Authors: Falk Herwig, Pavel Denissenkov, and Eric Burns
First Writer’s Establishment: Astronomy Analysis Centre and Division of Physics and Astronomy
College of Victoria, Victoria, British Columbia V8W 2Y2, Canada
Standing: Revealed in Bodily Evaluation Letters (2026 June 12) [open access]
Meet COSI, NASA’s New Gamma-Ray Observatory
The launch date of the Compton Spectrometer and Imager (COSI), as seen in Determine 1, is swiftly approaching, with astronomers worldwide holding their breath to see the way it enhances our understanding of contemporary physics. With a launch window deliberate for August of 2027, we’re formally one 12 months away from a brand new gamma ray observatory lifting off for Low-Earth Orbit. COSI is a soft-gamma ray survey telescope, which means it should observe within the 0.2-5 MeV frequency vary, and has a area of view of roughly 25% of the night time sky. By probing the soft-gamma ray regime, probably the most understudied portion of the electromagnetic spectrum, it seeks to reply essential questions on i-process nucleosynthesis, and uncover the origin of galactic positrons.
With its launch window swiftly approaching, astronomers usually are not ready patiently for liftoff. As a substitute, they’re operating assessments to find out the bodily limits of the devices aboard COSI, and how much questions they will count on to reply as soon as it sees first gentle. Right this moment’s authors sought to numerically decide COSI’s capability to detect the intermediate neutron seize course of in preparation for its launch.
A Secret Third Form of Neutron Seize
Many astronomy courses will point out neutron seize, the method by which nuclei are bombarded by neutrons earlier than decaying into new, secure isotopes. This course of is how most parts past iron on the periodic table are produced. Your professor will let you know that there’s a slow and rapid neutron capture, often known as s-process and r-process, respectively. However what they gained’t let you know is that there’s a secret intermediate course of (i-process), the place neutrons are captured too rapidly to be thought-about s-process, however too slowly to be thought-about r-process.
The isotopes sometimes produced by the i-process are sometimes discovered within the spectra of post-asymptotic giant branch stars (post-AGBs) and rapidly-accreting white dwarfs (RAWDs). It comes from {a partially} degenerate helium shell igniting in a runaway response. As a result of the shell is what permits for the i-process to happen, it might truly occur a number of instances for a similar star with out utterly destroying it.
The Hunt for the I-Course of
Nonetheless, trying to find the i-process is just not simple. It creates related parts because the r and s-process, however completely different isotopes. To establish whether or not or not a star has undergone the i-process, astronomers search for extraordinarily excessive abundances of rubidium, strontium, yttrium, and zirconium in opposition to a reference star.
Utilizing this understanding, the authors estimated the higher restrict of abundances for a single i-process occasion in an effort to decide if COSI shall be able to observing it. They in contrast the photon flux of seven i-process emission strains from such an occasion to the sensitivity of COSI over a given time-frame and located that three sigma detections can be faint, though nonetheless resolvable by COSI.
COSI will pave the way in which for brand new discoveries within the soft-gamma ray regime, answering extra questions in regards to the origin of excessive vitality particles each inside our galaxy and past.
Edited by: Kaz Gary
Characteristicd Picture Credit score: UC Berkeley; NASA; NRL; Northrup Grumman
