We were fascinated by the recent study surrounding what may have been the earliest stars to inhabit the universe, which was accepted for publication in the Astrophysical Journal. We reached out to the lead author, Dr. David Sobral of the Institute of Astrophysics and Space Science in Lisbon, Portugal, to find out more.

1) How did you notice the galaxy in the first place?

We first conducted a very wide survey of the sky (approximately 40 full moons on the sky, but spread over different places in the sky) with the Subaru telescope in Hawaii. We wanted to look for rare sources when the Universe was only less than 6% of its current age and that may have been missed before from looking at only very small areas. We discovered quite a few bright galaxies and found out that they are much more common than people thought, something like 30 times more common.

Then, out of those, we identified two which stood out, and the brightest was CR7. When we followed CR7 up with Keck in Hawaii and VLT in Chile, we measured its redshift (approximately 7, thus the name), which told us that it really was very distant.

2) What is unique about these early stars?

What is unique about the first generation of stars is that they are formed using only gas from the Big Bang. That means only Hydrogen and Helium (and traces of Lithium). There is no Carbon or Oxygen or anything else that allows us to be here on planet Earth. Those stars are thus tremendously special: they created the heavy elements that allow us to exist.

3) How does the discovery change our understanding of the origins of the universe?

It shows that the first generation of stars, those made of “pristine” gas, may still be forming later on the Universe, and that we may be able to find more and start to actually study. Up to know this field has been mostly theoretical. Maybe this has now changed and this will be tremendously exciting, as we will finally be able to make observations and test predictions.

4) What was the most challenging aspect of the study?

The fact that we covered very large areas made it very challenging. Also, we always need to be extremely careful to be sure that other strange sources don’t contaminate our samples. That’s why we made sure that we used other telescopes to confirm the galaxy and also to study it further. We kept questioning ourselves more and more, and getting new information as we went along. It was really challenging, but, at the same time, really exciting.

5) Are there any plans to follow up on the study?

Yes, definitely. We hope to be able to point Hubble to CR7 again, to study it with even greater detail. We also aim to study it with ALMA. Moreover, we have many other very bright galaxies which may turn out to be equally or even more exciting, and our studies are continuing: we want to push up to even earlier epochs in the Universe.

6) What was the life-span of a star in CR7?

Depends on the mass of the star. These first generation of stars, particularly the most massive, should have lived for only a couple of million years, before they went super-nova and created the first heavy elements.