Galaxy crash sparks biggest spiral

VLT/Galex image of NGC 6872 Galex revealed a wealth of new stars at the galaxy's outer reaches

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Astronomers have spotted the largest known spiral galaxy - by accident.

A team was looking through data from the Galaxy Evolution Explorer (Galex) satellite for star-forming regions around a galaxy called NGC 6872.

But they were shocked to see a vast swathe of ultraviolet light from young stars, indicating that the galaxy is actually big enough to accommodate five of our Milky Way galaxies within it.

The find was reported at the American Astronomical Society meeting in the US.

NGC 6872, a galaxy about 212 million light-years away in the constellation Pavo, was already known to be among the largest spiral galaxies.

Near it sits a lens-shaped or lenticular galaxy called IC 4970, which appears to have crashed through the spiral in recent astronomical times.

Rafael Eufrasio of the Catholic University of America and Nasa's Goddard Space Flight Center and colleagues from the University of Sao Paulo in Brazil and the European Southern Observatory in Chile were interested in a number of regions away from the galaxy.

"I was not looking for the largest spiral - it just came as a gift," Mr Eufrasio told BBC News.

Galex - a space telescope designed to search for the ultraviolet light that newly born stars put out - hinted that NGC 6872 was made much larger in size by the collision.

The team went on to use data from a range of other telescopes including the Very Large Telescope, the Two Micron All-Sky Survey and the Spitzer space telescope - each of which sees in a particular set of colours, in turn evidencing stars of varying ages.

They found the youngest stars in the outer reaches of the galaxy's enormous spiral arms, getting progressively older toward the centre.

That suggests a wave of star formation that travelled down the arms, set off by the collision with IC 4970, with the newest stellar neighbourhoods pushing the galaxy into the top spot in terms of size.

"It's been known to be among the largest for two decades, but it's much larger than we thought," explained Mr Eufrasio.

"The galaxy that collided with the [central disc of NGC 6872] splashed stars all over the place - 500,000 light-years away."

A simulation of the galactic collision suggests it happened 130 million years ago A simulation of the galactic collision suggests it happened 130 million years prior to the situation we see today

Besides being one for the record books, NGC 6872 updates the catalogue of known galaxy smash-ups, demonstrating how dramatically galaxies can be changed and added to by collisions.

"It shows the evolution of galaxies in the larger context of the Universe - how the large galaxies we had before were accreted from small clumps in the early Universe," Mr Eufrasio said.

"We're just seeing one example of two interacting galaxies but in the past that happened much more often - that's how the big [spiral galaxy] discs we have were probably formed. Putting that in a larger context, it's a very cool system."


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  • rate this

    Comment number 231.

    Personally I'd be happy for an explanation as to why the force of gravity is so much weaker than predicted"

    Predicted by whom? Gravity is the weakest force. The electromagnetic force holds solid matter together and prevents gravity pulling us through; the strong force hold atomic nuclei together and the weak force is responsible for radioactive decay. The latter 2 are v short range.

  • rate this

    Comment number 230.

    Amusing to see all the anti-religious comments when one of the scientists involved is from the Catholic University of America.

  • rate this

    Comment number 229.

    "I'm no expert but I think they would only have to pass close enough to disrupt the delicate gravity, shifting a planet out of it's orbit to wipe out any life forms. Don't quote me though." CJFargo 11/1/2013 BBC Have your Say

    Sorry - couldn't resist.!

  • rate this

    Comment number 228.

    God made it

  • rate this

    Comment number 227.

    @223/224 - bringin' out the physics jokes!

    2 atoms standing at the bar
    First one says "I think I've lost an electron"
    Second one says "Are you positive?"

  • rate this

    Comment number 226.

    Just now
    "Looking up at the sky at night, the stars and galaxies are light years from each other. Yet we can see and perceive these vast distances in an instant. Therefore our minds' eyes are faster than the speed of light."

    No we see and percieve the photons striking our eyes which were emitted by these stars many years ago.

  • rate this

    Comment number 225.

    You only have to go to the supermarket sweet aisle to realise that a Galaxy is bigger than a Milky Way, you don't need a telescope.

  • rate this

    Comment number 224.

    To add to 223:
    There was an old lady called Wright
    who could travel much faster than light.
    She departed one day
    in a relative way
    and returned on the previous night.

  • rate this

    Comment number 223.

    Joke for the Physicists:

    Why are quantum physicists so poor at sex?

    Because when they find the position, they can't find the momentum, and when they have the momentum, they can't find the position.

  • rate this

    Comment number 222.


    It is no wonder you believe in the big fairy in the sky with such utterly logic lacking thought processes......

  • rate this

    Comment number 221.

    God would have to be a woman to be so spiteful that she cares what something as insignificant as me does in such an enormous universe.

  • rate this

    Comment number 220.

    massive yaaaaaaaaaaaaaaaaaaaaaaaaaawn

  • rate this

    Comment number 219.

    Being an amatuer astronomer, i am completely fascinated by the advances in technology that allow us to see our universe. People may think its a waste of money but personally i dont think enough is spent on it. Its only when you think about the scale of the universe that you realise how insignificant we are in the grand scheme of things. Our ability to explore the universe should be encouraged.

  • rate this

    Comment number 218.


    "I dont think that is right, how can it be, light passes/travels through darkness, so darkness got there 1st, it existed before light reached it & light cannot catch up with universal expanding darkness"

    Darkness is a lack of light!!

  • rate this

    Comment number 217.

    Looking up at the sky at night, the stars and galaxies are light years from each other. Yet we can see and perceive these vast distances in an instant. Therefore our minds' eyes are faster than the speed of light.
    God 1 - 0 Science

  • rate this

    Comment number 216.

    Just because we are used to seeing things close by, it doesn't mean that there are not things far away.

    In fact, there has to be. If there wasn't anything there then there would just be nothing.

    And then there was something. Positive and negative. Matter and anti matter. Sum of zero.

    Not a difficult concept.

    A famous Belgian came up with the idea. Years ago. A priest called George.


  • rate this

    Comment number 215.

    Some may be asking what is the point? In fact, astronomy is hugely important as it enables us to find, track and study near earth objects such as asteroids.

    In addition the science, combined with engineering enabled the Rover to be on Mars now.

    It also inspires children to get involved in science and opens their minds to future possibilities. Perhaps to even improve life on earth?

  • rate this

    Comment number 214.

    "ok let me rephrase: the universe is expanding faster the further back in time you observe."

    Again, no. In it's current phase the universe is accelerating, so if you look back in time it is moving more slowly. However some versions of inflation theory suggest that for a very brief instant after the big bang the expansion was faster than light. This is all currently very theoretical.

  • rate this

    Comment number 213.

    @205 Dr-G

    That's true. I was only expanding on your post friend, not disagreeing with you.

    If you were riding on a beam of light and shone a torch the light emitted would travel away from you at the speed of light. Completely unintuitive, bizarre and amazingly thought provoking. As someone once said it's all relative. :)

  • rate this

    Comment number 212.

    Really good to see that a science story gets some well desrved publicity from the BBC (Is it really a "new" story though?)

    Must be a slow news day at the BBC given the prominence also given to an item about that picture of the ex-Miss Middleton


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