A team of scientists used the Hubble Space Telescope to peer into the Milky Way’s central hub of stars has and for the first time has observed a population of ancient white dwarf stars, a discovery that could provide the blueprints for the earliest construction phases of our home galaxy.
The researchers, conducting what NASA called a “cosmic archaeological dig,” reviewed different Hubble images of the same portion of the sky taken nine years apart, Gizmag explained. Roughly 240,000 stars were captured in those images, and by carefully analyzing the movements of those stars, the authors were able to locate stars in the central bulge due to their slow movement.
Having located the 70,000 stars in that hub, they then set to work on picking out the white dwarfs by studying the colors of the stars and comparing them to theoretical models suggesting that their color had a stronger blue tinge to it. Ultimately, they detected 70 of these ultra-dense, Earth-sized stellar remnants that still burned hot enough to be detected in the Hubble images.
“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,” the US space agency said in a statement. “They serve as multi-billion-year-old time pieces that tell astronomers about the Milky Way’s groundbreaking years.”
Findings will shed new light on the galaxy formation
Thanks to these observations, which NASA said were the most detailed ever made of the central bulge, the researchers were able to find evidence supporting the notion that the hub formed first and that its stars were born in approximately two billion years. The second and third generations of stars grew more slowly on the outskirts, encircling the bulge as they formed.
“It is important to observe the Milky Way’s bulge because it is the only bulge we can study in detail,” said Annalisa Calamida of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, lead author of a new The Astrophysical Journal paper describing the findings.
“You can see bulges in distant galaxies, but you cannot resolve the very faint stars, such as the white dwarfs,” she added. “ The Milky Way’s bulge includes almost a quarter of the galaxy’s stellar mass. Characterizing 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.”
Calamida and her colleagues also found stars slightly more low-mass stars in the central hub in comparison to those in the galaxy’s disk population. She explained that this discover appears to indicate that the environment of the bulge may have been different than that of the disk, which would have resulted in a completely different star-forming mechanism there.
“These 70 white dwarfs represent the peak of the iceberg,” said study co-author Kailash Sahu, also of STScI. “We estimate that the total number of white dwarfs is about 100,000 in this tiny Hubble view of the bulge. Future telescopes such as NASA’s James Webb Space Telescope will allow us to count almost all of the stars in the bulge down to the faintest ones, which today’s telescopes, even Hubble, cannot see.”
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Image credit: NASA/A. Fujii
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