back to article If you thought black holes only came in S or XXXL, guess again, maybe: Elusive mid-mass void spotted eating star

Astronomers have discovered what they believe could be a black hole of intermediate-mass nestled on the outskirts of a large galaxy more than 700 million light years away. Observed black holes typically come in two sizes: small ones ten to 100 times the mass of the Sun, and gigantic supermassive ones that are millions to …

  1. Michael H.F. Wilkinson
    Thumb Up

    Only in Astronomy

    does 50,000 times the mass of the sun not qualify as super massive. The mind boggles at such numbers.

    Well done spotting this intermediate-mass black hole!

    1. ThatOne Silver badge

      Re: Only in Astronomy

      The issue is in the non-existing upper limit, for "50000 sun masses" is indeed rather big. The biggest "hypergiant" size stars we know about are AFAIK around 20-30 times the mass of our sun, so one can imagine the number of stars of all sizes this black hole had to gobble to get to that size!

      1. Brewster's Angle Grinder Silver badge

        Re: Only in Astronomy

        In ballpark terms, a star can range 0.1 - 100M. Wikipedia has a list of some inferred superweights - with it topping out at 315 M for R136a1.

        However, big stars tend to be shed a lot of mass duriing their short lifetimes, and turning into a blackhole typically involves shedding even more. So those aren't good guides to black hole masses. OTOH, a lot of star systems are binaries so a black hole can easily double it mass by slurping up its partner.

        1. ThatOne Silver badge

          Re: Only in Astronomy

          > with it topping out at 315 M☉ for R136a1

          Okay, that's bigger than I remembered! Thanks for the link.

          Anyway, still, and even in the unlikely case of a binary of those heavyweights, and even assuming they don't lose too much mass when they collapse, it would take a lot of those (definitely not common!) 630 M☉ binaries to dig that "intermediate" black hole... I wonder where it found all that mass, given most stars tend to be distant from one another. You'd need a huge concentration of mass to create something like that black hole, and if it is not living in the dense heart of a star cluster, where did it find enough mass to get that big? It doesn't move around, so what? Home delivery?...

          1. Anonymous Coward
            Boffin

            Re: Only in Astronomy

            I think the brief answer is 'we don't really know'. There are various theories as to how relatively large (tens of solar masses) BHs originate, including slightly strange ideas such as the direct collapse of large clouds of gas.

            Once you have some kind of seed BH then it needs to accrete mass, and I think that people think that most of this comes from gas rather than stars (there is a lot of gas). The problem with accreting mass is that you need to dump its angular momentum to get the orbit low enough, ultimately low enough that it reaches the no-stable-orbits region. This means dumping a lot of energy, which is why things like quasars are so absurdly luminous. Accreting gas is easier than accreting stars because it's easier to dump all this energy for gas by getting it very hot, which you can't really do for stars until they get close enough that they're tidally disrupted, and turned into gas which you can then get hot.

            Of course we observe quasars so we have evidence that this sort of thing happens, but I don't think there's a full picture of what the evolution of the things from the initial assumed few-tens-of-solar-masses objects looks like. But remember they have billions of years to do this: it's not the case that you get some initial object and then a million years later you have something with thousands of solar masses: you might have to wait most of the age of the universe for that.

            Of course the problem is hugely worse for SMBHs.

            All of the above is my understanding and may be wrong.

  2. Pascal Monett Silver badge

    “Intermediate mass black holes might not be rare,"

    So we now know that there are indeed intermediate-mass black holes, which we did not know before. Since we didn't know that, we could not factor their mass in our calculations for the amount of normal matter that exists in the Universe, which means our ratio of dark matter to normal matter is wrong.

    Of course, we still don't know how much mass is harbored inside those things, and evaluating that is not going to be easy.

    Add to that the fact that brown dwarfs are also an unknown quantity and it seems to me that there is significantly more normal matter than we initially thought. Probably not enough to do away with dark matter, but likely more than the 15% it is apparently currently pegged at.

    1. ClockworkOwl
      Boffin

      Re: “Intermediate mass black holes might not be rare,"

      Not very much, space you see is really big...

      They are seemingly rare, and whilst very massive, are only 5 orders of magnitude smaller than their biggest cousins.

      The above is true for brown dwarves too, though they may not turn out to be quite as rare.

      Overall I'd be very surprised if it made as much as a ppm adjustment, however I'm not a boffin,

      he is>>>

    2. Anonymous Coward
      Boffin

      Re: “Intermediate mass black holes might not be rare,"

      In fact we do know there are not enough relatively small, electromagnetically quiet objects (such as intermediate-mass BHs, brown dwarfs &c) to account for a significant amount of the missing mass, because we can 'see' such things through gravitational microlensing: when they pass in front of more distant objects the light from those objects gets bent and you get, for instance, multiple images of them.

      One of the early hypotheses for dark matter was lots of quiet BHs and this got ruled out by the lack of enough observed microlensing.

      So although it's nice that we now know there are some, we already knew there were not enough to account for the missing mass, aka dark matter.

    3. eldakka Silver badge

      Re: “Intermediate mass black holes might not be rare,"

      While the exact ratio is always subject to change, the existing (approximate) 5:1 ratio is unlikely to be changed much by this discovery.

      For a very quick and simple view, this video is interesting (it's only a 15 minute video, I linked to the bit where the narrator talks about why some things have been eliminated).

  3. Anonymous Coward
    Anonymous Coward

    Lower and upper limits

    1) Lower limit: this comes from extrapolating the observed clumping effect, gravity, up to the point at which the escape velocity matches the constant 'speed of light' at which point light cannot escape and we have an event horizon and a black hole.

    2) Upper limit: this is from estimating how much clumping could occur since God 'Bigus Bangus' created the universe and all of space and time, but not the dimension that inflation works in, that dimension is different.

    Those two define the assumed limits for black hole sizes.

    And at the sub-atomic end, gravity is some clumping effect of (some) matter particles which disappears when matter is converted to energy. And somehow when energy becomes matter, the gravity property returns, and light stops moving, somehow it doesn't escape, but this time nothing to do with gravity, no sir this is an energy to matter conversion that just happens, poof, and there it is.

    And if I slap a mass of equations over that, label everything with magic keywords, this is the state of physics today.

    1. ClockworkOwl
      Facepalm

      Re: Lower and upper limits

      Yes of course, it's so simple...

      Why didn't I think of that???

    2. Jimmy2Cows Silver badge

      Re: Lower and upper limits

      Too many shrooms with your full-English this morning?

    3. Cuddles Silver badge

      Re: Lower and upper limits

      "And if I slap a mass of equations over that, label everything with magic keywords, this is the state of physics today."

      Said equations being rather fundamental to the whole thing. Anyone can throw together a description of how they think things work that may or may not sound silly to other people. Putting together a consistent mathematical description that is able to accurately describe actual observations is a little trickier. You're free to argue with and/or complain about the maths all you like, but you're unlikely to be able to convince it to agree with you.

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