Astronomers Discover Medium-Sized Class of Black Holes

Article written: 1 Jul , 2009
Updated: 24 Dec , 2015


It’s the Goldilocks variety of black holes: not too big and not too small.

The new source HLX-1,  the light blue object to the top left of the galactic bulge, is the ambassador for a new class of black holes, more than 500 times the mass of the Sun. It lies on the periphery of the edge-on spiral galaxy ESO 243-49, about 290 million light years from Earth.

The discovery, led by Sean Farrell at Britain’s University of Leicester, appears today in the journal Nature.

Until now, identified black holes have been either super-massive (several million to several billion times the mass of the Sun) in the center of galaxies, or about the size of a typical star (between three and 20 solar masses).

The new discovery is the first solid evidence of a new class of medium-sized black holes and was made using the European Space Agency’s XMM-Newton X-ray space telescope. At the time of the discovery, Farrell and his team were working at the Centre d’Etude Spatiale des Rayonnements in France.

black hole is a remnant of a collapsed star with such a powerful gravitational field that it absorbs all the light that passes near it and reflects nothing.

“While it is widely accepted that stellar mass black holes are created during the death throes of massive stars, it is still unknown how super-massive black holes are formed,” Farrell said.

It had been long believed by astrophysicists that there might be a third, intermediate class of black holes, with masses between a hundred and several hundred thousand times that of the Sun. However, such black holes had not been reliably detected until now.

One theory suggests that super-massive black holes may be formed by the merger of a number of intermediate mass black holes, Farrell said.

“To ratify such a theory, however, you must first prove the existence of intermediate black holes. This is the best detection to date of such long sought after intermediate mass black holes. ”

Using XMM-Newton observations carried out in 2004 and 2008, the team showed that HLX-1 displayed a variation in its X-ray signature. This indicated that it must be a single object and not a group of many fainter sources. The huge radiance observed can only be explained if HLX-1 contains a black hole more than 500 times the mass of the Sun. The authors say that no other physical explanation can account for the data.

Lead image caption: Artist’s impression of HLX-1 in the periphery of the edge-on spiral galaxy ESO 243-49. Credit: Heidi Sagerud.

Sources: Nature and the University of Leicester

11 Responses

  1. CinIN says

    Beautiful image, but I’m puzzled by the difference in the diffraction spikes around HLX-1 and the other bright object to its right. Shouldn’t the diffraction patterns look more similar (allowing for differences in brightness.) Could the image of the black hole been altered for emphasis?

  2. Member
    IVAN3MAN says

    @ CinIN,

    I think that the difference in the diffraction spikes is probably due to the above image being a composite of two image sources — one from an optical telescope (e.g., Hubble) and the other from the XMM-Newton X-ray space telescope.

  3. mikester says

    What is this BH doing there relative to the beautiful edge-on galaxy? Is it the center core of a satellite subgalaxy or part of straggling cluster?

  4. Lawrence B. Crowell says

    The 500M_{sol} BH is in orbit around the galaxy. Eventually it will coalesce with the much large BH in the galaxy.

  5. opencluster says

    What is accreting onto the bh to make it shine if it is not in the galaxy? A naked bh would be invisible, except perhaps for gravitational lensing.

  6. Dave Finton says

    Lawrence: I can hear the supermassive BH right now, “GET IN MAH BELLY!”

  7. nimo says

    this photo is said to be an “artist-impression” @
    “//This is an artist’s impression of the new source HLX-1 (represented by the light blue object to the top left of the galactic bulge) in the periphery of the edge-on spiral galaxy ESO 243-49. This is the first strong evidence for the existence of intermediate mass black holes. Credit: Heidi Sagerud..”

  8. Lawrence B. Crowell says

    The blue object is some sort of accretion process. I have found some XMM paper by the author Farrell et al,

    but have not found this one referenced above. I am not clear about the source of energy released by the BH. It is most likely the evidence for the BH rests with the X-ray flux.

    The image is indeed an artistic representation. It is meant to illustrate the energetic object with respect to the galaxy.

  9. Jon Hanford says

    mikester brings up a good point as to the immediate enviroment of this purported IMBH. IMBHs have been proposed (and in a few cases, claimed to have been found) in either globular clusters, dwarf galaxies or ultraluminous x-ray sources( ULXs). A ‘naked’ IMBH, perhaps ejected by a close gravitational encounter with another massive object in the galaxy also seems plausible. I would be interested in reading the original paper to see the authors discussion of this issue. @nimo, thanks for finding that info regarding the illustration. The picture just looked too ‘good’, even if it was a multiwavelength composite (check out the DSS images. Also note several peculiar or distorted galaxies nearby on the DSS images – possible past interactions with this galaxy?) 🙂

  10. Jon Hanford says

    From the story posted at the PhysOrg site, it would appear that the researchers classify this object as an ULX. from the article: “This new source, dubbed HLX-1 (Hyper-Luminous X-ray source 1), lies towards the edge of the galaxy ESO 243-49. It is ultra-luminous in X-rays, with a maximum X-ray brightness of approximately 260 million times that of the Sun.

    The X-ray signature of HLX-1 and the lack of a counterpart in optical images confirm that it is neither a foreground star nor a background galaxy, and its position indicates that it is not the central engine of the host galaxy. ” Concerning the XMM x-ray observations, the PhysOrg piece states: “Using XMM-Newton observations carried out on the 23rd November 2004 and the 28th November 2008, the team showed that HLX-1 displayed a variation in its X-ray signature. This indicated that it must be a single object and not a group of many fainter sources. “

  11. Jon Hanford says

    A recent paper on a proposed 1000 solar mass BH at the heart of the Sagittarius Dwarf Galaxy can be found here: . Other candidates have also been proposed.

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