September 29, 2022

Our solar system is a single-star system. But this is not necessarily true for all star systems in the Milky Way, the galaxy where our solar system is located. There are several multi-star systems in this galaxy. While most of these are binary systems comprising two stars, there are others which have more than as well. With stars, comes the talk of supernova, the last stage in the evolution of a massive star, when it bursts into a luminous stellar explosion. Astronomers are always looking out for any potential supernova explosion because these have ramifications for all of the universe. In that effort, a team of researchers have found that a quadruple star system – known as HD 74438 – could represent a new channel by which thermonuclear supernova explosions can occur in the universe.

Discovered in 2017, the HD 74438 system is a quad. It consists of a pair of stars orbiting each other and simultaneously around another close two (2+2 configuration). Subsequent studies showed that HD 74438 is the youngest among all such systems, only 43-million-year old. Now, astronomers at the University of Canterbury Mt. John Observatory in New Zealand have found that this quadruple is made up of four gravitationally bound stars.

In their study published in the journal Nature Astronomy, they have shown that the gravitational effects of the outer binary system are changing the orbits of the inner binary, making it more eccentric. So, the researchers tried to simulate the orbits of the stars in the future. They found that such gravitational dynamics can lead to one or multiple collisions and merger events producing evolved dead stars, or white dwarfs, with masses just below the Chandrasekhar limit. As a result, these white dwarfs can lead to a thermonuclear supernova.

Named after Indian-born astrophysicist Subrahmanyan Chandrasekhar, this limit is the maximum mass of a stable white dwarf star. The currently accepted value of the Chandrasekhar limit is about 1.4 solar masses.