Early universe less dusty than thought

Dust may be rarer than expected in galaxies of the early universe, according to an international research team. In a local dwarf galaxy named I Zwicky 18, the team measured the lowest dust mass of a galaxy that has ever been found.

“It’s not just that the dust mass is low. We found that the dust mass is 100 times smaller than would be expected based on commonly assumed theories,” said lead investigator Dr David Fisher, an astrophysicist at Swinburne University of Technology in Melbourne.

The American, German and Australian astronomers were studying the galaxy because it is nearby, making it easier to study. But it also has properties that are very similar to galaxies of the high redshift universe.

“It’s an extreme galaxy in the local universe, but it tells us a lot about a stage that almost all galaxies have gone through, so it gives us a picture of what the first galaxies looked like,” Fisher said.

He said the results implied that galaxies of the early universe might have less dust than had been expected. This meant that they would look different than astronomers expected and would make different populations of stars.

“Secondly, they will be much more difficult to observe, even with state-of-the-art facilities being built now, such as the Atacama radio telescopes in northern Chile.

“I Zwicky 18 is typical of very high redshift galaxies because it is very actively forming stars, and has a chemistry that is more like galaxies of the very early universe with a very low abundance of metals and a lot of gas in the form of hydrogen.”

Fisher said the result implied that current theories to describe the formation of stars when the universe was very young were incomplete, and built on invalid assumptions. The amount of dust was very important for the formation of stars and the astrophysicists believed the harsh environment inside the galaxy was adversely affecting the amount of dust in it.

“The radiation field measured inside I Zwicky 18 was roughly 200 times stronger than what we experience here in the Milky Way and, based on the findings, current theories should be amended to account for environment in making stars.”

The research was published in Nature.