Astronomers detected a population of ancient white dwarfs, the remnants of burned out stars, at the central bulge of our galaxy.
Hubble Space Telescope has discovered for the first time a population of ancient white dwarfs, the leftovers from the once vibrant stars, at the center of our galaxy Milky Way.
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A very deep and detailed study was conducted about the stars found in our galaxy, which provided some clues to the Milky Way’s early formation.
The stars existed about 12 billion years ago long before the Earth and solar system was formed. The stars were burned out and collapsed into white dwarfs. These white dwarfs are expected to serve as a time capsule, revealing the details of when our galaxy just bloomed because it has been believed that Milky Way’s central bulge was created first and the stars inside it born very quickly – in less than 2 billion years. Then, more generations of stars burst out and moved around the bulge like a giant sombrero.
“It is important to observe the Milky Way’s bulge because it is the only bulge we can study in detail,” explained co-author Annalisa Calamida of the Space Telescope Science Institute (STScI) in Baltimore, Maryland.
“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. 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.”
The team of researchers analyzed about 70 of the white dwarfs from the cluster of tens of thousands of stars existing in the bulge. These stellar remnants were about the size of Earth but weigh a lot more – almost 200 times denser than Earth. The relics were so dim that astronomers had a difficult time identifying them. It was almost as difficult as spotting a glowing pocket flashlight on the surface of Moon.
Astronomers used the sharp-eyed Hubble Telescope to uncover them and to separate them from the crowd of bright stars populated in the galaxy’s disk. They tracked their movements as stars in the central bulge move at a different rate than disk stars and halo stars, which encircle the outer edge of the Milky Way. The bulge stars also have different colors compared to other stars. Extremely hot white dwarfs have a relatively bluer color but as they become old, they get cooler and fainter and become difficult to detect even with most advanced space telescopes.
The 70 bulge stars that have been picked out for analysis were the hottest and most observable of the bulk.
“These 70 white dwarfs represent the peak of iceburg,” said Kailash Sahu of STScI, and the leader of the study. “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 bulge down to the faintest ones, which today’s telescopes, even Hubble, cannot see.”
Astronomers will use these white dwarfs to determine the age of the bulge more accurately and they will also try to find whether the formation of these stars was different from those that are younger and seen in the disk of the galaxy.
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