Hubble data reveals ancient white dwarfs at the core of the Milky Way
Images taken by the Hubble Space Telescope have beenanalyzed by a team of astronomers, uncovering a population of veryold white dwarf stars. It's the first time the ancient stars havebeen observed, and their study provides clues regarding the earlyconstruction phase of our home galaxy.
Thenew observations are the most detailed of their kind, looking closelyat the foundational bulge at the very heart of the Milky Way. Looking specificallyat the white dwarf star remnants gives us valuable information aboutthe galaxy's distant past.
Carefullystudying the data, the team was able to pick out the white dwarfs,selecting 70 of the hottest examples for in-depth analysis. The stellarremnants are only about the size of the Earth, but are are astaggering 200,000 times denser. As they're so small, they're alsopretty dim, making them challenging to observe.
Tofind the remnants, the team looked at different Hubble images of the same spot of sky, which contains around240,000 stars, taken nine years apart. They then carefullyanalyzed the movement of the stars, picking out those in the bulgethanks to their slower speed. The region itself resides some 26,000light years away, and can be seen particularly clearly thanks to theunusually dust-free space between the it and the Earth.
Havingpicked out the bulge stars, of which there were some 70,000, the teamthen set to work identifying the white dwarfs. They did so bystudying the colors of the stars and comparing them to theoreticalmodels that suggested that hot white dwarfs should appear with a bluetinge relative to younger stars. The team picked out 70 prime examples – those still burning hot enough to be detectable in the Hubble imagery.
Thedata from the sample supports theories that the bulge of the MilkyWay formed early on, and that the stars within it ignited within thefirst two billion years of its existence. The vast disk of stars thatsurround the bulge formed much more slowly.
Morebroadly, there were also found to be more low-mass stars in the bulgethan in the surrounding disk, suggesting that the environment in thebulge, early on the lifespan of the Milky Way, was a little differentexperienced by later stars, located farther from the central core.
"These70 white dwarfs represent the peak of the iceberg," says studyleader Kailash Sahu. "We estimate that the total number of whitedwarfs is about 100,000 in this tiny Hubble view of the bulge."
Toget a better look at the full population of white dwarfs, we'll have towait until next-generation installations like NASA's James Webb Space Telescope become operational. Such telescopes should be able to viewpractically all of the stars in the bulge, right down to the veryfaintest bodies.
Inthe meantime, the team plans to expand its sample of white dwarfs byanalyzing other Hubble data, an endeavour that it hopes will lead toa more precise estimation of the age of the Milky Way's galacticbulge, as well as giving us a clearer picture of potentialdifferences between star formation in the core and arms of the galaxy.
Theresearchers published the results of their findings in The Astrophysical Journal.
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