In the embers of once vibrant white dwarf stars in the central bulge of the galaxy
Space news (December 08, 2015) – Looking through a cosmic keyhole 26,000 light-years away in Sagittarius –
Astronomers trying to understand the formation and evolution of the Milky Way by studying the first stars to be born in the galaxy have a problem. The stars within the central bulge of the galaxy formed first according to stellar theory. Unfortunately, the light from these suns is blocked by massive clouds of gas and dust, which makes studying their role in the formation and evolution of the Milky Way difficult.
In order to view the central bulge of the galaxy, astronomers looked through a small keyhole in the sky, called the Sagittarius Window. Making it possible to study the formation and evolution of the Milky Way and galaxies as a whole by comparison. A view giving us a look into the very heart of the galaxy and the blueprints nature uses to construct these island universes.
Current astronomical theory believes the central bulge of the Milky Way grew first, followed by the relatively quick birth of the stars making up the rest of the galaxy. Peering deep into the heart of the central bulge, astronomers have discovered a family of 70 ancient white dwarf stars, they believe are the smoldering remnants of once-vibrant suns that inhabited the core long ago. Ancient stars scientists are studying to uncover clues to the processes that formed the Milky Way and by relation the family of galaxies in the cosmos. Marking the deepest, most detailed archeological study of the central bulge of the Milky Way and by extension its formation and evolution.
These ancient white dwarf stars hold the keys to opening the door to better understanding the history of the Milky Way. To gaining knowledge and facts concerning 12 billion-year-old suns that existed when the galaxy was young. Knowledge and facts giving astronomers clues to the early years and evolution of the Milky Way and the billions of island universes in the cosmos.
“It is important to observe the Milky Way’s bulge because it is the only bulge we can study in detail,” explained Annalisa Calamida of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, the science paper’s lead author. “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.
Astronomers have only looked at about 70 of the hottest white dwarfs Hubble can pick out of at least 70 thousand stars in the small area of the bulge of the Milky Way they looked at. White dwarf stars detected by making extremely precise measurements of the motion of over 240,000 stars they detected over a decade of viewing as part of the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS). Precise measurements astronomers used to determine which stars are disk stars or suns inhabiting the bulge of our galaxy. Stars that inhabit the bulge move at a different rate than suns in the disk of the galaxy as compared to our Sun. Extremely hot white dwarfs are also slightly bluer relative to stars like our own sun and they become fainter and cooler as they age. Facts that allowed Hubble’s Advanced Camera for Surveys to pick out 70 of the brightest white dwarf stars inhabiting the bulge of the Milky Way.
“Comparing the positions of the stars from now and 10 years ago we were able to measure accurate motions of the stars,” said Kailash Sahu of STScI, and the study’s leader. “The motions allowed us to tell if they were disk stars, bulge stars, or halo stars.”
“These 70 white dwarfs represent the peak of the iceberg,” Sahu said. “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.”
The team’s going back to work
This team of intrepid astronomers and scientists now plan to increase the sample size of the white dwarfs currently being studied. This will be done by analyzing additional parts of the SWEEPS field of study, which they hope to use to get more precise measurements of the exact age of the bulge of the Milky Way. They’ll also take a look at the possibility the star formation processes used to create the bulge billions of years ago, could be slightly different than current star formation processes at work in the younger disk of the galaxy.
You can learn more about the Hubble Space Telescope here.
Read and learn about white dwarf stars here.
Read about the discoveries of the Space Telescope Science Institute (STScI) here.
Learn more about the formation and evolution of the Milky Way here.
Read about the discoveries of the Sagittarius Window Eclipsing Extrasolar Planet Search (SWEEPS) here.
Learn more about galactic nurseries where stars are born.