Is Betelgeuse about to go Supernova?
You might have seen pieces on various media claiming that Betelgeuse, an elderly star in the constellation of Orion is about to provide us with the spectacular show of its final moments. Is this the case ?
Let’s start from the beginning: what is Betelgeuse, and how on Earth do you pronounce it?
Contrary to popular opinion, it is not pronounced “Beetlejuice” like the film with Michael Keaton. Sorry.
Betelgeuse, or αOri, is a Red Supergiant that lies on the top left hand side of the constellation of Orion as it is seen from the Northern Hemisphere. You can easily tell it apart from its orange-red hue from the other members of the constellation away from the influence of light pollution.
Orion, the Hunter, is depicted having his right arm raised and Betelgeuse lies right at his armpit. Its name in Arabic means exactly that, Ibt-al-jowza, “armpit of Orion”. This became corrupted to “Bit-al-jooz” and finally to Betelgeuse. So “Bit-Al-Jooz” is perhaps the better way to pronounce it rather than Beetlejuice (still wrong but hey).
Betelgeuse is a Red Supergiant of the spectral type M1; it has depleted the hydrogen in its core and is now fusing Helium into heavier elements. It is a huge star with a radius almost as large as the orbit of Jupiter. Its atmosphere is pulsating (expanding and contracting) and that is the cause behind its variable nature. The latter means that its brightness varies with time. This has been known since the observations of Sir William Herschel in 1836.
It is an extreme variation that has sparked the discussion and articles on the internet; Betelgeuse’s brightness has dropped to the lowest level ever recorded. Red Supergiants are elderly stars that are in the final stages of their life. They all explode in massive Supernovae explosions that blow their body to smithereens, enriching the interstellar medium with the elements that they fused during their lifetimes. Any element heavier than Iron that exists in the Universe today comes from such an explosion, including the material that the wedding ring I am currently wearing on my finger is made of (whether I should have mentioned that to my wife when I presented her with a ring is debatable). These explosions release so much energy that they outshine entire galaxies, and their unusually bright light can be visible for days.
Is this unprecedented drop in the stars’ brightness cause for alarm? Does this mean that the star is about to die in a spectacular supernova?
We need some more tools to answer that.
In 1987, another star known as Sanduleac, blew up in such a massive supernova. Scientists were able to analyse the light coming from it as it was undergoing its final stages over the course of a few months. The spectral lines were changing within a matter of weeks, days and finally hours, revealing that the star was rapidly going over its last nuclear fuel in its core, fusing heavier and heavier elements until it formed an inert core of Iron. When nuclear fusion ceased in its inert core, the outward radiation pressure which balanced the inward force of gravity also ceased. The spectacular collapse which ensued (within a fraction of a second!) brought the subatomic particles making up its core to such proximity with respect to each other, to levels where the strong nuclear force – normally attractive and binding the nucleus together- became repulsive. The shock of this “bounce” and the energy stored in the field of the strong nuclear interaction is what powers the star’s demise in the devastating explosion that follows. It’s like a slingshot being pulled back to unimaginable extremes and then released, scattering the star’s atmosphere and leaving a neutron star or a black hole where the star used to be.
The procedure of a star’s death has been observed in the case of Sanduleac, which became known as SN1987a after its demise. In other words, not only do Astrophysicists have a theory to describe the mechanics of a Supernova explosion, but we have actually seen it take place live.
We now have the tools at our disposal to answer the original question: Is Betelgeuse about to explode? The answer is ….no. There have been no changes in its spectral lines that suggest that it has started the final chain of fusion which will lead to a Supernova within a matter of a few years, months or weeks. It simply has an interesting dip in its brightness, which means that something unusual is taking place as its atmosphere is pulsating.
Sorry everyone, it seems we will continue to enjoy Betelgeuse in the way humanity has known it for the last few thousands of years.