When I turned 40 recently, people kindly told me, “But you still look young.” So, what do you tell someone who is young but looks old? This is my brilliant segue into a description of a strange discovery by astronomers who observed a galaxy cluster that’s only three billion years old but looks much older. Here’s a neat vid showing its location in the sky (but don’t bother looking for it tonight unless you’ve got a world-class telescope):
Galaxy clusters are the main structures of the universe. A single cluster can contain thousands of galaxies, all gravitationally bound to each other. Because this particular cluster is so far away, astronomers are seeing it as it was when it was very young. (The idea in astronomy is that the further away you look in space, the earlier in time you’re observing the universe. That’s because light, although extremely fast, travels at a finite speed.) Astronomers therefore expected to see typical signs of youth in the cluster — stars actively forming in the galaxies and very little hot, X-ray emitting gas. Instead, what they observed was an older population of stars with very little star formation, and a significant amount of X-ray emitting gas, which usually takes time to accumulate and get trapped in the cluster. Astronomer Raphael Gobat comments, “Such clusters are expected to be very rare according to current theory, and we have been very lucky to spot one. But if further observations find many more, then this may mean that our understanding of the early universe needs to be revised.”
That’s how science works. Observe, hypothesize, observe, theorize, observe, revise … .