Early in the Universe's history, before the formation of the first stars, nearly all of the regular matter existed in the form of the three lightest elements: hydrogen, helium, and lithium. Initially, the Universe was so energetic that these elements couldn't hang on to any electrons; instead, all of the normal matter existed as a plasma. When the Universe finally cooled enough to allow atoms to come into existence, the photons that resulted formed the cosmic microwave background, which provides us with a detailed look at the physics of the Big Bang.

At that point, the Universe entered what's called its dark ages. Stars and small galaxies started to form, but the dense fog of atoms they were born in kept any record of the events from being visible for hundreds of millions of years. It was only later, once enough stars had formed, that their emissions re-ionized the interstellar gas, making the Universe transparent again. By that time, many of the most interesting events in the Universe's history had already happened.

Scientists have lately been able to make observations that are beginning to shed light on the Universe's dark ages. In the latest example, they looked at how an early supernova lit up the galaxy it occurred in, revealing the presence of heavier elements, but in much smaller quantities than we currently see.

The observations rely on the detection of a gamma-ray burst from an extremely energetic supernova. NASA's orbiting SWIFT observatory is designed to rapidly detect the area of the sky where these bursts originate, allowing other observatories to capture the event at additional wavelengths. That's exactly what happened in June, when SWIFT spotted GRB 130606A, and researchers were able to arrange additional observations at the MMT Telescope in Arizona and Gemini North in Hawaii.

Measurements suggested that the gamma ray burst was incredibly distant, at 12.7 billion light years from Earth. That places it about a billion years after the Big Bang, around the time that the dark ages were coming to a close. The researchers also captured the spectrum of the light emitted by the supernova, which had distinct regions where intervening material had absorbed some of the photons, creating a sharp drop-out at specific points in the spectrum. These drop-outs, or lines, could be used to identify the elements that were present in between the supernova and us.

Some of the material that absorbed the light was in the galaxy itself. But it's hard for light to travel for 12.7 billion years without running into anything else, and the researchers detected indications of at least four additional objects that left their marks on the light received at Earth (which didn't even come into existence until eight billion years after the supernova took place). But it was actually possible to identify and account for each of the sources thanks to a phenomenon known as redshift.

You can think of redshift as a bit like the Doppler effect, in that objects that are moving away from you have the light they emit shifted to longer—meaning redder—wavelengths. As the light was emitted from the supernova, elements nearby absorbed some of it at specific locations. As the light travelled out toward Earth, the locations of those absorption lines became more and more red-shifted. By the time they ran into another object, with its own set of elements to absorb things, the original absorption lines had redshifted out of the way. The same process took place for each of the three remaining objects, leaving a complicated fingerprint of elemental absorption lines on the light that eventually reached Earth.

To find the original galaxy, the researchers simply had to work backward, identifying the fingerprint of the first object, eliminating it, and then moving on to the next. By the time they had gotten rid of all four, what remained was the most distant object itself, the galaxy that hosted the supernova. The process also contained its own validation, as the redshifts provide distance information, and the ones from the galaxy nicely lined up with the measurements made by other observations.

The authors of the paper were able to detect elements that included nitrogen, oxygen, carbon, and silicon. However, the apparent amount of these heavier elements (called "metals" in an astronomy-only usage of the term) was quite limited, being about 10 percent of what we see in the modern Universe. That makes sense, as there hadn't been enough time for more than the first generation of stars to go supernova by then. Later events of this sort added to the mixture of heavy elements available to form planets and moons.

The authors could also use some of the features of the absorption lines to infer things about the environment around the supernova (some of the elements were clearly moving). They could also combine those with measurements made using other distant objects, like early quasars, to infer some things about the reionization era in general. So far, it looks like the era was complex, and it probably didn't occur evenly throughout the Universe. But as more of these distant objects are observed, we may get a clearer picture of how the dark ages came to an end.

The arXiv. Abstract number: 1306.3949 (About the arXiv). To be published in The Astrophysical Journal.