Researchers from MIT have uncovered three of the oldest stars in the universe, which were surprisingly close to us all along but moving in an unexpected direction. These celestial objects were found within the “halo” of stars encircling the outer regions of the Milky Way galaxy.
The stars are believed to have originated around 12 to 13 billion years ago, as detailed in a recent publication in the journal Monthly Notices of the Royal Astronomical Society.
In a statement, Anna Frebel, a physics professor at MIT and co-author of the study, expressed her thoughts. Frebel said, “Interestingly they’re all quite fast—hundreds of kilometers per second, going the wrong way.” Frebel continued, “They’re on the run! We don’t know why that’s the case,”
The universe is estimated to be about 13.8 billion years old, while our sun is relatively young at 4.6 billion years old. These stars, known as SASS (Small Accreted Stellar System stars), are believed to be among the oldest in existence.
They likely formed during the early stages of galaxy formation, each originating from its own small primordial galaxy. These galaxies were likely absorbed into the Milky Way over time, with the SASS stars being the sole survivors of their original galaxies.
Positioned approximately 30,000 light-years away from Earth within a cluster of stars at the outer fringes of the Milky Way, these stars have been identified as remnants of ancient cosmic history. The researchers also found three other ancient stars in the study, although these were slightly younger than the SASS stars.
“These oldest stars should definitely be there, given what we know of galaxy formation,” added Frebel. “They are part of our cosmic family tree. And we now have a new way to find them.”
The Big Bang Theory stands as the primary explanation for the universe’s origin. In its simplest form, it describes the universe’s inception from a tiny singularity, expanding over 13.8 billion years to the vast cosmos we observe today.
As the universe expanded, it cooled, enabling the formation of subatomic particles and basic atoms. Initially, hydrogen and helium were the predominant elements created in the aftermath of the Big Bang.
The first stars likely consisted mainly of hydrogen and helium, lacking heavier elements like strontium and barium, which are produced in the intense environments of stellar supernovas.
Consequently, stars with minimal levels of strontium and barium in their spectral signatures could be among the earliest entities in our universe.
Discovered initially by the Magellan telescope in 2013 and 2014, these three ancient stars exhibited a spectrum low in metals, indicating their age. However, a detailed analysis of these stars had not been conducted until now.
Researchers have now concluded that these stars likely date back 12 to 13 billion years and possess a chemical composition resembling that of ancient dwarf galaxies.
Additionally, their unique motion within the galaxy, contrary to the typical stellar movement, suggests that these stars might have originated from another location and been pulled into the Milky Way.
“The only way you can have stars going the wrong way from the rest of the gang is if you threw them in the wrong way,” Frebel said.
Upon examining additional ancient stars, the researchers observed a similar retrograde motion in their orbits around the galaxy, moving in an unconventional direction. This peculiar movement pattern emerged as a significant and common characteristic among these ancient celestial bodies.
“It was the piece to the puzzle that we needed, and that I didn’t quite anticipate when we started,” added Frebel. Their objective is to uncover additional ancient SASS stars by identifying metal-deficient stars moving in a direction contrary to the majority of stars. By leveraging these SASS stars, they aim to delve into the origins and evolution of the dwarf galaxies from which these stars originated.
Frebel said, “Now we can look for more analogues in the Milky Way, that are much brighter, and study their chemical evolution without having to chase these extremely faint stars.”
