Revisiting the Whirlpool

By Phil Plait | February 2, 2010 7:00 am

One of the closest and most spectacular galaxies in the sky is M51, the Whirlpool. A grand design face-on spiral with a small, irregular companion, it’s so bright and big that it’s a favorite target for amateurs. So you just know when you point Hubble at it, what you get is nothing short of jaw-dropping heart-aching beauty.


[Click to galactify.]

This image, using the Hubble Advanced Camera for Surveys, was originally released in 2005, but was recently reprocessed by the phenomenal astrophotographer Robert Gendler. And yeah, you absolutely want to click that link to see the work Robert has done. He’s incredible.

I could go on and on about the galaxy, the glorious spiral arms, the red glow of nebular star birth factories, the odd companion that apparently has drawn out that long tidal tail of stars from the spiral, and so on… but you’ve read that stuff here before.

Instead, while looking this image up, I found the behind-the-scenes story on how they observed it that I think will interest you, my BABloggees. Extra cool is the page showing the galaxy observations in different colors, and you can see just what a big spiral looks like when you use different filters:


You can see the ACS field of view, and the final version on the left. The different observations are listed (each frame is clickable to embiggen on that page, which lets you explore the galaxy on your own). The filters are labeled on the top of each image: B (blue), V (visual, or really yellow), I (near-infrared), and Hα + [NII], the reddish light given off by hot hydrogen clouds laced with nitrogen. That last bit is where stars are being born, and traces the spiral arms very well. The I-band shows very warm dust as well as stars, so it looks smoother since all that stuff is rather smoothly distributed in the galaxy. The B-band has hot stars in it, so again shows where stars are being born; blue stars don’t live very long, and can barely escape their gas cloud nurseries before blowing up as supernovae.

When you put these all together you get the majesty of a spiral galaxy, a city of stars much like our own Milky Way. I’ve seen M51 myself with binoculars and through countless telescopes at star parties, and while it doesn’t look as glorious as it does here — of course — just knowing what’s going on in the galaxy and what it really does look like through the big guns is enough to thrill. It may look blurry and fuzzy through a small telescope, but our brains are big enough to encompass all those light years, and to understand what it is we’re seeing.

Image Credit: NASA, Hubble Heritage Team, (STScI/AURA), ESA, S. Beckwith (STScI). Additional Processing: Robert Gendler

CATEGORIZED UNDER: Astronomy, NASA, Pretty pictures

Comments (26)


    Dr. Phil Plait:

    It may look blurry and fuzzy through a small telescope, but our brains are big enough to encompass all those light years, and to understand what it is we’re seeing.

    Unless you’re a freaking creationist!

  2. Phil- Our minds eyes tends to perceive images like this as planer, without any visual clues to show depth. So is that companion behind the galaxy, or in front? In other words, if we saw it from the side, how far away is the companion?

  3. It’s photos like this that make me want to print out a whole bunch of NASA space posters and paper the ceiling of my office with them. Then I can code web pages in space.

  4. T.E.L.

    This PDF,, gives some valuable insight to the subtleties of dealing with the data. It tells of identifying and subtracting probable cosmic ray artifacts. Another fascinating thing they did was to identify the trail of a satellite traced in the foreground during the exposure, which was also systematically subtracted from the M51 image .


    @ Jim G,

    Decades ago, it was not known with certainty whether the companion galaxy NGC 5195 was a true companion, or another galaxy passing at a distance. The advent of radio astronomy and subsequent radio images of M51 unequivocally demonstrated the reality of the interaction.

    Recent simulations bear out that M51’s spiral structure was caused by NGC 5195 passing through the main disk of M51 about 500 to 600 million years ago. In this model, NGC 5195 came from behind M51 through the disk towards the observer and made another disk crossing as recently as 50 to 100 Myrs ago until it is where we observe it to be now, slightly behind M51.

    Source: Wikipedia — Whirlpool Galaxy; Companion.

  6. Techy-Dad: Sometimes I wish the folks who make picture wallpaper would start making it with things like this instead of old shuttle shots and such. I know I’d love it. (looks into the cost of giant printers).

  7. Crazy Tom

    I’m at the library looking at Gendler’s website now, and it’s too bad I’m in public because I’m most definitely drooling. Orion’s Sword is beautiful as ever, and his shot of the Galactic Center makes me want to get a Spaceballs-sized vacuum cleaner and clear the dust out of the way.


    I used to be a creationist until I saw the light. I can tell you firsthand, those poor people deserve pity, not derision.

  8. T.E.L.

    Crazy Tom Said:

    “I used to be a creationist until I saw the light. I can tell you firsthand, those poor people deserve pity, not derision.”

    That’s a very humane way to see it.

  9. firemancarl
  10. Pat Durrell

    @Jim G
    The presence of dust (from M51) in front of NGC 5195 suggests that the companion galaxy is behind M51, although by how much is less clear; as noted, the most recent interaction between the two was `somewhat’ recently. Another recent simulation of the M51-NGC 5195 system has the last (single) close passage about 300 million years ago, where the companion came from the `bottom’ (of the images shown here) but in front of M51, moving `upwards’ and behind M51 at closest passage, and after this the companion continued to move `upward’ and further behind M51.

  11. Need to rotate it 90 degrees, but NEW DESKTOP! :)

  12. Why should something this spectacular be any different whether it was created by a very creative God or self-collected itself out of random fluctuations in the background radiation? Either way it’s entirely mind-bogglingly amazing that it exists at all!!

  13. Memlaw

    This is a picture of what was there 31 million years ago. What does it look like there now? pretty much the same?

  14. Messier Tidy Upper

    Awe inspiring superluminous image BA – thanks. :-)

    I wish I could have that M51 Whirlpool galaxy photo displayed as a giant mural on my house. :-)

    The Whirlpool surely has to be the beautiful spiral galaxy of all with NCG 2997 in Antlia being its closest rival or possibly tying with it. ( )

    Of course, as seen in the sky the Large Magellanic Cloud looks better or at least so much bigger! But a) the LMC has the unfair advantage of being so much closer and b) its not a spiral but a messy and loose *barred* spiral & so gets disqualified on that technicality. ūüėČ


    Another neolgism (spelling?) to your credit BA? ūüėČ

    It may look blurry and fuzzy through a small telescope, but our brains are big enough to encompass all those light years, and to understand what it is we’re seeing.

    You know I sorta agree with you there but also sorta wonder if we really do fully understand what we’re seeing in the deeper sense.

  15. Adam

    What I find so incredible about the full sized view of this image is the countless galaxies in the background. Despite the beauty of M51, the star formation, the colors, the rich texture of the arms, etc… it is not alone… there are countless other galaxies filling what seems to our eyes nothing more than void. There is so much out there, so many awe inspiring wonders to behold, each more brain twistingly beautiful and amazing than the last.

    It is truly humbling to think that we are capable of viewing the cosmos from our tiny speck of a rock. Thank you for sharing this image.

  16. Charles

    Irrelevant to M51, but definitely worth mentioning…

    The Lancet retracted Wakefield’s 1998 antivax article.

  17. HrothgirOD

    “Extra cool is the page showing the galaxy observations in different colors, and you can see just what a big spiral looks *at* when you use different filters:”

    Shouldn’t that be ‘like?’

  18. @Emory (#12)

    Because this is evidence that the earth may just be a little older than 6000 years? Just saying. :)

  19. FoxtrotCharlie

    There’s a boardgame called Galactic Destiny that uses the Whirlpool Galaxy as its map board.

  20. Would you bickering twits just shut up for ONCE.

    If you still think your pointless quibbles about ontology are important enough to spew them all over my monitor, please quit typing and look at the picture of the galaxy, because it has not yet humbled you sufficiently.

    No, no retorts. Yes, you. Yes. I know you’re just aching to tell me how very serious the problem of your political opponents actually is. Shut up. Look at the picture.

    It is not a picture of you being right.

  21. Brandon

    You never cease to engage me in the field of Astronomy!

  22. James (#20): cool it. This is not bickering, but just some friendly chatter. If this bugs you so much, I suggest you don’t read the comments to the posts. And I do suggest you read my commenting policy.

  23. Chris A.

    @James (#20):
    Welcome to the blogosphere, where, like in any large crowd, you only get heard if you shout loud and often. I applaud the sentiment of you post, but suspect it is a whisper in the cacophony.

    We each have our personal cyberspace tolerance threshold. (I, for one, will never, under any circumstances, waste my time reading youtube comments.) You simply have to ask whether the signal to noise ratio on this blog is high enough to make you want to tolerate the noise floor. For me it is, more often than not. But not always (e.g. global warming troll posts).

  24. bruce

    I would think (because I’m ignorant) that if the blue stars don’t live very long, and they are so many of them, that a super nova would be popping off rather frequently, seeing as that galaxy is so very old and so many light years away. And yet that is not the case, why?

  25. Would you bickering twits just shut up for ONCE.

    As a bickering twit, I am offended, sir, by your demand.

  26. @bruce (#24)

    Actually, a supernova went off in 2005 (2005cs). I got a picture of it entirely by accident; I was just showing some friends how to use the university’s CCD camera to make a color image. A few weeks later I heard about the supernova, checked the image, and there it was!

    Supernova 2005cs is the bright dot directly above the core of M51 in my picture (link in name). You can see it’s on (actually, in) a galactic arm, while none of the stars in the Hubble image are, not even the yellow one that’s almost in the right place.

    As for why we don’t see tons of them going off, I think it has to do with how incredibly rare those bright blue stars are. Mathematically speaking, if they last five million years, you’ll need five million of them to get approximately one going off every year.

    There are about 6,250 star systems expected within 25 parsecs of the Sun, none of them contains a star capable of core-collapse supernova (I’m ignoring type 1a white dwarf supernovae). That means the fraction of stars that CAN is something much less than, say 1 in 10,000. If there are 100 billion stars in M51, there will only be 10 million supernova-producing stars, tops. That would seem to work, but I’m betting my 1 in 10,000 is far, far too high.


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