Early disk galaxy puts formation models in a spin

Published today in Nature, an international team of researchers has observed a massive, rotating disk galaxy just 1.5 billion years after the Big Bang-1.5 billion years earlier in cosmic history than astronomers had expected to find such a galaxy based on previous studies. The research has fuelled debate about how galaxies in the early Universe assembled.

The observations were made using one of the most powerful radio telescopes in the world, the Atacama Large Millimeter/submillimeter Array (ALMA), in the Atacama Desert in northern Chile.

“This is an exciting discovery for astronomers because it provides clues as to how large-scale structure began to form in the Universe,” said Dr Alfred Tiley from the UWA node of the International Centre for Radio Astronomy Research (ICRAR).

According to our current understanding of cosmology, galaxy formation follows a hierarchical order. First, dark matter ‘haloes’ are thought to develop, which then draw in surrounding gas that cools to form stars and eventually galaxies.

“In the early stages, some models predict that the gas heats up as it falls into the dark matter halo,” Tiley said.

“Over a long period the gas cools and allows the galaxy’s disk to form.

“But the discovery of a massive disk galaxy just 1.5 billion years after the Big Bang tells us its formation may have followed a different path-possibly a cold-accretion model in which the infalling gas remained cold, allowing for the rapid condensation of the disk.

“At this stage, this is just one galaxy, so we need to find more like it to further test our models and help us better understand what exactly was going on in the early Universe.”

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