Hubble peers in on a galactic snack

By Phil Plait | September 19, 2012 7:00 am

Galaxies come in a lot of shapes and sizes: huge ellipticals, big spirals, weird squishy irregulars. There is a sub-class called "dwarf galaxies" which are smaller than usual. We actually think they dominate the Universe by number, but because they have fewer stars – a few billion or so tops, compared to the hundreds of billions of a big one like our Milky Way – they fade rapidly with distance. Only a handful are close enough to study well.

One of these is DDO 190, a nice little dude something like 9 million light years away. That’s close enough to resolve individual stars in the galaxy, as you can see in this really pretty Hubble image of it:

[Click to galactinate, or grab the cosmic 3700 x 2600 pixel version.]

DDO 190 is small, but not tiny: about 15,000 light years across. That’s about 1/6th the size of our galaxy. It’s also well outside our Local group of nearby galaxies (the Andromeda galaxy is less than 3 million light years distant from us, for comparison) and is thought to be part of the M94 galaxy group. But if true it’s fairly isolated even from the others on its team; the nearest neighbor appears to be another dwarf galaxy several million light years away from it.

This image is pretty nifty. For one thing, you can see lots of far more distant background galaxies, some right through DDO 190, which always gives me a kick. But the dwarf galaxy itself has some surprises. The bluish fuzzy regions are clouds of gas lit by young, hot stars. These stars don’t live long (a few million years or so), meaning there’s still some star birth going on in the little guy. That blue patch at the bottom is the brightest of them – it looks a bit like a more distant galaxy, but don’t be fooled.

Interestingly, it has two different populations of stars in it. The younger ones I mentioned (100 million years or younger) tend to be close in to the center, while older ones (4 billion years or more) are located in the outskirts. This is common in dwarf irregular galaxies. The older stars may be showing us what the primeval galaxy looked like, but now a burst of star birth has occurred near the center, making the galaxy look more condensed.

Since the vast majority of galaxies in the Universe are dwarfs like this, we think bigger ones like ours get to their size by gravitationally colliding with and absorbing dwarfs. In fact, we know the Milky Way is eating several right now!

Galaxies are cool, and pretty, and magnificent, but they’re also cannibals. DDO 190 is isolated enough that it may be safe from that fate for quite some time. But the Universe is young, and galaxies patient. In a trillion years or so, we’ll see who has whom over for dinner.


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CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (9)

  1. Pete Jackson

    Nifty pic! The color gradient from (younger) blue stars near the center to (older) red stars in the outskirts is obvious.

    Can this galaxy eventually evolve into a spiral galaxy?

  2. cosmicJC

    After observing pictures like this, it seems absurd to suggest life doesn’t exist elsewhere in our astoundingly large universe.

    Simply amazing.

  3. Zafod

    Great pic, I don’t see any gravitational lensing effects on the spirals. Is it that they are not far distant enough for the effect to be seen or isn’t the galaxy massive enough to produce the effect?

  4. There’s a second wave of star formation going on in a dwarf galaxy?

    This is incredibly good news! For the longest time, the only types of galaxies with multiple generations of stars in them — that I knew about, at least — were the spiral galaxies like our own.

    The gas and dust clouds that form second- and third-generation stars tend to have enough heavy-element enrichment (from the death throes of the biggest and earliest-dying first generation stars) to allow for the formation of large, rocky planets. And large, rocky planets mean potential EARTHLIKE planets.

    More kinds of galaxies with potential Earthlike planets means we might have greater odds of meeting green-skinned alien space babes!

  5. Infinite123Lifer

    “In a trillion years or so, we’ll see who has whom over for dinner.”

    I do wonder who will be hosting the cannibalization . . . Can someone turn on Deep Thought?

    —–
    How the Universe Works is awesome, not as awesome as your hat Phil but still an awesome episode nevertheless.

    I feel wonder every time I think about space and whats out there. E-V-E-R-Y single time! The show left me in grand, a glorious state of mind. I needed a break and so I found the show and just sat back and zoned out . . . but because of the show it was more of a zoning in zoning out ITMS. Just left me feeling good and thinking about Kepler and our history and all the other Earths and well you know . . . your basic amazement.

    BTW Phil you bet your house in that episode but don’t ever bet the hat ;)

  6. Messier Tidy Upper

    @1. Pete Jackson asked : “Can this galaxy eventually evolve into a spiral galaxy?”

    Well it can merge with one and become part of a spiral I think! ;-)

    But otherwise, I don’t think so . My understanding is that spiral galaxies form via large clouds of gas collapsing and spinning in a particular way and this mostly happened fairly early on cosmologically and requires a particular set of circumstances. Don’t think any spirals are still forming today and large scale galaxy mergers usually (always?) result in elliptical type galaxies being produced instead – although I could be mistaken here.

    Great image and write up. :-)

    PS. I was indeed briefly “fooled” or at least wondering about the fuzzy blue cluster of stars at the bottom there being a background galaxy in its own right! Cheers BA. :-)

  7. Other Paul

    … 9 million light years away. That’s close enough to resolve individual stars …

    Is anybody else kinda mindblown by this rather casually emitted statement? Stars aren’t that big, yet our instruments can resolve ‘em at that utterly ridiculous distance. Sometimes one forgets what clever little monkeys we are. And in case that sounds like hubris, we’re pretty unlikely to be the brightest bulb in the bunch …

  8. CB

    @ Other Paul
    Indeed! But what really blows my mind away is Edwin Hubble being able to resolve individual stars in Andromeda (3 million ly away) back in the 1920s. After recovering from that mind-blow, being able to resolve stars 3 times as far away seems pretty natural. Hubble didn’t have the Hubble, after all. :)

  9. Zyggy

    Cool Pic!

    I was wondering, though… The blue bit at the bottom has kind of a “butterfly” shape reminiscent of NGC 6302 (and others, I’m sure). I was kind of under the impression that these type of structures have one massive construct (black hole, etc) at the center and the butterfly shape is the result of various magnetic and gravitational forces acting on the surrounding gasses (like the polar emissions of some black holes).

    Do we know if there is a black hole or some other object at the center of that nebula?

    ~Zyg

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