36B solar mass black hole at centre of the Cosmic Horseshoe gravitational lens | Hacker News Reader

36B solar mass black hole at centre of the Cosmic Horseshoe gravitational lens

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163 pointsbookofjoe129 comments

Using the formula for black hole density, a black hole of this mass would have an average density about the same as the near-vacuum atmosphere of Mars(!)

https://physics.stackexchange.com/questions/26515/what-is-ex...

And it would take 10 days from event horizon to the singularity.

from which perspective? I have yet to wrap my head around it(this usually means I am wrong about something), but there may be no singularity because it takes matter an infinite amount of time to reach the center due to time dilation effects.

https://modern-physics.org/time-dilation-near-massive-bodies...

This is the origin of my favorite science fiction theory. (little to no actual science but you could write a fun space romp around it) If you get a large enough black hole where the tidal forces will not rip you to shreds instantly, you could just scoot across the event horizon right, now what happens? you can still move around, everything feels normal, but really you have lost half a dimension, everything "out" from the center is completely gone from the universe. Now the theory, back to our universe, What happened to time? why does time only go one way? we can accelerate and decelerate along the time axis, but can't reverse it. Where has our missing half of a time dimension gone?

It's not quite true that everything feels normal. If I am standing with my feet toward the singularity, my hand cannot move above my head, the best it can do is fall toward the singularity slower than my head does. Especially at very slow speeds this has some very weird physical effects, not the least of which is the immediate impossibility of all systems that make you 'you' continuing to function.

Is this true?

My understanding is that for extremely large black holes the tidal forces are negligible near the event horizon. So things should function pretty much the same other than you can't move in reverse and get out.

If two rockets fall past the horizon at the same time, one accelerating forward towards the singularity, and the other accelerating backwards away from the singularity, then shouldn't the distance between the rockets increase, even though they are both moving inexorably forward?

If the tidal forces are low, I'd assume that my muscles are still strong enough to "slow down my hand enough" to move it above my head.

The relevant quantities are the curvature scalars near the horizon, and for a sizable black hole they are small there. As an example, consider the Kretschmann scalar (KS). The KS is the sum of the squares of all components of a tensor. In Schwarzschild spacetime KS looks like R_{\mu\nu\lambda\rho}R^{\mu\nu\lambda\rho} = (48 G^2M^2)/(c^4r^6), where R is the Riemann curvature tensor, and we can safely set G=1 and c=1 so (48 M^2)/r^6. In this setting, KS is proportional to the spacetime curvature. At r = 2M, the Schwarzschild radius, the number becomes very small as we increase M, the black hole's mass. However, for any M at r = 0, the Kretschmann scalar diverges.

For a large-M black hole, there is "no drama" for a free-faller crossing the event horizon, as the KS gradient is tiny.

Since the crosser is in "no drama" free-fall he can raise his hands, toss a ball between his hands, throw things upwards above his head, and so forth. The important thing though is that all these motions are most easily thought of in his own local self-centred freely-falling frame of reference, and not against the global Schwarzschild coordinates. His local frame of coordinates is inexorably falling inwards. Objects moving outwards in his local frame are still moving inwards against the Schwarzschild coordinates.

You might compare with a non-freely-falling frame of reference. Your local East-North-Up (ENU) coordinates let you throw things upwards or eastwards, but in less-local coordinates your ENU frame of reference is on a spinning planet in free-fall through the solar system (and the solar system is in free-fall through the Milky Way, and the galaxy is in free-fall through the local group). That your local ENU is not a freely-falling set of coordinates does not change that the planet is in free-fall, and your local patch of coordinates is along for the ride.

A comparison here would be a long-running rocket engine imparting a ~ 10 m s^-1 acceleration to a plate you stand on. In space far from the black hole, you and the rocket engine would tend to move away from the black hole, but you'd be able to do things like juggle or jump up and down, and it'd feel like doing it on Earth's surface. This is a manifestation of the equivalence principle. Inside the horizon the rocket would still be accelerating the plate and you at ~ 10 m s^-1, but you, the plate, and the rocket would all be falling inwards.

Tidal forces are not the constraining factor - the transformation of space into a timeline property is. There is no out, no away direction. All paths lead to singularity. No particle can travel away from singularity .

Two rockets can diverge in distance, because one is slowing itself along the timeline space dimension toward singularity. If you are moving 1 m/s toward singularity, the fastest your hand can raise above your head is 1 m/s with infinite energy expenditure. The same goes for blood pumping to your head, electrical impulses to your brain, etc.

You can move away from a singularity once you are inside the event horizon. You just can’t achieve escape velocity anymore once you’re inside the event horizon.

After you pass the event horizon, all your possible paths become elliptical. That doesn’t mean all possible paths instantly point directly at the center.

This is not true. There are some special exceptions (rotating kerr ring singularities) but in general there is no 'upward' direction away from the singularity. Space becomes timelike. There is only forward, toward the singularity. You can expend energy and accelerate toward the singularity slower, but every particle within the event horizon can move only closer to the singularity. There is absolutely no moving away from the singularity. Full stop. If you think there is, you are misunderstanding something fundamental about the model.

> Space becomes timelike. There is only forward ...

No. It's a fanciful analogy on a particular family of coordinate charts, particuarly systems of coordinates which do not smoothly/regularly cross the horizon. The black hole interior is still part of a Lorentzian manifold, there is no change of the SO+(1,3) proper orthochronous Lorentz group symmetry at every point (other than spacetime points on the singularity). One can certainly draw worldlines on a variety of coordinate charts and add light-cones to them, and observe that the cones interior to the horizon all have their null surfaces intercept the singularity. However, there's lots of volume inside the interior light cones (and on the null surfaces) and nothing really constrains an arbitrary infaller's worldline, especially a timelike infaller, to a Schwarzschild-chart radial line (just as nothing requires arbitrary infallers to be confined to geodesic motion).

The interior segment of a Schwarzschild worldline in general can't backtrack in the r direction, but there are of course an infinity of elliptical trajectories which don't. (That is to say that all orbits across the horizon are plunging orbits; but one can also say that of large families of orbits that cross ISCO, which is outside the horizon).

A black hole with horizon angular momentum and general charges offer up different possibilities, as does the presence of any matter near (including interior to) the horizon (all of these also split the ISCO radius, move the apparent horizon, and may split the apparent and event horizons). The Schwarzschild solution of course is a non-spinning, chargeless, vacuum solution everywhere, and is maximally symmetrical, and is usually probed with a test particle. An astrophysical system like a magnetic black hole formed that passes through a jet from a companion pulsar, for example, does not neatly admit the Schwarzschild chart (and has no known exact analytical solution to the field equations). At least one such astrophysical binary is known (in NGC 1851 from TRAPUM/MeerKAT) (and if you don't immediately run away from A. Loeb papers like you should, he added his name to one that argues there are thousands of such systems in the galaxy centre near Sgr A*, which itself is now known to have strong magnetic fields (thanks to EHT's study of the polarized ring)).

You really laid the text on thick here to end up exactly conceding the point.

No, not really. To boil it down to thinner text, and to focus on your "Space becomes timelike", I think you are stuck on (a) a particular system of coordinates that (b) are not regular across the horizon and (c) thinking that either of these does anything physical to free-falling infalling test particle.

The huge flashing red warning sign on (a) & (c) is that you drop in the words "'upward' direction", "{toward, closer to, away from} the singularity" and most especially "slower": you are clearly implicitly slicing spacetime into space and time.

If you can handle thicker text, Unruh has a nice discussion of regular systems of coordinates at http://theory.physics.ubc.ca/530-21/bh-coords2.pdf Additionally, Martel & Poisson 2001 <https://pubs.aip.org/aapt/ajp/article-abstract/69/4/476/1055...> (arXiv version <https://arxiv.org/abs/gr-qc/0001069>) is a nice discussion of PG coordinates.

More visually, one can compare the light cone structure on a KS diagram like at <https://tikz.net/relativity_kruskal_diagram/> (just before the "Edit and compile if you like") and a randomly chosen but very typical diagram in Schwarzschild coordinates <https://www.researchgate.net/profile/Ward-Vleeshouwers/publi...> or (in German) <https://yukterez.net/f/einstein.equations/files/schwarzschil...> (hovering over a diagram displays some light cones). Which cone appears to topple over in their respective coordinate charts is pretty obvious, and should give you plenty of shaded grey to think about the coordinate-dependence of "Space becomes timelike".

That doesn't sound right. If you're on the event horizon you're not going at very slow speeds in that sense, the space around you is already falling into the black hole faster than light.

If you're "travelling at 1m/s so you can only raise your hand above your head at 1m/s by expending infinite energy" then you're already travelling at c-1m/s away from the black hole through local space just to 'stay still' at 1m/s 'velocity'. No wonder you need infinite energy to accelerate your arm 1m/s further and things get weird - you're travelling at relativistic velocities.

There's no reason I need to cross the event horizon at C. I can cross the horizon as slow as I want. Particularly at the event horizon of an ultra massive black hole, gravitational acceleration can be as low as a couple G, easily defeated right up until the horizon is crossed.

I'm not sure how that's relevant. You're saying that below the event horizon you can't lift your hand above your head faster than your head is moving towards the singularity. But that's only true of your hand and your head in relation to their position and 'velocity' in global coordinates, which is not 1m/s.

nor can you swivel your head to look backwards, as all the particles in your head are tidal locked in a falling trajectory towards the center

> but there may be no singularity because it takes matter an infinite amount of time to reach the center due to time dilation effects.

The outside observer’s view doesn’t stop physics inside. For a massive black hole, you absolutely do reach the singularity in finite time by your own clock.. likely minutes to hours for the largest ones we've known about so far.

> but there may be no singularity because it takes matter an infinite amount of time to reach the center due to time dilation effects.

Wouldn't that just mean that the singularity is located infinitely far into the future?

Isn't it another way of saying that the singularity is never going to exist?

>To an external observer, an object falling into a black hole appears to slow down and never actually crosses the event horizon, seemingly freezing in time.

It takes infinite time to reach event horizon, not the center.

Yeah, that is the tricky part. The problem is that black holes are eldritch interstellar cryptids, and for the most part physics gives up and goes to cry in the corner the minute you start asking about "what's in a black hole?"

But in this specific case, you get one odd conclusion. if it takes forever to enter a black hole. is it impossible for anything to pass the event horizon? It sounds like this is observation dependent. but from an external point of view you are unable to observe anything entering the black hole. and from an internal point of view, the universe will instantly age and die when you try and enter the hole.(and if hawking radiation actually exists you will see the black hole shrink and pop the instant you try and enter it) either way nothing is getting in.

Is most of the mass of the star that formed the black hole actually stuck in a time dilated shell just outside the event horizon? Or perhaps all the mass is eternally stuck collapsing. and never actually reaches the density required to pass the event horizon. is that another way to define the event horizon? the point where time stops.

Time dilation makes my head hurt.

It never actually reaches the density required to form the event horizon.

> It takes infinite time to reach event horizon, not the center.

Even that is only true to a distant observer, not the one crossing the horizon.

How so?

The black hole has two conceptual parts - the event horizon and the singularity. The event horizon is a one-way imaginary shell where once you pass it, you will end up at the singularity which is a point at the center of the event horizon. It’s the hole in black hole. Because the radius of the spherical horizon grows linearly with mass, but the size of the hole is fixed at effectively 0, it allows for a bit of sightseeing on your way to impending doom if the mass of the hole is large enough.

This is also the light barrier where light can no longer escape the gravitational forces (causing the blackness of the black hole).

Your “sightseeing tour” would be a kaleidoscope of light as it brushes past you on its way to the singularity.

Uh, that is the event horizon?

Yup, you’re trapped, so is light, and as gravity bends you and everything around you into pretzels, you’ll see everything yet nothing, as even the light will escape your retinas, before they pop like little grapes.

Eventually your atoms will make their way to the center singularity.

Yes, I’m not sure why you keep repeating what everyone else is already saying?

This agent lacks context to the rest of the conversation, sorry.

One of the more mind bending aspects of this is how the horizon becomes inescapable. The singularity is the only “forward” that exists anymore. You cannot conceivably go anywhere else. Every direction becomes “in”.

another way of saying it is that the singularity is a place in time, not in space. it's a place in your future, and you cannot escape your future.

in a black hole time and space get switched in a sense.

One could say the same thing about death (or life). Once you’re born, death is the only “forward” that exists. You can’t calculate its exact distance but it’s inevitable.

And seeing as how time is only something observed at the macro level and is still completely unexplainable scientifically, you're really hitting the nail on the head here.

My point is not that they’re scientifically similar but that philosophically there is little difference.

Hydras tend to disagree.

it is not that hard to understand, if you jump out of a plane, there is also a spacetime singularity in your future, the ground

It's not similar to this at all. There is still a safe direction which exists - if you could reverse your fall, it would take you back to the plane. There is no reversing your "fall" into a singularity. "Out" no longer exists. Even if you reverse your direction, you'll still be falling towards the event horizon.

space becomes time and the singularity becomes the future.

That calculation of density is nice, but since we don’t know what’s inside a black hole, it doesn’t mean anything.

Passing the event horizon doesn’t mean you’ve reached the potentially ultra dense singularity, but it does mean you won’t escape.

we don't know how the mass inside a black hole is doing, but we have a pretty solid understanding of the volume and the total mass of black holes

Definitely a dumb question but I had read "a teaspoon of black hole is more dense than Mt Everest" or something like that.

The near-vacuum atmosphere of Mars seems very light...? What fundamental concept am I misunderstanding?

> but I had read "a teaspoon of black hole is more dense than Mt Everest" or something like that.

That sounds more like a description of the stuff neutron stars are made of. I don't think that description really works for black holes - how exactly do you take a teaspoon out of a black hole?

> The near-vacuum atmosphere of Mars seems very light...? What fundamental concept am I misunderstanding?

The linked Physics.SE answer does a decent job at explaining it, but the short of it is that for Schwarzchild black holes mass ~ event horizon radius, so if you define density as mass / (Schwarzchild volume) you get density ~ 1/(mass^2) - in other words, the more massive a black hole the less dense it is by that measure.

You can't make a teaspoon of neutroniun, either. The neutrons would immediately drift off and quickly decay (half life about ten minutes). It's just a way of illustrating the density.

You actually can have a black hole with the volume of a teaspoon, and it's stable. It will eventually decay by Hawking radiation, but not for umpteen gazillion years until the CMB gets cold enough.

> You can't make a teaspoon of neutroniun, either. The neutrons would immediately drift off and quickly decay (half life about ten minutes).

Technically speaking that sure sounds like scooping out a teaspoon of neutronium to me. Nothing said it had to be stable :P

But in any case, I suppose what doesn't work for me is that when the teaspoon illustration is being used it's in the context of picking out some sample/subset of a larger whole - take a whole neutron star and examine the properties of this supposed representative part of it, same way one might scoop out some ice cream out of a container. While that's technically not totally correct for neutron stars since they don't exactly have a uniform density, I feel that it's usefully-close-enough compared to black holes, since as far as we know all the mass of a black hole is concentrated in a point at its center so your "scoop" is either going to get nothing or everything.

> You actually can have a black hole with the volume of a teaspoon, and it's stable.

Sure, but at that point I wouldn't use the wording "a teaspoon of black hole"; something more like "teaspoon-sized black hole" would be more appropriate (though to be fair that's still technically somewhat ambiguous).

Saw some Youtube vid years ago about what happened if you accidentally dropped the content of your teaspoon on the carpet of your living room. Earth would be relatively fine for a long time afterwards was the gist, if I remember correctly.

Small black holes are light, a large black hole with the mass of our visible universe would have an event horizon larger than the visible universe, because the area, not volume, scales linearly with the contained mass.

Black holes become less dense as they get bigger.

Radius is linearly proportional to the mass: r = 2GM/c²

(So volume grows faster than mass)

Which isn't surprising if you think about it. Imagine the whole nothingness of the solar system being filled with even that density of gas. That's a metric ton of gas.

This reminds me of when I was a physics undergrad way back in the mid 80s. We used to spend nights drinking beer and hacking some simulations from the Computer Recreations section of Scientific American.

Once we wanted to simulate the dynamics of galaxies. I don'it think it was an SA article, but we did it the slow way by calculating the force on every star individually from each other star. It was excruciatingly slow and boring.

Then some time later, I don't recall where I picked that up, I updated the simulation to just model the force on each star coming from the galaxy's centre of mass.

I could simulate many more stars, have galaxies collide and see them spin off with their stars scattering around.

What struck me was that they looked like real galaxies we see out there.

I wasn't aware of the postulations made in the 60s/70s about there being supermassive black holes at the centre of galaxies, but to me, this simplified simulation was kind of like a smoking gun for that... from an 80286 IBM PC AT.

Even the largest SMBHs mass is a minute fraction of their host galaxies' total mass so it is not the case that everything is just orbiting the SMBH.

Ah, yes, of course! Thanks.

If we're assuming that the galaxy is radially symmetrical, doesn't it immediately follow that the combined gravitational force on a given star is the same as if we applied the force from a combined mass at the center?

This wouldn't work for something like the Solar system with a very sparse distribution of mass, but at the galaxy level it seems right even without the presence of a black hole.

Even when the distance between the centres of mass of two colliding galaxies become comparable to their size?

It's a long time ago, but what I remember was being fascinated by the shapes of the galaxies emerging from a collision under this centre-of-mass approximation, and that it created shapes we see out there. It was as if the main effect were a central mass in each galaxy dominating the dynamics.

Cosmic Horseshoe galaxy, with pics

https://en.m.wikipedia.org/wiki/Cosmic_Horseshoe

Interesting. Given that the horseshoe shape is due to gravitational lensing of one far off galaxy ~19 Gly away by another "only" 6 Gly away, wouldn't that mean that any motion of those galaxies, or our galaxy, would realign the lensing and alter the shape of the horseshoe?

So... how long before we see the shape change? How fast do galaxies move anyway?

About 9000 times the mass of the supermassive black hole at the center of our galaxy (Sagittarius A*).

Mind boggling. Wish they included images of the scale compared to our sun, solar system, galaxy etc to help me wrap my head around this beast.

Unfortunately a picture would not clarify anything with that sort of object. A video will: https://www.youtube.com/watch?v=0FH9cgRhQ-k

Thanks, that helped.

With all the lensing going on out there, is it possible for us to observe the light from our sun (and potentially our planet) billions of years ago?

A cool achievement would be, observe the moon/earth separation event(s)

Theoretically yes but although this black hole is big enough to make that more realistic, the redirected light would be have lost so much energy we’d likely be unable to observe it. We’d need an orbital hypertelescope to even stand a chance. Even then we wouldn’t see the earth because it would be drowned out by the sun.

The bigger problem is all the dust and other stars in the way. I’m not aware of any black holes close enough that would have a direct path for the light to cross without being absorbed and scattered.

The other problem is the angle at which the light must be redirected. The Cosmic Horseshoe is composed of two systems almost directly in line, the light comes from the farther system and bends infinitesimally around the black hole to come to us. I don't know if a 180 degree bend is possible.

Also, the foreground galaxy/supermassive black hole in the Cosmic Horseshoe is 5.6 billion light years away, so any light that could come from our solar system, go around the black hole, and come back to our hypothetical hypertelescope would be over 11 billion years old - almost triple the age of our sun.

Saggitarius A* in our own galaxy is, of course, directly in the elliptic and therefore badly occluded by dust, but it would be interesting to look at as it's only 27k light years away. In the absence of that pesky dust, it would give us a picture of the solar system as of the Paleolithic. Andromeda, at 2.5 million light years away, would give us 5-million-year-old light. There are other black holes in the Milky Way on the order of a thousand light years away which are not at the center of the galaxy but have masses comparable to or slightly larger than our sun, these are far closer (within a few thousand years) but have much smaller gravitational fields. Luminous intensity drops off with the square of the distance, but I'm not sure how the gravitational field strength affects the ability of a particular galaxy to bend light.

> The other problem is the angle at which the light must be redirected. The Cosmic Horseshoe is composed of two systems almost directly in line, the light comes from the farther system and bends infinitesimally around the black hole to come to us. I don't know if a 180 degree bend is possible.

It is possible to get a deflection angle of 180 but under a few million solar masses, hitting the “sweet spot” in between the photon sphere and the boundary of the shadow would basically be a once in the lifetime of the universe type probability, if it were possible at all. At billions of solar masses that sweet spot become much bigger, but then those are much further away.

> almost triple the age of our sun.

In this insanely hypothetical scenario, would it be possible to see a sun before our sun? (In the same galactic vicinity)

I was under the impression that our sun is not large enough to form the heavier elements on earth and this means supernova or collision of neutron stars had to be responsible for creating these elements, some of the stuff flying off this explosion formed our solar system, so we could see those progenitor stars.

I thought elements were created inside stars and dispersed by supernovas... Our sun has clearly not exploded yet (and I don't think it's big enough to ever ho supernova), so why does it matter what elements it can create?

How big would the diameter of this be ? Something like 8 light days ?

Sounds about right. Wiki has a correctly scaled picture with the two biggest known black hole event horizons and the solar system:

https://en.wikipedia.org/wiki/TON_618

Event horizon radius would be about roughly 1000 times the distance between Earth/Sun.

The Schwarzschild radius would be approximately 106 billion kilometers or about 7 light days (r = 2GM/c²).

A bit off topic: Is there any theoretical upper limit on the mass of a black hole?

It doesn't seem like there's a limit to how big they can get just a limit to how quickly they can get bigger due to what's called the Eddington Limit which explains how matter falling into the black hole emits radiation and if enough radiation around the accretion disk builds up, it can overcome the pull of the black hole and push matter away, at least until enough matter is pushed away that the radiation levels fall back under the limit and matter starts falling in again.

PBS Spacetime had an episode somewhat recently about a black hole which is growing at many (hundreds? thousands? I forget) times the Eddington Limit. And, as far as I remember, it isn't the only one to exceed the Eddington Limit - just the one with the record for how much it exceeded it.

I'll try to dig it up when I'm not at work (or if I remember the exact episode through the day).

I remember this episode too. The answer is four thousand times bigger than the Eddington Limit. Blimey!

The episode is called “The NEW Ultimate Energy Limit of the Universe”. https://youtube.com/watch?v=0rzgYzbzq5Q

Importantly, the Eddington limit does not apply to black hole mergers, theoretically allowing as much growth rate as you're able to feed in from smaller black holes.

This said, the final parsec problem isn't solved/understood. We know black holes do merge, but we don't understand what energy is being bled out of the system so supermassive black holes crash into each other in the timeframes we're seeing it occur.

So then the only theoretical limit on black hole mass would just be how fast you can put matter in black holes and/or merge existing black holes versus how fast the universe expands?

I'm 100% an armchair physician so take my words with a grain of salt but it seems like according to the math there is no limit to how massive a black hole can get. There are limits on the size of how big and small things can get and how hot or cold they can get, the second part is pretty cool, Physics Explained on yt has a good video on it (he's got a lot of good videos) but I enjoyed this one on what the maximum temperature is in the universe: https://www.youtube.com/watch?v=NVlEQlz6n1k

> I'm 100% an armchair physician

Not to be that guy, but a physician is a doctor.

Not to be cet homme, but in French a physicien is a physicist.

Not to be that guy, but English is not French

But that's not important right now.

Just pointing out a simple mistake.

In the time that it took you to type that response, you could have learned 10 new words.

I do it because I appreciate it when people do it for me.

That was the purpose of my comment. What was the purpose of yours?

I heard a joke about a nerd who dies and finds himself in a very hot underground cavern. The devil is there, and says "Welcome to Hell! This over here is the lake of molten lava where you'll spend the rest of eternity". The nerd says "well actually, since it's underground it's called magma rather than lava". The devil replies, "um, you do understand why you're here, don't you?".

I try to remember that when I'm tempted to point out mistakes that are fine to overlook.

https://youtube.com/watch?v=AK3gB7DpaM0

shirley you cant be serious

https://en.wikipedia.org/wiki/List_of_most_massive_black_hol... shows the maximal theoretical limit as 270B solar masses.

To expand on this, as stated in your source:

> [270B solar masses] is the maximum mass of a black hole that models predict, at least for luminous accreting SMBHs.

as well as:

> The limit is only 5×10^10 M [50B solar masses] for black holes with typical properties, but can reach 2.7×10^11 M [270B solar masses] at maximal prograde spin (a = 1).

However in the chapter before, it's stated:

> New discoveries suggest that many black holes, dubbed 'stupendously large', may exceed 100 billion or even 1 trillion M.

There's a theory that the universe we live in is itself inside a giant black hole. No idea how it is supposed to have gotten so biig.

If you assume constant density, anything becomes a black hole at certain volume. The question is: is our universe big enough to be a black hole or not.

It couldn't have, the theory is nonsense.

https://en.wikipedia.org/wiki/Black_hole_cosmology

I know this article. It's citing a bunch of speculative hypothesis by mostly this one person which relies on something super exotic called Einstein Cartan theory. I stand by my statement. I even suspect the article was written by them.

https://www.scientificamerican.com/article/do-we-live-inside...

I hate random links being thrown at me, because I don't know what you are trying to tell me. Perhaps you can spare a few key strokes.

For everyone else reading the thread, let me summarize. The article agrees with me:

> the entire observable universe exists within a black hole—except, that is, for all the evidence to the contrary

>....

> It does not seem likely that we live inside a rotating universe, let alone a black hole.

You have elsewhere in this thread objected to people providing links without giving context, so I hope you won't mind being asked to unpack this claim a little. Why is it nonsense? If, as you say, it's principally pushed by one person, who is that, and why does that argue against it?

(I'm not thinking this is too much to ask; saying it's wrong might require empirical support, but the claim that it's "nonsense" should be easier to justify.)

First of all, black holes have an interior and an exterior. Our universe only has an interior. Next, black holes have a singularity into which everything vanishes, or at least moves towards. Im our universe, everything moves away from a singularity. So if anything, it resembles a white hole more than a black hole. Also, our universe is expanding, whereas black holes shrink (unless matter falls into them, which can't happen to our universe because it has no exterior).

It really looks nothing like a black hole.

The interior and exterior are isolated; we have no idea if are universe has an exterior or not and, according to present theory, never will.

As another comment pointed out, in GR our "future" is a singularity which everything moves towards (so what we see as a time dimension).

"Expanding" and "contracting" depend on your coordinate system. If your rulers are shrinking, you can't tell this from space expanding.

The common factor here is you are wanting to use our reference frame (somewhere in this universe, not near a black hole) to describe things as they would be seen from other reference frames.

Agreed, how do you feel about our universe being some sort of post evaporated BH-like-thing from a previous universe-like-thing?

>Next, black holes have a singularity into which everything vanishes, or at least moves towards

I mean, everything in our universe does move towards something. The future.

> giant

How would we know the size? Relative to what?

So what happens if two such black holes collide?

Can black holes even collide? I guess their horizons can merge somehow... Probably a spectacular show.

Disclaimer: This is my own work

https://www.youtube.com/watch?v=doS85Mh78Vc

This is what they look like when they merge, its pretty darn cool

That’s precisely what LIGO measures, the gravitational waves from black hole mergers (or neutron star mergers, etc).

>Cosmic Heavyweights Collide – LIGO Detects Largest, Fastest-Spinning Black Holes Yet

https://scitechdaily.com/cosmic-heavyweights-collide-ligo-de...

I love to contemplate galactic-scale synchrotrons that accelerate supermassive charged black holes to collide at relativistic speeds. The thought never really goes anywhere, but I'm sure it'd be a spectacle to behold.

It would be just about the only way we could get the data required to resolve the contradictions between the Standard Model and general relativity. The unification energy is simply stupendous.

That could be a good question for AI to answer.

Given things like https://en.wikipedia.org/wiki/TON_618 and https://en.wikipedia.org/wiki/Phoenix_Cluster#Supermassive_b..., probably not. Seems like you can just keep shoving mass into it.

Poking around those articles (and knowing nothing really), it is interesting to note a couple references to a 50B solar-mass limit for “luminous accreting black holes hosted by disc galaxies.” (In your Phoenix cluster link). I guess these ones are easier to spot, based entirely on the word “luminous.”

There are other larger ones out there, looming in the darkness.

Those supermassive black holes are very old, from a time when the universe was much denser - they likely collapsed directly without any star formation

Yes - but it's basically the same as the total mass of the universe.

EDIT: I believe the above could be incorrect - if the universe has too much electrical charge or angular momentum. (And some other cosmological properties, so you couldn't get around the charge & spin issues.)

Might there be a black hole astrophysicist in the house, to comment on this?

There is this whole theory that the observable universe is inside a black hole.

So the upper limit is the weight of the universe.

https://youtu.be/EGzvGgNmaiY?t=58s

With good quantization, I bet we can get it down to 8B and it will easily fit on consumer grade galaxy.

(Sorry, I had to, with all the AI flood, I really was about to skip this info after the first 3 characters)

Don't be sorry, that was pretty good

They very rare great HN joke.

How true this is

Researchers discovered the black hole has been consuming AI VC money, at the rate of $50M per day, and so finally explaining why it is gotten so big.

That sounds low...

With good quantization you can get 36GB down to 8GB. To get 36B down to 8B you need good pruning.

I had a bit of a pause trying to figure out if someone named a model „black hole” from that title.

Hype is strong.

thanks for brightening the day :)

So you're saying it might fit on the S26?

Glad you wrote it, the title took me down the same path for a few seconds :-D

that's too good, haha

But can you make it talk dirty to me

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