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Astronomers Discover Incredibly Rare ‘Fossil Cloud’ Created Minutes After the Big Bang

The fossil cloud is only the third of its kind ever seen by astronomers, but could pave the way for their systematic discovery in the future.
Simulation of galaxies and gas in the universe.
Simulation of galaxies and gas in the universe. Image: Keck Observatory

Astronomers working at the mountaintop Keck Observatory in Hawaii have discovered an incredibly rare “fossil cloud” of pure hydrogen created minutes after the Big Bang. According to the astronomers, it is one of only three fossils—pristine clouds of gas that provide astronomers with an unadulterated look at materials from the early universe—known to exist. Researchers believe the hydrogen within the cloud was produced minutes after the Big Bang and has somehow managed to remain almost entirely untainted by metals from exploding stars for 1.5 billion years, making this fossil incredibly rare. Understanding the distribution of these fossil clouds can help astronomers better understand how heavy metals were distributed in the early universe and why some gas clouds formed stars and galaxies while others didn’t.


“Everywhere we look, the gas in the universe is polluted by waste heavy elements from exploding stars,” Fred Robert, a graduate student at the Swinburne University of Technology and lead author of the research paper describing the fossil, said in a statement. “But this particular cloud seems pristine.”

As detailed in a preprint of a forthcoming research paper in Monthly Notices of the Royal Astronomical Society, Robert and his colleagues discovered the cloud by using a spectrograph and spectrometer on the massive Keck telescope. These instruments analyze the light spectrum of celestial objects in order to determine qualities such as their temperature and chemical composition, which give a unique “fingerprint” for these objects.

In the case of this fossil, the astronomers analyzed a quasar located behind the cloud. Quasars are incredibly bright star-like objects that are characterized by large energy emissions as material falls into supermassive black holes. By analyzing the way the energy from the quasar passed through the cloud, Robert and his colleagues were able to determine that it was likely a rare Big Bang fossil.

“If it has any heavy elements at all, it must be less than one-ten thousandth of the proportion we see in our sun,” Robert said. “This is extremely low [and] the most compelling explanation is that it’s a true relic of the Big Bang.”

Read More: Why Some Scientists Think the Speed of Light Slowed After the Big Bang

The only other two Big Bang fossils were serendipitously discovered at the Keck Observatory in 2011. By contrast, Robert and his colleagues discovered the latest fossil by doing targeted searches of area where other astronomers had seen traces of hydrogen, but no other heavy metals.

John O’Meara, the head scientist at the Keck Observatory and one of the discoverers of the first two Big Bang fossils, said in a statement that he thought his 2011 discovery was just “the tip of the iceberg.” But over the past seven years no other astronomers managed to find additional pristine relics from the Big Bang.

Robert and his colleagues’ discovery is exciting in and of itself, but it’s also significant insofar as it represents the first time that a Big Bang fossil was discovered through a systematic search. The researchers hope that this will pave the way for the discovery of more fossils in the future, which will give astronomers a clue to exactly how rare they are in the universe.