The image up top is an artist's impression of a gamma-ray burst blasting through a pair of galaxies on its billion-year journey to Earth. These ancient, incredibly powerful explosions reveal the composition of early galaxies. It's not what we expected.
One recent gamma-ray burst, which has the catchy name of GRB 090323, has attracted a lot of attention from astronomers. First seen by NASA's Fermi Gamma-ray Space Telescope, the burst has been extensively studied by the Very Large Telescope by the European Southern Observatory in Chile. This particular explosion happened over twelve billion years ago, and its light passed through two galaxies, including its own, on the way to Earth.
Astronomers were able to catch this burst the day it exploded (plus twelve billion years worth of travel time, of course), which shone an unusually bright light on the ancient galaxies from which it originated. This allowed researchers at the ESO to study the light from the burst for telltale signs of different chemical elements, and from that work out the basic composition of those galaxies.
As Max Planck Institute researcher Sandra Savaglio explains, the results were unexpected:
"When we studied the light from this gamma-ray burst we didn't know what we might find. It was a surprise that the cool gas in these two galaxies in the early Universe proved to have such an unexpected chemical make-up. These galaxies have more heavy elements than have ever been seen in a galaxy so early in the evolution of the Universe. We didn't expect the Universe to be so mature, so chemically evolved, so early on."
It's surprising to find so many heavy elements because these elements are created in the explosions of stars, and it takes many stellar generations to build up a lot of them. At first glance, it wouldn't seem as though galaxies from such a relatively early point in the universe's history - just two billion years after the Big Bang - would have had enough time to amass so many heavy elements.
The best way to explain this is that we're observing these ancient galaxies while they're in the middle of extremely energetic star formation, which is enriching the interstellar gas with heavy elements at a very fast rate. The positions of the two galaxies suggest they're in the process of merging, which would also help supercharge the formation of heavy elements. Whatever went on in these ancient galaxies, it's likely that it didn't last for too long after the Big Bang, and they eventually fell back into relative quiet, with few new stars being born.
Via the European Southern Observatory.