Milky Way’s Bulge Holds Oldest Stars

Pointing the Australian National Univ.’s SkyMapper telescope towards the center of the galaxy, astronomers surveyed the dense bulge of the Milky Way. They were searching for celestial bodies that might hold clues to the galaxy’s start.

“We found what we think are the oldest stars in the galaxy and potentially the oldest objects ever discovered,” said Louise Howes, a PhD student at the university’s Research School of Astronomy & Astrophysics and the lead author of a recent study published in Nature.

“Pretty much the galaxy formed around them,” she said of the nine stars discovered and analyzed for the study

According to Howes, the stars formed during a time astronomers call the Epoch of Reionization. According to the Massachusetts Institute of Technology, the epoch defines a period when the universe went from being a predominantly neutral intergalactic medium to an ionized one. Multiple luminous sources, which may have been stars, galaxies, quasars or a combination of the three, ignited, giving light to the universe.

The studied stars, according to Howes, are probably 50 times the size of the sun but around the same weight. The researchers said the star formed when the universe was only 300 million years old.  

“The (Australian National Univ.) SkyMapper has a unique ability to detect the distinct colors of anaemic stars—stars with little iron—which has been vital for this search,” said Prof. Martin Asplund, the project’s leader.

After selecting the purest celestial specimens, and therefore the oldest, the team used the Anglo-Australian Telescope in New South Wales and the Magellan telescope in Chile to reveal their chemical make-up.

“The stars have surprisingly low levels of carbon, iron and other heavy elements, which suggests the first stars might not have exploded as normal supernovae,” said Howes. “Perhaps they ended their lives as hypernovae—poorly understood explosions of probably rapidly rotating stars producing 10 times as much energy as normal supernovae.”

According to NASA, hypernovae can produce around 100 times more energy than supernovae.

Howes hopes to uncover how the Milky Way formed. Observing these stars are the building blocks to that goal, she said.