A tiny galaxy that hides a big secret

By Phil Plait | January 11, 2011 11:30 am

Astronomers have just announced something that took me by surprise: the dwarf irregular galaxy named Henize 2-10 has a fairly beefy supermassive black hole in it! Here’s a picture of the galaxy:

[Click to unendwarfenate.]

The image is a composite of images from Hubble (red, green, and blue), radio images from the Very Large Array in New Mexico (yellow), and X-rays from the Chandra Observatory (purple). The cross marks the location of the black hole.

Henize 2-10 is pretty dinky, only about 3000 light years across — the Milky Way is 100,000 for comparison. It’s about 30 million light years away, which is kinda sorta close by, at least close enough to get a decent look at it. Now, we know that big galaxies like ours have these monster black holes in their very centers; the Milky Way’s is about 4 million times the mass of the Sun. Many galaxies have much larger ones, like Andromeda which harbors one 35 times as massive as ours.

Some smaller galaxies have supermassive black holes as well, but in general these dwarf galaxies have some structure to them, with a well-defined core. Henize 2-10, as you can see, it a mess! It doesn’t have much overall structure, which is why it’s classified as an irregular galaxy. The thinking for big galaxies is that the black hole forms at the same time as the galaxy itself, and to regulate the growth of each other. When you look at lots of big galaxies, there’s a pretty clear overall correlation between the mass of the black hole and the galaxy around it.

So it’s pretty weird that Henize 2-10 has a supermassive black hole at all, but it turns out the hole is also about a million times the mass of the Sun — that’s pretty freakin’ big for such a tiny galaxy! That’s 1/4 the mass of our own black hole, in a galaxy that itself is far smaller than ours.

As I wrote earlier today, black holes can focus and expel tremendous beams of matter and energy which blast away from the hole. In this case, these beams have slammed into material hundreds of light years away, well outside the core of Henize 2-10, lighting this gas up at different wavelengths. You can see that as the yellow (radio) blobs to the left and right of the black hole’s location in the big picture at the top, or as the pink areas in this smaller inset image of the galaxy (which just shows the Hubble image only). The bright region around the black hole is also bright in X-rays, a dead giveaway that the black hole is actively feeding.

So why does this goofy galaxy have a dragon at its heart? The Milky Way as two companion galaxies, called the Magellanic Clouds, which are roughly the same size as Henize 2-10, but neither hosts a black hole like this one. What makes Henize special?

That’s a good question, and one for which we don’t have a good answer yet. But finding special cases like this help astronomers constrain their ideas; any models they have for black hole formation and growth now have to account for this tiny, amorphous galaxy that doesn’t seem to care that it’s breaking the mold.

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CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (20)

  1. Oli

    Would life be possible in that galaxy? I can imagine that radiation from the black hole would sterilize many planets orbiting nearby stars, but are there regions far away to be safe?

  2. [irrational tard]See, here is something else that science didn’t know. Man, you can’t trust those dang scientists to keep the universe all static and stuff… [/irrational tard]


    That is a very interesting little fellow there. I wonder what other surprises it may hold.

  3. Dave Kraus

    Is it possible this galaxy used to be much larger and the black hole has just swallowed most of it up? What would happen if one of our Magellanic Clouds DID have a super-massive black hole sucking all of its matter in? How long would it take to completely consume the local star cloud?

  4. DrFlimmer

    Somehow I have to think of MUSE right now. I wonder why this could be…

    @ Dave Kraus

    As a matter of fact, the radius of influence of a supermassive black hole (SMBH) is fairly low, at least, if we talk about the gravitational influence. At our position, we do not feel anything of the gravity of the SMBH at the center of the Milky Way, just for instance.

    A second point: Actually it is quite hard to suck something in at all. This may seem odd at first, but since everything (stars, gas, etc) is in motion it also contains angular momentum. And this must be carried away before something can be sucked into a black hole. So, a SMBH at any galactic center is not able to eat an entire galaxy; no need to panic.

  5. JMW

    I’d guess it’s more likely Henize 2-10 was much larger, but that there was a near miss in the semi-distant past, with a much larger neighbour galaxy, which cannabalized most of the outer parts of our little friend.

    By the way, isn’t it ironic that a small galaxy has “2-10” as part of it’s name. It’s just a little guy…

  6. Steve_cosmo

    What JMW said. I’m starting a project on SMBHs in ultra compact dwarf galaxies to see if the mass ratios of the SMBH and galaxy are out of whack indicating some kind of possible tidal “threshing” of the galaxy’s outer envelope. most UCDs and compact ellipticals have been spotted orbiting larger neighbors. If the mass of the SMBH is higher than expected that indicates it has probably lost some mass. Irregulars are weird though, I deal with ellipticals that have analytic suffice brightness profiles. UCDs are denser than globular clusters so I don’t see how one could be disrupted into an irregular. That line of thinking is just my scifi desire for some kind of crazy galaxy ripping monster to be out there. :-)

  7. Jawad

    I would love to travel into that galaxy

  8. qbsmd

    “I‚Äôd guess it‚Äôs more likely Henize 2-10 was much larger, but that there was a near miss in the semi-distant past, with a much larger neighbour galaxy, which cannabalized most of the outer parts of our little friend.”

    That’s what I was thinking. Does anyone have the data to plot the positions of galaxies back in time and find out if there was such a collision and if so, what galaxy it collided with?

  9. Messier Tidy Upper

    Fascinating news & galaxy thanks BA. :-)

    Henize 2-10 does remind me quite a lot of the Large magellanic Cloud.

    Is it too a satellite of some other larger galaxy?

    What would happen if the Tarantula Nebula (aka 30 Doradus & NGC 2070) at the core of the LMC collapsed into a single Black Hole or the central star cluster R136 was to do so – would that combined have around that much mass perhaps?

    What might have happened in its past to create this disparity – could Henize 2-10 have passed through a larger galaxy and captured a supermassive black hole in the process?

    Could Henize 2-10 have captured an ejected supermassive black hole wandering in intergalactic space?

    Could any of those ideas possibly explain this intriguing situation I wonder? :-)

  10. Messier Tidy Upper

    See :


    for more on the Tarantula Nebula & also see :


    For the star cluster near its heart & see :


    For the wiki-basics overview on the Large Magellanic Cloud. :-)


    “[The Tarantula Nebula’s] luminosity is so great that if it were as close to Earth as the Orion Nebula, the Tarantula Nebula would cast shadows. In fact, it is the most active starburst region known in the Local Group of galaxies.”

    – Wikipedia : 30 Doradus page linked above.

  11. Messier Tidy Upper

    could Henize 2-10 have passed through a larger galaxy ..

    In a way like the smaller galaxy that passed through Cartwheel galaxy did :





    Any sign of a nearby disturbed or interacting galxy here?

  12. Brasidas

    Hah! Old news to us Brits, this was highlighted last week in one of a series of really good 3 1-hour live prime-time astronomy programs hosted by Brian Cox and Dara O’Briain! Thanks goodness for the BBC.

    I think they mentioned that there is a “mysterious” bright (and brightening) spot that they as yet can’t explain. All round a pretty cool object i have to agree.

  13. Messier Tidy Upper

    @4. DrFlimmer : Somehow I have to think of MUSE right now. I wonder why this could be…

    Er .. Sorry, I don’t get that ref. Could you please explain further?

  14. Mark

    Maybe a collision of two galaxies where their black holes also collided and merged? Maybe as a result of the collision much of the other material either got devoured by the black hole or was flung away?

  15. Unspeakably Violent Jack

    @ 14 Messy

    The reference is to the song “Supermassive Black Hole” – by Muse.

    It’s really good, if you like that sort of thing.

    (I like that sort of thing)

  16. Joseph G

    @#4 Doc Flimmer: “Black Holes and Revelations”?
    They do make a good soundtrack for astrophoto viewing…
    @16: Which I believe is from the aforementioned album.
    I used to really like Muse, but their whole conspiracy theory thing rubbed me the wrong way…

  17. Anchor

    Evidently this is one guy that doesn’t follow the SMB mass-central bulge correlation. It would be interesting to find out how much dark matter is associated with this irregular dwarf. Perhaps the anomalous heft of this SMB may be explained as a relic of an SMB that had reached a modest mass long ago in a typical early galactic setting, then interacted with another system with an SMB, but for one reason or another, instead of merging with the other SMB, as most such encounters end up, it got tidally tossed out of the core (possibly because of a near-simulataneous interaction with a third SMB player) and then scooted away from the scene just picking up remnant gas and stars on the way out, which have since been forming stars to produce this dusty irregular dwarf. That could explain why it appears to be deficient in an appropriately-sized galactic bulge: it left its original bulge stars behind at the scene of the accident. For this to work the SMB might have had to hitch a ride in a fairly dense clump of dark matter which might have contributed to the ejection if it had itself interacted with other dense clumos of dark matter in the skirmish. Such clumps or clouds of dark matter are indicated in some simulations and there is observational evidence for clumpy dark matter distribution in some galaxy clusters. The main puzzle is how this SMB came to be missing its appropriately-sized bulge. Its harder to think that an elliptical dwarf (which is like a bulge without the accoutrements of gas-laden disk and spiral arms) comes to be laden with lots of gas to induce enough star-formation to produce that much dust PLUS getting so disrupted it doesn’t resemble a bulge anymore…not without having tangled with other galaxies which usually tends to end in merger. If only there was a way to determine its real velocity at its location, to see how much it departs from the general expansion. If it was moving faster than other galaxies in its vicinity, it could be circumstantial evidence for it being a runaway. Alas, real motion is hard to pin down; all we can bet on is radial velocity, but true distance is hard unless there is a decent set of standard candles in this system. Whatever happened, there aren’t very many like it, or we’d already have seen more examples. Its history must have quite different from the typical to survive to the present epoch.

  18. @16. Unspeakably Violent Jack : Okay, thanks, now I get it.

    Click my name for the song in question on Youtube. :-)


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