Astronomers have gathered additional evidence that stars began forming when the universe was less than 200 million years old.
Although first-generation stars have never been observed, researchers can determine their age by measuring concentrations of heavy elements in the second generation of stars. The greater the time elapsed between the birth of the first stars and of the next generation, the greater should be the concentration of heavy elements in the second generation.
One complication of this approach is that most heavy elements—considered by astronomers to be anything beyond helium—were not evenly distributed in the early universe. Therefore, measuring the amount of, say, carbon in a few stars that formed long ago may not reflect the average cosmic concentration of that element at that time.
Beryllium is a welcome anomaly. The early universe’s supply of beryllium formed in the aftermath of collisions between heavy and light nuclei from dying stars. The high-speed collisions dispersed the beryllium evenly in space.
Using a spectrometer at the Very Large Telescope in Paranal, Chile, Luca Pasquini of the European Southern Observatory in Garching, Germany, and his colleagues have for the first time detected beryllium in two of the Milky Way’s oldest stars, residing in the globular cluster NGC 6397.
The minuscule amounts of beryllium detected indicate that only 200 million to 300 million years elapsed between the first and second generations of stars.
Various evidence shows that the cluster NGC 6397 is 13.4 billion years old. With other observations pegging the universe’s age at 13.7 billion years, the first stars must have formed less than 200 million years after the Big Bang, the team reports in an upcoming Astronomy & Astrophysics.