Hubble discovers clues to how Milky Way was formed

This is how our galaxy, Milky Way was formed.

Image courtesy: NASA

Zee Media Bureau

New Delhi: NASA used it's Hubble Space Telescope recently, to conduct a “cosmic archaeological dig” at the very core of our galaxy – Milky Way.

For the first time, Hubble researchers have discovered a population of ancient white dwarfs, which are smouldering remnants of once-vibrant stars that inhabited the very heart of the Milky Way.

This means that astronomers have uncovered the blueprints of our galaxy’s early construction phase.

The findings are deep and NASA's most detailed study of the galaxy’s foundational city structure— its vast central bulge that lies in the middle of a pancake-shaped disk of stars, where our solar system dwells.

According to NASA, 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 a giant sombrero.

NASA also quoted Annalisa Calamida of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, the science paper’s lead author, who said that, “It is important to observe the Milky Way’s bulge because it is the only bulge we can study in detail. 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 Hubble survey also found slightly more low-mass stars in the bulge, compared to those in the galaxy’s disk 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.

The astronomers identified the white dwarfs by analyzing the colours of the bulge stars and comparing them with theoretical models. The extremely hot white dwarfs appear bluer relative to sun-like stars. As white dwarfs age, they become cooler and fainter, becoming difficult even for sharp-eyed Hubble to detect.

The observations were so sensitive that the astronomers also used the data to pick out the feeble glow of white dwarfs. The team based its results on an analysis of 70 of the hottest white dwarfs detectable by Hubble in a small region of the bulge among tens of thousands of stars.