Spectacular Infrared Photo of a Nearby Spiral Galaxy

The entire universe in blog form
Dec. 1 2012 8:00 AM

Blowing the Dust Off a Spiral Galaxy

I was digging around the web looking for some info and stumbled on something that really surprised me: a picture of an old friend I had never seen before!

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

Of course, I’m an astronomer, so when I say “old friend” I mean some gorgeous astronomical object. In this case, it’s the spectacular face-on spiral galaxy M83, also called the Southern Pinwheel, for obvious reasons:

Spiral galaxy M83 as seen by Spitzer Space Telescope
Spiral galaxy M83 as seen by Spitzer Space Telescope. Click to galactinate.

Image credit: NASA/JPL-Caltech

Advertisement

Isn’t that breathtaking? This image was taken by the space-based Spitzer Space Telescope, which sees the Universe in infrared light, outside the range our eyes can detect. It uses filters to distinguish various wavelengths (colors) of IR light, and then astronomers turn them into images we can see by assigning a visible light color to each wavelength. In this case, what you see as blue is actually light at 3.6 microns (a wavelength about 5 times longer than what your eye can see), green is 4.5 microns, and red is 8 microns.

For the most part, warm objects emit light at these wavelengths. But to an astronomer, -170 Celsius (-270 Fahrenheit) is warm! Don’t ask us what “cold” is.

In a galaxy, strewn between the stars, are vast clouds and ribbons of complex molecules called polycyclic aromatic hydrocarbons, or PAHs for short. We also just call it “dust”. This stuff is essentially soot, and it’s created when stars are born, and when they die. Regions where galaxies furiously make stars are littered with this dust, and it warms up due to the nearby stars. It then glows in infrared, and can be seen by Spitzer to make the above picture.

M83’s lovely spiral arms are where all those stellar nurseries are, so we see them festooned with the cotton-candy-like dust emitting infrared light. The picture looks similar, but different, in visible light. Here’s a shot using the European Southern Observatory’s MPG/ESO 2.2-meter Telescope:

Spiral galaxy M83 in visible light.
M83, this time in visible light. Click to embiggen.

Image credit: ESO

The spiral arms are still there, but now you can see the pink glow of gas clouds, and the blue of hot, young, massive stars blasting light into space. Stars give off infrared light too, so you can see some of the same ones in both images (those stars, I’ll note, are in the foreground, in our own Milky Way). I rotated the image to match that of Spitzer so you can compare them. As gorgeous as this is, I think my favorite part of this picture is the two nearly edge-on spiral galaxies in the upper left. M83 is about 15 million light years away, but those two guys are much more distant, hundreds of millions of light years away at least.

And one other thing: take a look again at the Spitzer image. It looks a bit off-center, doesn’t it? Too low? When I cropped the image I thought I had messed it up, but in fact the center of the galaxy is centered in the image. Measure it yourself! It turns out the galaxy itself is a bit lopsided, asymmetric. The bottom half stretches out farther than the top, both in the infrared and visible light images. That’s interesting! Not all galaxies are perfectly symmetric; a nearby galaxy passing by can distort them, for instance.

Hubble closeup of M83 spiral arm, where stars are being born.
Hubble closeup of a spiral arm in M83, where scads of stars are being born. Click to edwinenate.

Image credit: NASA, ESA, R. O'Connell (University of Virginia), the WFC3 Science Oversight Committee, and ESO

However, nothing like that is near enough to M83 to have done this. I did a quick journal search, and discovered that M83 almost certainly recently ate a smaller galaxy. I don’t know if this is enough to explain the asymmetry, but it’s interesting. I’ll note that there’s a vast cloud of hydrogen surrounding the galaxy (that’s fairly common), but it too is off-center, and in the same direction the galaxy itself is. Recent observations indicate M83 has (at least) a double nucleus, which is what you get when you’re still digesting a smaller galaxy. This can also trigger star formation, which is definitely the case for M83. I also dug up a reference to a huge arc of material obviously associated with the galaxy, but with unclear origins. I have no clue if that has anything to do with this or not.

So I’m thinking something happened to M83 to knock it around. A collision and eventual merger with another galaxy would explain it, but who knows?

And that’s the best part, isn’t it? I don’t know what the answer is, and I’m not convinced I’ve seen anything in the literature explaining it either (in fact, I saw several references to M83 being remarkably symmetric, an observation with which I now don’t agree).

Funny. I intended this to be a short post just describing a fun galaxy I happened upon… and now look! Everything I wondered about led me to another interesting path, which I merrily walked down. Now I know a lot more about M83 than I did before... and in some ways maybe less, because now I have even more questions. Which is awesome.

Science! I love this stuff.

TODAY IN SLATE

Sports Nut

Grandmaster Clash

One of the most amazing feats in chess history just happened, and no one noticed.

The Extraordinary Amicus Brief That Attempts to Explain the Wu-Tang Clan to the Supreme Court Justices

Amazon Is Officially a Gadget Company. Here Are Its Six New Devices.

Uh-Oh. The World’s Oceans Have Broken Their All-Time Heat Record.

The NFL Explains How It Sees “the Role of the Female”

Future Tense

Amazon Is Now a Gadget Company

Food

How to Order Chinese Food

First, stop thinking of it as “Chinese food.”

The NFL Should Lose Its Tax-Exempt Status, Which It Never Should Have Had Anyway

The Country Where Women Aren’t Allowed to Work Once They’re 36 Weeks’ Pregnant

The XX Factor
Sept. 18 2014 11:40 AM The Country Where Women Aren’t Allowed to Work Once They’re 36 Weeks’ Pregnant
Moneybox
Sept. 17 2014 5:10 PM The Most Awkward Scenario in Which a Man Can Hold a Door for a Woman
  News & Politics
Politics
Sept. 18 2014 6:52 PM Ground Zero for the Fight Over Female Voters  Colorado Democrats and Republicans are testing theories for reaching women that will resonate far beyond the Rocky Mountains.  
  Business
Moneybox
Sept. 18 2014 6:02 PM A Chinese Company Just Announced the Biggest IPO in U.S. History
  Life
Outward
Sept. 18 2014 4:15 PM Reactions to a Sketch of Chelsea Manning Reveal Transmisogyny
  Double X
The XX Factor
Sept. 18 2014 3:30 PM How Crisis Pregnancy Centers Trick Women
  Slate Plus
Behind the Scenes
Sept. 18 2014 1:23 PM “It’s Not Every Day That You Can Beat the World Champion” An exclusive interview with chess grandmaster Fabiano Caruana.
  Arts
Brow Beat
Sept. 18 2014 4:33 PM The Top 5 Dadsplaining Moments From The Cosby Show
  Technology
Future Tense
Sept. 18 2014 6:48 PM By 2100 the World's Population Could Be 11 Billion
  Health & Science
Science
Sept. 18 2014 3:35 PM Do People Still Die of Rabies? And how do you know if an animal is rabid?
  Sports
Sports Nut
Sept. 18 2014 11:42 AM Grandmaster Clash One of the most amazing feats in chess history just happened, and no one noticed.