We had a fantastic production meeting yesterday morning, and I’m really looking forward to the rest of the year. We also had a quick rundown of what we’ve missed in the two months without news notes, and I was generally mocked for suggesting that NASA’s announcement on dark matter yesterday was likely to be interesting.
I was right. Here’s what they’ve done. Take this image of a cluster of galaxies:
Then spend a long time looking at the shapes of all the small background galaxies, looking for the distortion caused by the passage of their light through the massive foreground galaxy cluster. Then use those distortions to work out where the mass is in the cluster – not just the mass that happens to shine, but all the dark matter too. Colour the result a pretty shade of blue.
The first thing you notice is that it really is a very nice shade of blue, and that NASA’s graphics are getting better and better. Then you notice that the matter in the cluster forms a ring around the centre. This is a slightly crazy result, and the astronomers involved spent a year refusing to believe their eyes (or slightly more accurately, their computers). What seems to have happened is that this is a collision between two clusters, which we’re viewing head-on. The ring is a ripple moving outwards as an aftershock of the collision. There’s a simulation of this here, or you can look at high resolution images (and non-quicktime movies) here.
It’s a stunning result, and the observers deserve a huge amount of credit for what must have been a massive (pun intended) amount of work. But I’m not sure this quote, from first author Myungkook James Jee, is correct
“This is the first time we have detected dark matter as having a unique structure that is different from the gas and galaxies in the cluster”
Have a look at my article on the Bullet Cluster over on the Bang! site.
Alice Sheppard on May 16, 2007
I like blue too – I had noticed one rarely seems to find it, as opposed to red, black, pink, green, etc., in astronomy.
Isn’t dark matter in a different structure from our Galaxy, if it’s making it rotate at the same speed at the edges as at the middle? I.e., more to the outside? (Don’t put that up if I’ve got that hideously wrong, please, Chris!)
In any case, quote from my tutor at Sussex: “The best science isn’t always when someone shouts ‘Eureka’. More often, it’s when someone looks at something and says, ‘That’s funny’.”
Stuart on May 16, 2007
I noticed that too. The ESA/Hubble press release does mention the Bullet Cluster. It says that in that case it was only the gas that was separated out, with the dark matter still following the distribution of galaxies. So the ‘and’ in the quote is important.
Robert Simpson on May 16, 2007
I think we all have to be careful abut how we present this result. Chris, you are in a particularly good position to help ensure that images like this are not shown as ‘images’ in the normal sense at all. You’re right when you say that NASA has gotten very good at making this look nice. In fact it almost looks real. But it isn’t real, the distribution of blue here is a representation of the effect of gravity, and we must be extra careful when trying to communicate this results to a non-astronomical audience.