'Ultramassive' black hole discovered – bigger than the majority of galaxies | Hacker News Reader

'Ultramassive' black hole discovered – bigger than the majority of galaxies

bbc.com

170 pointsachow108 comments

I can't tell how certain we are of its size - it's so big that it makes me wonder whether the easiest explanation is that our methods were incorrect.

For example, if we are measuring how light bends - how do we know there aren't many hidden (i.e. not large or bright enough to be noticed from earth) objects causing additional distortion and therefore throwing off our measurements? Do we also observe it over time to get more confidence, or have some other cross-checks that give us more certainty?

Either way, every once in a while I find it wild just how much we can deduce about the universe from our tiny fixed vantage point.

Don't know the answer to your questions but we are not at a fixed vantage point

Fixed relative to other galaxies...

we move on Earth as the planet rotates, Earth moves within its orbit in the Solar system, our Solar system moves within its orbit in the galaxy, and our galaxy moves (we believe) within the universe, though I don't think we know how fast or what direction; generally, everything outside our local group is moving away, though.

Our sun moves around the galaxy at about 500,000 mph...and thus so do we.

The things aren't moving apart.

Space itself is expanding.

space is expanding AND things are moving apart.

where does red shift come from if things aren't moving apart?

Yes, all this movement occurs and is infinitely small compared to the distance to other galaxies.

In a cosmological scale, we are goldfish in a bowl (Earth). We can move around inside our bowl, but we cannot move the bowl itself, and if we leave the bowl we won't last very long.

Thus, our vantage point is fixed.

The bowl (and the table, for that matter) move enough for useful measurements to be made wrt things inside the milky way.

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

I learned now at least that our parallax measurements have been improved but they are still limited to tens of thousands of light years, i.e not reaching out of the galaxy, see https://en.wikipedia.org/wiki/Stellar_parallax#Space_astrome...

Astronomy is afforded very few epistemological amenities. In a sense, N can only go up if we get independent verification from different techniques. However, our tools have become incredibly sophisticated and sensitive so we can be very sure about what we're seeing, if not what it means.

I'd imagine one of the techniques used is to look for time-varying influences in the data, which implies there are bodies orbiting each other. If there aren't any, then you can look at the spectroscopic signature of the light and see if it makes sense for a black hole. I'd imagine black holes do nothing to refracted light, but dark bodies would result in slightly blueshifted light as 'newer' light reflects off its surface. This might be what PyAutoLens does (as well as fitting the shape of distortions and such)

Even in astronomy, when one starts to say "this black hole is about the size of our galaxy", it should raise epistemological questions.

This finding seems to have a highly complex relationship to the data, and to not have been replicated anywhere yet. This is the perfect place to add a "something that looks like" before the "galaxy sized black hole".

But well, this is a criticism of journalism anyway, not of astronomy.

If a photon is deflected by a black hole, it must also impart momentum to the black hole. But this means it imparts energy as well, so shouldn't it be red shifted as well?

That's true but it's also true of some other dark body of the same mass. "do nothing to refracted light" was poor wording, my bad - it's more like gravitational lensing is the only thing that happens to its light, as opposed to adding new peaks to the spectrograph and such.

it is much more likely that our understanding of the early universe is imperfect, than it is that multiple gravity wells of that strength line up perfectly. we know our tools pretty well; well enough to have confidence that what is observed is actually representative of what is actually there.

the confusion here is because if this formed in 13 billion years, our understanding of the formation of the universe is very flawed, and generally, scientists both do and do not like it when stuff like this is proven wrong with new evidence.

they like it because discovery and increased understanding is the whole reason they became scientists in a lot of cases.

they don't like it because if this is wrong, what else is wrong, and what does that mean for everything else we think we know? what gets upended because of this?

Nothing gets upended, you just say "dark matter" and call it a day.

> than it is that multiple gravity wells of that strength line up perfectly.

This kind of alignment happens all the time. Stars that line up perfectly but are separated by light years, galaxies that line up perfectly etc.

The 30 billion times the size of the sun is BBC making a mistake. It is 30 billion solar masses. Direct from durham [1] from the arxiv article [2].

techwiz137 pointed out[3] an existing known black hole, TON618, is 66 billion solar masses[4]. So the new find is large but not the largest ever found.

[1]https://www.durham.ac.uk/news-events/latest-news/2023/03/lig... [2] https://arxiv.org/abs/2303.15514 [3] https://news.ycombinator.com/item?id=35360780 [4] https://en.wikipedia.org/wiki/TON_618

The puzzle here is that astronomers have no clear picture of how these ultra massive black holes are formed so early in the evolution of the universe. if you wait long enough galactic black holes can eat stars, gas, and other black holes, but there was no time for that early on. It is conjectured there were huge ‘Population III’ stars that grew rapidly because radiation transport was different when there were tiny amounts of elements heavier than helium (‘metals’ in astronomer lingo.)

Pop III stars are a bit less mysterious than dark matter but they could have played important roles in the early universe.

The hypothesis is that these black holes were not created from stars, but exists from right after the big bang.

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

One of the hypotheses. Pop III stars could have gotten pretty big but probably not as big as that one. Hopefully JWST will turn up some direct evidence for them.

Yeah, the issue is that when large amounts of matter gathers into the accretion disk of a black hole it creates more and more friction as it falls in. This friction generates a lot of heat (and therefore pressure) which pushes back on the in-falling matter, slowing down the accretion process. If there's an overwhelming amount of matter the accretion will disk will get so jammed up and energetic the black hole will start firing off high-energy relativistic jets from its poles.

If you start with a stellar black hole of say 10 solar masses and then throw millions of solar masses of material at it, the above processes will slow things down dramatically, and you won't be able to get a supermassive black hole instantly.

what if those old giant blackholes were created by all the missing antimatter that we dont see in the CMBR.

>The puzzle here is that astronomers have no clear picture of how these ultra massive black holes are formed so early in the evolution of the universe.

Perhaps we're in a black hole now, and the universe only seems "young" (its current age of ~13B years) because that's when it fell into the black hole.

Oh man, you're breaking my brain.

Another theory is that black holes (or some black holes) are what we understand under dark energy.

https://phys.org/news/2023-02-scientists-evidence-black-hole...

https://www.youtube.com/watch?v=EGe5qvIzjTY

It's worth noting that there is a limit to how fast black holes can grow [1] so ultra-massive black holes like this tell a story, namely:

1. It starts placing limits on how young the black hole can be. IIRC black holes like this must've been formed very early in the Universe, which may be earlier than our models otherwise predict, suggest or even say is "possible"; and

2. It is theorized (again, IIRC) that a lot of ultra-massive black holes such as those at the center of many if not most galaxies can only really form by the merger of black holes due to the above limits. These must be unbelievably energetic events. It's possible that such events may actually star formation in nearby nebulae.

[1]: https://physics.stackexchange.com/questions/167250/is-there-...

So then why is TON618 at 66 billion solar masses? https://en.wikipedia.org/wiki/TON_618

edit the bbc article got it wrong withe 30 billion times the size and it supposed to be 30 billion solar masses see [1] or the arxiv article [2]

The bbc article says 30 billion times the size while TON618 is 66 billion times the mass.

Wikipedia says TON618 has a Schwarzschild radius of 1,300 AU (390 billion km in diameter) vs teh sun's 1.3927 million km diameter. Which makes TON618 ~280k bigger than the sun.

So if my math is right that makes the Ultramassive balck hole in the bbc article ~107k larger than TON618.

edit give the R = 3M relation for black holes twice the radius means twice the mass. So 107K times the radius means 107k times the mass.

The Ultramassive balck hole in the bbc article would have ~2354000 billion solar masses.

edit give the above I want to fact check BBC's 30 billion times the size vs 30 billion solar masses since the later seems more reasonable.

edit 30 billion solar masses is what is given directly by durham and arxiv[2]

[1] https://www.durham.ac.uk/news-events/latest-news/2023/03/lig... [2] https://arxiv.org/abs/2303.15514

My understanding of the abstract is (I'm not an astronomer):

TON 618 is an active SMBH ("hyperluminous, broad-absorption-line, radio-loud quasar" [0]).

The SMBH they found has a smaller mass [2], but it is passive (= much darker).

From the abstract:

"Outside the local Universe, measurements of MBH are usually only possible for SMBHs in an active state: limiting sample size and introducing selection biases. Gravitational lensing makes it possible to measure the mass of non-active SMBHs." [1]

[0] https://en.wikipedia.org/wiki/TON_618

[1] https://academic.oup.com/mnras/article-abstract/521/3/3298/7...

[2] "it could be a supermassive black hole equivalent to 13 billion suns: 1.3±0.6)×10^10 M" https://en.wikipedia.org/wiki/Abell_1201_BCG

I mean...There are others bigger than that with Phoenix A, but these are quasars and very visible, even if billions of LY away.

https://en.wikipedia.org/wiki/Phoenix_Cluster#Supermassive_b...

It seems the bigger tact is HOW it was discovered using gravitational lensing that may open up the ability to see otherwise "non-active" blackholes, even supermassive ones that otherwise dont have accretion discs or other forms of waves (radio, light or otherwise) that would make them directly observable.

https://arxiv.org/pdf/2303.15514.pdf

I am also not an astronomer, so dont take my word for it. Just seems that it may be a new method that may open up the doors to a more discoveries that may make things like this a bit more....common.

TON618 and Phoenix A even are somewhat outliers from a discovery standpoint it seems. And frankly the sizes, distances etc are basically incomprehensible to me.

The article is about the Abell 1201 black hole. The paper referenced in the article is paywalled though[0].

And Wikipedia has a List of most massive black holes[1]. Quite fascinating, although the list is about their masses and not their sizes.

I'm not an expert on the subject, but the Abell 1201 black hole and the others in the list are near the theoretical limit of a black hole's mass (5 * 10^10 solar masses).

[0] https://academic.oup.com/mnras/article-abstract/521/3/3298/7...

[1] https://en.wikipedia.org/wiki/List_of_most_massive_black_hol...

Here is a copy of the paper

https://arxiv.org/pdf/2303.15514.pdf

> their masses and not their sizes

Do black holes even differ in density? I would have thought all black holes have a constant and consistent density but I don't think I've ever really considered it before.

They do! Or at least, the volume bounded by the event horizon has variable density. The small ones are much denser, and the large ones are much less dense.

(Whatever the degenerate matter at the center is like, that’s another matter.)

Sure. Supergiant BHs are less dense than water

The size of a black hole’s event horizon is pretty much directly correlated to its mass; I think the only thing that really modifies it in practice is very fast rotation.

(Remember, it’s a phenomenon of gravity, not a physical object. The physical stuff inside is just some really intense matter squeezed together in ways that might be interesting, if they were observable.)

My favourite theory is that stuff inside black holes is more universes like ours, which is also inside the black hole.

For those wondering, the radius of this black hole (assuming a Milkyway’s worth of mass), based on the Schwarzschild radius, would be anywhere from 10-1000x larger than Sagittarius A, the supermassive blackhole at the center of the Milky Way. I don’t think the article stated this.

I think it’s about 7,500x.

This one estimated to be 30B solar masses. Sag A is estimated at 4M solar masses.

Nice, that's probably closer then. I just plugged in the mass of the milky way for the mass.

30 billion solar masses, numbers kind of loose the meaning at this scale.

Not masses, size. The article says size.

In the case of a black hole mass and size (radius) are inextricably and linearly linked. All black holes with a given mass have the same radius (modulo a small effect of angular momentum).

I did a rough calc in: https://news.ycombinator.com/item?id=35361280 When it was pointed out TON618 has ~66 billion solar masses.

But if it is 30 billion times the size of the sun then I think that means it is ~2354000 billion solar masses.

I believe for black holes the volumetric size is a known function of mass. If you exclude the rest of any Lyman-alpha blob present around the black hole.

But it's compared to the sun which has a different size to mass ratio.

So it's a huge difference between 30B times size of the sun and 30B times mass of the sun.

Ah, thank you.

Mass is the only really meaningful measure of a blackhole, as they occupy a spacial singularity, which is to say, the have no measurable size.

The event horizon has a diameter, but that's not the object itself.

Guessing that "size" for black holes can mean mass, volume, or radius. But I'm pretty sure the relationship between those three quantities is well defined and directly proportional, so any way you look at it, this thing is incomprehensibly huge.

30B time the mass of the sun is already huge but 30B times the size of the sun would be much much bigger.

It is not possible to have an intuition about 1 solar mass, by easily 10 OOM. Adding OOM can't make it less comprehensible.

If they want people to relate to their numbers, they have to use units people understand, and also they need to be accurate about which dimension they are talking about.

If it's mass the correct popular science dumb reporting unit is the blue whale. Ie "The mass of this black hole is almost 3 x 10^35 blue whales"

If it's size, the correct popular science dumb reporting unit is the football field unless it's specifically length, in which case it's acceptable to either go with football field or switch to double-decker bus or blue whale.

Well, most people can't properly understand the scientific notation, as in getting a proper scale of how big one order of magnitude is supposed to be. They may see ^35 and say "oh, so it is like less than 100 of something, meh".

If you doubt that, remember the quarter pounder ads where they made people think 1/4 is kinda more than 1/2 because 4>2...

The point is how are people ever going to get intuition about the numbers if they don't report them in blue whales/football pitches/double decker busses?

At these scales, it really doesn't make much of a difference, as a sibling commenter pointed out.

I was being sarcastic. Pretty sure it's impossible for the vast majority of people (myself definitely included) to gain any kind of intuition for numbers of this scale. I also don't gain any intuition for things by comparing them to a blue whale etc (and I'm not really sure anyone else does either) and find it pretty weird that it seems to be a go-to comparison for science articles in the press.

Armadillos. Now we use armadillos as our unit of measurement.

> 3 x 10^35 blue whales

That’s way more confusing. Most people have never seen a blue whale to scale, let alone can imagine how dense it is. Once you’re at 10^35, why not just increase the exponent and use humans, basketballs or soda cans.

I would imagine that the best scale of measurement would be between 1/100 and 100x.

If the Milky Way is about 1.9T solar masses, then this black hole is about 1.5% the mass of our galaxy.

It’s still a pretty meaningless number, but at least I can look at a picture of the Milky Way and envision 1.5% collapsing into a single object much more easily than I can envision 10^35 of anything.

A billion is three groups of three zeroes. So for visualizing I would think of a cubic meter compared to a cubic millimeter.

A grain of sand serves for a cubic millimeter. For the cubic meter you can either visualize a cube that size, or four oil drums, or a small hot tub.

Now for the 30 out front, That’s about 27 which is 3^3 so let’s just size a smaller grain of sand which is only 1/3mm on a side. Maybe table salt would be good.

So a grain of table salt in a small hot tub.

If you perform this thought experiment with actual solar masses, use sufficiently long tongs and wear eye protection.

That's really neat. Thank you.

If a black hole is just constantly eating up surrounding matter and growing, why haven't we gotten sucked up by one yet?

Because space is very big.

because space is facking huge.

Estimates are an average of six protons per cubic meter of space. A whole lot of nothing!

"Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."

Black holes don't "suck", they have gravity like anything else. If you replaced the Sun with a black hole of the same mass, all the planets would continue in their orbits.

I'd imagine there would be at least some deviance from their current orbits. The sun experiences tidal forces, just like any other body, and the distance between each planet and the closest/furthest atoms of the black hole would be different than that of the sun. Not sure how much different the orbits would be, but they would certainly be different to some degree.

We'd all be dead anyway so who cares

The point is, the planets would keep orbiting and not go plunging into the black hole due to its incredible gravitational power, as some might picture.

The radius of a 30 billion solar mass black hole is still less than 1% of a light year. For comparison, the nearest star \{Sol} is about 4 light years away.

For comparison, the nearest star \{Sol} is about 4 light years away.

I'm completely confused by this sentence.

\ = not.

{Sol} = The Sun.

So, the nearest star relative to what? Our sun? The black hole?

I think from context it's pretty safe to assume "to us". Especially since the nearest star to us, Proxima Centuri, is indeed about 4ly away.

They're saying the "nearest star other than the Sun", but with some geek-in-group-signalling with the "not" syntax and referring to the Sun as "Sol", which some science fiction writers (and some non-English languages, of course) use as the Sun's name.

Can anyone confirm the accuracy here? Sounds rather significant however I don't know the theoretical limit of how big a black hole can be - or the implications of that (haven't considered it). Seems like we are in an era of discovery in space - heady times!

There's no real limit, since you can just keep dumping stuff in forever. There is however a soft limit that the stuff has to be close enough to get dumped in, and this one is extremely old so we aren't sure where it got its mass from!

Au contraire! There's plenty of mass to feed such a black hole, the real question is "when you run things backward" in the lambda-CDM model why isn't the entire universe a black hole? Or why wouldn't it be the case that there wasn't a primordial mega star that quickly (in universal time) collapsed into a supermassive black hole and the remnants of the supernova is the mass of the remainder of the universe and form the CMB radiation?

This is a cool idea I've never heard before. The universe we're in is the result of a cosmically massive star going supernova.

I don't know the number but the limit is the speed of light and expansion of the universe. In the modern phase of the universe a black hole would only be able to eat its own galactic cluster (or maybe supercluster). Hubble expansion means superclusters experience the expansion of spacetime so certainly any matter beyond a black hole's own supercluster will move away from the black hole faster than light and thus never be able to fall into it. In practice a black hole can't even get near that limit because angular momentum can't just vanish... much of the matter would (over a long time) end up in distant orbit around that super super massive black hole and never fall into it.

In the early universe spacetime expansion was happening so quickly that it was difficult for large black holes to form at all. If that were not the case most matter in our universe would have collapsed due to gravity and ended up in black holes but we know it did not. Actually if gravity were that strong or expansion were slower/weaker then the universe would never have formed at all and stayed as a singularity. To get formation of super large black holes very early you'd need a knife-blade balancing act of gravity vs expansion to just barely form super super massive black holes without the "permanent singularity, no universe" scenario. We can see billions of stars, galaxies, etc so we know that scenario did not happen.

Super super massive black holes are neat objects though. If this one really is as big as they say then it will be one of the last objects left in the universe. It would take trillions and trillions of years for it to evaporate due to Hawking radiation. I wonder if the last life left in the universe will end up gathered around this black hole, surviving on the Hawking Radiation energy gradient?

If the bulk of the universe was inside a black hole, including us, would we know it? My understanding was, not necessarily.

Second question, if that's the case: Can singularities recurse? Could you have local blackholes inside a super-massive blackhole?

We don't know what the inside of a black hole is like. My guess is that it's some esoteric state of matter. Like a neutron star, but up to eleven.

0. Seems there are a half dozen other SMBHs also close to the theoretical limit. What's novel about this discovery?

1. Is the Great Attractor a SMBH > 1e10 M(.)?

The Great Attractor is likely a cluster of galaxies with lots and lots of SMBHs.

I wonder about inflation vs. gravity of these massive structures.

"Locally" in the supercluster scale, I'm wondering to what degree gravity swamps dark energy inflation.

I think the novelty here is the way of discovery, at least that is how I read the paper.

Ah thanks for the elucidation. I'm too ignorant in this subject area to compare or contrast this paper with the corpus of literature from any point of expertise or reference.

The use of the term "bigger" here is frustrating. Mass or volume?

Black hole volume is entirely a function of mass.

Black holes don't have a volume, they only have a surface area, and it depends strictly on their mass.

And spin/charge, no?

This isn't true at least in the case of the ordinary black hole solutions in general relativity. These solutions tend to be valid throughout the volume of the black hole (except at the singularity, which takes on different shapes depending on spin or charge but doesn't occupy the whole interior volume of the black hole if you think of the event horizon as bounding the volume).

I thought they were valid throughout the volume/radius, but that the solution only gives you the surface area for that radius, not the volume.

Perhaps I have misunderstood though as I am just a hobbyist :)

The volume inside the event horizon isn't what you would expect if you consider the black hole as a sphere with its external area, but it has a volume. It might be the case that in quantum gravity there isn't an interior, but in GR the idea of the volume is a little weird, but not problematic.

Definitely mass. (It is "ultramassive", after all.) An explanation of black hole volume I found from NASA [1]:

> Our intuitive sense of volume breaks down in the strong gravitational region in a black hole. So while the "size" of a black hole is given by the radius of its event horizon, it's volume is not determined by the usual 4/3pir3. Instead, relativity makes it more complicated than that. As you pass the event horizon, the spatial direction 'inwards' becomes 'towards the future'-- you WILL reach the center, it's as inevitable as next Monday. The direction outsiders think of as their future becomes a spatial dimension once you are inside. The volume of a black hole, therefore, is its surface area times the length of time the hole exists (using the speed of light to convert from seconds to meters). Since a black hole last practically forever, the black hole's volume is almost infinite. (This is also a way of explaining the fact that you can pour stuff into a black hole forever and never fill it up. Another reason why black holes never fill up is that the radius of the event horizon increases as the mass of the black hole increases.)

[1] https://imagine.gsfc.nasa.gov/ask_astro/black_holes.html

Thank you for quoting this passage. My mind is spinning after reading it.

a particle falls into a black hole. does it ever stop falling, from the particle’s reference frame?

For a non spinning black hole in general relativity, the particle reaches the singularity within finite time in its own reference frame.

thanks, does it fall infinitely far to do so?

I never made the connection between mass and massive until your comment. Can’t believe I’ve gone so long without connecting them.

BBC article innit. Hardly a scientific paper.

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