The Cosmic Web

Just a short one this week, as I’m very busy at work. I’m also working on a couple of astronomy podcasts, the first of which will be online in a few weeks. I’ll let you know when they’re up.

Stephan's Quintet, by Hubble. Click to enlarge.

This beautiful group is a cluster of galaxies called Stephan’s Quintet. Its members are orbiting each other in a slow dance which, many millions of years in the future, will most likely end with a series of mergers to form a single super-galaxy. Two of them, near the centre, are already quite easy to mistake for a single object.

But one of the galaxies here is an odd one out, not really part of the cluster at all: in fact it’s about seven times closer to Earth than the others, at a mere 40 million light years instead of 290 million. Can you tell which one?

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(This was meant to come out on Tuesday as is traditional, but some sort of vengeful internet gnome seems to have prevented it. Well, here it is.)

Here’s a new image from the Hubble Space Telescope - specifically, the Wide Field Camera 3 which was successfully installed this May. The picture’s of an area that Hubble’s photographed before, producing the famous Ultra Deep Field image containing some 10,000 distant galaxies. This new picture repeats the feat in near infrared light (for the benefit of human eyes the colours have been shifted, so the light which now appears red is really in the farther infrared, while the blue is only just outside our visible range).

New Hubble Ultra-Deep Filed in infrared. Click for credit and larger versions.

Take a moment to look into that picture. Each of those tiny blobs is a galaxy.

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Lots of galaxies are spiral-shaped like our Milky Way. Some we see face-on and some edge-on, depending on their orientation towards the Earth. Those which look edge-on are generally pretty flat, sometimes with a pronounced bulge in the disk’s centre.

ESO 510-G13. Click for Hubblesight release.

But not this galaxy, the charmingly-named ESO 510-G13. Its disk, which we can see perfectly edge-on, has a definite warp to it as though someone had grabbed the edges and given it a twist. In fact this is evidence of a recent collision with another galaxy, whose gravitational effect has shifted millions of stars huge gas clouds off their orbits. The disk is being rippled through by titanically slow waves of density, like a pool’s surface after a bucket of water’s dumped into it. Although the shape of the starry and gassy components of the disk is hard to make out against the bright glow of the central bulge, the warp is easy to spot because of the dark dust lanes running through the disk. This dust, made up of tiny particles a fraction of a millimeter in diameter, absorbs and scatters the starlight from behind it.

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Here’s another Hubble galaxy image: NGC 1300, a galaxy about 70 million light-years away. I recommend taking a look at the details of the spiral arms in the high-resolution version.

NGC 1300. Click for a (14 MB) high-resolution version.

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This is the Whirlpool Galaxy, or M51, a famous and spectacular example of a spiral galaxy. It’s probably most well known for its picture taken by the Hubble telescope, but it has another claim to fame: it was the first ever galaxy identified as a spiral, in 1845.

Lord Rosse's 1845 sketch of the Whirlpool Galaxy

That may sound surprisingly late, but it’s not really: looked at from far away - the Whirlpool is about 31 million light years distant - and with a small telescope, even the most complicated structure is smeared out into an ellipsoidal blur. It takes a high resolution to see the kind of pretty images we’re used to from Hubble, even with the advantage of not having to look through the turbulent atmosphere that putting your cameras in space brings!

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