You’d think large galaxies in the early universe would have plenty of “fuel” left for new stars, but a recent discovery suggests that wasn’t always the case. Astronomers using the Hubble Space Telescope and the large millimeter / submillimeter series Atacama (ALMA) have discovered six early galaxies (about 3 billion years after the Big Bang) that were unusually “dead” – that is, they ran out of cold hydrogen needed to star formation. This was the peak period for the birth of stars, according to lead researcher Kate Whitaker, so the disappearance of that hydrogen is a mystery.
The team found galaxies thanks to a strong gravitational lens, using galactic clusters to bend and increase light from early space. Hubble identified where stars formed in the past, while ALMA discovered cold dust (a substitute for hydrogen) to show where stars would have formed if the necessary ingredients were present.
Galaxies are believed to have expanded since then, but not with star formation. Instead, they grew by merging with other small galaxies and gas. Any formation thereafter would be most limited.
The findings are evidence of the combined strength of Hubble and ALMA, not to mention Hubble’s abilities decades after launch. At the same time, it emphasizes the limitations of both technology and human understanding by asking a number of questions. Whitaker noted that scientists do not know why galaxies died so quickly, nor what happened to cut off fuel. Was the gas heated, expelled, or just consumed quickly? Giving answers can take some time, if answers are possible at all.
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