Astronomers find clouds of primordial gas from the early universe, just moments after big bang
For the first time, astronomers have found pristine clouds of the primordial gas that formed in the first few minutes after the Big Bang. The composition of the gas matches theoretical predictions, providing direct evidence in support of the modern cosmological explanation for the origins of elements in the universe.
Only the lightest elements, mostly hydrogen and helium, were created in the Big Bang. Then a few hundred million years passed before clumps of this primordial gas condensed to form the first stars, where heavier elements were forged. Until now, astronomers have always detected “metals” (their term for all elements heavier than hydrogen and helium) wherever they have looked in the universe.
The researchers discovered the two clouds of pristine gas by analyzing the light from distant quasars, using the HIRES spectrometer at the Keck Observatory in Hawaii. By spreading out the bright light from a quasar into a spectrum of different wavelengths, the researchers can see which wavelengths were absorbed by material in between the quasar and the telescope. In the spectra from the gas clouds, the researchers saw only hydrogen and its heavy isotope deuterium.
Prior to this discovery, the lowest measurements of metal abundance in the universe were about one-thousandth the metallicity of the sun. Scientists had thought that nothing could be less than one-thousandth the solar enrichment. That’s because the metals produced in galaxies were so widely dispersed in the universe. The researchers estimated a metallicity for the pristine gas of about one-ten-thousandth that of the sun. At the other extreme, stars and gas with the highest metallicities are almost ten times as enriched as the sun.
The spectrographic analysis of the pristine gas clouds places them in time at about 2 billion years after the Big Bang, or nearly 12 billion years ago. At that time, theoretical models predict that galaxies were growing by pulling in vast streams of cold gas, but these “cold flows” have never been seen. The pristine gas clouds are potential candidates for these elusive cold flows.
Above: This image from a simulation of galaxy formation shows streams of gas feeding the growing galaxy. The newly discovered gas clouds may be part of a “cold flow” of gas similar to these streams.