Astronomers have found a ‘gold standard’ star in the Milky Way galaxy
The Milky Way galaxy has a relatively bright star next to our Sun, and in it, astronomers are still able to identify the widest range of elements in a star beyond our solar system.
The study, led by University of Michigan astronomer Ian Rodrरguez, identified 65 elements in the star HD222925. Forty-two of the identified components are heavy components that are listed at the bottom of the periodic table of components.
Identifying these elements in a single star will help astronomers understand the “rapid neutron-capture process” or the formation of heavy elements in the universe, which is one of the major ways. Their results have been posted on arXiv and have been accepted for publication in the Astrophysical Journal Supplement series.
“To the best of my knowledge, this is a record for anything beyond our solar system. And what makes this star so unique is that the proportions of the two-thirds of the elements listed at the bottom of the periodic table are very high. We also discovered gold,” Roder said. “These elements are made by the process of rapid neutron capture. This is what we are trying to study: physics to understand how, where, and when those elements were made.”
The process, also called “R-process”, begins with the presence of light elements such as iron. Then, neutrons are added to the nuclei of the fast-second sequence-fading elements. This produces heavy elements such as selenium, silver, tellurium, platinum, gold, and thorium, which are found in HD 222925, and all of these are rarely found in stars, according to astronomers.
“You need a lot of neutrons that are free and you need a very high energy set to release them and attach them to the nuclei of atoms,” Roder said. “It’s unlikely that this will happen – two, maybe.”
One of these atmospheres is confirmed: the merging of neutron stars. Neutron stars are the collapsing cores of giant stars and are the smallest and densest known celestial bodies. The collision of pairs of neutron stars produces gravitational waves, and in 2017, astronomers discovered gravitational waves from the merging of neutron stars. Another method of R-processing is after the explosive death of huge stars.
“It’s an important step: to identify where the R-process could take place. But ‘What did that incident actually do? What happened there?’ Roderick said. “That’s where our study comes in.”
The production of the Roder and his team of components, identified in HD 222925, took place very early in the universe, either by merging giant supernovae or neutron stars. The material was taken out and thrown back into space, where it was later modified. Roederer is studying today.
This star can then be used as a proxy for what might have been one of those events. Any model that develops in the future that shows how R-process or nature elements form on two-thirds of the bottom of the periodic table must have the same signature as the HD 222925, Roder says.
Importantly, astronomers used a device on the Hubble Space Telescope that could collect ultraviolet spectra. This device was important in allowing astronomers to collect light in the ultraviolet part of the light spectrum – the light coming from a cold star-like HD 222925 is blurred.
Astronomers used one of the Magellan telescopes – of which U-M is a partner – at the Las Campanas Observatory in Chile to collect light from HD 222925 in the optical part of the light spectrum.
These spectra encode the “chemical fingerprint” of the elements in the stars, and reading these spectra allows astronomers to not only identify the elements in the star but also how many elements there are in the star.
Anna Freibel is the study’s co-author and professor of physics at the Massachusetts Institute of Technology. She helped with the complete explanation of the HD 222925 Element Absence pattern and how it informs you about the origin of the elements in the cosmos.
“We now know the detailed component-by-component output of some of the R-process events that took place at the beginning of the universe,” Freibel said. “Any model trying to understand what is going on in the R-process should be able to reproduce it.”
Many of the study’s co-authors are part of a group called the R-Process Alliance, a group of astronomers dedicated to solving the big problems of the R-Process. This project is one of the team’s main objectives: to identify which components, and to what extent, were created at an unprecedented level in the R-process.