back to article Not one, but 20,000 black holes hiding in Milky Way's heart

The Milky Way may be teeming with tens of thousands of black holes lurking at its centre, according to a new study published on Wednesday. A group of astrophysicists analysed X-rays emitted from the heart of the galaxy to hunt for black holes using data taken from NASA’s Chandra X-ray Observatory. Black holes are greedy. As …

  1. TechnicalBen Silver badge


    Or hot.

    I wonder if this has any effect on the search for dark matter or energy? I would assume as they are gravitational, they already make up the predicted mass, just we know they are denser now?

    Though if they get ejected from galaxies, and become cold/naked singularities, they may be halo objects?

    The plot thickens!

    1. Brewster's Angle Grinder Silver badge

      Re: Cool.

      You answer your own question below: there just isn't any missing mass in the centre of the galaxy. And, anyway, it appears these black holes are already budgeted for and predicted to exist -- we just haven't found them yet.

      And if a black hole halo was to explain dark matter, there'd need to be five black holes for every star in the galaxy. Which should give you pause for thought. And we'd definitely have detected them through gravitational lensing events. (Also, theories of galaxy formation would be borked and we'd need to rethink the spectrum of cosmic microwave background radiation.)

    2. Ken Strain

      Re: Cool.

      The point about dark matter on the scale of the Universe as a whole is that, even if all the material that could ever be stars or ever has been stars is included along with the mass of the visible stars, the physics of how the elements formed just after the big bang tells us that most of the gravitational attraction is not due to normal matter (called "baryonic", as it is protons and neutrons mainly).

      The accepted view of the origin of black holes like the "20,000" mentioned is that these are collapsed stars and hence were in fact accounted for in the baryonic matter budget. If instead they were made separately (in the big bang) without ever have being in the form of normal matter, then they could count for some of the cosmological dark matter, but that is viewed as rather unlikely.

      So, while these black holes could (very slightly) affect the rotation curves of galaxies and be called dark matter in that sense, they are probably not part of the cosmological dark matter.


    3. onefang Silver badge

      Re: Cool.

      "I wonder if this has any effect on the search for dark matter or energy?"

      Not Dark Matter, Really Really Really Dark Matter.

      I'd get my coat, but it's too black to find it.

  2. Ugotta B. Kiddingme

    I've asked before but...

    the surrounding facts keeps changing with new discoveries and theories like this. Therefore: Could these "new" black holes account for at least some of the missing mass required to bind the galaxy together and keep it spinning at current speed?

    IIRC, currently identified baryonic matter accounts for about 15% of the total mass required for the galaxy (and by extension, the universe) to behave the way it does. If there turn out to be significantly more black holes in existence than previously thought, then perhaps baryonic matter makes up a greater percentage of the total.

    I am not a physicist nor any other form of scientist - just a bloke trying to wrap my mind around the concepts and actually learn something.

    1. 2+2=5 Silver badge

      Re: I've asked before but...

      > Therefore: Could these "new" black holes account for at least some of the missing mass required to bind the galaxy together and keep it spinning at current speed?

      No. Because the missing mass (dark matter) needed to make galaxies spin the way they do needs to be spread throughout the galaxy, not just be in the centre.

    2. Tom 64

      Re: I've asked before but...

      No. Even if there was one black hole for every star in the galaxy, there still wouldn't be enough mass to explain the nature of the milky way's rotation.

      1. TechnicalBen Silver badge

        Re: I've asked before but...

        These ones are in the galactic centre. The "missing" mass and energy appears to be at the edges.

        So far, like with Mercury and General Relativity, the place of the difference it seems is key to understanding why there is one. With Mercury, all the other planets orbited within our predictions/understandings. Mercury was "wrong". ;)

        Then we figured out/observed it was spacial distortion from being so close to the Sun.

        With Dark Matter it appears to be around the outskirts/just outside the edges of Galaxies that the discrepancy appears (faster rotation than expected IIRC).

        So if these objects are involved, they could be a source. They would however still need to move throughout history to the new positions. Though that is possible I think and neutrinos/wimps/machos all do similar orbits of the galaxies... however, those do not cause massive problems should they intersect us!!!

  3. handleoclast Silver badge


    I see two commentards already got here before me and speculated that maybe it's these mini black holes, rather than dark matter, that account for the missing mass.

    Coincidentally, a few days ago I watched this about astronomers recently finding a distant, small galaxy with almost no dark matter. It was touted as evidence that dark matter is not a result of gravity/relativity behaving different;y from what we'd expect (or else it, too, would seem to have dark matter).

    However, it's distant. Which means it's young (old now, but what we're seeing is when it was young), so not as much time for mini black holes to form. And small, so not as much mass flying around to form mini black holes.

    I don't understand any of this stuff well enough to give anything but a totally uninformed opinion, but it makes me wonder.

    1. Pascal Monett Silver badge

      Re: Interesting

      Glad to finally find a brother mind watching SciShow.

      Have an upvote and keep spreading the word.

      1. harmjschoonhoven

        Re: Interesting

        Did not know about SciShow, I just get all pressreleases from NOVA in my inbox. Moreover a few weeks later Nature drops on my doormat.

        See here for a picture of the team and its Dragonfly Telescope. Warning: gender imbalance.

        1. Paul_Murphy

          Re: Interesting

          Also a bit dutch... :-)

  4. Voyna i Mor Silver badge

    Too much whining.

    Astronomer complaining that black holes are black and difficult to detect.

    Within my living memory physicists were speculating about black holes and working out their properties when not a single one had been detected. Now they complain it would be nice if they produced more X-rays.

    Scientists of today want it all done for them. In our day we had to mine the silver, electrolyse the bromine, boil down the hooves and melt the glass to make our own plates, then climb the trees to get the galls to make the pyrogallic acid to develop them. And we thought we were lucky because our predecessors had to just stand there till the image burned into their retina.

    Get off my lawn!

    1. soulrideruk Bronze badge

      Re: Too much whining.

      That's one of them logical fallacies fandangles..

      You say that astronomers are complaining that they can't see black holes, and then compare it to physicists calculating black holes using mathematical theorems.

      Two different art forms..

      1. Voyna i Mor Silver badge

        Re: Too much whining.

        "That's one of them logical fallacies fandangles."

        No it isn't, just pointing out that 50 years ago nobody had observed - or could observe - a black hole and now someone is complaining that they are hard to see and that there are in fact vast numbers of them.

        My point such as it was was about how theoreticians predict and only later does the technology come along to confirm. See also Higgs Boson, Majorana particles.

        In the same way, by about 1918 the mode of operation and thermodynamics of just about every type of internal combustion engine had been worked out, but it took decades for most of them to come into common use because new metallurgy and metal forming methods were needed. In 1916 people were speculating on whether the jet engine would eventually replace the piston aircraft engine, even though nobody would make one till the 1940s.

        1. GruntyMcPugh Silver badge

          Re: Too much whining.

          Re Voyna i Mor "See also Higgs Boson, Majorana particles."

          I think it was Majorana particles that burned little holes in my favourite tee shirt.

    2. Neil Barnes Silver badge

      Re: Too much whining.

      Upvoted simply for the historic Yorkshire photography. Kids today don't know they're born!

    3. Anonymous Coward
      Anonymous Coward

      Re: Too much whining.

      > Astronomer complaining that black holes are black and difficult to detect.

      Holly explains the difficulty:

  5. John Smith 19 Gold badge

    Thie "dark matter" business is strange. I keep thinking of Occam's razor

    IOW why go all around the houses with exotic "stuff" before considering the more mundane (but in quite extreme form) options first?

    But 12 black holes together....

    1. M man

      Re: Thie "dark matter" business is strange. I keep thinking of Occam's razor

      isnt that too many black holes.

      85% black holes?

      You wouldn't be able to move for the buggers(in a very literal way)

      Im an ocrams razor guy but i think the test-tube jugglers have missed somthing really obvious and its to do with the Lyman-alpha forest.

    2. Charlie Clark Silver badge

      Re: Thie "dark matter" business is strange. I keep thinking of Occam's razor

      "dark matter" == "missing mass" and "dark energy" == "missing energy"

      We can observe effects that suggest the existence of both but we have thus far not come up with any theories to explain that can be verified.

      The names are not very good but I'm with Knuth on this that names are hard. Using "dark" instead of "missing" or "undetectable" does unfortunately bring associations with black holes but the theory for those is completely different and has been verified by observation.

      The missing matter is needed to explain why galaxies are observed to rotate differently than they should given their known mass. There have been several theories to explain the missing matter including WIMPs and, more recently, "sterile neutrinos".

      The missing energy is needed to explain why the universe seems to be expanding faster than current theories suggest. AFAIK and, I'm not a theoretical physicist, there's currently nothing close to a theory for dark energy. Maybe relativity is just wrong at that scale?

    3. Nano nano

      Re: Thie "dark matter" business is strange. I keep thinking of Occam's razor

      The simpler "answer" does not account for observed behaviour ...

      " At the edges of most galaxies, stars orbit so quickly that they should be flung away. The fact that they don’t implies that these galaxies have far more mass than we can see, and the gravity of that extra mass – dark matter – holds them together."

      NOTE - "at the edges"

  6. Aqua Marina Silver badge

    So they’ve discovered...

    ... the Kessel Run!

    All they have to do now is figure out how to navigate through it in 12 par-secs!

  7. Stuart21551

    With 20,000 black holes, who needs dark energy?

    1. Roj Blake Silver badge

      Re: With 20,000 black holes, who needs dark energy?

      Dark energy pushes everything apart. Black holes pull everything together.

  8. Brian Scott

    "The researchers found 12 black holes with similar masses as the sun surrounding the supermassive black hole Sagittarius A* that lives in the galaxy’s center."

    I don't claim to be an expert at this but I thought the mass of the sun was too low to form a black hole.

    1. arctic_haze Silver badge

      Our Sun is too small to end up as a Supernova and this is how you create black holes. However, remember that the black hole is the former core of an exploding star and most of its mass is scattered around (most of the atoms we are build with have been created this way - the exception is hydrogen). So the mass of the resulting black hole mass is only a fraction of the original stellar mass. The only limit is the collapsed core must be heavy enough not to become a neutron star. The views on maximum mass a neutron star can have not to collapse further becoming a black hole are not well constrained but probably around twice the mass of our Sun. So most probably the black holes in the paper were only "in the order of solar mass" which may mean 2-5 times heavier.

    2. eldakka Silver badge

      > I don't claim to be an expert at this but I thought the mass of the sun was too low to form a black hole.

      "around the size of the sun" generally refers to 'stellar-mass' black holes. Black holes are generally divided up into 3 categories (4 if you include the micro blackholes that get created and evaporate within seconds):

      1) Stellar-mass black holes, anything less than about 100 solar masses;

      2) Intermediate black holes, 100-100,000 solar mass;

      3) Super-massive, generally 100,000+ times the mass of the Sun.

      These categories are fairly loose, they are approximations.

      Therefore often whey they say 'about the mass of the sun', they generally mean stellar-size black holes, i.e. anything less than 100 solar masses. When you have supermassive black holes at 10 billion solar masses or more, then relative to that, a 50 solar mass black hole is "about the mass of the sun" when engaging in general discussion.

      Also note that the initial mass of a star has to be much greater than the Sun's to form a black hole, but that doesn't mean the resulting black hole will be the mass of the parent star. A Supernova is caused by a large star ejecting much of its mass, so as part of the supernova/collapsing into a black hole, most of the stars mass is blown away into space and doesn't become part of the black hole. (at least in the star->supernova->blackhole mechanism, there are several black hole creation mechanisms, such as direct collapse and others)

  9. Anonymous Coward
    Anonymous Coward

    On the flip side

    If we ever encountered a solar mass or smaller black hole, we wouldn't know much about it because the gravitational forces involved would convert the Earth into chunky salsa (tm) long before getting anywhere near the event horizon assuming the radiation didn't get us first.

    Factor 1,000,000 would be completely inadequate. (Arnie voice)

    1. Nano nano

      Re: On the flip side

      Nice series of videos - one about black holes ....

    2. Rich 11 Silver badge

      Re: On the flip side

      If we ever encountered a solar mass or smaller black hole, we wouldn't know much about it

      If a solar mass black hole drifted into our solar system we would know about it very quickly, because the planets would take up new orbits dependent upon its location and line of motion. All the probes out there would stop pointing their antennae at Earth since they would no longer be able to calculate correctly where Earth was.

      The less massive the black hole the less likely it is that we'd find out about it before it came close enough to harm us. There could be a black hole of a hundred tonnes mass in the Earth's core right now, for all we know, but even then we'd probably be able to detect it if its orbit around the Earth's centre of mass was as much as a hundred kilometres or so.

  10. TVU Silver badge

    "Not one, but 20,000 black holes hiding in Milky Way's heart"

    I would want verification and more studies done before I accept this new result. The existing orbits of stars near the centre of the galaxy indicate that they are orbiting around a single, same point.

    Not only that, if there are as many as 20,000 black holes at the centre of this galaxy in close proximity to each other then I would expect black hole mergers which would surely be detectable.

    1. Anonymous Coward
      Anonymous Coward


      The orbits would not change. The number of black holes changes the density, not the total amount of gravitation. As at distances gravity extends to infinity, and very close can be a point (or in QM ignored ;) ), we can average and get the "same" result.

      Mergers depend on age. If none of these are close enough for the age of *our* galaxy, then we could expect zero mergers until our galaxy gets to the average age of the first merger. Other galaxies though can be older/younger and have more/less mergers depending on requirements.

      While your arguments would then be valid, they would only be so if ignoring all other data.

      1. TVU Silver badge

        Re: 20,000

        "The orbits would not change. The number of black holes changes the density, not the total amount of gravitation. As at distances gravity extends to infinity, and very close can be a point (or in QM ignored ;) ), we can average and get the "same" result"

        I get that and that's not my issue. If these purported black holes were close together, then by their very nature there would be a tendency for them to move towards each other and merge.

        If they were more spread out, then there'd be the greater possibility of perturbations and pulls on the stars orbiting the centre of the galaxy but so far we don't see that; only nice elliptical orbits.

        It's interesting work but I'd want other groups to take a look at it, repeat it and verify it (or not) which is, after all, how science is done.

        1. Anonymous Coward
          Anonymous Coward

          Re: 20,000

          As said. Number of mergers depends on age. I've not seen it suggested yet these are old (close) enough to have mergers.

          Orbits are the same. A star of mass 10 times the sun, and a black hole the mass 10 times the sun has the same orbits!

          So nothing changes, except the number of black holes. Should these be much older than said stars, then yes, we would expect more changes gravitationally (waves or collisions). As they are the same age of the predicted stars that would have been there, gravitationally nothing changes gravitationally.

          Thus the gravitational part of dark matter/gravity is not changed. The visible/invisible discrepancy may be, slightly.

  11. Richard Scratcher


    That's enough black holes to fill the Albert Hall.

    1. Anonymous Coward
      Anonymous Coward

      Re: 20,000!

      Only if they are in Blackholeburn, Lancashire.....

      1. onefang Silver badge

        Re: 20,000!

        Considering the size of these holes, I think it's the other way around. Do we know how many Albert Halls it takes to fill a black hole?

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