spaceSpace and Physics

New Stage in Cycle of Galaxies

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Caroline Reid

Guest Author

766 New Stage in Cycle of Galaxies
Young stars photographed by Hubble. NASA.

The universe is infinitely big, and the deeper we look, the more oddities we come across. After peering deep into the universe, back to only 1 billion years after the Big Bang, astronomers have spotted some galaxies with unusual properties. These galaxies may introduce a brand-new early chapter in the galactic life cycle.

Scientists think the universe started with the Big Bang: a rapid expansion of boiling spacetime that contained all the matter and energy that makes up our universe today. After this initial expansion, spacetime began to cool and the first elements – hydrogen and helium – could form. It wasn't until many years after this that heavier elements could start to form since they can only be fused in the bellies of stars. And stars didn't form overnight.


Young galaxies are thought to have fewer stars and therefore less dust than their older counterparts. So, when looking far into the distant universe, astronomers should see galaxies with very little dust. But until now, technology wasn't accurate enough to measure dust in these faraway galaxies.

"Before we started this study, we knew that stars formed out of these clouds of gas and dust, and we knew that star formation was probably somehow different in the early universe, where dust is likely less common. But the previous information only really hinted that the properties of the gas and the dust in earlier galaxies were different than in galaxies we see around us today. We wanted to find data that showed that," says lead author Peter Capak of the California Institute of Technology (Caltech).

Using ALMA, astronomers surveyed an array of normal galaxies seen when the universe was only 1 billion years old. ALMA (NRAO/ESO/NAOJ), P. Capak; B. Saxton (NRAO/AUI/NSF), NASA/ESA Hubble.

As described in Nature, the researchers peered at these distant galaxies using the Atacama Large Millimeter Array (ALMA). ALMA can look at wavelengths longer than visible light, which gave scientists data unobtainable through visible light telescopes. The results indicate that there may be a new, early stage in the life of a galaxy that doesn't contain all the dust that we associate with galaxy formation.


The carbon readings from the nine galaxies that were examined confirmed that these early-universe galaxies contain, on average, 12 times less dust than galaxies formed 2 billion years later. 

Capak thinks that these results imply something different is going on in these early-universe galaxies. We know that galaxies form when gas and dust clump together and eventually form stars. Then these stars die and release gas and dust, which then become stars again. However, these early galaxies lack this dust, signifying a never-before-seen stage in the lifecycle of a galaxy.

"This is just an initial observation, and we've only just started to peek into this really distant universe at redshift of a little over 5. An astronomer's dream is basically to go as far distant as we can. And when it's complete, we should be able to see all the distant galaxies that we've only ever dreamed of seeing," says Lin Yan, co-author of the paper.

[Via Caltech, Nature, ALMA Observatory]


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