Astronomers discovered a 1-in-10 billion binary star system using the SMARTS 1.5-meter Telescope at the Cerro Tololo Inter-American Observatory (CTIO). It is the first verified observation of the star system that will one day generate a kilonova, which is an ultra-powerful, gold-producing explosion by merging neutron stars.
These star systems are so rare that only about 10 are known to exist in the Milky Way. The findings of the study, titled "A High-mass X-ray Binary Descended From an Ultra-stripped Supernova," is published in the journal Nature.
Binary Star System CPD-29 2176: A Kilonova Progenitor System
CPD-29 2176 is a peculiar system situated around 11,400 light-years from Earth. According to SciTech Daily, NASA's Neil Gehrels Swift Observatory was the first to spot it but later observations with the SMARTS 1.5-meter Telescope allowed astronomers to deduce its orbital characteristics and the types of stars that comprise this system.
They found it is composed of a neutron star created by an ultra-stripped supernova and a closely orbiting massive star in the process of becoming an ultra-stripped supernova.
An ultra-stripped supernova is the end-of-life explosion of a giant star whose outer atmosphere has been stripped away by a partner star. The explosive force of a regular supernova, which would otherwise "push" a close companion star out of the system, is absent in this type of supernova.
Noel D. Richardson at Embry-Riddle Aeronautical University and lead author of the paper explained that the current neutron star would have formed without ejecting its companion from the system. The star would need to explode as an ultra-stripped supernova so the two neutron stars collide, merge, and one day create a kilonova.
Aside from being the discovery of a highly uncommon cosmic anomaly, identifying and researching kilonova progenitor systems like this can help astronomers solve the enigma of how kilonovae occur, revealing information on the genesis of the Universe's heaviest components.
Persistence and Collaboration Needed To Study These Kinds of Binary Star System
Clarissa Pavao, one of the study's co-authors, plotted the spectra of the bright star known as a Be-type star. But before that, Phys.org reported that she had to clean the data so that they were less noisy. Pavao managed to learn more about data processing and computer coding until her persistence paid off.
Pavao and Richardson found one simple line from the star that was not influenced by the disk around it and created a scatterplot. After running it into a special computer program, Richardson realized they found the orbit of the star but it was different than expected. He noted that it was not a typical binary star system.
Jan J. Eldridge, another co-author of the paper and an expert on binary star systems and their evolution, reviewed thousands of binary star models and found only two analogous systems to what Richardson and Pavao were studying.
Eldrige created a diagram of the life cycle of the two binary star systems and explained how the supernova relic puffed up and dumped mass into the Be star. He said that the supernova became a low-mass helium star that exploded and left a neutron star but transferred much of its mass to the Be star.
That means the ultra-stripped supernova interacted with the Be star, revealing the weird life cycle phases of the system. One day, the Be star will be a supernova neutron star to continue the cycle and become a binary system with two neutron stars.
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