, so they see very little environmental
| noise to decohere them? Would they also predict there's (much
| smaller) dark matter halos around ordinary planets and stars, and
| these also have quantized atom-like states?
| wwarner wrote:
| yes, just heard about it on Physics Frontiers. Monsalve &
| Kaiser are talking about primordial black holes, and are
| offering a theory that if they were imbalanced in color charge,
| they could be surrounded by a particle cloud, in a big quantum
| state.
|
| https://pca.st/episode/f0db6ab1-18ff-4201-a6b2-a30b780a266a
| InDubioProRubio wrote:
| Stupid question, but between two singularities merging, there is
| tiny space, with gravitation zeroing out and appearing plank
| matter being ripped towards one and the other. Can one spot that
| location in the middle where anti-matter and matter bleed from
| the nothing on modern telescopes?
| elashri wrote:
| Regardless of the gravity canceling out in this region (which
| is more complicated and probably will not happen). The current
| LIGO and Virgo wouldn't have enough spatial resolution to
| pinpoint tiny regions between black holes.
|
| To explain what will happen is that gravitational field in
| region you are describing would have a steep spacetime
| curvature and a point where it will cancel gravitational forces
| would be more of a saddle (lagrange point classically) point
| rather than zero gravity region.
|
| Now you also have quantum fluctuations that now with this
| strong gravitational field you will have virtual particle -
| anti particle paris pop in and out of vaccum. This is not going
| to be only in thia region but all around. Also merging process
| will enhance this phenomenon but deciding where actually this
| middle point will be difficult.
|
| Now it would be impossible at least for our current
| observational tools to have resolution for the scale we are
| talking about. Event horizon telescope for example is designed
| to observe areas around singularities on much larger scales
| that what you are interested in here.
|
| But the interesting part would be If matter and antimatter
| pairs were produced between merging black holes, they would
| likely be short-lived. In this intense gravitational
| environment, any particles created would be rapidly torn apart
| or accelerated towards one of the black holes. The annihilation
| of such pairs might emit gamma rays, but this signal would be
| extraordinarily faint compared to the other high-energy
| processes occurring during a black hole merge.
|
| So the answer is probably No, at least with our current
| technology.
| pdonis wrote:
| _> gravitational forces_
|
| Gravity is not a force in GR. The spacetime curvature in a
| spacetime with two black holes that merge is not describable
| in terms of a simple "gravitational field". Spacetime
| curvature is a fourth rank tensor with twenty independent
| components. In vacuum ten of those vanish identically,
| leaving ten independent components.
| oneshtein wrote:
| Each black hole has tiny spot with zero gravitation in the
| centre.
| pdonis wrote:
| _> between two singularities merging_
|
| Two black holes merging does not mean two singularities
| merging. The singularity (singular, not plural) is a moment of
| time that is to the future of all other moments inside the
| hole. If two black holes merge, there is just one singularity
| inside the merged hole.
|
| Remember that GR is a model of _spacetime_ , not space. In
| spacetime, a single black hole looks, heuristically, like a
| cylinder, and the singularity inside is at the future end of
| the cylinder. Two black holes merging look, heuristically, like
| a pair of trousers, and the (one) singularity inside the merged
| hole is at the future end of the trousers (the "waist").
| Jerrrrrrry wrote:
| very good, but I would say (since "light cone" is of such
| common parlance) that the physical 3d analogous projection
| would be two slightly overlapping 3d-venn diagram funnels
| conjoining at an "indefinitely" (asymptotically smaller)
| small space-time minkowski manifold.
|
| naked singularities themselves, however, do not exist.
| pdonis wrote:
| _> the physical 3d analogous projection would be two
| slightly overlapping 3d-venn diagram funnels conjoining at
| an "indefinitely" (asymptotically smaller) small space-
| time minkowski manifold._
|
| I'm not sure what you mean by this, but it doesn't seem to
| correspond to any actual physical model that I'm aware of.
| api wrote:
| My most recent physics rabbit hole was the black hole hole. They
| are fascinating.
|
| My favorite is the idea of primordial black holes which formed in
| the instants after the Big Bang. Many models and theories predict
| them and they could be an excellent dark matter candidate. The
| universe could be full of black holes in the asteroid mass range
| the size of hydrogen atoms.
|
| There is also a hypothesis that the predicted (by many solar
| system simulations and models) planet nine far beyond Neptune
| could be a captured primordial black hole in the 1-5 Earth mass
| range and about the size of a golf ball to a tennis ball.
|
| I really really hope that exists because if it did it would be
| within probe range. Going and checking out a black hole could
| allow us to solve physics and develop a complete tested unified
| theory.
|
| Then there's spooky shit like:
|
| https://en.m.wikipedia.org/wiki/Black_hole_electron
| renox wrote:
| > The universe could be full of black holes in the asteroid
| mass range the size of hydrogen atoms.
|
| ? Not if there's Hawking radiations.
| api wrote:
| If the Hawking temperature is below the CMB no net
| evaporation happens. This means there is a mass cutoff and
| it's below asteroid mass. Any smaller PBHs would have
| evaporated by now assuming we are right about Hawking
| radiation. The math says it should exist but we have AFAIK
| not proven it.
|
| The big black holes will last insanely long amounts of time.
| ithkuil wrote:
| I'm confused.
|
| Hawking temperature is inversely proportional to the mass.
| I assume most black holes except the very small ones would
| thus have a hawking temperature lower than the CMB.
|
| Does that mean that effectively no black holes will ever
| evaporate not even a tiny bit well until the future time
| when the CMB will be so red shifted that black holes will
| start to have net radiation?
| LegionMammal978 wrote:
| Wikipedia suggests that this is the case [0]:
|
| "However, since the universe contains the cosmic
| microwave background radiation, in order for the black
| hole to dissipate, the black hole must have a temperature
| greater than that of the present-day blackbody radiation
| of the universe of 2.7 K. A study suggests that _M_ must
| be less than 0.8% of the mass of the Earth -
| approximately the mass of the Moon. "
|
| I'm not sure where the discrepancy between the mass of
| the Moon vs. an asteroid comes from, though.
|
| [0] https://en.wikipedia.org/wiki/Hawking_radiation#Black
| _hole_e...
| ck2 wrote:
| Black holes can't be dark matter.
|
| Dark matter is a WIMP
|
| The universe was built on a scaffold of dark matter like an old
| spiderweb that slowly collects dust.
| api wrote:
| That's another leading hypothesis. Some classes of WIMPs have
| been ruled out but the whole idea hasn't been.
|
| BTW primordial black holes could still exist even if they
| aren't a significant dark matter component.
| pavel_lishin wrote:
| > _Then there's spooky shit like:_ >
| _https://en.m.wikipedia.org/wiki/Black_hole_electron_
|
| From the article:
|
| > _However, Carter 's calculations also show that a would-be
| black hole with these parameters would be "super-extremal".
| Thus, unlike a true black hole, this object would display a
| naked singularity, meaning a singularity in spacetime not
| hidden behind an event horizon. It would also give rise to
| closed timelike curves._
|
| I wonder if there's a fun sci-fi story in the discovery that
| all electrons _are_ in fact naked singularities.
| ithkuil wrote:
| In quantum field theory electrons are excitations in the
| electron field.
|
| If they also were tiny black holes, what would it mean to be
| an excitation in the electron field which when the wave
| function collapses it would behave like a black hole. Does it
| mean that it's not a black hole anymore when the wave
| function spreads out?
| jefb wrote:
| Let's not forget that the radius of the observable universe is
| ~= the Schwarzschild radius i.e. we're all almost certainly
| inside a black hole ;)
|
| https://en.wikipedia.org/wiki/Black_hole_cosmology
| gerad wrote:
| I guess that'd explain the big bang nicely. It does make it
| the "outer universe" disappointingly unobservable though.
| pdonis wrote:
| _> we 're all almost certainly inside a black hole_
|
| No, we're not. The universe is rapidly expanding. Equating
| the Schwarzschild radius for a given blob of matter with the
| event horizon of a black hole requires that the matter be
| static or collapsing.
|
| The "black hole cosmology" models referred to in the
| Wikipedia article are misnamed. It is theoretically possible
| that our observable universe is a patch of a Schwarzschild
| spacetime, which is what the models referred to are
| asserting, but if it is, then, since the universe is
| expanding, it would be a patch of the _white_ hole portion of
| the spacetime, _not_ the black hole portion. And the
| "horizon" would be a _white_ hole horizon, i.e., one from
| which the universe 's expansion would eventually cause us to
| pass _out_ of.
|
| However, such a model is extremely unlikely because it has no
| way of explaining where the white hole horizon came from. A
| _black_ hole horizon can come into being from gravitational
| collapse, but a _white_ hole horizon would have to have been
| "built in" to the overall universe from the very beginning.
| Nobody has any reason to think that is actually possible,
| even if we have a theoretical mathematical model that
| includes it.
| api wrote:
| What if we're expanding because we are in a black hole that
| is being fed by a collapsing star or other object in a many
| orders of magnitude larger scale universe?
|
| Of course these kinds of things are probably 100%
| untestable.
| pdonis wrote:
| _> What if we 're expanding because we are in a black
| hole that is being fed by a collapsing star or other
| object in a many orders of magnitude larger scale
| universe?_
|
| Expanding and collapsing are two different things. So I
| don't see how your suggestion here makes any sense.
| Jerrrrrrry wrote:
| complexity of life's scale somehow trillions of
| magnitudes "smaller" than a similarly constructed
| universe is not only completely irreconcilably untestable
| (outside of one thought one) but also reminiscent of
| m-theory (11 dimensions) and the plot of men in black
| jefb wrote:
| > Equating the Schwarzschild radius for a given blob of
| matter with the event horizon of a black hole requires that
| the matter be static or collapsing.
|
| If the space containing the matter is stretching does that
| still count as expansion?
| pdonis wrote:
| _> If the space containing the matter is stretching does
| that still count as expansion?_
|
| "Space stretching" is a vague pop science description
| that doesn't really correspond to anything in the actual
| physics model. So it doesn't count as anything; you
| should just ignore it.
| Jerrrrrrry wrote:
| magnitude difference between dark energy and the
| schwarzschild radius
| ndsipa_pomu wrote:
| I recall seeing something (likely a youtube video on
| cosmology) that suggested that the Big Bang would be the
| white hole horizon (i.e. a singularity in out past) and
| that does make some kind of sense as it'd be impossible to
| go inside the Big Bang. I recall there being some good
| reasons as to why that's not believed to be the case though
| and also why the visible universe doesn't have an event
| horizon.
| pdonis wrote:
| _> the Big Bang would be the white hole horizon (i.e. a
| singularity in out past)_
|
| The white hole horizon is not the same thing as the white
| hole singularity. The "Big Bang" as an initial
| singularity in our universe (which is not actually the
| correct usage of the term "Big Bang", but that's a whole
| other discussion) would be the white hole singularity,
| not the horizon.
|
| Note also that in a white hole model of our universe, we
| would be _inside_ the white hole horizon, not outside it.
| treis wrote:
| Why wouldn't the primordial black holes condense into bigger
| ones like the matter that makes up planets and stars did?
| kadoban wrote:
| Some of them would, some wouldn't, depends on where they were
| and how they were moving.
|
| This is a bit like asking why Jupiter isn't part of the Sun
| but other stuff is.
| itishappy wrote:
| Some would, but the vast majority of matter is not found in
| planets and stars. Most stuff just floats around on it's own
| out there.
| skykooler wrote:
| If we did have a tennis-ball-sized black hole out beyond
| Neptune, it would be far beyond our capabilities to locate and
| track - we can barely track debris that small in low Earth
| orbit, and black holes aren't even courteous enough to provide
| a radar return. We would not be able to send probes near it any
| time soon.
| ck2 wrote:
| Apparently I am not watching enough PBS SpaceTime because I still
| do understand what a "gravitational atom" might be.
|
| They are not implying a particle that causes gravity right?
| Because I thought it is pretty well accepted there isn't a
| "gravaton" like there are photons.
|
| They also don't mean atom-sized black-holes, so I still don't get
| it.
|
| Hoping Matt does an episode on this so I can grasp it.
|
| https://www.pbs.org/show/pbs-space-time/
| tectonic wrote:
| I think they are more drawing an analogy between the atom one
| or more black holes with a cloud of particles around them.
| Black holes are quantum mechanical and so the resulting system
| could behave much like an atom, including having things that
| look like energy levels. The universe rhymes.
| pdonis wrote:
| _> I still do understand what a "gravitational atom" might
| be._
|
| It's a vague gesture in the direction of a speculative theory
| of quantum gravity. It's not anything we have any actual
| evidence for.
| swframe2 wrote:
| We were told that nothing can escape a black hole.
|
| But when black holes merge, the combined mass is smaller.
|
| It is described that the lost mass is converted to gravitational
| waves.
|
| But gravity is the curvature of space caused by mass, it is not
| described as a form of mass.
|
| How do you understand this process of matter escaping a black
| hole?
|
| Is it that the gravitational waves are caused by a "quantum
| gravity" particle that can't be converted back to any of the
| other quantum particles?
| cyberax wrote:
| > But gravity is the curvature of space caused by mass, it is
| not described as a form of mass.
|
| Gravitational waves carry momentum and energy (and therefore
| mass), just like electromagnetic waves. Theoretically, you can
| extract that energy from gravitational waves, by using
| oscillating masses tuned to the wave's frequency.
| pdonis wrote:
| _> Gravitational waves carry momentum and energy (and
| therefore mass), just like electromagnetic waves._
|
| No, EM waves do not have mass. They are massless. They carry
| momentum and energy, yes, but not mass.
|
| In GR, the source of gravity is not "mass", it's stress-
| energy. EM waves carry stress-energy even though they are
| massless.
|
| Gravitational waves do have some aspects that are analogous
| to EM waves, but there is a key difference: gravitational
| waves do not have any stress-energy. They are pure spacetime
| curvature in vacuum. So while there is a sense in which they
| carry momentum and energy, since properly constructed
| detectors can extract momentum and energy from them, they do
| not carry any stress-energy and the momentum and energy they
| carry cannot be localized the way momentum and energy in EM
| waves can.
| cyberax wrote:
| > No, EM waves do not have mass. They are massless. They
| carry momentum and energy, yes, but not mass.
|
| OK, EM waves can get _transformed_ into mass.
| pdonis wrote:
| _> EM waves can get _transformed_ into mass._
|
| In the sense that they can be absorbed by matter and
| (possibly) increase the invariant mass of the matter,
| yes.
| pdonis wrote:
| _> How do you understand this process of matter escaping a
| black hole?_
|
| No matter escapes. Gravitational waves are not matter. They are
| spacetime curvature. Nor do they "escape" the black hole; they
| are emitted from outside the horizon. The reason the mass of
| the merged hole can be smaller than the combined masses of the
| original holes, with the difference being emitted as
| gravitational waves, is that black holes are not made of
| matter, they are made of spacetime curvature, and when they
| merge, some of the spacetime curvature doesn't get included in
| the merged hole. That's just how spacetime curvature works.
| LegionMammal978 wrote:
| > Nor do they "escape" the black hole; they are emitted from
| outside the horizon.
|
| That's interesting, I'd never really thought about that
| before. Does GR predict that there would be any waves
| confined to the inside of the merged black hole?
| pantulis wrote:
| If there is anything combined inside the resulting event
| horizon it doesn't matter what it was: as far as GR is
| concerned it has been reduced to the effect of its mass,
| charge and spin. But we already know that GR isn't the
| whole story when it comes to BHs. See "soft hair" black
| holes.
| pdonis wrote:
| _> we already know that GR isn 't the whole story when it
| comes to BHs. See "soft hair" black holes_
|
| More precisely, most physicists _believe_ that GR isn 't
| the whole story. But we have no actual _evidence_ for
| quantum gravity speculations like "soft hair". They're
| just speculations at this point. We don't _know_ that any
| of them will actually turn out to be right.
| pdonis wrote:
| _> Does GR predict that there would be any waves confined
| to the inside of the merged black hole?_
|
| Yes, but we would of course never observe those, and they
| would not reduce the externally measured mass of the merged
| hole.
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