AAS #6: Lonely stars between galaxies

By Phil Plait | January 8, 2008 5:00 pm

M81 and M82 are bright nearby galaxies; you can spot them with binoculars easily in the northern sky, and they are a mere 12 million light years from us (for comparison, the Milky Way Galaxy is 100,000 light years across, so if you think of the Milky Way as a DVD, M81 and M82 would be about 14 meters away). These two galaxies interacted a couple of hundred million years ago, and the gravitational interaction drew out long tendrils of gas (which is very common in colliding galaxies).

Astronomers examined this bridge of material using Hubble, and found clusters of stars in it. That was totally unexpected; the gas was thought to be too thin to form stars! Amazingly, many of the stars are blue, indicating they are young (blue stars burn through their fuel much more quickly than redder stars. This means that the gas is still forming stars, even 200 million years after the collision!

In the image below, almost all the stars you see are young blue stars formed in the aftermath of that titanic collision. The reddish stars are stars in our galaxy, and the bigger objects are distant background galaxies.

Most likely, the stars formed when turbulence in the tendril caused local regions of denser gas, which could collapse to form stars. Before these observations, it wasn’t really thought it was possible to form stars in the regions between galaxies, so this is an interesting new find.


Comments (27)

  1. I guess this a bit off topic, but the sheer magnificence of our universe is astounding. How is it again that atheists are supposedly putting forth a view of the universe that doesn’t offer anything positive?

  2. Michael Lonergan

    I wonder if there are life bearing planets around any of those stars?

  3. Chip

    I sometimes wonder about older, stable long-lived stars that were thrown out by gravity during a collision long ago and “now” reside with younger blue stars between galaxies. Are they there too?

  4. Eric TF Bat

    So the Krikkit homeworld doesn’t need to be in a nebula; it could be somewhere outside the galaxies. What would the view be like from a lone star in between, say, the Milky Way and M81 or M82? Would you be able to see galaxies with the naked eye, presuming you owned such an organ and it worked more or less like a human eye? Or would it all be dark and silent and thoroughly lonely?

  5. DavidHW

    Does anyone have a link to one of those astronomical paintings depicting “galaxy-rise” over a planet of a rogue star high above the galactic plane? I was looking for one the other day and this article seems a perfect segue.

  6. Chip

    Eric TF Bat asked: >>>”Would you be able to see galaxies with the naked eye, presuming you owned such an organ and it worked more or less like a human eye?”<<<

    Depending on many factors, such as much of your sky the galaxies took up and if conditions were the same as Earth, and you were away from a (presumably advanced brightly lit alien city with cool monorails that work better than Disneyland’s,) and your eye was human; you’d see awesome galaxy shapes that were technically dim but still spectacular. You’d likely see them in the same way that the Milky Way is spectacular on a good dark night on Earth. Unlike the Milky Way, which we are in, the galaxy spirals might be clearly perceived.

    The human eye does not collect photon impressions as a time-exposure camera would, so distant objects tend not to get brighter in general however the assumption that we would only see averted-vision faint fuzzies even if much closer is a misnomer. There are other factors, such as dim though more highly detailed structures and brighter local nebula and star fields that, due to enormous distances are invisible unless you were closer.

  7. RayCeeYa

    It would be interesting if they could do one of those dark matter surveys to see if the dark matter flows out into the tendrils as well or if it is still concentrated in the galaxies.

  8. Bryan

    Poul Anderson wrote a short novel about a planet orbiting a “lonely star” – its inhabitants could see the Milky Way in its entirety, and (as I recall) worshipped it. Of course, the best thing about that story was the song, “Mary O’Meara.”

  9. Bryan

    Quick Wikipedia search – title was “World Without Stars”.

    (hmm – is the phrase “quick Wikipedia” redundant?)

  10. Steve P.
  11. Remek

    I wonder if there are life bearing planets around any of those stars?

    Unlikely, at least for the stars we can see there. They’re much too hot and have very short short lifespans (only in 100’s of millions of years). Any planets that managed to be formed, and happened to be in a habitable zone, would never have the chance to cool enough nor escape constant bombardment by remaining orbital debris to have a chance for ‘life’ to get organized and flourish before their parent star explodes or expands.

  12. csrster

    I wouldn’t describe M81 and M82 as easy binocular objects – unless you mean “easy so long as you have very good binoculars, well-trained eyes, and a very dark sky”. They are however quite cool in even a fairly small telescope – even my 4-inch refractor shows a hint of structure M82.

  13. Just to provide a bit more background and info on the M81/M82 pair, I have a post at my blog about them.

  14. At 200 million years old, none of those stars would yet have life-bearing planets, most likely. Any Earth-sized planets would still be undergoing the same kind of bombardment Earth took during the Hadean eon, and would have a magma ocean for a surface. That being said, there might be F-M type stars in the mix that will someday have life-bearing planets, or even planets with intelligent life.

    In their early space-travel era, they would surely be depressed at the difficulty of reaching neighboring star systems. They wouldn’t even be able to tell whether other stars had planets; their nearest neighbors might be too far away for even radial velocity techniques to work.

    I hope that star travel using some variant of hyperspace or the Alcubierre drive turns out to be possible, just so those folks (if any exist) won’t be too isolated.

  15. Mark Martin

    “Before these observations, it wasn‚Äôt really thought it was possible to form stars in the regions between galaxies, so this is an interesting new find.”

    Reminds me of this TED-talk by David Deutsch: http://www.ted.com/index.php/talks/view/id/47

  16. Michelle

    Woah that’s pretty cool…

    so they have no host galaxy? They’re like unwanted kids or something. ūüėõ

  17. Quiet_Desperation

    I feel their pain. :(

  18. Mapnut

    How far are we from the Large Magellanic Cloud? That might be a good model of what a galaxy would look like to the naked eye from outside of it.

  19. Stupid question: When you’re observing stars that are red or blue in color, how do you know the hue has to do with their age rather than their light being shifted due to motion towards or away from us?

  20. Chip

    Previous posters in “Lonely stars between galaxies” thread wrote:

    >>> “In their early space-travel era, they would surely be depressed at the difficulty of reaching neighboring star systems.”<<>> “…so they have no host galaxy? They’re like unwanted kids or something.”<<>> “I feel their pain.”<<<

    Now folks let’s not get too depressed. They do have the best gourmet restaurants in the outskirts, not to mention the tourist trade from vacationing galactic advanced alien snowbirds. (And let’s not even talk about the black market in Dark Matter.)

  21. Mark Martin

    Hi Toast,

    That’s actually quite a good question. Star ages are estimated more by their whole spectra than just by the predominant color seen in optical light. Stars of different ages have different abundances of chemical elements present in their outer layers, these elements having been synthesized by its history of nuclear fusion in the core.

    And the spacing of spectral lines is constant even with a red or blue shift, although those lines are of course shifted over by an amount appropriate for the star’s relative radial velocity. It’s like this:

    Hypothetical star with zero velocity:
    Red orange yellow green blue violet
    | || | ||| | | ||| |

    Same star with some receding velocity:
    Red orange yellow green blue violet
    | || | ||| | | ||| |

    So if the precise spacings of the lines can be matched up with a known mixture of chemical elements, the composition of the star is determined and its age estimated. Assuming that the match is accurate, the amount of redshift is also of course determined directly from the shift in the lines.

    An independent way of determining the shift is by passing the starlight through a sample of a known gas on its way to the astronomer’s photographic apparatus. If that gas is present and emitting light in the star’s atmosphere, then it’ll make an absorption spectrum as it interacts with the gas sample here on Earth. This in turn will be shifted over by some amount, from which the velocity is determined.

  22. Mark,

    Thanks for the explanation. Fascinating stuff.

  23. Mark Martin

    Hey, Toast, I just noticed something that might be confusing. When I wrote that post originally the spectral lines were shifted between the two sets. I now see that the formatting wasn’t preserved and both sets are in the same position. The lines in the top set should be (imagined to be) noticeably off to the right.

  24. no one

    Thanks for explaining that to Toast, that’s what I thought the answer was.

    And a tip for everyone for writing on the internet:
    You can create some       spacing with the Non-Breaking Space entity: &nbsp;

  25. Chris

    I know that it is considered bad form/sour grapes to point out when other astronomers aren’t citing previous work, but not only was this done before, but the AAS had a press release in 2003 about this discovery. See the following abstract:


    (yes, I pointed to an IAU abstract and not an AAS abstract, but the abstract from the AAS meeting didn’t say what they had discovered, but when they presented the poster and issued their press release they presented what they say they discovered in the IAU abstract, that is, blue stars in the gaseous tidal tails).

    So as neat as I find this result, it is disappointing to see that no one seems to have realized that essentially this exact same result was first publicized five years ago.

  26. astrolieber

    Wow !
    No wonder astronomy’s my obsession.
    Can life can get any cooler ?
    @Phil Plait:
    I assume that all the blue stars are O/B and very metal rich ?
    Or am I wrong ?

  27. Duilia de Mello

    Hi Chris,

    I am aware of Pat Durrell’s work, of course. I read the literature and know Pat, even discussed my results with him at the meeting in Austin! Just one detail, he has not looked at this particular region and he has not used Hubble’s ACS to resolve the blue blobs that we have. We found 2000 stars in that region. Previous work done by Makarova and collaborators used the old WFPC2 camera but missed most of the blue blobs and detect only 200-300 stars. So, yes, we are the first ones to ever see the blue blobs in between M81 and M82 in detail. There are plenty of other areas around M81, Pat has seen them and published them. His results are very important too and help us build a better picture of what happens in the outer disk and halos of spiral galaxies. Anyway, just thought I should clarify this and not let people think that we have rediscovered the wheel…


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