Kepler's Supernova occurred in the constellation Ophiuchus. Appearing in 1604
The life cycle of a star like our Sun.
A star is formed where an amount of Hydrogen roughly equal to at least 90 times the mass of Jupiter coalesce in the same place in space. At that size the pressure and heat at the core is sufficient to begin nuclear fusion, fusing Hydrogen into Helium, and a small star will form. Stars with more Hydrogen will be bigger and brighter, but all stars face the same eternal struggle to exist – to create enough outward energy via fusion to withstand the cataclysmic pressure of their own size and mass.
Stars have a finite amount of fuel, take our own Sun for example, currently a distinctly ordinary Yellow Dwarf star formed approximately 4.5 billion years ago. Calculations made in 2018 by NASA showed that it is made of 91.0% Hydrogen and 8.9% Helium. It fuses about 600 million tons of Hydrogen every second, creating 596 million tons of Helium, with the remaining Hydrogen converted into to energy, which makes it shine and radiate the heat we all need to survive. So far so good, but in another 5 billion years or so, the Sun will have used up all the available Hydrogen fuel in its core.
With the fusion process stalling, there will be insufficient outward energy to counter the crushing force of gravity, the core will be compressed and contract and in doing so become both denser and hotter over time, igniting the remaining Hydrogen outside the core. This process will generate enough energy to push the top layers of the sun outwards, causing the sun to expand almost three times its current diameter, turning it in a Red Subgiant star.
Over billions of years the core will continue to contract, getting denser and hotter until it reaches the magic temperature of 100 million °C – at that point the temperature and pressure will be such that the Helium in the core will be able to fuse into heavier elements like Carbon and Oxygen and push out the diameter of the sun yet further, almost to the orbit of Earth, creating a Red Giant star. This phase will be brief, because in just 100 million years the available Helium will have been used up, and as the sun isn’t massive enough for its core to ever reach the 600 million °C necessary for Carbon fusion to occur – gravity will finally win over fusion.
The ejected mass of the sun will drift away from the white-hot core and the sun will have become a White Dwarf. This dense white star will illuminate the material it ejected over its traumatic final years as a planetary nebula, but even this stage is temporary. The Sun will begin to cool and eventually stop producing any heat or light, leaving our home star to end its days as a cold dense Black Dwarf, and not a spectacular supernova.
Why is Betelgeuse not like our sun?
Put simply when talking about stars, size matters. Betelgeuse is one of the largest known stars ever found and is estimated to be about 700 times the size of the Sun and at least 15 times as massive. It is this enormous size which leads scientists to believe Betelgeuse is altogether a much more explosive candidate for a Supernova.
So why do scientists think it is about to go Supernova?
The Saio Research has been looking at the different brightness rates, or pulse rates, of Betelgeuse and used complicated modelling to determine what may be happening inside the star to explain the unexpected variations in brightness currently being observed. Every star has several different pulse rates, a bit like a heartbeat, that are caused by regular changes in fusion rates, and other variations which occur during the titanic struggle between gravity and fusion. In the case of Betelgeuse, the star has been observed very closely for hundreds of years due to its brightness and prominent position in the night sky. These observations mean we have a detailed record of brightness changes over time, Betelgeuse is currently 142% brighter than expected.
The Saio Research suggests that these large fluctuations in brightness indicate that Betelgeuse is nearing the end of the Carbon fusion stage of its life, meaning that the Supergiant star has fused all its available Hydrogen into Helium and fused all that Helium into Carbon which it is now using as fuel. However, the modelling also suggests it may have as little as 17% of its available Carbon left for fusion, but that estimate drops yet further to less than half of 1% in some of the calculations. So what? Well, each subsequent phase of stella nucleosynthesis (the process of fusion within star) takes less and less time to complete.
Whilst it can take billions of years for a star to fuse all its Hydrogen into Helium, for a star the size of Betelgeuse it would take just 1000 years or so to fuse its Carbon into Neon, then maybe just a few decades to fuse that Neon into Oxygen, then maybe a year to fuse its Oxygen into Silicon, and finally just a day to fuse Silicon into Iron, and it is this creation of Iron which heralds the immediate, and explosive, death of stars the size of Betelgeuse. Iron is too dense to be fused into anything elementally heavier within a star’s core, fusion will be stopped, nucleosynthesis will have ended resulting in no more outward energy, the core instantaneously collapses in on itself causing a massive explosion - a supernova.
Do all scientists agree it will go supernova soon?
Whilst most scientists do agree that Betelgeuse is acting very strange when it comes to its brightness, and there is almost universal agreement that Betelgeuse will eventually end its days with a supernova, there is no agreement yet in relation to the Saio Research findings themselves. The paper is yet to peer reviewed, and some scientists are already pointing out the large range of variables which make determining the complex chemistry at the core of a star very difficult. So, it is definitely not a certainty that Betelgeuse will do anything spectacular just yet.
If they are right, what can we expect from a supernova?
First, Betelgeuse is 642.5 light years away from Earth, so it may well have already happened, and we are simply awaiting the light to reach us so we can see it. When that light does reach us, then the visual effects alone will be breathtaking. A significant brightening of the shoulder star of Orion to the same levels as a full moon, potentially even forming shadows on the ground. It is almost certainly going to be visible during the day too. Its brightness will fade over a period of months, until the star is no longer visible as it takes on its new role as either a neutron star or maybe even a black hole.
It is important to note that whilst we are too far away from the Supernova to feel any direct negative effects in the form of radiation, heat or shockwave, the effect on our night sky will be marked. Orion will lose one of his shoulders, and we will lose the 10th brightest (and probably most loved) star in the night sky - but what a way to go!
Are you looking forward to seeing Betelgeuse explode - or will you be sad to see Orion lose a limb? Let us know in the comments below.
WRITTEN BY WoorLord
EDITED BY Solace
IMAGES SOURCED FROM NASA - CXO/HST/Spitzer Space Telescope - Newsweek.com - Sportskeeda.com
