Image of the Week 30/07/10: Star birth gone wild

At Galaxy Zoo, several of us have been lucky enough to get this soft-looking beauty to classify:

From the SDSS telescope in New Mexico, which supplied the images for Galaxy Zoo’s first two projects. You can look up more details from the SDSS pages here.

From the funny shape, especially the loops towards the right, we can see that it’s a past merger – a collision of two galaxies many millions of years ago. While it’s unlikely that any stars or planets crashed into each other (they are just too far apart), the immense gravity drags both structures around like an adventurous octopus playing with ribbons.

We can also see that it’s got a huge dust lane in the middle. Dust is usually larger particles than the hydrogen and helium gas which is abundant in the Universe, and from which stars form – it’s much rarer, but if it lies over a large enough area it blocks light (this is why we can’t see the centre of our own Galaxy).

The name ARP 220 comes from the Atlas of Peculiar Galaxies, compiled by Halton Arp. ARP 220 is in the constellation Serpens, and 250 million light years away.

It’s been an object of interest before. Back in 1997, it was Astronomy Picture of the Day.

And it’s continued to be interesting. Yesterday, Chris Lintott sent a tweet about a conference he’s attending – an entire talk was given to this object. I did not know until that moment that ARP 220 is the most luminous object in the local Universe.

Here is Hubble’s view:

Hubble has just had a bit of a field day imaging this monster with its Advanced Camera for Surveys, which revealed a cosmic sort of “baby boom”. This often happens with mergers: gas clouds, formerly minding their own business and cheerfully orbiting the centre of their Galaxy with everything else, suddenly get slammed into other gas clouds from the intruding galaxy, collapse, and set off a firework display of new star birth.

In ARP 220, it’s happening as never before. Over a 5,000 light year area – which is pretty titchy for space, only 5% of the Milky Way – there is as much gas as the Milky Way contains.

The clusters of star birth are so close together that they look like individual stars. There are two main groups which have been surveyed: one is only 10 million years old, the other about 70 million. The younger group contains larger stars. It is not yet known whether there were two “baby booms” or whether ARP 220 is undergoing a continuous starforming phase.

The dust blocks the view, but glows brilliantly in infra-red light. Its X-ray output has also captured the attention of astronomers – the intense activity has created a “superwind” that Chandra has picked up, and its effects can be seen 75,000 light years away.

The further out lobes are probably remnants of the merger. These filaments of gas are still hot – glowing, but unlikely to form new stars for a long time.

Astronomers say the conditions in ARP 220 may mimic an earlier, smaller Universe in which galaxy collisions and outrageous star formation were a lot more common.

One final version of this picture comes not from the past but from the Futurity science blog – the Saburu telescope obtained a false-colour image of the merger’s far-flung tidal debris.

If that’s not enough pretty pictures for you, Google Images yields a healthy crop. French speakers should particularly enjoy this one!