Washington: Astronomers using NASA`s Galaxy Evolution Explorer have shed new light on why some of the most massive stellar explosions ever observed occur in the tiniest of galaxies.
"It`s like finding a sumo wrestler in a little ``Smart Car,`` said Don Neill, a member of NASA`s Galaxy Evolution Explorer team at the California Institute of Technology in Pasadena, and lead author of a study.
"The most powerful explosions of massive stars are happening in extremely low-mass galaxies. New data are revealing that the stars that start out massive in these little galaxies stay massive until they explode, while in larger galaxies they are whittled away as they age, and are less massive when they explode," said Neill.
Over the past few years, astronomers using data from the Palomar
Transient Factory, a sky survey based at the ground-based Palomar
Observatory near San Diego, have discovered a surprising number of exceptionally bright stellar explosions in so-called dwarf galaxies up to 1,000 times smaller than our Milky Way galaxy.
Stellar explosions, called supernovae, occur when massive stars - some up to 100 times the mass of our Sun - end their lives.
Now, astronomers are using ultraviolet data from the Galaxy Evolution Explorer to further examine the dwarf galaxies.
The result helps explain why massive stars in little galaxies undergo even more powerful explosions than stars of a similar heft in larger galaxies like our Milky Way.
The reason is that low-mass galaxies tend to have fewer heavy atoms, such as carbon and oxygen, than their larger counterparts. These small galaxies are younger, and thus their stars have had less time to enrich the environment with heavy atoms.
According to Neill and his collaborators, the lack of heavy atoms in the atmosphere around a massive star causes it to shed less material as it ages.
In essence, the massive stars in little galaxies are fatter in their old age than the massive stars in larger galaxies. And the fatter the star, the bigger the blast that will occur when it finally goes supernova.
This, according to the astronomers, may explain why super supernovae are occurring in the not-so-super galaxies.
The study was published in the Astrophysical Journal.