There is a relatively bright star in our sun's cosmic neighbor, the Milky way, in which astronomers have been able to identify the widest range of elements in stars outside the solar system The new study, led by Ian Roederer, an astronomer at the University of Michigan, has identified 65 elements in the star called HD 222925. Among the identified elements, 42 are heavy elements, which are listed at the bottom of the periodic table
Identifying these different elements in a star will help astronomers understand the so-called "rapid neutron capture process", or one of the main ways of producing heavy elements in the universe. Their research conclusions have been published online and have been accepted and published in the supplement series of the Journal of astrophysics.
"As far as I know, this is a record of anything outside our solar system. What makes this star so unique is that it has a very high relative proportion of elements listed along the bottom two-thirds of the periodic table. We even detected gold," Roederer said. "These elements are produced by fast neutron capture. This is really what we are trying to study: to understand how, where and when these elements are produced."
This process, also known as the "r-process", starts with the presence of lighter elements such as iron. Then, quickly, for example, in one second, neutrons can be added to the nuclei of lighter elements. This produces heavier elements, such as selenium, silver, tellurium, platinum, gold and thorium, the kind found in HD 222925, all of which are rarely found in stars, according to astronomers.
"It takes a lot of free neutrons and a set of very high-energy conditions to liberate them and add them to the nucleus of the atom," Roederer said. "There are not many environments where this can happen, maybe only two."
One of these environments has been confirmed: the merger of neutron stars. Neutron star is the collapse core of supergiant, which is the smallest and most dense object known. The collision of neutron star pairs will cause gravitational waves. In 2017, astronomers first detected gravitational waves from merged neutron stars. Another way in which the R process may occur is after the explosive death of massive stars.
"This is an important step forward: recognizing where the r-process can happen. But, to ask, what actually happened to that event? What happened there?" Roederer said. "This is the significance of our research.
The elements Roederer and his team found in HD 222925 were produced in the merger of large-scale supernovae or neutron stars in the early universe. These materials were thrown out and back into space, where they later re formed the star Roederer studied today.
The star can then be used as a feature of these events. Any future model that demonstrates how r- processes or nature produce the two-thirds of the elements at the bottom of the periodic table must have the same characteristics as HD 222925.
Crucially, astronomers used an instrument on the Hubble Space Telescope that collects ultraviolet spectra. The instrument is the key to allowing astronomers to collect the ultraviolet part of the spectrum - faint light from cold stars such as HD 222925.
Astronomers also used one of the Magellan telescopes at the Las Campanas Observatory in Chile - an alliance with MIT as a partner - to collect the spectrum of the optical part of HD 222925. These spectra encode the "chemical fingerprint" of elements in stars. Reading these spectra enables astronomers to identify not only the elements contained in stars, but also the amount of certain elements contained in stars.
Anna frebel is a co-author of the study and a professor of physics at MIT. She helped explain the overall element abundance pattern of HD 222925 and how it informed our understanding of the origin of elements in the universe. Astronomers now know the detailed element by element output of some r-process events that occurred in the early universe. Any model that tries to understand what's going on in r-process must be able to reproduce this.
Many of the co authors of the study are members of a group called the r-process alliance, which consists of astrophysicists working on solving the big problems of the r-process. This project marks one of the key objectives of the team: to determine which elements and the quantities produced in the R process in unprecedented detail.