They are effectively the blueprints of the galaxy’s early construction phase.
It is the first time the population of ancient white dwarfs — smoldering remnants of once-vibrant stars that inhabited the core – have been imaged and they may provide clues as to how our galaxy was built.
The Hubble site explains:
As with any archaeological relic, the white dwarfs contain the history of a bygone era. They contain information about the stars that existed about 12 billion years ago that burned out to form the white dwarfs. As these dying embers of once-radiant stars cool, they serve as multi-billion-year-old time pieces that tell astronomers about the Milky Way’s groundbreaking years.
An analysis of the Hubble data supports the idea that the Milky Way’s bulge formed first and that its stellar inhabitants were born very quickly — in less than roughly 2 billion years. The rest of the galaxy’s sprawling disk of second- and third-generation stars grew more slowly in the suburbs, encircling the central bulge like the brim of a giant sombrero.
“It is important to observe the Milky Way’s bulge because it is the only bulge we can study in detail,” says Annalisa Calamida of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, the science paper’s lead author.
“You can see bulges in distant galaxies, but you cannot resolve the very faint stars, such as the white dwarfs. The Milky Way’s bulge includes almost a quarter of the galaxy’s stellar mass. Characterising the properties of the bulge stars can then provide important information to understanding the formation of the entire Milky Way galaxy and that of similar, more distant galaxies.”
The Hubble survey also found slightly more low-mass stars in the bulge, compared to those in the galaxy’s disc population.
“This result suggests that the environment in the bulge may have been different than the one in the disk, resulting in a different star-formation mechanism,” Calamida said.
Bill Condie is a science journalist based in Adelaide, Australia.
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