Unwind with some spirals

By Phil Plait | October 27, 2010 6:00 am

A very important aspect of astronomy often overlooked is how much our eyes don’t tell us. We see a very limited range of the spectrum of light emitted by astronomical objects, and many times it’s what we don’t see that tells us what’s going on.

That’s why the European Southern Observatory has the HAWK-I camera: it sees in the infrared, in wavelengths invisible to our eyes. And when we train it on the skies, well, we see some pretty cool stuff. Like, say, gorgeous spiral galaxies:


[Click to galactinate.]

That’s NGC 1232, an open face-on spiral some 65 million light years away. This to me is a perfect spiral: the arms are distinct and easy to trace, starting near the center and going all the way around the galaxy. Several spurs — short, disconnected, straighter offshoots — can be seen. There’s also a bar: the center of the galaxy isn’t a sphere, it’s elongated in an oval.

All of these features are due to the weird gravitational field of a galaxy. In our solar system, the Sun dominates in the gravity department, and the planets orbit it. In a big galaxy, though, the gravity of every star adds up, making the force of gravity stronger farther from the center than if all the mass were concentrated there. This causes all sorts of odd manifestations like the bar, the spirals, and the spurs. I have a blog post discussing this in more detail, if you’d like to read that.

Incidentally, given the distance of NGC 1232 of 65 million light years, the photons you are seeing from this galaxy in this image left it when dinosaurs still roamed the Earth… but their time was juuuuussssst about up.

eso_hawk_ngc1300HAWK-I was used to study several galaxies, and not just NGC 1232– five more, in fact, for this particular study, but I want to point out one in particular: NGC 1300, a magnificent elongated spiral, shown here on the right. The bar in this one dominates, stretching over a much larger relative distance than the one in NGC 1232, which is dinky in comparison.

As I mentioned above, we can learn a lot when we compare light from objects in different wavelengths. Here is that same HAWK-I infrared image of NGC 1300, with a Hubble image in visible light below it. I rotated and scaled the top image to match Hubble’s:


Ignoring the difference in things like resolution (Hubble can see smaller objects) and such, there are still obvious differences. In the visible image, dust between stars is dark, because it blocks visible light. However, IR goes through it, so the dust disappears in the top image. The dust adds a lot of sculpting and contouring to the visible Hubble image, and that’s gone in the IR image, so the top one looks smoother. That’s no illusion! That’s real, and it’s telling us where the dust is.

As you’d expect, objects that look red in the Hubble image are also bright in the IR, but the blue stuff is much fainter and difficult to spot in the HAWK-I view. Blue is emitted by hot, young, massive stars, which is easy to spot in the visible. The yellow-red glow in the bottom image is from older, redder stars, and they are prominent in the top image. See how the very center of the galaxy is bright in the HAWK-I shot? That tells me that there are far more older stars there, right in the very center. Star formation must have shut down long ago right smack dab in the heart of NGC 1300, or else we’d still see blue stars there.

… or, alternatively, there are blue stars there, but the dust is so thick their light gets reddened, like the setting Sun looks red from haze in our air. There are ways of telling the difference, but I don’t think it can be done with images like this; we’d need spectra, which is a whole other story. Still, it once again shows that you need to look at objects in different ways if you want to figure out what’s happening with them.

Looking in the infrared tells us a lot more about what’s going on than visible alone. Combine that with ultraviolet, radio, X-ray, gamma-rays, and we get a much more complete picture of what the Universe is showing us. It’s more than a double rainbow; it’s the whole rainbow, and the best part is we really do know what it means.

Related posts:

Barred for life
HAWK-I peers into a stellar cocoon
Setting the bar
Sculpting a barred galaxy

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (28)

Links to this Post

  1. Astronews Daily Etx. Edition (2455498) | October 28, 2010
  1. Exactly the sort of thing one wants to see in the morning. Thank you!

  2. Being able to “see” things outside our normal range of senses is so amazing. I just finished Dawkins’ The God Delusion and absolutely loved the last bit “The Mother of All Burkas”. Dawkins compares our range of senses (and world view) to the slit in a burka. By enlarging that slit we see more and our world view changes.

    I also just watched a fantastic video which included the same idea about our senses. It’s The Poetry of Science with Dawkins and Neil deGrasse Tyson. http://www.youtube.com/watch?v=9RExQFZzHXQ
    Well worth the hour.

  3. Jack Mitcham

    Nice reference at the end.

  4. Is it just me, or do others find the visible-light image “prettier”?

  5. Oli

    Imagine what the Rainbow Guy would be like if he saw a double rainbow, from Gamma to Radio…

  6. Messier Tidy Upper

    Beautiful. :-)

    I love these spiral galaxy images.

    My faves from here have to include :


    & this one :


    of M66 one of my all-time fave jaw-dropping pictures.

    Plus this one :


    (NCG 4921 & a backdrop of plenty others!)

    and so many more. :-)

  7. He’d say it’s FULL ON. 😮

    Wonderful images!! It’s amazing how much we miss by only having little eyeses sensitive to visible (a relative term) light.

    Hm. The thing is, when we convert IR, UV, x-ray, etc. light to something we can see, it’s still only an interpretation. Makes one (um…me) ask the question: what color is infrared? 😛
    If a tree falls…..

  8. Chris A.

    I’d be curious to know if NGC 1232 is considered a Milky Way “twin.” It appears to match the descriptions of our home galaxy, but I wonder how it compares in size/mass.

  9. Gary Ansorge

    Superb imagery.

    Now, if we could just control the Destiny, we could stop off in one of these,,,

    Gary 7

  10. @ j major:

    Hm. The thing is, when we convert IR, UV, x-ray, etc. light to something we can see, it’s still only an interpretation. Makes one (um…me) ask the question: what color is infrared?

    I recall an old science fiction story, called something like “Beyond Violet”, about Martians who can see a much broader range of the spectrum than humans. One man makes a deal with them and they do a procedure that allows him to see as they do for one day. After the effect wears off and he is returned to the boring old ROYGBIV of human vision, he quickly goes insane.

    Moral: don’t be mucking about with 3.75 billion years of evolution!

  11. UKBob

    Anybody else experience a kind of post orgasmic chill when looking at pictures like these. And thinking about the Universe at large, so to speak…

    … or is it just me? … ahem… er…

  12. Messier Tidy Upper

    @9. Chris A. Says:

    I’d be curious to know if NGC 1232 is considered a Milky Way “twin.” It appears to match the descriptions of our home galaxy, but I wonder how it compares in size/mass.

    NCG 1232 has its wiki-page here :


    which notes it’s an intermediate spiral unlike our barred spiral galaxy and that a satellite galaxy, NGC 1232A, is thought to be the cause of unusual bending in it’s spiral arms.

    Our Milky Way Galxy’s wikipage is here :


    for comparison purposes.

    @12. kuhnigget :

    I think I’ve read the story you’re referring to but I’ve googled “beyond Violet” and can’t seem to find it although my search uncovered another seemingly different Lovecraftian style horror story with a similar name :


    Don’t think that’s it though. I think the one you’re referring to was an Asimov or Clarke one – I’ll see if I can find it & get back to you later.

  13. Messier Tidy Upper

    @5. Oli Says:

    Imagine what the Rainbow Guy would be like if he saw a double rainbow, from Gamma to Radio…

    Rainbow Guy? Who’s he? Tried a wikisearch and found nothing. [Puzzled.]

    Thinking rainbows and galaxies reminds me of this quote :

    “Quasars are so luminous that if one was in action in a local group galaxy its brilliance would rival that of the Sun.”
    – P.284, Ferris, ‘Seeing in the Dark’, Simon & Schuster, 2002.

    Making me wonder if quasars can cast rainbows and what a quasar cast rainbow might look like as well as double / multiple rainbows caused by other suns.

    Imagine a scene where a bright quasar is near enough to cast rainbows – would we get two rainbows one from each quasar jet? Plus one from that planet’s sun? Hmmm .. :-)

  14. Oli

    @MTU: Kind of reminds me of a drawing of a planet with six suns that I once saw. Image what it’s like to live in the center of an active galaxy, with a huge black hole blasting out loads of gammarays and gazillions of nearby stars all around you… Or being on a planet orbiting a star which is extremely close to a galaxy’s black hole.
    I have a link to the rainbow guy video in a comment, but it’s still awaiting moderation. You’ll have to be patient (=

  15. Zathras

    Reminds me of the Battlestar Galactica episode where one of the human Cylons is bemoaning the fact that his senses are so limited, and he wants to really SEE the supernova in gamma and x-rays, and so on……

  16. Grand Lunar

    Didn’t the open of Doctor Who with Sylvester McCoy feature a spiral? :)

    I find those barred spirals to be weird looking, what with that thick center and the arms eminating from them.
    Galaxies sure do have a sublime beauty to them.

    BTW Phil, you never told us you made an appearence on Head Rush!
    That surprised me. What else are you hiding from us?

  17. @16. Oli: personally I prefer this version http://www.youtube.com/watch?v=6g0yZDMBXiE

    @12. kuhnigget: some bugs and critters can see in UV wavelengths, and other things can “see” infrared (in terms of heat detection….I picture something akin to Predator-Vision™), so apparently nature has tried out some different types of eyes than ours. Unless ALL THE INSECTS ARE INSANE…..oooh, creepy thought. :) But I guess it would be pretty much a downer to suddenly lose the ability to see what you never even knew you were missing.

    I suppose the world would be a pretty bright place if we could see in radio.

  18. Oli

    @20. J. Major: Hmm, I prefer Schmoyoho’s song.
    I’d love to look up to the sky and see everything in X-rays or gamma-rays. If humans were unable to see visible light (now that’s a bit of a paradox) but only gammarays and X-rays, what would we think about the universe? We’d hardly see stars, mostly just quasars, pulsars and the likes. Would we call stars ‘pre-pulsars’?
    When people say that the truth is always stranger than fantasy, they are right, because we are unable to imagine some of these things. We just lack the ability to do so – just like how we can’t imagine how well dogs smell (that sounds rather strange).

    So basically our lives are terrible.
    Why? Because the rent is too damn high. I would sooo vote for that party if I lived in NY (=

  19. Jess Tauber

    I’m still waiting for the development of telescopes that operate by concentrating skotons, the anti-energy equivalent of photons. Then we’ll be able to directly image dark matter. Too late for this Thanksgiving holiday, however, where millions of Americans will ingest thousands of tons of dark matter from beakless alien avians. The Gobble Telescope!

  20. Jamey

    I’d like to see an image with radio freqs done in red, microwave in orange, infrared in yellow, visible in green, UV in blue, and X-ray in purple… I think it would be fascinating to see an image combined all the way across the EM spectrum, compressing the whole spectrum down to the visible light range.

  21. Yeebok

    @8,20 / J Major – the only way I can think of to describe it to you is kinda like this.
    Imagine the whole EM spectrum from micro to gamma or whatever the entire spectrum is as a rainbow. Then, of the entire rainbow what is normally “visible light” would be a small band – perhaps just the greens. Radio might be just orange, X/Gamma rays would be blue and violet.
    Of course that’s overly simplified, but I would imagine if we could see infra red, it’d be a ‘negative red’ colour (as opposed to white light with the red removed, which is cyan – #00FFFF)) :)

    I wonder what colour talkback radio would be if we can see it .. I am hoping a disturbing brown for some reason..

  22. Messier Tidy Upper

    @19. Grand Lunar Says:

    Didn’t the open of Doctor Who with Sylvester McCoy feature a spiral?

    Yup. Looks like the TARDIS causes a fair bit of gravitational or spacetime disruption of the galactic structure too! 😉

    Watch here : http://www.youtube.com/watch?v=bJeM2buWAw8 for nostalgia fix. :-)

    @16. Oli & # 20. J. Major : Thanks. Now it makes sense. Whoah, maa-aan that dude was tripping! 😉

    Nice double rainbow though! :-)

  23. @24 and others – Yep, I’d love to see radio (HI) maps of these galaxies as well. I have no clear opinion about the colour, red/orange will do, but it could be something underlying and diffuse because the HI is far more extended than the other wavelengths. I haven’t seen data or so, but I would expect that the spatial size of these images has to be blown up by a few factors to cover everything. Now that would really show how extended a galaxy is and what the eye cannot see :)

  24. Messier Tidy Upper

    Another awesome videoclip on Youtube here :


    starting with a stellar and nebular journey and featuring a spiral at the 2 min. 15-20ish seconds mark then ending in “death from the skies” in a *very* major way! :-)


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