Stars light up our night sky from vast distances across the cosmos, with up to six thousand stars visible on any one night to the naked eye from a dark location.
These stars form just a fraction of the estimated 300 billion stars making up just our own galaxy, the Milky Way – one of billions of estimated galaxies in the universe. In this myriad of stars, diversity is not lacking. Some stars are relatively faint and small; others are monstrous, outshining our own star, the Sun, thousands of times over. Some of these stars are visible in summer, while a completely different set of stars is visible in our winter skies.
However, notwithstanding the mind-boggling number of known stars, few stars intrigue astronomers more than the supergiant star Betelgeuse, visible to the naked eye the world over.
Located in the winter constellation Orion, Betelgeuse is classified as a red supergiant star. It is found at an approximate distance of some 600 light years from earth, with one light year being approximately equivalent to 9.5 trillion kilometres (9,500,000,000,000 km) – the distance that light travels in one year.
Yet, even though it is found so far from earth, Betelgeuse is one of the brightest stars in our skies and is also one of the biggest stars known. Estimates put Betelgeuse at a diameter about 1,000 times that of the sun, burning its fuel supply at ridiculously high rates.
What makes Betelgeuse so special? When large stars such as Betelgeuse run out of fuel, they go out in one of the most spectacular and terrifying events in the entire cosmos – a supernova explosion. When this happens, the exploding giant star briefly shines so bright that it outshines the entire galaxy, producing as much energy as the Sun will produce in its entire lifetime of 10 billion years in an instant. Such an explosion is not only seen within the galaxy where the supernova occurs, but also across vast distances between different galaxies, millions or billions of light years apart. Betelgeuse itself happens to be at the very last gasps of its lifetime and is expected to explode any time between today and one million years from today.
When it does, Betelgeuse will increase in brightness to outshine the full moon in our night sky, as seen from earth, and will be visible for a few weeks as a very, very bright star in the night sky, or a second star (fainter than the Sun, but still visible) in the morning sky.
Even though Betelgeuse will explode with such ferocity, however, earth is well out of harm’s way. Betelgeuse would need to be at least six times closer to us to be a potential hazard to life on earth.
So if Betelgeuse does explode within our lifetime, there will be no need for sounding the horns of an impending doomsday. Rather, sit back and enjoy one of the biggest spectacles that the universe has to offer unfold; a supernova leading to the creation of all the elements which make up our own planet, and by extension, us humans, in an instant. We are, quite literally, star dust.
Josef Borg is currently a PhD student within the Institute of Space Sciences and Astronomy, University of Malta, and also the president of the Astronomical Society of Malta.
Did you know?
• The most abundant type of star in our galaxy cannot be seen with the naked eye. Red dwarf stars are the most abundant type of star in the Milky Way galaxy, and yet, they are too small to be seen with the naked eye from anywhere on earth. Only with the use of telescopes have these small, faint stars been discovered!
• Red dwarf stars are also the longest-lived stars. Notwithstanding their small size and faint nature, red dwarf stars are also the most resilient stars in the universe. Since the beginning of the universe, not one of these small stars has reached the end of its lifetime, as they continue burning fuel at their relatively slow rate for an estimated trillion years! By comparison, stars like the sun last for a few billion years and giant stars like Betelgeuse only last for a few million years.
• Upon exploding, giant stars form a supernova remnant with either a neutron star or a black hole at the centre. After the supernova explosion, the outer layers of the supergiant star are flung out into space, creating a supernova remnant. What was the star’s core before, however, can form one of two very strange objects with immense gravity, depending on the size of the giant star’s remnant core. If the core is below the mass of 2.8 suns, a neutron star is formed, whereas if it is of a higher mass, a black hole is formed.
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