Blue Stellar Oddballs Spied Inside Andromeda: Big Pic

Jan. 12, 2012 -- Astronomers have spotted a swarm of stellar oddities surrounding the core of the neighboring Andromeda galaxy: ultra-hot, blue stars that shine brightly in ultraviolet... despite their advanced age.

Typically, as sun-sized stars age, they run out of stellar fuel and expand into red giants, eventually ejecting their outer layers into space. These stars have gone through that process but have somehow lost much more of their outer layers, exposing bright, blue-hot cores.

WATCH VIDEO: Discovery News unlocks the mysteries of stars and finds out why a star's age matters.

BIG PIC: Star Birth (and Murder) Spied in Cygnus X

The team, led by Julianne Dalcanton of the University of Washington in Seattle, used Hubble Wide Field Camera 3 data as part of the Panchromatic Hubble Andromeda Treasury survey to find this population of unusual stars, which numbers about 8,000.

The stars are all within 2,600 light-years of the Andromeda galaxy's core.

"We were not looking for these stars. They stood out because they were bright in ultraviolet light and very different from the stars we expected to see," said Dalcanton.

The team studied the stars for almost a year before determining they were in fact of considerable age, and thus "past their prime".

Theories as to why these stars evolved differently are being suggested. One is that the stars were richer in heavier elements, and so when they ejected their outer layers more mass was lost simply because heavier elements would be more affected by outward-pushing solar winds. Previous observations have shown that stars nearer the galactic center have more heavier elements, and these particular stars may have had even more than usual.

ANALYSIS: Massive Star Birth Revealed

Another theory puts the blame on binary systems, suggesting that the stars are part of binary pairs and that one star could have lost some of its mass to the other, exposing its core.

More research will be needed to determine which, if either, of these explanations are indeed the cause of such stellar curiosities.

The findings were announced at the American Astronomical Society's meeting in Austin this week. Read the Hubble news release here.

--by Jason Major

Image credit: NASA, ESA, and B. Williams and J. Dalcanton (University of Washington, Seattle)