At the Big Bang only two elements were formed, hydrogen and helium. Nowadays there are many other substances, which among other things make life possible on Earth. These substances are normally formed by fusion in stars but it is unknown how the first heavier elements were formed. These must have formed directly from hydrogen and helium at some point after the Big Bang, but before the most distant observed galaxies containing heavier elements came into being.

“The dominant theory of how the first heavier elements were formed is that a class of stars, called Population III stars, existed. They consisted of only hydrogen and helium, but has since formed heavier elements by fusion and spread them out by exploding as supernovae. This class of stars has not yet been observed. Until now when we think we have discovered two galaxies which may consist of Population III stars”, says Claes-Erik Rydberg at the Department of Astronomy, Stockholm.

According to Claes-Erik Rydberg, if this is confirmed, it could imply that the "missing link" between the hydrogen and helium formed in the Big Bang and the stars and galaxies we have observed has been found.

Facts about the study:
According to simulations, it is possible that entire galaxies of Population III stars formed. To look for these, the observational program CLASH was used. There is a finished Hubble Space Telescope program that observed 25 galaxy clusters at 16 different wavelengths. Galaxy clusters were used as gravitational lenses, because they are so massive that they sharply curve space-time so the galaxies hidden behind are enlarged. Two objects, behind galaxy clusters MACS1931 and RXJ1347, was discovered. The two objects are enormously far away and (because the speed of light is finite) far back in time. In fact, the age of the universe was only about 5% of its current age when the light we observe dispatched. The measured radiation at different wavelengths was found to fit much better into the Population III galaxies than normal galaxies.

For further information contact:
Claes-Erik Rydberg, at the Department of Astronomy, Stockholm University.