By analyzing the faint starlight of a far-off dwarf galaxy, a team of researchers from the MIT Kavli Institute for Astrophysics and Space Research (MKI) have finally solved a decades-long mystery surrounding the origins of precious metals such as gold, silver, and platinum.
While the majority of chemical elements that make up planets and just about everything else in the universe were forged in nuclear furnaces like the sun, the roots of specific heavy and usually valuable elements like gold, silver, lead, and uranium have remained an enigma, according to the authors of a new study published earlier this year in the journal Nature.
To solve this puzzle, they monitored an old dwarf galaxy in the local group known as Reticulum II, which is contains stars abundant in these so-called “r-process” metals. Based on their research the MKI team believes that a collision between extremely dense objects called neutron stars that took place billions of years ago created the large quantities of heavy elements in the galaxy, and that those elements then became intermingled with its gas and dust reservoirs.
This now r-process metal rich material ultimately went on to form Reticulum II’s unique stars, they explained in a statement. While scientists had long suspected that these collisions played a key role in the process, this marks the first observational evidence to support that hypothesis.
‘Cosmic genes’ provide a window to early star, galaxy formation
Two of the researchers involved in the study – Anna Frebel, an assistant professor in the MIT Department of Physics, and Alexander Ji, the graduate student who first discovered the enriched stars in Reticulum II and lead author of the Nature paper – talked about their findings this week as part of a roundtable discussion at the Kavli Institute.
“Understanding how heavy, r-process elements are formed is one of hardest problems in nuclear physics,” Frebel said at the event, according to Phys.org reports. “The production of these really heavy elements takes so much energy that it’s nearly impossible to make them experimentally. The process for making them just doesn’t work on Earth. So we have had to use the stars and the objects in the cosmos as our lab.”
Frebel added that their research demonstrates how an increasingly popular technique called “stellar archaeology” is helping scientists determine the history of galaxies by analyzing the contents of the stars found there. She added that their work had “opened a new door for studying galaxy formation with individual stars and to some extent individual elements. We are seriously connecting the really small scales of stars with the really big scales of galaxies.”
Approximately two percent of neutron stars have a companion, and a fraction of those are orbited by another neutron star, the study authors pointed out. If the neutron stars are close enough, they will eventually collide, causing some of the material to be ejected into space at close to the speed of light. Their atoms would then become mixed with ambient gas and dust, and this newly mixed material would be used to form the next generation of now r-process metal enriched stars.
“Because the elements that we observe in our stars today were made prior to the stars’ birth – the stars inherited these heavy elements like ‘cosmic genes’ – we have this incredible opportunity to look back in time to study the early chemical and physical processes that ushered in stars and galaxy formation soon after the Big Bang,” Frebel said.
Image credit: Dana Berry / Skyworks Digital, Inc.