back to article Galaxy's smallest known black hole discovered

Two NASA scientists have measured the puniest black hole yet - it has a diameter of just 15 miles and a mass about 3.8 times greater than the size of our sun. The black hole is located in the Milky Way Galaxy binary system called XTE J1650-500 (oh, NASA and your flowery names) — roughly 10,000 light years away. Astronomers …


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  1. Mark C

    They're not trying very hard

    It has a diameter of just 15 miles .... surely Basildon is smaller?

    No love - mines the donkey jacket with the XR3 keys in ...

  2. Chris Miller

    1.7x to 2.7x solar mass

    I presume this must be the mass of the remnant black hole. To undergo a supernova explosion, a star must start with at least 8x solar mass (except for type 1a, caused by matter accretion onto an existing white dwarf). Hence there's no possibility of Earth being destroyed in this fashion.

  3. Anonymous Coward

    @ Chris

    Gee and I was hoping to be collapsed into a tiny bit - and have time warped so as to live 'forever'. Of course I am afraid of falling so that might be a bit of a problem.

    It is the one in the tardis

  4. Anonymous Coward
    Anonymous Coward


    a black hole is a single point with no size. Its event horizon has a diameter of 15 miles.


  5. Rob Haswell

    Even more technically

    Quantum mechanics and string theory both postulate that a black hole is matter condensed into its smallest possible volume, which also makes more sense. So on the numbers game, the black-hole-is-a-zero-point camp is losing :-)

  6. Michael H.F. Wilkinson

    Even even more technically

    Our understanding of physics has problems, because quantummechanics and and general relativity are at odds with eachother: they cannot both be right, and are probably both wrong in these extreme conditions.

    However, when talking about the size of a black hole, any astronomer knows you are talking about the Swarzschild radius, simply because it is only observable dimension of the black hole.


  7. Anonymous Coward
    Anonymous Coward

    Surely... mean the diameter is 174.5719 Brontosaurus' (Brontosauri?)

    Not had enough caffeine to try to calculate how many jubs it is

  8. jai

    general theory

    i thought i saw a program on telly a couple of weeks ago that had Stephen Hawking in it (so it must be right, right?) about how one of his colleagues had come up with super-string theory that does account for general relativity and quantummechanics - but to be honest, as fascinating as it was, most of it went over my head and i can't remember any of the more technical details

  9. JCL

    Isle of White

    Hmm, so it's just bigger than the Isle of White (crow flying Cowes to St Catherine's Point) then?

    Also, so that I actually learn something from El Reg, could someone please explain the Swarzschild radius in layman English?

  10. David Rollinson

    How many Sarah Beenys?

    I'm assuming that you don't need to quote a margin of error in this figure because of the inherent variability of the unit...

  11. Andy


    surely quantum physics/mechanics is both right and wrong at the same time?...

    ok, mine is the red one thats also blue.... :)

  12. amanfromMars Silver badge

    Confusion Rains/Reigns/Reins in Orders of ChaOS/Low Level Programs

    "Quantum mechanics and string theory both postulate that a black hole is matter condensed into its smallest possible volume, which also makes more sense. So on the numbers game, the black-hole-is-a-zero-point camp is losing :-)" .... By Rob Haswell Posted Wednesday 2nd April 2008 03:47 GMT


    Your conclusion ..."So on the numbers game, the black-hole-is-a-zero-point camp is losing :-)" is at odds with/contrary to your view..... "Quantum mechanics and string theory both postulate that a black hole is matter condensed into its smallest possible volume, which also makes more sense." ... thus does IT create Confusion and/or Chaos...... as surely the smallest possible volume is one that cannot be seen or measured thus to XXXXtraOrdinarily Render it via IT, Not There in any Sense you would Care 42 Imagine/Postulate.[the black-hole-is-a-zero-point]

    It may very well be better considered for Beta Use as a Virgin Start Point rather than being capable of being discovered as a Result End Point of Reverse Engineering........ although such Work has been Invaluable in Realising that Inescapable Fact/Undeniable Fiction.

    After All, what do any of us know of the Real Hawking World from the Confines of our Chair........ for there are so many Spinning Yarns which we are expected to Follow as if True..... which suggests that they are no more than Subjective Tales in Support of Hidden Agenda$.

    MeThinks their Stories should do Beta........ given the Grief that the Present delivers in its News of Yesterday.

    Future News which is a Universal Pleasure to Follow would be AI Novel innovation Worthy of Funding rather than writing off thousands of billions in Failed Schemes and Scams. Or would you prefer to sustain and reinforce further untold Losses?

    A Bit of a No Brainer, that question, ....... which sadly, more than a few will Fail to Comprehend.

  13. Britt Johnston

    remnants? @chris miller

    Assuming more mass could be "used up", the minimum black hole would become coloured or, worse, regurgitate its spoils.

    Help, my mind is being sucked in.

  14. peter Silver badge


    "Also, so that I actually learn something from El Reg, could someone please explain the Swarzschild radius in layman English?"

    Its where the escape velocity matches the speed of light - i.e. the event horizon of a black hole. Once you're within the Schrwazchild radius not even light can escape, and you ain't never coming out. (And any object smaller than its Schwarzschild radius must a black hole.)

    SMALLPRINT: it applies only to non-rotating, uncharged, spherically symmetric mass distributions as modelled by general relativity. The value of the Schwarzschild radius may go down as well as up.

  15. Anonymous Coward

    Schwarzschild radius

    In layman's terms, it's the size an object has to be compressed to in order to become a black hole. If I remember right, the Sun's is less than 2 miles (ie compress the Sun into a 2 mile sphere and you've got a black hole), and the Earth's is less than 1cm.

    Equation is (2Gm)/(c^2)

    G - grav constant

    m - mass of object

    c - speed of light

  16. Andy White

    Schwarzschild Radius

    Yo JCL,

    The Schwarzschild radius (also called the event horizon) is the point at which the curvature of space-time (gravity pull) is so great that light can't escape. So we don't know much about anything inside the schwarzschild radius because no light gets out for us to look at. The only thing we can know about a black hole is the mass, angular momentum and charge because they affect the curvature of space-time and we experience that directly even when outside the event horizon.

    Does that help?


  17. Senor Beavis

    Measuring diameter of black holes

    "Hold me legs while I get me tape measure out"

  18. Anonymous Coward
    Thumb Down


    "Half a Sun is approximately 1.9891 x 10^15 kg"

    1 solar mass = 1.98892 × 10^30 kg.


    0.5 solar mass = 9.9446 × 10^29 kg.

  19. Anonymous Coward

    "Half a sun..."

    "(Half a Sun is approximately 1.9891 x 10^15 kg, or about 49.9 per cent of the total mass of our solar system.)"

    In other words, half the sun is about half the total mass of the solar system, meaning that the sun is basically the entire mass of the solar system, and therefore that any people (or planets) you may meet from time to time are merely the products of a deranged imagination.

  20. John Freas

    Has everyone missed the most important point about the Schwartzchild question?

    It's spelled "Isle of Wight."

  21. Anymouse


    How big a Blaque whole wood the I'll of White make? And what's it got to do with how big Stormin Norman's kids radios are?

  22. Peter Mellor

    Sizes of black holes, plus confidence bounds

    The size of the black hole under discussion seems to be about 1 Stevenage plus or minus a Hitchin. For the 2- and 3-standard deviation limits, include Letchworth and Baldock, too.

  23. JCL
    Thumb Up


    Thanks for that, it's appreciated.

  24. Ian R

    Volume of a black hole

    Ah, but we are talking volume here, so we should have a Much Hadham at the top and bottom, then working toward the centre, a Baldock, then Letchworth, then Hitchin, with a Stevenage as the middle slice. Posssible with an associated Knebworth orbiting at near light show speeds ;-).

  25. Slaine

    Half a sun

    <pedant1> a pin prick still has "volume" albeit small without which there would be no hole through which to see blood oozing when the cusomary finger has been pranged with it. The key is density.

    <pedant2> whilst Sol may not have sufficient mass to implode, that does not guarantee our safety from being swallowed up in the "area of influence" of a transitory event. I like to consider this as the "unknown next event horizon", or "poling day".

    <observation> A more dense substance has been found between Gordon Brown's ears, the effects of which are well in exess of the physical boundaries of the United Kingdom.

    <explanation> "Swarzschild radius in layman English" is the distance from the perceived visible edge of a black hole (where it starts to be black) to the actual centre (a place so dark and foreboding only tax returns go). There is an equation that links mass, gravity and the speed of light but since the speed of light is not a constant it is only and estimation.

    <explanation> At very low temperatures (-273.14 or something) the speed of a laser light was resently measured at 37 mph (a fairly brisk bicycle). It takes a special breed of lunatic to go... "mmm all the laws of physics have broken down have they, lets shoot it with a laser", but then, physists are a very special breed. If you have any doubts, check out a certain donut in Switzerland.

  26. Terence McCarthy

    "Half a sun..." By Anonymous Coward

    "(Half a Sun is approximately 1.9891 x 10^15 kg, or about 49.9 per cent of the total mass of our solar system.)"

    Our solar system is approximately 2 x 10^30 kg, so the Sun is approximately half of that.

    To transpose the previous argument, I weigh 12 stone, my daughter 8. On the argument presented I weigh 4 stone?

  27. Andre
    Black Helicopters

    Alien physics experiment gone wrong?!

    Hmm. I wonder, is it possible that a few MYA that "black hole" used to be a planetary system? Perhaps one with an intelligent civilization experimenting with high energy physics on a grand scale.

    You see where this is going. "I wonder what happens if we push the energy past 250TeV on the Equatorial Large Muon Collider"... BOOOOM!

    Sure they discovered a limitless power source, but weren't around to harness it. Pwned.

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