Desktop Project Part 16: A dinky galaxy with a big gas problem

By Phil Plait | April 10, 2012 6:36 am

[This is another in a series of posts I’m doing to help me clear off the zillions of cool astronomy pictures I have sitting on my computer desktop. I’ve been posting one of these every day and will continue until my desktop is cleared!]

One important aspect of science is its ability to question its own tenets. Some people think that’s a weakness, but it’s a strength! A stiff tree breaks in the wind, but a flexible one survives.

There are, of course, a lot of basic things we do know pretty well. Evolution is real, the Universe is expanding and billions of years old, and so on. As we observe nature more, we learn more, and we can add to these ideas, fill in the details. Sometimes, of course, we learn something that means our models may be wrong, or need to be modified. Again, this is a strength of science: it improves our understanding. We don’t want to think something wrong is true! We need to be flexible.

Which brings us to the weird little galaxy I Zwicky 18, which is so odd-looking I thought at first this Hubble image of it was a drawing!

But no, this is real! [Click to galactinate.]

It’s an amazing shot: it’s the sum of nearly 200 separate Hubble observations of the galaxy, giving a total exposure time of 243,000 seconds: nearly three solid days!

Wow. When I worked on Hubble, many of the images I analyzed had exposure time of only a few minutes. So yeah. This is a deep image.

And it revealed something rather surprising: the gas in the galaxy extended out much farther than expected — 16 times farther out from the center than the stars! Not only that, but all that gas adds up; the gas emits at least 1/3 of the total light seen from the galaxy, and could account for as much as half the light emitted. Recent observations also indicate it’s 20% farther away than previous estimates. That means it’s even more luminous — that is, emitting more energy — than previously thought.

Well, OK, that’s cool. But what’s the big deal?

The thing is, these dwarf galaxies were common in the early Universe, and they’re so far away they’re difficult to study in detail. We rely on observations of nearby dwarf galaxies to bootstrap the observations of the more distant ones. What we learn about objects like I Zwicky 18 affects how we study the early Universe!

Long ago, when the Universe was young, these dwarf galaxies collided and merged, forming bigger galaxies like ours. They’re a stepping stone in galaxy formation. How much gas they have relative to stars is important to understanding how galaxies form, and the distribution of that gas plays a role as well. The amount of light they emit is also important, since that tells us a lot about what kind of stars and gas they’re composed of. Because of this new information about I Zwicky 18, models of galaxy formation need to be looked over again. They may very well need to be updated to include this new data.

Let me be clear: this does not mean we have to trash everything we know about how galaxies form and how they collide! This is more of a fluctuation on how we figure things out, a correction to be assimilated into the physics. These results are no doubt of great interest of people who study how galaxies form and evolve, as it will allow them to make their models represent observations even better, and get ever-closer to understanding just how we got to where are today: living in one of the Universe’s bigger galaxies, looking out into a cosmos that’s filled with them.

Image credit: NASA, ESA

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: gas, Hubble, I Zwicky 18, stars

Comments (16)

  1. You know, it’s sad that you have to remind readers that just because one element of a much larger theory is in need of modification, it does not invalidate the entire theory… However, since that is a favorite tactic of anti-reality nutters, I suppose it’s required still.

    That said, that is a very cool image. And I love the name! Any background on Zwicky (I’m assuming this one is for Fritz)? Although the name sounds like a character on The Big Bang Theory. ;)

  2. Wzrd1

    Of REAL interest is, it’s only 59 million light years away, which dates what we’re viewing far from the early universe, hence it’s puzzling why star formation was delayed for so long.
    Perhaps other galaxies prevented the usual massive star formation in that galaxy’s early life? A dark matter cloud interfered with star formation? Central singularity accretion disk radiated too much radiation to permit the usual star formation?

  3. Chris

    I’m assuming that I Zwicky 18 is the big thing in the center, but what about that mass at the upper right corner? That looks pretty odd as well.

  4. Peter Davey

    Evolution may be real, but how do we prove that the Universe is?

  5. bungaloebill

    Looks like… never mind, I’m sure it’s just me.

  6. Jon Hanford

    @3 Chris:

    “I’m assuming that I Zwicky 18 is the big thing in the center, but what about that mass at the upper right corner?”

    According to the paper Phil has linked in his article, the detached portion of stars and star clusters at upper right of the main galaxy is known as I Zw 18C (see Figs 1 & 4). While this region is embedded in the same cloud of hydrogen as I Zw 18 and contains a population of very young stars (<~100 Myr old), star formation is proceeding slowly in I Zw 18C and most of its' star-forming gas has escaped. I Zw 18C lies at a projected distance of 2 kpc from I Zw 18.

  7. gopher65

    I was looking at some of the background galaxies and noticed that a few one them (one in particular, just south of the righthand upper corner) are on the red side. Is that an artifact of colourizing the image, or is that down to the objects in question being far enough away that they are strongly redshifted?

  8. Larry

    I don’t mean to doubt you, Phil, but that looks like the chunk of space that Death leads the dead people to in The Meaning of Life. Hence it was probably drawn by Terry Gilliam.

  9. Digitalaxis

    If memory serves, I Zwicky 18 was one of the prototypical “Dark” galaxies, which is to say a galaxy that had not started star formation AT ALL until very recently (and hence a very interesting remnant of the early universe). I believe 10 billion year old stars have since been found in it (and other such galaxies), but still… for some reason, there was a meager burst of star formation and then basically NOTHING for the next 9.75 billion years. Why? No idea.

  10. Its pretty easy actually. The Doctor realized that the late universe would have little gas with which to build stars and power civilizations. So he started dragging entire dark galaxies forward in time as stores for later times.

  11. LAG

    “One important aspect of science is its ability to question its own tenets. Some people think that’s a weakness, but it’s a strength!” True, so why doesn’t that ever seem to work with AGW?

    And,

    “We don’t want to think something wrong is true! We need to be flexible.” How about adding that ‘we don’t want to think something true is wrong’? Like with AGW.

  12. Sam H

    @11 LAG:

    ……my friends….go get him ;)

  13. Nigel Depledge

    Peter Davey (4) said:

    Evolution may be real, but how do we prove that the Universe is?

    In absolute terms, you can’t. But then, nothing empirical can ever be absolutely proven.

    Of course, it all comes down to how you define “real”.

  14. Nigel Depledge

    LAG (11) said:

    “One important aspect of science is its ability to question its own tenets. Some people think that’s a weakness, but it’s a strength!” True, so why doesn’t that ever seem to work with AGW?

    The answer is it has already happened with AGW. Throughout the 1970s and 1980s, first the reality of GW, and then humanity’s role in it, was questioned intensely and critically. The data spoke. The genuine scientific criticisms were answered.

    As far as anyone can tell (anyone who takes an unbiased look at the actual evidence, anyhow), AGW is as real as you or I.

    The only remaining criticisms of the reality of AGW are fabrications with little or no real scientific merit.

    And,

    “We don’t want to think something wrong is true! We need to be flexible.” How about adding that ‘we don’t want to think something true is wrong’? Like with AGW.

    Erm, because that would be meaningless.

    People who have studied the Earth’s climate for decades have been convinced by the evidence that AGW is a real phenomenon. I’m sure that they would love for it to be an illusion as much as I would, but these guys are honest scientists doing their level best to understand one of the Earth’s most complicated natural systems. And their best understanding is that AGW is real.

    Of course, if you believe in the “climate conspiracy”, then no amount of evidence is likely to persuade you otherwise.

    I would, however, ask you to explain how, if AGW is a conspiracy, it got started.

    Who started it? When? How did they recruit additional converts? How come no-one blew the whistle when approached?

    In short, unless someone can come up with a credible scenario whereby a global conspiracy among climate scientists could have been concocted, then the postulated conspiracy idea is dead before it starts. Even so, I won’t accept the notion of a global conspiracy until some hard evidence is forthcoming.

    If you believe instead that the world’s climate scientists are deluded, what is the basis for this belief? IOW, what makes you think that the world’s best-qualified climate scientists have adopted a wrong conclusion where some random commentator can see flaws that the experts cannot?

  15. LAG

    Nigel (14), it has nothing to do with ‘belief, ‘ at least as I understand the scientific method. Religion is based on ‘belief’ and revisits aren’t welcome. Rather they are condemned as heretical. Which I guess is your point when you say, “The answer is it has already happened with AGW.” I presume by that that revisits, reassessments, new data, etc, are not allowed. On the other hand, you might want to say in some way what it would take to convince you otherwise,

  16. LAG

    Nigel (14), it has nothing to do with ‘belief, ‘ at least as I understand the scientific method. Religion is based on ‘belief’ and revisits aren’t welcome. Rather they are condemned as heretical. Which I guess is your point when you say, “The answer is it has already happened with AGW.” I presume by that that revisits, reassessments, new data, etc, are not allowed. On the other hand, you might want to say in some way what it would take to convince you otherwise.

    If the answer is, ‘nothing,’ then you’re proselytizing and not engaging in reasoned discourse.

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