Galaxy on the edge of space

By Phil Plait | January 29, 2011 7:00 am

For your weekend eye candy pleasure, I have an unusual galaxy for you. Actually, it’s an unusual picture of an unusual galaxy!

Check out NGC 6503:


This picture is brought to you by the good folks of Hubble Space Telescope. Click it to get the galactinated 4000 x 2200 pixel version.

This picture is wee bit odd because it combines images from two different filters not generally seen together. One is a near infrared filter just outside the range of the human eye (0.814 microns, if you’re keeping a log of all this) and shows mostly stars, colored blue in the picture. The pink/red is coming from a filter that isolates the light from hydrogen gas, and shows where stars are actively forming in giant nebulae. These factories are like our own Orion Nebula, cranking out stars.

I’ve seen images of NGC 6503 before — like the one inset here from NOAO — so I have a passing familiarity with it. Like most spirals, it has more older stars toward the center and bluer, younger stars forming in the spiral arms, and that’s pretty obvious in the more natural color NOAO image. But in the Hubble shot, the IR filter doesn’t really distinguish very well between bright blue stars and older, red ones. Both pour out IR light, so we just see stars all over the place. Of course, the red nebulae are really striking too, making the Hubble image look, well, odd.

The galaxy is a bit of a weirdo, too. First, it’s small: only about 30,000 light years across, a third the size of the Milky Way. But size hardly matters, clearly, when forming beautiful spiral arms. This galaxy obviously has no trouble maintaining them.

But its location is strange too. It’s on the edge of the great local void: a vast region of space where galaxies are few and far between. Galaxies tend to exist in clusters and superclusters. The Milky Way is part of the the Local Group, a small collection of a few dozen galaxies which itself sits on the outskirts of the Virgo Cluster, 60 million light years away. In the opposite (more or less) direction, toward the constellation of Draco, is the Local Void. Our galaxy is near the edge of this void, but NGC 6503 is actually further into it, 17 million light years away from us. Even then, it’s only on the void’s edge; estimates vary but the empty region extends for something like 30 – 200 million light years in that direction!

So you can picture it: on one side of us is a collection of hundreds of galaxies in the Virgo cluster, which itself is part of a much larger supercluster containing thousands of galaxies. On the other side of us is an empty region of roughly the same size. Somehow, when the Universe itself was young, the matter in this region must have all condensed toward Virgo, leaving the void nearby. We think the entire Universe is this way, with dense regions of matter surrounding bubble-like voids. If you could step back and look, the Universe might appear like a giant sponge!

Think about that the next time you’re scrubbing your dishes.

Image credits: ESA/Hubble and NASA; Adam Block/NOAO/AURA/NSF

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (39)

  1. Scottie Davis

    I really like pictures like these.. Everything about it is epic!

  2. Weirdo galaxy? Come on now Phil, it’s no-name-calling week.
    Let’s set an example.

  3. I can’t look at that picture without hearing John Williams’ music from the end of The Empire Strikes Back..

  4. Daniel J. Andrews

    Off-topic but since Phil has covered this material in the past, here it is. Another “teach the controversy” bill that “assist teachers to find more effective ways to present the science curriculum where it addresses scientific controversies”. Time to bring out the doomed picture or the eternal squirrel vigilance picture?

  5. Robert

    You just Men-in-Black’ed me with that last image, Phil. Things I can no longer do without thinking I’m screwing around with someone else’s universe: play marbles, do dishes,…

  6. Robin

    #3 “I can’t look at that picture without hearing John Williams’ music from the end of The Empire Strikes Back..”

    I hear Beethoven’s Pastorals (7th ? ) when I peruse the universe.

    What do others hear?

  7. Dr_Cy_Coe

    Question: In the 4000 x 2200 pixel version, at the area centered around (1980(x),1600(y) pixels). Are those shockwaves? Or are we looking at an example of gravitational lensing?

  8. Chief

    It looks like we are looking up from below on this one. Don’t see too many from that angle for a strange reason.

    So it is on the edge of the great blight. Bummer.

  9. Crudely Wrott

    I lived in Florida during the seventies. The seasonal weather, particularly the daily squalls and rain of late summer were easily observed. It was not unusual to be close to the edge of a rainstorm. At least once I was walking downtown and being soaked while those on the opposite sidewalk were perfectly dry. And looking on with amusement.

    When you fish for trout in a stream your chances of obtaining a satisfying supper are increased if you present your bait where still water and moving water meet.

    In order for organic chemistry to proceed apace there needs to be a mixing, a constant turnover and exposure. Where this happens life thrives.

    It’s all about the edges, where things come together. That’s where the action is.

    Ergo, we may all be “tweens”.

  10. some guy

    I love this blog! The last couple weeks it hasn’t been appearing in my gmail reader the same, it’s cut off about half way through so I have to actually visit the site to finish reading the entry. It’s so annoying!! If there’s anything to be done to fix that, please do.

  11. Firemancheesehead

    Hey, anyone else notice that if you embiggenate the smaller insert picture, the star in the lower righthand side has a ring extending outward from it?

    Any guess as to what it could be?

  12. Jon Hanford


    Looks like an internal reflection (ghost) of the bright star to the left of the galaxy.

  13. Vision Engineer

    I don’t know the name of the music I am hearing, but it is one of the pieces that was often used in Cosmos when the ship of the imagination is flying around between galaxies.

  14. OtherRob

    Pics of spiral galaxies are my favorites. They just take my breath away. (Though my absolute fave is the pic of Saturn lit from behind with the tiny blue dot of the Earth inside the rings.)

    @Crudely Wrott, #9: I grew up in Florida and I can remember plenty of times when it would be raining in the front yard and be bright and sunny in the back. :)

  15. Trebuchet

    Uh Chief, #8, you know there isn’t any “up”, “down”, “top” or “bottom” out there, don’t you?

    Except that relative to earth, everything in space is “up”, and within the galaxy, I guess you could say the direction to the core is “down”.

  16. Chief


    I know but we like to use a familiar to keep perspective on a object. I bet any pilot of a spacecraft will reference up and down (starboard and stern as well?) for navigation.

    I was thinking of a lot of the galaxy’s represented in movies and a few here on this site that always seem to be referenced from either edge on or from above (perspective to my laptop that is.)

    I have to add that with all the fantastic imagery that is coming out as of late, I really want to get up and visit them. As other comments have said, where’s the warp drive….

  17. Chief


    I was thinking about the imaging of the galaxy’s and the red shift properties. Is there anyway to image the captures in 3D, or is the distance calculations using the shift not able to give enough of a distance variable from one side of the disk to the other over the millions of light years distant.

  18. RwFlynn

    This isn’t related to the Galaxy or the void or anything, but what is that in the bottom right corner of the NOAO picture? I don’t know enough astronomy to even guess. Thanks!

  19. AR

    Spiral galaxies are absolutely gorgeous! I dig the “weird” picture of this one.

  20. Joseph G

    Unusual picture of an unusual galaxy? Really?

    Let’s see: Amazingly vast, beautiful and intricate structure located untold quintillions of miles (and millions of years in time) away – check.
    Incredible imaging technology that can capture individual photons of varying wavelengths to give us an almost magical window on the mind-boggling universe in which we live – check.
    Captivating and accessible explanation of the wonders being revealed to us – check.

    *yawn* I dunno, Phil – seems like just another ordinary day on your blog 😀
    (Yes, we’re spoiled!)

  21. Robert

    @Chief, I think I see what you mean, but I can’t tell which end (top in the picture, or bottom) is closer to us. You must be seeing the “top” edge of the galaxy as closer, but it’s ambiguous to me.

  22. Robert

    Hmm, I take that back. The dark spots show which edge is closer to us, right? So I guess the edge at the top really is closer. Neat!

  23. @rwflynn:

    That appears to be a more distant galaxy, which just happens to have that bright foreground star in front of it. It might even show signs of a ring structure, but you can’t really tell from the image.

  24. Joseph G

    WOW – if anyone here hasn’t tried out Celestia, I highly recommend it!
    It really gives you some sense of how amazingly far away these things are, and how they are arranged in relation to some local “landmarks” (the Milk Way and satellite galaxies, Andromeda, and Triangulum).
    From here on in, I’m looking up every object that’s posted here in Celestia – if I have time for it 😀

  25. Thameron

    One of these days your exclamation point key will break and then where will you be?

  26. Joseph G

    @ Thameron: Are you talking about Phil, or me? 😛

    @#16 Chief: For interstellar trips, they’ll likely use some version of the Galactic Coordinate System (it’s on Wikipedia, I don’t want to post a link and have to wait for moderation). It looks like galactic north is the side of the galaxy from which the stars appear to be orbiting the galactic center in a clockwise direction. Which is kinda odd, because from the point of view of Earth north, the planets rotate AND orbit the sun counterclockwise.

  27. Messier Tidy Upper

    Great picture(s), interesting galaxy. Thankyou. :-)

    @6. Robin : What do others hear?

    The radio on in the background and my dog barking as another dog walks past! 😉

    Seriously though, the mental background soundtrack for that would have to be the Blue Danube music from ‘Space Oydssey 2001’ or one of the quieter pieces from Gustav Holst’s Planets Suite or perhaps Pink Floyd’s ‘Set the Controls for the Heart of the Sun.’ Other folks mileage may vary, natch. :-)

  28. Messier Tidy Upper

    @26. Joseph G : For interstellar trips, they’ll likely use some version of the Galactic Coordinate System (it’s on Wikipedia, I don’t want to post a link and have to wait for moderation).

    Oh well, here it is then I can wait (sometimes!) :

    While on with linking things here’s the Pink Floyd one :

    & here’s the Blue Danube docking scene from 2001 – the movie not the year.

  29. Messier Tidy Upper

    More links for the music mentioned :

    For Holst’s ‘Neptune’ composition.

    See this link :

    For Holst’s ‘Planet Suite’ info via Wikipedia perhaps the one good thing astrology has done for the world! 😉

    Plus perhaps this one :

    For another musical option of more recent vintage? :-)

  30. Jojo

    So galaxies do not work like molecules where they try to fill empty space and distribute themselves evenly?

  31. Phil:
    When you say”the light from hydrogen gas” do you mean Hydrogen alpha?
    Explaining that term (the rest of the Balmer series and maybe the Lyman series too) to the folks here might make a nifty post or 2…

  32. Joseph G

    @Messier Tidy Upper: Ooh, I like that Holst composition. I like my space music to be somewhat dramatic :) Stuff like “Blue Danube” feels altogether too playful and frivolous to me when it comes to trying to capture the, well, gravity of the universe 😛

  33. Joseph G

    As long as we’re throwing links out here, everyone who’s always wanted to be an astronaut when they grow up really needs to check out the Orbiter space sim.
    It’s been around quite some time, and it’s getting better all the while. I see they’ve added solar sails, among other stuff, since I last used it. I haven’t thought of it in quite some time, but there are some good videos up on youtube. All this talk of space music must have reminded me of it in some roundabout way.
    Anyway, it’s got a steep learning curve, but it’s reeeeeally worth it. Learning how to to transfers and synch orbits and whatnot really teaches you a lot about orbital dynamics in a really intuitive way. I feel like I understand (planetary) space a lot better having used it.

    ps: If you get it, be sure to go to and download his excellent OrbiterSound addon. The author of Orbiter is mainly concerned with physics, so he lets other people handle stuff like sound.

  34. Chief

    My thinking of the orientation of the galaxy is based on the fact that the stars in the back of the spiral seem to have more obscuring dust/gas/whatever. The upper seems clearer thus closer.

    I would pick the Blue Danube music for a slow pan around, but can’t think of one for a fast fly by or one for coming into a new system and going into orbit.

  35. mfumbesi

    Again, your explanation was great and illuminating……..The Local Void beautiful.

  36. reidh

    But that Void must be full of Dark Matter, held together by Dark Energy.

  37. CB

    @ 30:

    So galaxies do not work like molecules where they try to fill empty space and distribute themselves evenly?

    A lot of the same forces are at work, but at the galactic scale gravity plays a major role in keeping things together, while for say the air inside a balloon the mutual gravitation of the gas molecules is negligible.

  38. Apropos of nothing, but I couldn’t figure out how to ask Phil the question directly:

    Is there a reason that when we speak of exiting the solar system or galaxy, it’s always radially instead of axially? Is it impossible, is there nothing there? Just wondering…


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


See More

Collapse bottom bar