When a star struggles to be free of its chrysalis

By Phil Plait | February 12, 2010 8:59 am

I have a fondness for bipolar nebulae: double-barreled gaseous clouds formed when stars are born, and sometimes as they age and die. I’ve seen a lot of them, and studied a lot of them, so I was surprised to see this image from the Gemini North telescope of a BPN I’m not that familiar with, called Sharpless 2-106:


Oooo, pretty! Sharpless 2-106 is about 2000 light years away, located in a region of the galaxy known for birthing stars. The nebula is only about two light years across — small for a star-forming region, but still over 2,000 times bigger than our entire solar system!

Deep in the middle of the cloud is a star struggling to be born. It may have about 15 times the mass of the Sun, big enough to put it squarely into the "massive star" category. It’s flooding the nebula with ultraviolet radiation, causing the gas to glow. Different atoms glow at characteristic colors, allowing us to identify what elements are present, at what quantities, and even at what temperatures. In this case, special filters were used to pick out the elements helium (purple), hydrogen (red), oxygen (green), and sulfur (blue). The result is not really a true-color image — it’s not what your eye would see if you were out there floating around — but it’s close. Amazingly, to me, each filter was exposed for only 15 minutes, resulting in a one-hour total exposure time for this image!

[Note: the purple glow surrounding that bright star is just an internal reflection, light scattering around inside the telescope. That’s most likely a bright foreground star blasting out more light in the purple filter than the others; it doesn’t mean that star has a giant shell of helium around it!]

The nebula is double-lobed because the star is probably surrounded by a thick disk of material: gas, dust, silicates and other junk swirling around that forms the star itself (and perhaps planets, though we can’t tell in this case because there’s simply too much stuff there obscuring our view). A typical disk is on the order of the size of our solar system, so is invisibly tiny in this image.

But the star is blowing out material too in a stellar wind. It gets stopped by the equatorial disk, so it can only blow up and down, above and below the disk, forming these two great lobes that stretch for trillions of kilometers.

If we compare this image to one taken in the infrared by Subaru, we learn even more:


Like the Orion Nebula picture the other day, the IR image shows that a cavity is being carved out the surrounding gas, most likely from the winds from that massive star. Streamers of gas can be seen on the left, probably formed as the outflowing gas slams into dense knots of surrounding material, a bit like a sandbar that forms when water flows around a patch of sand. You can also see lots more stars than in the optical image, including many bright ones you don’t see at all in the optical. The thick dust surrounding Sharpless 2-106 blocks the optical light from stars, but IR can pierce that veil and reach our telescopes, showing us the hidden treasures.

We see bipolar nebulae all over the place… I have another one I’ll be telling you about soon, one of my very favorite objects in the whole sky. If you’ve been reading my blog for more than a couple of weeks you’ve already seen it, probably without even knowing it. But that’s the only hint I’ll give for now. Stay tuned and I’ll tell you all about it. Promise!

Until then, soak in the beauty of this nascent star, which, in a few million more years, will blow away the tattered remnants of its cocoon, and emerge as another bright blue-white star to light up our galaxy.

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (20)

  1. jb

    ok..now that was a cool pic ..love the infrared pic to compare!!

  2. On a slightly side note… If one were to be able to see it happen, what would a star “igniting” look like? How long does it take? Has most of the dust settled into the equatorial disk, or is there still a lot of cocoon left, surrounding the entire star?

  3. Is it just me…. or do I see Gamera ? ūüėČ Seriously though, great pic.

  4. 2000 light-years away? This is obviously a sign from our lord and savior Jesus Christ!

    Seriously though, excellent image. I especially like the Infrared.

  5. Rob

    Great pictures, thanks. How long do objects like this last? What’s the life-cycle? (Well, I guess those could be decent research questions … but in a few sentences?)

  6. cisko

    Phil says: The nebula is only about two light years across ‚ÄĒ small for a star-forming region….

    I’m curious: is that size small because of observational capability (we have a hard time finding star-forming regions that small)? Or do we know that it’s unlikely to have stellar nurseries that small or smaller?

  7. The nebula is only about two light years across ‚ÄĒ small for a star-forming region, but still over 2,000 times bigger than our entire solar system!

    Exactly how are you measuring our entire solar system? I consider the Oort cloud to be part of it as well, so that makes our little slice of the universe about 1 lightyear across. :)

  8. Stan9FOS

    The Stellar Wind… Comes blowin’ in… From the nebulae…. Sorry . Couldn’t resist. Now YOU’LL have that tune running thru your head for the rest of the day. Carry on.

  9. AbuMaia

    I guess they had to call it Sharpless because they couldn’t call it Dull. It’s anything but! Nice images there, though I do like the Subaru image better ^_^.

  10. jest

    Curious… in both the Gemini and Subaru images (though far more visible in the Gemini image), to the bottom left of the bright blue-purple star there is a small arc. I wonder what that is, and how it was created?

  11. Re: Larian and cisko – the number Phil used is ~50-75 AU, or a little bit outside of the orbit of Pluto, which I think is a fair “classical definition” of the solar system radius.

    Re: cisko: Some of both. There are probably a lot of small star forming regions similar to this one, but we can only see them nearby because of their size and generally because they’re faint and hidden by other objects. However, most stars form in clusters – even though there are more of these small regions, the big regions form enough stars to make up for their lower numbers.

    Re: jest – it’s an arc of gas and dust that looks like it’s being blown away from the central star. These kinds of features are common particularly around bright, hot stars that emit lots of UV radiation. It could have been a blob before it was illuminated and reshaped. Its position may indicate that it’s in the foreground, moving towards us, or it could just be coincidence that there is only one feature like that.

    Does anyone know what’s special about these filters? They look like normal H-alpha, S-II, O-III, and He-II filters…. though I guess He-II filters aren’t that common.

  12. Ari

    Hmmm, I’ll take a stab and guess eta carinae, though I’m struggling to figure out how it’s frequently seen in the blog. In some logo?

  13. Kimpatsu

    Phil, just in case you didn’t know, “Subaru” is the Jpaanese word for the Pleiades.

  14. Messier Tidy Upper

    15 solar mass that’d make it a class O dwarf when it finally reaches the main-sequence right right?

    About the same mass as Acrux (Alpha Crucis) A and Hadar / Agena (Beta Centauri) – and one that will evolve into a red supergiant like Betelgeuse or Antares before go (type II) supernovae after a few million years of blazing luminence in our sky leaving behind a neutron star pulsar or even black hole. Yes?

    Amazing to think we chart its future & to think of the life ahead of this new forming blue “dwarf” star! :-)

    Oh & would I be right in guessing the star in question is Sher 25 – a blue supergiant star similar to Sanduleak -69 degrees 202 – the one that produced supernova 1987 A? ūüėČ

    See : http://en.wikipedia.org/wiki/Sher_25


  15. sylva333

    Hmmm…. we need to stay tuned…. just like we have to stay tuned for the tattoo…. interesting.

  16. “I guess they had to call it Sharpless because they couldn‚Äôt call it Dull. It‚Äôs anything but! ”

    I at first thought they were calling it the Slurpee Nebula.

  17. Sylvia

    >Kimpatsu, I guess that explains the Subaru logo, right? Now I can impress my son, at least a little.

  18. Mark the Sundog

    I’ve had this backwards for years, then. I always thought bipolars were a kind of planetary nebula.

    9 ‘clock on a Sunday morning and I learn stuff! Brilliant!

  19. About the bipolar aspect of the outflow. Isn’t it also possible that the accretion disk is launching a wind via magnetic torques (i.e. Blandford & Payne 1982)? This mechanism has been invoked to describe the launching of collimated relativistic jets (e.g. AGN/quasar jets).


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