SCI: Scientists show Milky Way likes it both ways

AAP General News (Australia)
12-13-2007
SCI: Scientists show Milky Way likes it both ways

Eds: Embargoed until 0500 AEDT Thursday, December 13



By Samuel Cardwell

CANBERRA, Dec 13 AAP - Two scientists studying at the Australian National University
are part of an international team that has discovered the Milky Way galaxy actually spins
in different directions.

In their paper to be published in the journal Nature, the scientists describe how the
outer edge of the Milky Way, the halo, is made up of two components that rotate in opposite
directions.

The findings prove that the Milky Way halo was not assembled all at once but rather
over time, something scientists have suspected for around 30 years.

The lead author of the report, Daniela Carollo, a researcher at Italy's Torino observatory
now undertaking her Phd in Canberra, said that they made the discovery by studying the
motions and chemical makeup of the halo.

"By examining the motions and chemical makeup of the stars, we can see that the inner
and outer halos are quite different beasts and they probably formed in different ways
at different times," Ms Carollo said.

The discovery also shows that the different parts of the halo have different chemical
makeups with the inner stars containing three times more heavy elements than outer halo
stars.

Ms Carollo said that these differences gave a much clearer picture of the formation
of the early universe.

"Although it was once considered a single structure, an analysis of the stars shows
that the halo is clearly divisible into two, broadly overlapping components. The discovery
gives us a much clearer picture of the formation of the first objects in our galaxy and
in the entire universe," she said.

This discovery may help to find some of the most primitive stars in the galaxy a quest
that another team member ANU Professor John Norris has spent more than two decades on.

"These fossils of the early universe are extremely rare so finding them remains a classic
needle in a haystack problem and the discovery of a chemically distinct outer halo, gives
us a much better way to search the haystack," he said.

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