One might think that large galaxies in the early Universe still had a lot of “fuel” left for new stars, but a recent discovery suggests that this was not always the case. Astronomers with the Hubble Space Telescope and the Atacama Large Millimeter / Submillimeter Array (ALMA) have found six early galaxies (about 3 billion years after the Big Bang) that were unusually “dead” – that is, they ran out of cold hydrogen that was necessary for star formation. This was the peak time for star births, according to lead researcher Kate Whitaker, so the disappearance of this hydrogen is a mystery.
The team found the galaxies thanks to powerful gravitational lenses and used galaxy clusters to bend and enlarge light from the early universe. Hubble identified where stars had formed in the past, while ALMA discovered cold dust (a substitute for hydrogen) to show where stars would have formed if the necessary components had been present.
The galaxies are believed to have expanded since then, but not as a result of star creation. Rather, they grew by merging with other small galaxies and gas. Any formation after that would have been limited at most.
The results are testament to the combined power of Hubble and ALMA, not to mention Hubble’s capabilities decades after its inception. At the same time, it highlights the limits of both technology and human understanding by raising a number of questions. Whitaker noted that scientists don’t know why the galaxies died so quickly or what happened to cut fuel. Was the gas heated, expelled, or just consumed quickly? It may take a while to provide answers, if answers are possible at all.
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