Stars come in a plethora of different masses, ranging from small red dwarf stars to massive giant stars. While the smallest of all stars are expected to last upwards of a trillion years, giant stars go through their entire lifetime in a mere few million years.

This might seem counter-intuitive at first, since the more massive the star, the more material it is expected to have available for fusion. However, giant stars fuse through the hydrogen available in their core at an incredibly rapid rate, due in most part to the increased gravitational pressure they experience from their huge mass.

In addition, while only the core hydrogen is available for fusion in most stars, red dwarfs retain convection of material between their core and the outer star layers, and thus all hydrogen present in a red dwarf – not just the hydrogen initially found in the core – is available for fusion. The slower fusion rates, coupled with the fact that they remain fully convective, yields red dwarfs their resilience.

The question then becomes – what happens when a giant star runs out of available hydrogen for fusion? Giant stars have enough gravitational pressure to continue fusing heavier and heavier elements, with each fusion reaction generating a net gain in energy to counter gravitational pressure, until fusion of iron commences. Fusion of iron is actually endothermic, and as a result, it saps up energy rather than generate energy.  Thus, nothing is left to oppose the star’s gravitational pressure, and the star collapses.

Betelgeuse is one of the closest supernova candidates to Earth, at an estimated 600 light years away

The collapse itself results in the compression of the stellar core, so much so that protons and electrons merge to form neutrons in a process called electron capture, releasing neutrinos. The collapsing material is stopped by neutron degeneracy pressure at the neutron core, which releases a shockwave and a fresh wave of neutrinos that commences a supernova explosion – thus reversing the collapse of material towards the core, flinging it outwards in a supernova instead.

Betelgeuse is one of the closest supernova candidates to Earth, at an estimated 600 light years away. While recent estimates had put its likely time of supernova at least hundreds of thousands of years away, a recent study, still under review, simulated the supergiant star using the latest observational data.

It found that Betelgeuse might actually be at a late stage of its carbon fusion phase, which would place the estimated date of a supernova possibly just a few decades away, and at most a few hundred years away. If this is the case, Betelgeuse might actually have already gone supernova, but the light from the supernova would still be making its way towards us on its 600 year journey to Earth!

While this study still needs to be reviewed and verified by subsequent studies, it definitely highlights our need to study supergiants like Betelgeuse further in order to attempt to identify at which point they have arrived in their stellar evolution.

Josef Borg completed a PhD in astronomy at the Institute of Space Sciences and Astronomy, University of Malta, and is currently a researcher at the Faculty of Health Sciences at the University of Malta. He is also Malta’s representative on the European Astrobiology Network Association (EANA) council.

Sound Bites

•        Just one year ahead of launch, Artemis 2 astronauts autograph their own rocket. In a ceremonial activity, the Artemis 2 crew of four astronauts signed the adapter for the Orion spacecraft, which will be attached to the SLS rocket that will take them on their round trip to the moon. While the Artemis 2 crew will not be landing on the moon in 2024, their mission shall be the first to send a crew to lunar orbit and back since the end of the Apollo programme in 1972. Their mission will also pave the way for Artemis 3, due to launch in December 2025, and which shall see the return of astronauts on the surface of the moon.

For more soundbites, listen to Radio Mocha every Saturday at 7.30pm on Radju Malta and the following Monday at 9pm on Radju Malta 2 https://www.fb.com/RadioMochaMalta/.

DID YOU KNOW?

•        The last observed Type II supernova explosion in the Milky Way occurred in 1680. Observed by John Flamsteed in 1680, this supernova explosion left behind a supernova remnant, Cassiopeia A. Supernovae of this kind are typically expected to occur, on average, between one and three times every century in the Milky Way galaxy.

•        The closest star to the Sun is a red dwarf star. At a distance of around 4.25 light years, Proxima Centauri is the closest star to our sun, and yet it is too faint to be seen with the naked eye. It forms part of a triple star system – the Alpha Centauri star system.

For more trivia, see: www.um.edu.mt/think.