Few winter sky sights parallel the majestic beauty of the Orion constellation, one of the more well-known regions in the night sky. Imaged with appropriate telescopes and cameras, the entire constellation is rife with nebulae, with the Orion molecular cloud complex encompassing a large part of the entire constellation itself. The Orion nebula, one of the closest star forming regions to Earth, is just one small part of the entire molecular cloud complex, which is a massive stellar nursery in its own right. To the naked eye, however, the nebulae are too faint to observe, and the brightest stars in the area take centre stage instead. One of the more notable stars in the area is Betelgeuse, a red supergiant star on the shoulder of the Orion constellation.
Betelgeuse was once much smaller, albeit always being much larger than our star, the Sun. Being a giant star with over 10 times the mass of the Sun, Betelgeuse reached significantly higher temperatures in its core, meaning that even though it had a significantly higher mass of hydrogen to fuse, it went through its entire supply at a much faster rate than the Sun.
While the Sun has been fusing hydrogen into helium for almost 5 billion years, and still has another 5 billion years to go, Betelgeuse ran through its entire supply of core hydrogen in under 10 million years. The giant star subsequently underwent a core contraction, starting to fuse helium instead. This process resulted in increased heat radiating from the core of Betelgeuse, and the outer layers of the star expanded tremendously, almost to a 1000 times the Sun’s diameter, as a result. The surface temperature of the star dropped in temperature to around 3500 degrees, with the supergiant star getting its characteristic red colour as a result.
Stars like Betelgeuse dim and brighten again periodically over time, as a result of extensive mass flows inside the star itself. Material from the hotter interior wells up to the surface before sinking into the star’s depths again, giving rise to the star’s variable brightness. Over the past few weeks, Betelgeuse has been dimming significantly, leading to wide speculation that Betelgeuse could be nearing the end of its life.
However, this is extremely unlikely, and even though Betelgeuse is indeed a supernova candidate, expected to go supernova anytime in the next few thousand years, such dimming has occurred several times in the past century, even though its current brightness is one of the lowest recorded. In fact, astronomers expect Betelgeuse to start increasing in brightness again soon, reaching a minimum sometime in January. The chances of Betelgeuse going supernova in our lifetime is in fact extremely low.
What would it look like when Betelgeuse goes supernova? At a distance of over 600 light years, the supernova will be easily visible from Earth, with Betelgeuse appearing to increase in brightness to around the brightness of the full moon. It is far enough from the Earth that no harmful radiation will reach us in significant amounts, which means that we are safe from this particular threat.
The supernova will remain visible for weeks, probably even several months, before slowly dimming away. In its place, over the course of thousands of years, a supernova remnant will be left behind, with a neutron star or black hole at the centre.
So should we keep an eye out on Betelgeuse? Certainly! Anyone observing Orion right now will notice the red supergiant’s significantly diminished brightness when compared to its brightness over the past decade. But will it go supernova soon? Most probably not, so don’t hold your breath!
Mr 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?
• Chinese astronomers documented their observation of a supernova in 1054AD. They did not know what it was at the time, of course, but Chinese astronomers documented their observation of a ‘new star’ suddenly appearing in their skies in the constellation Taurus in 1054AD. This new star eventually faded away – in its place, today, we see the Crab nebula – a supernova remnant with a neutron star at its centre – the remnant of the supernova they had observed.
• Although unlikely, Betelgeuse might have already gone supernova. Betelgeuse is located between 600 and 700 light years away from Earth, meaning that light takes that long to travel from there to here. This means that our current observations of a dimming in Betelgeuse correspond to a dimming which actually happened between 600 and 700 years ago! If Betelgeuse exploded anytime in the past 600 years, therefore, we would still be seeing the light from before the explosion reaching us here on Earth, not knowing that Betelgeuse has gone supernova in the mean time!
• The closest supernova recently observed occurred in 1987. This supernova was the closest supernova observed since Kepler’s supernova, observed in 1604. It occurred in the Large Magellanic cloud, a dwarf galaxy just over 160,000 light years away. The supernova remnant was observed for signs of the expected neutron star at the centre, which was finally found in 2019 with ALMA telescope.
For more trivia see: www.um.edu.mt/think
Sound bites
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The head of India’s space agency confirmed Jan. 1 that it will attempt a second lunar landing, making that mission one of the top priorities of India’s space programme. At a New Year’s Day press briefing, Kailasavadivoo Sivan, chairman of the Indian Space Research Organisation (ISRO), said that the Chandrayaan-3 lunar lander mission, along with the Gaganyaan human spaceflight programme, will be top priorities for ISRO in 2020, although neither may fly until 2021.
https://spacenews.com/india-confirms-plans-for-second-lunar-lander-mission/
• Astronaut Christina Koch breaks record for longest space mission by a woman
A Nasa astronaut has set a new record for time spent in space, and she still has six weeks to go before she returns to Earth. Christina Koch has surpassed the record for the single longest space mission by a woman as previously established by Nasa astronaut Peggy Whitson in 2017. The 40-year-old Expedition 61 flight engineer exceeded Whitson’s record of 289 days, 5 hours and 1 minute on Saturday, December 28, 2019.
https://www.space.com/nasa-astronaut-christina-koch-breaks-female-spaceflight-record.html
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