§3 Discussion: "The estimated mass is also too large for one neutron stars or two neutron stars in a close orbit, so we are left with the possibility of: 1) a single BH; 2) an inner binary containing two BHs; or 3) a BH and another compact object. Although the single BH is the simplest explanation, the hypothesis of an inner binary of two BHs cannot be excluded [...] radial-velocity [...] perturbations are too small to be detected in the Gaia RVS [radial-velocity] data[.] For the purposes of the subsequent discussion we have adopted the single BH hypothesis as the most likely explanation."
Someone with more patience (or more troll-energy) than I have right now might try to introduce this into the handful of threads here containing various complaints that (clearly assuming a single BH), "size" is being punned as mass in the newspaper article linked at the top. If, for example, the ~33 M_sun ("mass of the sun") mass is evenly divided between two central BHs with the giant branch star companion orbiting them (cf. Alpha Centauri AB + wide companion Alpha Centauri C and similar triples), what's the most reasonable understanding of "size"? Or what if the dark component has a mass-ratio of ~ 30:2 split between a BH and a satellite NS? Total mass remains ~33 M_sun, how has "size" changed?
(Answer: "it hasn't". Generally I agree with the comments that read "size" as meaning mass and disagree that it should mean the Schwarzschild radius, and not just because the dark component might not be very Schwarzschild-like at all. Perhaps someone might do an ELI5 of dimensional analysis g = T^-2 L -> M = T^-2 L^3 or Gauss's law for gravity. (Serious ambition would be ELI12 of the argument around the "scale separation" towards the end of the excellent <https://physicscourses.colorado.edu/phys2210/phys2210_fa20/l...>, where we'd distinguish the scale of a possible inner-binary from the scale of the giant star's orbit around it.))
Astronomers have not discovered the Milky Way's biggest stellar black hole. They have found the largest stellar black hole of all the galactic stellar black holes they've found so far. Since the Milky Way likely has 100 million stellar black holes, finding the largest is going to be quite a task.
Bart: this is the biggest stellar black hole.
Homer: this is the biggest stellar black hole so far.
Somewhat of an aside: I've grown tired of Roman mythology being foisted upon our planet names. But I'm even more tired of hearing NASA spokespeople talk about e.g. "exploring the heavens". At least they don't say "firmament" or refer to the Earth's mantle as being infernal.
"Sagittarius A has the combined mass of several million suns. It lurks at the heart of the galaxy and formed not from an exploding star but the collapse of vast clouds of dust and gas."
How is that known? Isn't "dust and gas" also how stars form?
Every galaxy we know of contains a massive black hole in the center. Until recently, the widely held belief was that massive black holes are formed via the process of mearging smaller black holes in large timeframes. However, once the JWST came online, astrophysicists discovered early massive black holes close to big bang that could not be explained by that cumulative process. There just was no time for the cumulative creation to a such large black holes.
So the current working hypothesis for massive black holes in galaxies is that they formed directly from the gravitational collapse of "vast clouds of gas and dust" with such high gravitational pressure that the core couldn't keep up, and the entire mass of gas and dust collapsed into a massive black hole. There is no supernova involvement; merely a direct transition into a black hole.
Of course, take my laic simplification into account.
A vast cloud of what gas and what dust? I thought we had started with only hydrogen and I thought that collapsing the hydrogen creates stars first. How could it even cut directly to the stage of black hole?
Yes. It is kinda amazing to observe (as a professional astrophysicist) how people manage to find small (mostly irrelevant) things to nitpick instead of discussing a really interesting discovery.
I postulated in another thread yesterday that the use of exxagerations / superlatives might be triggering contra. If we had the same article, but with the title "Black hole with 33 times the mass of the sun discovered" we could measure if the reactions are less severe.
it unfortunately happens in every field, including more theoretical parts of computer science. the commenters usually don't understand the science, so choose to nitpick on the aesthetics.
Oh boy, this sent me down a memory lane. I remember arguing long and hard with my math teacher in elementary school that "two times as massive" and "two times more massive than" are not the same thing, but she did not agree. That's the point where I learned that the grownup world is weird and sometimes it's easier to just smile and nod.
Considering fractions might help you understand where he's coming from. If you say something is "0.5 times as long as a one meter thing" you would expect it to be 0.5 meters, but if it's "0.5 times longer than a one meter thing", you would expect it to be 1.5 meters. The same logic applies when you ditch fractions and use integers.
Where do you think the AI image model gets the data for what artist's impressions of astronomic phenomena should look like? From all the artists who painted these in the past.
Yet it will be replaced with another job to generate even less accurate images.
It reminds me of a hilarious article Josh barrow wrote about the SV bank run. He uses AI article art for a bank run, which ended up as 6 fingered joggers along the bank of a river.
That doesn't matter, you are toying with semantics. If astronomers say stellar black hole, they don't mean supermassive black holes at galactic centers. Even if Sagittarius A* was initially a stellar black hole, its more now.
I hadn't heard of the distinction stellar or non-stellar black hole before. It rather sounds like semantics to me to say this is one type of black hole and not another when it's physically the same thing and we don't know how it formed to begin with
The headline confused me as well: 33 solar masses (not sizes) seems tiny to me, I was sure we knew of bigger ones
To add to a sibling comment, the distinction is important, because observed mass of black holes falls largely into super massive (millions to billions solar masses) to stellar (dozens of solar masses). There is very, very, astonishingly few observed black holes with an intermediate mass. So, how super massive black holes form is a mystery, and finding large stellar mass black holes starts filling in (possibly) that evolutionary gap in black holes. Not a physicist, just read/watch a lot of pop astronomy/cosmology.
Also, super massive blackholes can only "swallow" so much matter at a time. Given what we know about how fast a black hole can grow, super massive black holes seem to be bigger than should be possible.
The distinction is clear and relevant because the mass distribution is strongly bimodal. A stellar black hole is the result of the gravitational collapse of a single star (well, or two at most). And maybe some of them have since then merged with a companion body. There are zillions of these in any given galaxy. Whereas there are maybe one or two supermassive black holes per galaxy, sitting in the center, with mass of millions or billions of suns, and we don’t quite know how they first formed and how they have accumulated so much mass. If the difference between "one" and "billion" doesn’t matter to you, well, ok then.
The difference is even more clear-cut because so-called intermediate mass black holes are something of a question mark. For a long time it wasn’t clear whether they even exist in any significant numbers, and even now the evidence is not especially rock-solid, especially with regard to candidate objects in the Milky Way.
Its not semantics. Its precise terminology. Ignoring this and redefining the precis terms because one lacks knowledge about the subject and arguing from faulty assumptions is a waste of everyone's time.
> I hadn't heard of the distinction stellar or non-stellar black hole before.
While it's possible that supermassive black holes were formed from stellar collapse, there are models where they didn't, while they _know_ that this one was formed from stellar collapse.
They don't seem too clear on the science they're reporting, but if I'm understanding it right, this is supposed to be the largest stellar origin black hole. The fact that Sagittarius A* is just a bit under 4.3 million solar masses, which is a bit over 33, was my first thought, too.
I'm guessing the 13km diameter refers to the event horizon rather than the singularity itself, which I gather could be considered as zero-sized, or maybe one Planck length in size because we can't definitively measure anything smaller, or ...
Admittedly, it gets a bit philosophical. The sphere of no return isn't the thing, but it might as well be for any outside observer, but it isn't, but it could be viewed as such, but... :) Suffice to say I'm glad the closest thing to black holes I have to contend with in my daily life is a 2+ million line php codebase dating from the late Clinton administration.
For a related visualization about size/mass of suns and black holes:
I Put 4M Suns in a Black Hole over New York [video]
https://www.youtube.com/watch?v=pDUUT2Y_9qk
(https://news.ycombinator.com/item?id=39735510)
I totally forgot about this video, the amount of work is wild.
Preprint: https://www.aanda.org/articles/aa/pdf/forth/aa49763-24.pdf
Thanks, that's always useful.
§3 Discussion: "The estimated mass is also too large for one neutron stars or two neutron stars in a close orbit, so we are left with the possibility of: 1) a single BH; 2) an inner binary containing two BHs; or 3) a BH and another compact object. Although the single BH is the simplest explanation, the hypothesis of an inner binary of two BHs cannot be excluded [...] radial-velocity [...] perturbations are too small to be detected in the Gaia RVS [radial-velocity] data[.] For the purposes of the subsequent discussion we have adopted the single BH hypothesis as the most likely explanation."
Someone with more patience (or more troll-energy) than I have right now might try to introduce this into the handful of threads here containing various complaints that (clearly assuming a single BH), "size" is being punned as mass in the newspaper article linked at the top. If, for example, the ~33 M_sun ("mass of the sun") mass is evenly divided between two central BHs with the giant branch star companion orbiting them (cf. Alpha Centauri AB + wide companion Alpha Centauri C and similar triples), what's the most reasonable understanding of "size"? Or what if the dark component has a mass-ratio of ~ 30:2 split between a BH and a satellite NS? Total mass remains ~33 M_sun, how has "size" changed?
(Answer: "it hasn't". Generally I agree with the comments that read "size" as meaning mass and disagree that it should mean the Schwarzschild radius, and not just because the dark component might not be very Schwarzschild-like at all. Perhaps someone might do an ELI5 of dimensional analysis g = T^-2 L -> M = T^-2 L^3 or Gauss's law for gravity. (Serious ambition would be ELI12 of the argument around the "scale separation" towards the end of the excellent <https://physicscourses.colorado.edu/phys2210/phys2210_fa20/l...>, where we'd distinguish the scale of a possible inner-binary from the scale of the giant star's orbit around it.))
[dead]
That is a fairly epic author list. Presumably everyone involved in the larger overall project.
Astronomers have not discovered the Milky Way's biggest stellar black hole. They have found the largest stellar black hole of all the galactic stellar black holes they've found so far. Since the Milky Way likely has 100 million stellar black holes, finding the largest is going to be quite a task.
Bart: this is the biggest stellar black hole.
Homer: this is the biggest stellar black hole so far.
I thought the “so far” was implied by science - this is what we know about the universe (so far).
Not a valid excuse here.
Somewhat of an aside: I've grown tired of Roman mythology being foisted upon our planet names. But I'm even more tired of hearing NASA spokespeople talk about e.g. "exploring the heavens". At least they don't say "firmament" or refer to the Earth's mantle as being infernal.
Code to fit the star's orbital parameters and make some of the plots in the paper: https://github.com/esa/gaia-bhthree/blob/main/Gaia_BH3_fit_a...
"Sagittarius A has the combined mass of several million suns. It lurks at the heart of the galaxy and formed not from an exploding star but the collapse of vast clouds of dust and gas."
How is that known? Isn't "dust and gas" also how stars form?
Every galaxy we know of contains a massive black hole in the center. Until recently, the widely held belief was that massive black holes are formed via the process of mearging smaller black holes in large timeframes. However, once the JWST came online, astrophysicists discovered early massive black holes close to big bang that could not be explained by that cumulative process. There just was no time for the cumulative creation to a such large black holes.
So the current working hypothesis for massive black holes in galaxies is that they formed directly from the gravitational collapse of "vast clouds of gas and dust" with such high gravitational pressure that the core couldn't keep up, and the entire mass of gas and dust collapsed into a massive black hole. There is no supernova involvement; merely a direct transition into a black hole.
Of course, take my laic simplification into account.
A vast cloud of what gas and what dust? I thought we had started with only hydrogen and I thought that collapsing the hydrogen creates stars first. How could it even cut directly to the stage of black hole?
Does every galaxy have a super massive black hole at the Center?
Nearly every. That’s the current thinking.
Article triggers critical mass of pedantry on HN, thread collapses in on itself
Yes. It is kinda amazing to observe (as a professional astrophysicist) how people manage to find small (mostly irrelevant) things to nitpick instead of discussing a really interesting discovery.
I postulated in another thread yesterday that the use of exxagerations / superlatives might be triggering contra. If we had the same article, but with the title "Black hole with 33 times the mass of the sun discovered" we could measure if the reactions are less severe.
it unfortunately happens in every field, including more theoretical parts of computer science. the commenters usually don't understand the science, so choose to nitpick on the aesthetics.
People's contributions rise to the level of their expertise.
>black hole – 33 times size of sun
>black hole 33 times more massive than the sun
What a confusing article. Its 33 times the mass of the sun
It's actually correct. The radius/diameter of a black hole is proportional to its mass.
Yes, but the size is not proportional to the suns mass, hence the error. size=/=mass
Also “33 times more massive than the sun” means 34 times the mass of the sun.
Oh boy, this sent me down a memory lane. I remember arguing long and hard with my math teacher in elementary school that "two times as massive" and "two times more massive than" are not the same thing, but she did not agree. That's the point where I learned that the grownup world is weird and sometimes it's easier to just smile and nod.
For me, it was the science teacher in middle school who insisted that rivers couldn't flow north, because on a globe, north was up.
Even pointing out the Nile didn't change her mind; I imagine there's a denial joke to be made there.
"That's the point where I learned that the grownup world is weird"
That's a generous thing of you to say.
How many people really want to be proven wrong? I'd like to think I am. Maybe I should make a t-shirt:
would you say the same for "33 times longer"? that ut means "34 times the length"?
for me "more X" and "Xer" are the same thing, so I don't get your system
Considering fractions might help you understand where he's coming from. If you say something is "0.5 times as long as a one meter thing" you would expect it to be 0.5 meters, but if it's "0.5 times longer than a one meter thing", you would expect it to be 1.5 meters. The same logic applies when you ditch fractions and use integers.
0.5 times longer is nonsense
0.5 times shorter makes sense
Largest "stellar" black hole in Milky Way. Not the "largest black hole" as some media are reporting it in their title.
The largest black hole in Milky Way is million times more massive than our sun. Falls in super massive category.
So they found the biggest one that isn't really big
They didn’t find the biggest one, they found the biggest one they’ve found so far. Which in all probability is pretty small.
[dead]
[flagged]
[flagged]
Where do you think the AI image model gets the data for what artist's impressions of astronomic phenomena should look like? From all the artists who painted these in the past.
Including the ones that did it for self expression for free instead of an inaccurate visualization at the top of every space related article
Just like they can do after that niche job goes poof
Next time you’re confused about why people seem to hate “techbros”, remember that this is the reason.
Why is that?
because of the image’s inaccuracy, masqueraded as something one of our telescopes could visualize, but instead is a contrived make-work programme
Yet it will be replaced with another job to generate even less accurate images.
It reminds me of a hilarious article Josh barrow wrote about the SV bank run. He uses AI article art for a bank run, which ended up as 6 fingered joggers along the bank of a river.
using 2 year old image models and prompting strategies?
they can all do accurate hands now
and what OpenAI’s working on understands physics
I think this undermines the point you were aiming for
So far, I assume.
„Size“ is misleading. 33 solar masses is in fact small for a black hole. Sigatarius A is still the biggest in the Milky Way.
Sigatarius A is not a stellar black hole now is it?
We don't know how supermassive blackholes form. It's a bit of a mystery.
That doesn't matter, you are toying with semantics. If astronomers say stellar black hole, they don't mean supermassive black holes at galactic centers. Even if Sagittarius A* was initially a stellar black hole, its more now.
I hadn't heard of the distinction stellar or non-stellar black hole before. It rather sounds like semantics to me to say this is one type of black hole and not another when it's physically the same thing and we don't know how it formed to begin with
The headline confused me as well: 33 solar masses (not sizes) seems tiny to me, I was sure we knew of bigger ones
To add to a sibling comment, the distinction is important, because observed mass of black holes falls largely into super massive (millions to billions solar masses) to stellar (dozens of solar masses). There is very, very, astonishingly few observed black holes with an intermediate mass. So, how super massive black holes form is a mystery, and finding large stellar mass black holes starts filling in (possibly) that evolutionary gap in black holes. Not a physicist, just read/watch a lot of pop astronomy/cosmology.
Also, super massive blackholes can only "swallow" so much matter at a time. Given what we know about how fast a black hole can grow, super massive black holes seem to be bigger than should be possible.
The distinction is clear and relevant because the mass distribution is strongly bimodal. A stellar black hole is the result of the gravitational collapse of a single star (well, or two at most). And maybe some of them have since then merged with a companion body. There are zillions of these in any given galaxy. Whereas there are maybe one or two supermassive black holes per galaxy, sitting in the center, with mass of millions or billions of suns, and we don’t quite know how they first formed and how they have accumulated so much mass. If the difference between "one" and "billion" doesn’t matter to you, well, ok then.
The difference is even more clear-cut because so-called intermediate mass black holes are something of a question mark. For a long time it wasn’t clear whether they even exist in any significant numbers, and even now the evidence is not especially rock-solid, especially with regard to candidate objects in the Milky Way.
It’s quite easy to describe the origin of a supermassive black hole.
It was just a stellar black hole that optimized logistics and utilized its gravitational pull to offer free shipping and one click accretion.
Its not semantics. Its precise terminology. Ignoring this and redefining the precis terms because one lacks knowledge about the subject and arguing from faulty assumptions is a waste of everyone's time.
> I hadn't heard of the distinction stellar or non-stellar black hole before.
While it's possible that supermassive black holes were formed from stellar collapse, there are models where they didn't, while they _know_ that this one was formed from stellar collapse.
They're probably not formed by the merger of stellar blackholes.
AI making too many paperclips again...
My bet is that they are older than 14 bln years.
Yeah, that's what I thought. TFA says (unconditionally) that SagA was formed by direct collapse of gas clouds.
They don't seem too clear on the science they're reporting, but if I'm understanding it right, this is supposed to be the largest stellar origin black hole. The fact that Sagittarius A* is just a bit under 4.3 million solar masses, which is a bit over 33, was my first thought, too.
The relevant definitions are explained in the article.
"Stellar" means star.
I was always under the impression there was only 1 black-hole in our galaxy, at it's centre.
There are many, many more, probably ranging in size to tinier than a period (.) to the 33 Sol mass (so far).
The one at the center of the galaxy is along for the ride! A good video: https://www.youtube.com/watch?v=e-P5IFTqB98
> probably ranging in size to tinier than a period (.)
"Probably" is a strong word, these are very hypothetical, the lightest observed black hole has a mass of 3 Suns.
A three solar mass black hole is still only ~13km across. Not full-stop-sized, but closer to that than the diameter of the sun.
I'm guessing the 13km diameter refers to the event horizon rather than the singularity itself, which I gather could be considered as zero-sized, or maybe one Planck length in size because we can't definitively measure anything smaller, or ...
Admittedly, it gets a bit philosophical. The sphere of no return isn't the thing, but it might as well be for any outside observer, but it isn't, but it could be viewed as such, but... :) Suffice to say I'm glad the closest thing to black holes I have to contend with in my daily life is a 2+ million line php codebase dating from the late Clinton administration.
"Do Black Holes have Singularities?" by Roy Kerr (Yes, that Roy Kerr)
https://arxiv.org/abs/2312.00841
https://www.pbs.org/video/what-if-singularities-do-not-exist...
There is even a theory about a mini black hole in our solar system pulling Uranus.
See e.g.
"What If Planet 9 Is a Primordial Black Hole?" by Jakub Scholtz and James Unwin [1]
[1] Phys. Rev. Lett. 125, 051103 – Published 29 July 2020 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.12...
Well, your impression was wrong then.
very wrong and I am a little sad I am getting down voted for not knowing something but here we are.