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Dwarf finding solves galactic conundrum

dwarf galaxy

The orange shows ionised hydrogen regions, the blue surrounding them are young stars, and the white dots are distant background galaxies(Source: Singg Survey)

Mystery solved A long-standing mystery relating to the evolution of galaxies has been solved thanks to a serendipitous find by an Australian astrophysicist.

As part of his doctoral studies David Nicholls, from the Australian National University's Research School of Astronomy and Astrophysics, was examining distant dwarf galaxies in the search for clues to the evolution of the universe.

Nicholls says dwarf galaxies provide a "historical record" of how the universe formed because they evolve more slowly than larger galaxies.

"By studying dwarf galaxies we can see what the universe was like long ago," he says. "They still have most of their 'old buildings' intact, so we know what they were like when they were first built."

To determine the age of the dwarf galaxies, Nicholls measured the brightness of various elements mixed into the hydrogen cloud using a spectrometer. The more heavier elements within the galaxy, the older it is.

Prediction wrong

However, Nicholls says when he attempted to analyse his findings, the results failed to fit the patterns predicted by various accepted theories.

"I found that the energies of the electrons in the gas clouds were not distributed the way people had always thought they should be," he says.

Nicholls says the problem is due to an assumption that atoms within gas clouds will eventually reach a state of thermodynamic equilibrium.

This is reached because as atoms "bump" into each other they transfer energy - hot atoms slow down and cold atoms speed up - until the distribution of hot, cold and intermediate atoms has reached a stable point.

"Everyone assumed this is what was going on in the hydrogen cloud," says Nicholls, "and it turns out it isn't."

Instead Nichols says it appears the atoms in the hydrogen cloud behave in a similar manner to those within our own atmosphere.

Nicholls says research dating back to 1968 shows the electrons in the Earth's magnetosphere never reach a state of equilibrium as there is a constant supply of energy-rich electrons.

The distribution of this electron energy is best explained by a power law known as the kappa distribution, which results in more hot and cold electrons, but less intermediate ones.

Problem solved

Similar distributions have been found in the magnetospheres of Mercury, Jupiter, Saturn, Titan, Uranus, Neptune and the solar wind.

"When I applied this physics to the spectra of dwarf galaxies it did make a big differenceell," says Nicholls.

He says his paper, published in The Astrophysical Journal, has been well received with its pre-publication online resulting in a call to attend the recent Mapping Oxygen in the Universe conference.

"This simple assumption has solved a long-term problem ... it will help people work out what is going on in these hydrogen clouds. It will give us more of an understanding of how evolution happened in galaxies and how stars are enriched."

Tags: the-universe, stars, galaxies