Blue stars found in Andromeda
A large, rare population of hot, blue stars, has been uncovered by NASA’s Hubble Space Telescope.
Using Hubble’s Wide Field Camera 3, astronomers found approximately 8,000 ultra-blue stars near the core of neighbouring galaxy Andromeda.
“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,” says Julianne Dalcanton of the University of Washington, leader of the Panchromatic Hubble Andromeda Treasury survey.
Blue is a colour generally implicative of a star’s heat and youth, so it was a shock when Dalcanton’s team determined that these stars were in fact aging. Physical models illustrate that only an unusual type of old star can be as hot and bright in ultraviolet light.
These stars expose their blue-hot cores by prematurely casting off their outer layers of material as they swell up to become red giants. They differ from normal Sun-like stars, due to the latter losing much less material in their equivalent stage of evolution. It is due to this material retention that the normal stars never look as bright in ultraviolet.
Two potential scenarios have been proposed as to why these blue stars evolve differently.
The first is that the stars are abundant in chemical elements other than hydrogen and helium. With a higher percentage of “heavy elements” lacing the star’s gas, its radiation is more efficient (or has more purchase) at pushing out against it, making it easier for the star to shed material.
The second option is that the blue stars are in close binary systems and have lost mass to their partners.
Simulations of these stars must be created in order to determine which scenario is most likely.
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