All Creatures Great and Small

The previous post was a farewell to black holes in the class, not here on the blog. (And it was not quite a farewell there either, since the midterm yesterday was all about the properties of the Reissner-Nordström black hole, representing a black hole with an electric charge, and a nice computation involving cosmic censorship.)

There have been two rather notable discoveries in the black hole astrophysics world this week. The first is the discovery of what seems to be another case of an intermediate mass black hole (there was only one example known before). Not the supermassive ones that live at the centers of galaxies (tens to hundreds of millions of times the mass of our sun), and not stellar mass ones of a few times the mass of our sun. Instead in a nearby Globular Cluster (quotes from Hubble news site):

Astronomers have found evidence for a medium-
size black hole at the core of Omega Centauri, one of the largest and most massive globular star clusters orbiting our Milky Way Galaxy.

The intermediate-mass black hole is estimated to be roughly 40,000 times the mass of the Sun. The black hole was discovered with NASA’s Hubble Space Telescope and Gemini Observatory on Cerro Pachon in Chile. The ancient cluster is located 17,000 light-years from Earth.


“This result shows that there is a continuous range of masses for black holes, from supermassive, to intermediate, to small, stellar types,” explained astronomer Eva Noyola of the Max-Planck Institute for Extraterrestrial Physics in Garching, Germany, and leader of the team that made the discovery. “This finding also is important because the theory of formation for supermassive black holes requires seed black holes that are exactly in the mass range of the one we found. Such seeds have not been identified so far. If these types of intermediate-mass black holes happen to be common in star clusters, then they can provide numerous seeds for the formation of the supermassive black holes.”

Astronomers have debated the existence of moderately sized black holes because they have not found strong evidence for them, and there is no widely accepted mechanism for how they could form.

Please read the nicely written press release for more information about the evidence that they used to conclude the above.

The second piece of news* is about the smallest black hole found so far! From an article by Andrea Thompson in

The low-mass black hole sits in a binary system in our galaxy known as XTE J1650-500 in the southern hemisphere constellation Ara. NASA’s Rossi X-ray Timing Explorer (RXTE) satellite discovered the system in 2001, and astronomers soon realized that the system harbored a relatively lightweight black hole. But the black hole’s mass had never been precisely measured.

And what are its vital statistics?

The new lightweight record-holder weighs in at about 3.8 times the mass of our sun and is only 15 miles (24 kilometers) in diameter.

“This black hole is really pushing the limits,” said study team leader Nikolai Shaposhnikov of NASA’s Goddard Space Flight Center in Greenbelt, Md. “For many years astronomers have wanted to know the smallest possible size of a black hole, and this little guy is a big step toward answering that question.”

More on that here.


*Thanks Adam!

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10 Responses to All Creatures Great and Small

  1. Elliot says:

    Since black holes evaporate, doesn’t the definition of “smallest” black hole need some clarification? I guess I am wondering if that means the smallest black hole after formation based on some minimum stellar mass vs. for example forming a neutron star. Forgive me if I am nit-picking but I was/am operating under the impression that black holes can conceivably be as small as possible during their evaporation.



  2. Clifford says:


    I think that the phrase used was “smallest found so far” or something to that effect. That is not the same as “smallest possible”. The issue, as you correctly surmise, is what is the smallest possible size at formation. Note also that for black holes of this size (astrophysics scales), the rate of evaporation due to Hawking radiation would be ridiculously slow so as not to change the size much anyway. Furthermore, the radiation temperature is so cold that it is overcome by even the temperature of the CMB, and so the holes won’t evaporate anyway.

    So to find arbitrarily small holes would need new mechanisms for black hole formation that we do not know about yet (perhaps primordial holes…oh, not counting surprises in particle collisions such as in cosmic rays or the LHC..ahem.)


  3. Ed says:

    If a star can have a mass of 70 times our sun and still not be a black hole, but some black holes supposedly have a mass only 3+ times our sun,then clearly mass alone is not what creates a black hole. (Hawking radiation has been shown to be insufficient to shrink black holes to this degree) Then what are the conditions necessary for the creation of a black hole?

  4. Clifford says:

    “clearly mass alone is not what creates a black hole”

    Of course not. It is a lot of mass compressed into a small enough space. (“small enough” = inside its Schwarzschild radius). Please see the earlier posts I’ve done on this… such as this one. A star is not a black hole since the internal pressure of its thermonuclear fusion keeps the mass from collapsing…. and so forth… I recommend Kip Thorne’s book (“Black Holes and Time Warps”) on all of this.



  5. Ed says:

    OK and speaking of that, where does all the extra energy come from in a fusion reaction? Is the process in a star the same exact process with the same (tritium and deuterium) elements as in a hydrogen bomb?

  6. Ed says:

    I guess the following from wikipedia is an example of why I thought a black hole was a collapsed star:
    “Stellar-mass black holes have masses ranging from about 1.5-3.0 solar masses (the Tolman-Oppenheimer-Volkoff limit) to 15 solar masses. These black holes are created by the collapse of individual stars. Stars above about 20 solar masses may collapse to form black holes; the cores of lighter stars form neutron stars or white dwarf stars. In all cases some of the star’s material is lost (blown away during the red giant stage for stars that turn into white dwarfs, or lost in a supernova explosion for stars that turn into neutron stars or black holes).”

  7. Clifford says:

    Hi Ed,

    Yes, collapsed stars can form black holes, if they start out massive enough. This is the most common way to make them. The stars run out of fuel eventually and the thermonuclear pressure that stopped them from collapsing goes away. (And yes, it is the same fusion we use here on earth.) There’s a lot more to the story – I really recommend reading some of the sources I mentioned.



  8. Plato says:

    Clifford:The previous post was a farewell to black holes in the class, not here on the blog.

    I wasn’t sure if there was some conclusiveness to this or not so, I am glad to hear you are still open to talking about it.

    At Backreaction there is some food for thought there.

    As we get “new information” what we know changes some of the context of the large and small.

    See:Bringing the heavens down to Earth

    Fig. 2. Image showing how an 8 TeV black hole might look in the ATLAS detector (with the caveat that there are still uncertainties in the theoretical calculations).

    While I see you have directed the attention back to astrophysics, I could not see the theoretical dismissed so easily? Has it been?

  9. Clifford says:

    Once again you have confused me. I don’t see a contradiction between the words “astrophysics” and “theoretical”. There’s theoretical work, and there is experimental/observational work. The two/three go together in all fields of investigation.

    This post was about two astrophysics discoveries.


  10. Plato says:

    I am not sure what goes on in the Professor’s mind?:)

    There’s a “Farewell to Blackholes,” and then, “All creatures great and small.”

    IN the one sense, the farewell might have been for your college students, while you are reassuring them that they is still more to consider from a cosmological perspective?

    I felt that when you said “great and small,” my mistake here again, was to think that the influence of some court battle would want you to remind people that the very astrophysics’s aspect of how we see the microscopic(blackholes), is still very much a part of what seems “nonsensical to you” with regards to “Law versus Law,” is still part of the cosmological aspect of seeing the perspective of the cosmos pushed back to those microseconds.

    Hence this article and perspective of blackholes.

    Clifford:I don’t see a contradiction between the words “astrophysics” and “theoretical”. There’s theoretical work, and there is experimental/observational work. The two/three go together in all fields of investigation.

    All is not lost then, when you consider the context of your response in terms of the definitions you offer. I see Bee has gone with it too?

    My apologies again.:)