The Very
Large Telescope has taken one of the best ever images of two galaxies locked in
a slow motion, disruptive collision, scientists say.
The image
has also given astronomers a peak at an unusual exploding star in the same area
of the sky.
The colliding
galaxies are known collectively as Arp 261, from Halton Arp's catalogue of
Peculiar Galaxies. With the the FORS2 instrument on the ESO's Very
Large Telescope in Chile, astronomers were able to photograph the oddball in greater
detail than ever before.
Arp 261 lies
about 70 million light-years away in the constellation of Libra, the Scales. Its
chaotic and very unusual structure is the result of the galactic close
encounter.
Although
individual stars are very unlikely to collide in such an event, the huge clouds
of gas and dust in the galaxies crash into each other at high speed, leading to
the formation of bright new clusters of very hot stars, which are clearly seen
in the picture.
The paths
of the existing stars in the galaxies can be dramatically disrupted, creating
the faint swirls extending to the upper left and lower right of the image.
Both interacting
galaxies were probably dwarfs not unlike the Magellanic Clouds
orbiting our own galaxy.
The images
used to create this picture were not actually taken to study the interacting
galaxies at all, but to investigate the properties of the inconspicuous object
just to the right of the brightest part of Arp 261 and close to the centre of
the image. This object is an unusual exploding star, called SN 1995N, that is
thought to be the result of the final collapse of a massive star at the end of
its life, a so-called core collapse supernova.
SN 1995N is
unusual because it has faded very slowly — the glow still shows clearly on this
image more than seven years after the explosion took place.
It is also
one of the few supernovae to have been observed to emit X-rays. It is thought that
these unusual characteristics are a result of the exploding star being in a
dense region of space so that the material blasted out from the supernova
ploughs into it and creates X-rays.
The image
also captured two small asteroids from our Solar System that lie between the
orbits of Mars and Jupiter and happened to cross the images as they were being
taken. They show up as the red-green-blue trails at the left and top of the
picture. The asteroid at the top is number 14670 and the one to the left number
9735. They are probably less than 3 miles (5 kilometers) across.
There is
also a star captured at the bottom of the image. Though it appears bright, it
is still about one hundred times too faint to be seen with the unaided eye. It
is most likely a star like the Sun and about 500 light-years from us.
Arp 261
itself, and the supernova, are about 140,000 times further away again than this
star. Much more distant still, perhaps some fifty to one hundred times further
away than Arp 261, lies a cluster of galaxies visible on the right of the
picture.
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