6 ms·

Can someone knowledgeable weigh in: is the "dark object" here believed to be a localized blob of dark matter? A dark star or black hole? Or is "dark" being used

by sixo 1y ago

Can someone knowledgeable weigh in: is the "dark object" here believed to be a localized blob of dark matter? A dark star or black hole? Or is "dark" being used generally to mean "not bright enough to see at this distance"?

b112 1y ago
Or a cloaked ship?
- gclawes 1y ago
  EXCESSION
- sixo 1y ago
  If so it's a big one, 1M solar masses.
  - layer8 1y ago
    That’s just how warp drives happen to appear from the outside.
- preisschild 1y ago
  ... and its heading right for us :P
alansaber 1y ago
They found a statistical anomaly that they're trying to atrribute to new physics, using some novel maths. So a tiny speck of evidence towards a new theory of matter (i know nothing about astro, just my supposition)
momoschili 1y ago
Dark in the context of astrophysics means specifically that the object/matter does not interact directly with electromagnetic radiation (eg absorb an optical/microwave/radio photon). So it is probably dark matter, but probably unlikely to be a black hole because we can typically detect a black hole's effects in an indirect manner :P
- deleted 1y ago
  [deleted]
  - deleted 1y ago
    [deleted]
  - Groxx 1y ago
    "dim" implies "there is something normal there that is just not emitting light". "dark" in this astronomical sense means essentially "dim and completely transparent" which is not what you get with e.g. a cold gas cloud - those are opaque.
    - ux266478 1y ago
      It's not just that. Remember that in space distance doesn't attenuate electromagnetic radiation. Given perfect line of sight, you could broadcast a 1mW 5GHz signal across the empty space between galaxies and have perfect reception (provided you're very patient) One also has to consider that at this scale, you cannot have a normal interaction with the EMF and be dim. The normal physical processes of matter at the scale of 1 million suns ends up being quite loud. Black holes that aren't actively eating things form an exception, but black holes aren't normally dark either. Whatever this is it's peculiar, but I wouldn't write-off that it might be an issue with the model they developed for interpreting the data.
bbor 1y ago
I'm an amateur but I feel confident enough to answer -- hopefully not a mistake! They're explicitly looking for "Dark Matter", which doesn't "interact" with normal ("baryonic") matter or electromagnetic radiation (e.g. light). So it's not a black hole for sure, as those are composed of regular ol' matter. RE:"dark star", that's really up in the air, I'd say! AFAICT the only academic reference to that term is for normal stars influenced by dark matter[1], but kinda the whole problem here is that we don't know much about what dark matter is composed of or into. Certainly it's not going to be a star in the traditional sense as it can't emit light, but I'm not aware of any reason this object can't end up being a giant sphere. FWIW, Wikipedia says "One of the most massive stars known is Eta Carinae, with 100–200 [solar masses]", whereas this object "has a mass that is a million times greater than that of our Sun". If we're going to use metaphors, I think "dark dwarf galaxy" might be more appropriate? [1] https://arxiv.org/pdf/1004.1258 https://arxiv.org/pdf/1004.1258
- bongodongobob 1y ago
  100-200 solar masses is not one of the largest known. There are many that are 1000s of times more massive than the sun.
  - shagie 1y ago
    I'm unaware of any stars in the 1000 Msun range. Wikipedia puts 291 Msun of R136a1 at the largest. After that, 195 M of R136a2 is the next. A star at 100 Msun would be in the most massive stars known. https://en.wikipedia.org/wiki/List_of_most_massive_stars#List_of_the_most_massive_known_stars https://en.wikipedia.org/wiki/List_of_most_massive_stars#Lis...
    - mr_toad 1y ago
      “ A number of the "stars" listed below may actually be two or more companions orbiting too closely for our telescopes to distinguish, each star possibly being massive in itself but not necessarily "supermassive" to either be on this list, or near the top of it. “ “ More globally, statistics on stellar populations seem to indicate that the upper mass limit is in the 120-solar-mass range,[1] so any mass estimate above this range is suspect. “ There are good theoretical reasons why a star shouldn’t normally get as big as the ones on the top of the list. Long story short: they’d very quickly shed mass due to their intense luminosity. Some of them might even be boiling with bubbles of pure radiation. https://en.wikipedia.org/wiki/Eddington_luminosity https://en.wikipedia.org/wiki/Eddington_luminosity Beyond that, there’s also the possibility of pair-instability supernova, which might cause the most massive stars to literally disintegrate.
t8sr 1y ago
Definitionally, yes. It’s inert but lenses light around it. The paper is more about the technical achievement of detecting it, IIUC. It’s not the first dark matter inference we’ve had, and doesn’t really tell us anything new about the stuff.
- daxfohl 1y ago
  It challenges warm dark matter and ultralight dark matter theories because they'd be less likely to clump into something so small. Similarly MOND would have trouble explaining a completely isolated chunk of it at this size (any baryonic matter trapped in a region this small would almost certainly emit enough light to detect).
  - t8sr 1y ago
    I’m admittedly a few years out of date in this, but weren’t those already kinda ruled out? I’ve never met anyone who took MOND seriously - it looks like it’s a pet project of a small number of people who cite each other, and people in different subfields have always been saying it doesn’t work for them (diffuse galaxies, etc.). I know the current models favor cold DM, I thought the hot DM model was abandoned already when it became clear that clusters of any size exist?
    - mr_mitm 1y ago
      Your assessment is spot on, but for whatever reason it's extremely popular with amateur physicists. The HN crowd likes it a lot, too. Almost every thread about dark matter has at least one comment that goes like "I'm not a physicist but dark matter always seemed like a cop out to me and will go the way of the luminiferous aether". I'm surprised that we're not seeing them here, perhaps because MOND can't explain this.
      - daxfohl 1y ago
        And yes, hot dark matter has largely been ruled out, but there are still extensions into warm dark matter and ultralight dark matter that seem more manufactured but are still plausible. The observations in this paper creates some additional challenges for those theories. But yes, CDM is what most researchers expect, by a large margin.
burnerRhodov2 1y ago
In this context, “dark object” really does mean a localized blob of dark matter, not a black hole or a dim, normal-matter object. The research team detected it only through its gravitational lensing effect — the way it slightly distorted the light from a more distant galaxy. There’s no emission at any wavelength (optical, infrared, or radio), and its gravitational signature matches a million-solar-mass clump of invisible mass rather than a compact point source like a black hole. They specifically interpret it as a dark matter subhalo — one of the small, dense lumps that simulations of “cold dark matter” predict should pepper the universe’s larger halos. It’s too massive to be a single star, far too diffuse to be a stellar remnant, and not luminous enough to be a faint galaxy. So “dark” here isn’t just shorthand for “too dim to see at this distance” — it’s used in the literal physical sense: matter that doesn’t emit or absorb light at all, detectable only via gravity. Eventually, all the dark matter clumps into rings around galaxies, but since this one is so distant, ~10B light years, so we are seeing that clump as it was that long ago before it difused into it's ring shape we can see in the galaxies around us.
- hermitcrab 1y ago
  Why does dark matter form halos/rings around galaxies. Why isn't it attracted to the centre of the galaxy like 'normal' matter?
  - devmor 1y ago
    I believe that you have the order of operations misunderstood. I probably don't know that much more than you about the subject, but from what I understand, the prevailing model suggests that these Halos formed early in the formation of the universe when spacetime had varying "pockets" of density that naturally led to these halos - the formation of the galactic disk therein was actually supported by the halo existing first, because baryonic matter (aka non-dark matter, the stuff that makes up planets, stars, etc) was still too energetic from the formation of the universe to become gravitationally bound to itself.
    - hermitcrab 1y ago
layer8 1y ago
From the paper, it could be the dark-matter halo of an otherwise too faint dwarf galaxy. They state that a “more definitive statement on what type of object [it] is will require deep optical/infrared observations to detect any potential EM emission”.
personomas 1y ago
[dead]
KolibriFly 1y ago
Basically: not a dark star, not a black hole, not just faint... probably a chunk of pure, clumpy dark matter

by sixo 1y ago

b112 1y ago

Or a cloaked ship?

gclawes 1y ago
EXCESSION
sixo 1y ago
If so it's a big one, 1M solar masses.
- layer8 1y ago
  That’s just how warp drives happen to appear from the outside.
preisschild 1y ago
... and its heading right for us :P

alansaber 1y ago

They found a statistical anomaly that they're trying to atrribute to new physics, using some novel maths. So a tiny speck of evidence towards a new theory of matter (i know nothing about astro, just my supposition)

momoschili 1y ago

Dark in the context of astrophysics means specifically that the object/matter does not interact directly with electromagnetic radiation (eg absorb an optical/microwave/radio photon). So it is probably dark matter, but probably unlikely to be a black hole because we can typically detect a black hole's effects in an indirect manner :P

deleted 1y ago
[deleted]
- deleted 1y ago
  [deleted]
- Groxx 1y ago
  "dim" implies "there is something normal there that is just not emitting light". "dark" in this astronomical sense means essentially "dim and completely transparent" which is not what you get with e.g. a cold gas cloud - those are opaque.
  - ux266478 1y ago
    It's not just that. Remember that in space distance doesn't attenuate electromagnetic radiation. Given perfect line of sight, you could broadcast a 1mW 5GHz signal across the empty space between galaxies and have perfect reception (provided you're very patient) One also has to consider that at this scale, you cannot have a normal interaction with the EMF and be dim. The normal physical processes of matter at the scale of 1 million suns ends up being quite loud. Black holes that aren't actively eating things form an exception, but black holes aren't normally dark either. Whatever this is it's peculiar, but I wouldn't write-off that it might be an issue with the model they developed for interpreting the data.

bbor 1y ago

I'm an amateur but I feel confident enough to answer -- hopefully not a mistake! They're explicitly looking for "Dark Matter", which doesn't "interact" with normal ("baryonic") matter or electromagnetic radiation (e.g. light). So it's not a black hole for sure, as those are composed of regular ol' matter. RE:"dark star", that's really up in the air, I'd say! AFAICT the only academic reference to that term is for normal stars influenced by dark matter[1], but kinda the whole problem here is that we don't know much about what dark matter is composed of or into. Certainly it's not going to be a star in the traditional sense as it can't emit light, but I'm not aware of any reason this object can't end up being a giant sphere. FWIW, Wikipedia says "One of the most massive stars known is Eta Carinae, with 100–200 [solar masses]", whereas this object "has a mass that is a million times greater than that of our Sun". If we're going to use metaphors, I think "dark dwarf galaxy" might be more appropriate? [1] https://arxiv.org/pdf/1004.1258 https://arxiv.org/pdf/1004.1258

bongodongobob 1y ago
100-200 solar masses is not one of the largest known. There are many that are 1000s of times more massive than the sun.
- shagie 1y ago
  I'm unaware of any stars in the 1000 Msun range. Wikipedia puts 291 Msun of R136a1 at the largest. After that, 195 M of R136a2 is the next. A star at 100 Msun would be in the most massive stars known. https://en.wikipedia.org/wiki/List_of_most_massive_stars#List_of_the_most_massive_known_stars https://en.wikipedia.org/wiki/List_of_most_massive_stars#Lis...
  - mr_toad 1y ago
    “ A number of the "stars" listed below may actually be two or more companions orbiting too closely for our telescopes to distinguish, each star possibly being massive in itself but not necessarily "supermassive" to either be on this list, or near the top of it. “ “ More globally, statistics on stellar populations seem to indicate that the upper mass limit is in the 120-solar-mass range,[1] so any mass estimate above this range is suspect. “ There are good theoretical reasons why a star shouldn’t normally get as big as the ones on the top of the list. Long story short: they’d very quickly shed mass due to their intense luminosity. Some of them might even be boiling with bubbles of pure radiation. https://en.wikipedia.org/wiki/Eddington_luminosity https://en.wikipedia.org/wiki/Eddington_luminosity Beyond that, there’s also the possibility of pair-instability supernova, which might cause the most massive stars to literally disintegrate.

t8sr 1y ago

Definitionally, yes. It’s inert but lenses light around it. The paper is more about the technical achievement of detecting it, IIUC. It’s not the first dark matter inference we’ve had, and doesn’t really tell us anything new about the stuff.

daxfohl 1y ago
It challenges warm dark matter and ultralight dark matter theories because they'd be less likely to clump into something so small. Similarly MOND would have trouble explaining a completely isolated chunk of it at this size (any baryonic matter trapped in a region this small would almost certainly emit enough light to detect).
- t8sr 1y ago
  I’m admittedly a few years out of date in this, but weren’t those already kinda ruled out? I’ve never met anyone who took MOND seriously - it looks like it’s a pet project of a small number of people who cite each other, and people in different subfields have always been saying it doesn’t work for them (diffuse galaxies, etc.). I know the current models favor cold DM, I thought the hot DM model was abandoned already when it became clear that clusters of any size exist?
  - mr_mitm 1y ago
    Your assessment is spot on, but for whatever reason it's extremely popular with amateur physicists. The HN crowd likes it a lot, too. Almost every thread about dark matter has at least one comment that goes like "I'm not a physicist but dark matter always seemed like a cop out to me and will go the way of the luminiferous aether". I'm surprised that we're not seeing them here, perhaps because MOND can't explain this.
    - daxfohl 1y ago
      And yes, hot dark matter has largely been ruled out, but there are still extensions into warm dark matter and ultralight dark matter that seem more manufactured but are still plausible. The observations in this paper creates some additional challenges for those theories. But yes, CDM is what most researchers expect, by a large margin.

burnerRhodov2 1y ago

In this context, “dark object” really does mean a localized blob of dark matter, not a black hole or a dim, normal-matter object. The research team detected it only through its gravitational lensing effect — the way it slightly distorted the light from a more distant galaxy. There’s no emission at any wavelength (optical, infrared, or radio), and its gravitational signature matches a million-solar-mass clump of invisible mass rather than a compact point source like a black hole. They specifically interpret it as a dark matter subhalo — one of the small, dense lumps that simulations of “cold dark matter” predict should pepper the universe’s larger halos. It’s too massive to be a single star, far too diffuse to be a stellar remnant, and not luminous enough to be a faint galaxy. So “dark” here isn’t just shorthand for “too dim to see at this distance” — it’s used in the literal physical sense: matter that doesn’t emit or absorb light at all, detectable only via gravity. Eventually, all the dark matter clumps into rings around galaxies, but since this one is so distant, ~10B light years, so we are seeing that clump as it was that long ago before it difused into it's ring shape we can see in the galaxies around us.

hermitcrab 1y ago
Why does dark matter form halos/rings around galaxies. Why isn't it attracted to the centre of the galaxy like 'normal' matter?
- devmor 1y ago
  I believe that you have the order of operations misunderstood. I probably don't know that much more than you about the subject, but from what I understand, the prevailing model suggests that these Halos formed early in the formation of the universe when spacetime had varying "pockets" of density that naturally led to these halos - the formation of the galactic disk therein was actually supported by the halo existing first, because baryonic matter (aka non-dark matter, the stuff that makes up planets, stars, etc) was still too energetic from the formation of the universe to become gravitationally bound to itself.
  - hermitcrab 1y ago

layer8 1y ago

From the paper, it could be the dark-matter halo of an otherwise too faint dwarf galaxy. They state that a “more definitive statement on what type of object [it] is will require deep optical/infrared observations to detect any potential EM emission”.

personomas 1y ago

[dead]

KolibriFly 1y ago

Basically: not a dark star, not a black hole, not just faint... probably a chunk of pure, clumpy dark matter