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 191.

    see comment 49

  • rate this

    Comment number 190.

    If you accept 'big bang' which seems the current most likely theoryand if you accept the constantly recurrng universe, then two things emerge.

    Firstly, it's gobsmackingly unlikely that you're sat here reading this but also that (infinity being so, well, infinite) it's inevitable that at some point in the future someone identical to you will be reading it again.

  • rate this

    Comment number 189.

    wow think of all the exciting things still to be discovered keep up the good work

  • rate this

    Comment number 188.

    I'm an atheist but this has got rather side-tracked - it's an article about galaxies not about belief. It's an amazing image - you can appreciate the wonders of creation whether you believe in a magical bearded creator or not. Incidentally this wll happen to our own galaxy too, since right now we're crashing towards a collision with Andromeda.

  • rate this

    Comment number 187.


    The big crunch is certainly one of many plausible and exciting theories. I particularly like the romance of this theory - we essentially live forever. M theory is another fascinating theory. What's for sure though is that - however mind boggling and incomprehensible - these theories have just as much credibility as God and any religion.

  • rate this

    Comment number 186.

    This kind of news along with experience of merchants in poor parts of Africa remind me that we have Science to thank for our current prosperity rather than business

  • rate this

    Comment number 185.

    Until the scientists can tell us what caused/was before the "Big Bang" then there is still a space for the concept of God."

    There is always space for a concept, no matter how bizarre, however there is nothing at all that shows or requires the influence of any god or creator.
    If a thing has no effect, it, effectively, has no existence.

  • rate this

    Comment number 184.

    Sheldon found this last year, it's old news

  • rate this

    Comment number 183.

    It's so great mankind is making such strides forward, hooray for science and technology !!

    Back on Earth, we are witnessing the greatest extinction since the dinosaurs, war and poverty as never before (no progress), economic disasters, environmental catastrophe, and the world slipping ever further over the edge.

    But still, a nice photo on your iPhone - and everything is ok !!

  • rate this

    Comment number 182.

    Two things I can't reconcile

    1) Last night on Star gazing Brian Cox said on the subject of the expanding universe - "everything is moving away from everything else."

    2) Galaxies crashing into each other.

  • rate this

    Comment number 181.

    I look forward to the day we understand the universe to a degree where we can travel the vast distances required to actually visit these phenoma. I'm sure in time we will unlock the true physics of space and time and travel the universe. I unfortunately won't be around to see it.

  • rate this

    Comment number 180.

    If this is true, surely mass is an illusion created by time? Or have I got it the wrong way round, is time an illusion created by mass?"


  • rate this

    Comment number 179.

    light speed may be possible i. iam no scientist but i read somewhere that a certain particle ( neutrino? ) can exist in two places simultaneously surley that is faster than light .

  • rate this

    Comment number 178.

    "If the universe is actually expanding at a faster rate further out.."

    The universe is not expanding faster further out. In fact there is no such thing as further out. Any point in the universe can be considered to be the centre and there is no edge. The further parts seem to us to move more slowly but this is a result of accelerating expansion and the speed of light limiting our observations.

  • rate this

    Comment number 177.

    @158 Indeed. Prof Hawking has suggested that time travel is in fact theoretically possible, so let's wait and see.
    If you refer to Time Dilation then yes, time moves differently for those at different relative speeds, or under effects of gravity. Backwards time travel - I cannot recall a current viable theory.

  • rate this

    Comment number 176.

    There is an accessable, easy to understand and thoroughly entertaining book by Bill Bryson entitled A Short History of Nearly Everything that explains in laymen's term this phenomenon and much else besides (hence the title!)
    A recommended read.

    I hope this isnt seen as advertising and against the rules.

  • rate this

    Comment number 175.

    Nothing can go faster than light, not even the combined speed. (This is totally absurd, but also happens to be true, and observable)
    Just an addition, no object can go faster than speed of light - however, the expansion of universe (i.e. space) close to the big bang was faster than light

  • rate this

    Comment number 174.

    What is the point? another "explosion" so far away we would be as well not knowing about it. The money wasted on these projects needs to be looked at. Unless there is something happening within our solar system what is the point of harping on about these galaxies when we will never get close. This looking for extra terrestrial life is a smoke and mirrors trick to waste grant after grant.

  • rate this

    Comment number 173.

    Are they sure it wasn't a flake?

  • rate this

    Comment number 172.

    @ 126 "if all matter was created by the big bang is the centre of the universe still exploding matter or has the bang gone out but just everything expanding away from it ."

    If I understood correctly what a bunch of Oxford University physics students explained to me, there is no actual pinpoint or "centre" to the big bang. The whole universe just plopped into place everywhere all at the same time.


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