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 431.

    To add to the physics jokes:

    Barman: We don't serve faster than light particles in here.
    A tachyon walks into a bar.

    I'll get me coat.

  • rate this

    Comment number 430.


    It might take millions of years for a collision to complete but our star is not simple affected by other stars - the space between stars in galaxies is not empty. Galaxies can be radically affected when these materials interact. Everthing interacts with everything no matter how small it is in the whole process and even a subtle change might be calamatous for a civilisation.

  • rate this

    Comment number 429.

    Oh common, Galaxy crash? One more thing to worry about from now on!

  • rate this

    Comment number 428.

    Look we can go on debating about god and so on all day long. The fact of the matter is NO ONE is more important than the other. Look at the composition of the universe, look at the composition of our bodies, look at the grass and the trees and the birds and the fish. we are ALL part of the unverse. We are all the same. You are quick to admire far off galaxies yet you quickly spite your fellow man

  • rate this

    Comment number 427.

    412. SJB

    The event has taken 130 million years to get to it's "current" stage (i.e. the stage at which the light started it's journey from there to here).

    The light has taken 212 million years to get here.

    So, the event is currently (i.e. now) 342 million years old.

    It will be another 212 million years until we can see it at 342 million years old though.

    Hope that helps.

  • rate this

    Comment number 426.

    @425 Habitual hero

    It isn't grammatically incorrect if the first word of the sentence is "science" ;-)

  • rate this

    Comment number 425.

    Incidentally, I've noticed a growing tendency among some people to capitilise the word "Science" even when it's grammatically incorrect to do so. I find this interesting. I wonder if they're aware that they're doing it.

  • rate this

    Comment number 424.


    "Physics is a science defined by mankind. Cosmology is revealing gradually the wonders of the universe created by God. Scientists say there was NOTHING before the 'Big Bang'. Assuming that is correct, where did the nuclear particle come from that was the initiator of the birth of the universe?"

    Assuming what you said is correct, where did God come from?

  • rate this

    Comment number 423.

    Genesis 1:16 "God made two great lights--the greater light to govern the day and the lesser light to govern the night. He also made the stars" "

    Done on the fourth day when there was "Light" created on the first day. One of these lights isn't a light but reflects light from the other light. The sort of mistake Stone/Bronze age peoples would easily make when describing what they see.

  • rate this

    Comment number 422.

    420. Howesyourview - Dear god you must be bored.

  • rate this

    Comment number 421.

    Howesyourview, my observational skills are disappointing because I haven't memorised all 400 odd comments? I hadn't seen your previous thread, and for that I apologise. All I could go on was that one standalone comment, which to me seemed a statement in its own right. Sorry (no sarcasm intended).

  • rate this

    Comment number 420.

    403. LeftLibertarian
    apparently god created adam (a bloke) in his appearance and then created eve using one of adams ribs .

    Everyone else. I was messing with you. I'm athiest. I was seeing whether you actually pay attention to comments or just mindlessly vote

    The reason why we can detect the collision is because such events leave evidence like a thief leaves finger prints.

  • rate this

    Comment number 419.


    Hi cs.

    Clearly, we can all appreciate galaxy collisions. As someone who believes in God, I do see scientific discoveries in much the light you suggest. However, I am not sure how worthwhile it would be to try to share that in a forum like this.

    I do, though, think that people should not be hit over the head with galaxy collisions just because they disagree on philosophy or religion.

  • rate this

    Comment number 418.

    But that is just so much wishful thinking, it'll never happen - the distance between us our nearest other star system is so immense
    The distance between you and i has been nullified by scientists and somewhat amazingly (some people on here might think magically...) what i'm typing now appears in your front room within a few moments...

  • rate this

    Comment number 417.

    391. Chris
    What the red/blue shift does is it tells us how old the light is when it reaches us"

    Erm, no it doesn't. It tells us the relative velocity between the thing that's emitting the light and the thing that's observing the light, not how 'old' the light is.

    From that relative velocity data scientists may be able to infer an age for the thing emitting the light based on some weird theories

  • rate this

    Comment number 416.

    Now I am really confused....

    I have just found out Moses was a motorbike enthusiast!!

    It is the Bible it says......"and the roar of Moses's Triumph was heard throughout the land!"

  • rate this

    Comment number 415.

    Einstein came up with the E=MC2 solution because he didn't follow protocols preferred by scientific institution's of today. It was explained by several reports of late, it was because of his brilliance in Philosophy that he refused to think within the box.

    Unfortunately, if he was born just 20 years ago then it would be likely that his efforts would be ignored. How can the next Einstein succeed?

  • rate this

    Comment number 414.

    390. Howesyourview

    Actually impossible to prove that some supernatural being didn't create the universe 6000 years ago and align every particle in position and trajectory to make it appear to be 13.5B years old. One might then ask why would such a being do that and then demand faith from us when he has provided vast evidence and investigative curiosity to undermine that faith.

  • rate this

    Comment number 413.

    @366. Dr Feelgood The event wasn't a 'collision' in the usual sense. As the space between stars and planets in a galaxy is vast(our own closest stellar neighbour is over 4 light lears away) it is very unlikley that any of the objects that make up the 2 galaxies came anywhere near each other. It also lasted millions of years. This was more of a very slow assimilation.

  • rate this

    Comment number 412.

    This is an interesting event, but I'm confused by the timeline, surely if we can detect the result of the collision in a galaxy that is 212 million light years away then the event must have happened on or prior to this time. If the event happened in the suggested 130 million year time frame then it would be another 82 million years before we would be able to detect the event.


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