The Hubble telescope, gazing deep into the heart of the Milky Way galaxy, has discovered the fading remnants of some of the galaxy's earliest stellar inhabitants.
In what astronomers are terming a "cosmic archaeological dig," the space telescope has found evidence of how our home galaxy was constructed long before our sun and the Earth formed.
Hubble has spotted a population of 70 ancient white dwarf stars, remains of a "homesteading" population of once-blazing pioneer stars in the giant central bulge sitting in the center of the Milky Way's flat stellar disk.
White dwarfs are what are left of stars that shone brightly 12 million years ago in our galaxy's groundbreaking years, astronomers say.
What Hubble sees supports the assumption that our galaxy's central bulge was what came into existence first and formed its first stars very rapidly, taking less than two billion years, they say.
The pancake-shaped surrounding disk is full of later generations of stars that came into being at a more leisurely pace in the Milky Way's "suburbs," they explain.
"It is important to observe the Milky Way's bulge because it is the only bulge we can study in detail," says Annalisa Calamida at the Space Telescope Science Institute (STScI) in Baltimore, Md. "You can see bulges in distant galaxies, but you cannot resolve the very faint stars, such as the white dwarfs."
Around 25 percent of our galaxy's total mass is in the central bulge, explains Calamida, lead author of a study appearing in The Astrophysical Journal.
Hubble found a bigger percentage of low-mass stars inside the bulge than are found in the surrounding disk, the researchers noted.
"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," says Calamida.
The region surveyed by Hubble is 26,000 light-years from Earth.
"These 70 white dwarfs represent the peak of the iceberg," says STScI study leader Kailash Sahu.
The astronomers estimate the total number of white dwarfs in the area of the bulge observed by Hubble may be as high as 100,000.
They say upcoming telescopes like the NASA James Webb Space Telescope will be able to find and count nearly all of the stars in the bulge, including the faintest ones today's telescopes, like Hubble, are unable to see.