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
    +2

    Comment number 471.

    Did Brian May say he still "had a feeling" we are alone in the universe? Or even in our galaxy? Is he crazy? Mind you, he did look a bit embarrassed after he said it.

  • rate this
    +2

    Comment number 470.

    If we could not see a massive galaxy such as this, I wonder how aliens could specifically find our galaxy and our planet and go around probing people secretly.

  • rate this
    +9

    Comment number 469.

    How wonderful that we can observe these amazing events. Well done all involved.

  • rate this
    +3

    Comment number 468.

    @459 “I would suggest to you that something that could conceivably happen today is a little more relevant and a damn sight more concerning than these 'discoveries'.”

    If the human race had adopted that point of view during the Stone Age, we would still be living in the Stone Age….

  • rate this
    +1

    Comment number 467.

    The sheer amount of galaxies and stars in our universe is beyond comprehension. Surely there must masses of lifeforms more advanced and civilized than we are.

    Can they help us though...we surely need it.

    Great to see these fantastic discoveries though.

  • rate this
    +8

    Comment number 466.

    459. darlo50
    Yes, and about 70 years ago, man learned how to split the atom, and from that, today we have at least a dozen countries who have the nuclear weapons capacity to destroy our planet...
    --
    We also have everything from radiotherapy to treat cancer (untreatable 70 years ago) to smoke detectors (which use Am241 and artificial isotope similar to plutonium) also from splitting atoms

  • rate this
    +2

    Comment number 465.

    I love the description "splashed stars all over the place". While in cosmological terms it's true, but it makes it so easy to forget that this has happened over millions of years.

    Our entire history is engulfed and forgotten in such timescales as things we view as explosive events.

    Humbling and comforting and astonishingly beautiful.

  • rate this
    +3

    Comment number 464.

    459. darlo50

    Really? I can't see any weapons of mass destruction based on the Higgs boson if they need a 27kn tunnel with superconducting magnets to manufacture handfuls! I can see commercial use for UV cameras of the type used to discover this collision. 200 years ago Faraday would have no idea the electricity industry would develop. 100 years ago Planck/Einstein similarly on modern electronics

  • rate this
    0

    Comment number 463.

    Pictures like this are a challenge to all those people who say the Earth was created a few thousand years ago and that woman was made in the Garden of Eden from Adam's rib. The Pope refused to look through Galileo's telescope when he discovered the moons of Jupiter because they weren't mentioned in the Bible and so couldn't possibly exist. What a pity some people still have the same view today.

  • rate this
    -1

    Comment number 462.

    Oh yes, I remember it well. I was younger then ,but, I thought there was something odd going on. Mum said Dad was tampering with the generator but the paper said what Dad said, "IT wasnae Him!"

  • rate this
    +5

    Comment number 461.

    "Of course it was by accident. How else do you discover something you didn't know was there?"

    Er - by a deliberate search for something previously unknown?

  • rate this
    +1

    Comment number 460.

    The implication of the word "discover" is that we didn't know it was there, so the words "by accident" are superfluous. Unless, of course, the discovery of penicillin and the use of stem cells were done "on purpose"!! The BBC should get someone to check the grammar and use of the English language in their sensational headlines!

  • rate this
    -8

    Comment number 459.

    449

    Yes, and about 70 years ago, man learned how to split the atom, and from that, today we have at least a dozen countries who have the nuclear weapons capacity to destroy our planet several times over. I would suggest to you that something that could conceivably happen today is a little more relevant and a damn sight more concerning than these 'discoveries'.

  • rate this
    +3

    Comment number 458.

    What a wonderful world.

  • rate this
    +4

    Comment number 457.

    Most exciting news story today...

    Wow! But then I like astronomy. This one's too far away for my telescope, but the wonders of the internet means that I can access observations from bigger and more varied 'scopes. Wonderful stuff!

  • rate this
    0

    Comment number 456.

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

    Of course it was by accident. How else do you discover something you didn't know was there?

  • Comment number 455.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • rate this
    +1

    Comment number 454.

    It's amazing news, almost as amazing as seeing all the God comments voted down and drowned out to be replaced with fact, science, logic and rational thinking... This gives me hope that one day we will see leaders referring to science and scientists in speeches rather than their imaginary sky wizards. And may Einstein bless the United States of America!

  • Comment number 453.

    This comment was removed because the moderators found it broke the house rules. Explain.

  • rate this
    0

    Comment number 452.

    Yes, I think it is an Sb type galaxy looking at the image.
    I wonder if its present classification is also the effect of the IC4970 crash?
    But the excitement of this new detail is due to using Galex, so was NGC 6872 only known by size but not by classifaction before?

 

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