Wonders of the Universe - Brian Cox [54]
Supernovae are so rare that since the birth of modern science we have never had the chance to see one close up. The last supernova explosion seen from Earth in our galaxy was in 1604, a few years before the invention of the astronomical telescope. On average, it is expected there should be around one supernova explosion in the Milky Way per century, but for the last 400 years we’ve had no luck. It’s long overdue and astronomers are always searching the skies for stars which they think might be the most likely candidate to go supernova.
One of the prime candidates is Orion’s shining red jewel, Betelgeuse. With so many telescopes trained on this nearby star, we have been able to follow its every move for decades. Charting its brightness, we have discovered that it is extremely unstable; it has dimmed by about 15 per cent in the past decade. As supernova candidates go, Betelgeuse is top of the list. It is generally thought that Betelgeuse could go supernova at any time. It is a relatively young star, perhaps only ten million years old, and has sped through its life cycle so rapidly because it is so massive. However, when you’re ten million years old, the end of your life can be quite drawn out and a phrase like ‘any time soon’ in stellar terms is not quite what you might expect. It means that Betelgeuse should go supernova at some point in the next million years, but equally it could explode tomorrow. What we do know is that when it does go it will provide us with quite a show. Betelgeuse is only 500 light years away, almost uncomfortably close, which means that the explosion will be incredibly bright. It will be by far the brightest star in the sky and it may even shine as brightly as a full moon at night and fill the sky as a second sun during the day.
The giant Orion Molecular Cloud is an extensive area of star formation about 1,500 light years from us, centred on the impressive Orion Nebula. This infrared image of it, from NASA’s Spitzer Space Telescope, shows light from newborn stars within the Orion Nebula. The nebula can be seen from Earth with the naked eye as a hazy ‘star’ in Orion’s sword.
NASA
This computer-generated image shows just how bright scientists believe the heavens will be once Betelguese has gone supernova; it will flood the skies with light – day and night.
When stars are more massive than about eight times the Sun, they end their lives in a spectacular explosion. The outer layers of the star are hurtled out into space at thousands of miles an hour, leaving a debris field of gas and dust. Where the star once was, a small, dense object called a neutron star is often found. While around only 16 kilometres (10 miles) across, the tightly packed neutrons it contains have more mass than the entire Sun. The bright blue dot in the centre of this X-ray image of RCW 103 is believed to show the neutron star that formed when the star exploded in a supernova 2,000 years ago.
NASA
In a single instant, Betelgeuse will release more energy than our sun will produce in its entire lifetime. As the explosion tears the star apart, it will fling out into space all the elements the star has created through its life.
Over millions of years these newly minted elements will spread out to become a nebula, a rich chemical cloud drifting in space. At the heart of it, all that will remain will be the super-dense core of neutrons; the remnants of the star that was once a billion miles across will have been squashed out of all recognition by gravity. This is a neutron star, the ultimate destiny of Betelgeuse; a dense, hot ball of matter which is the same mass as our Sun but only 30 kilometres (19 miles) across.
We may not have seen neutron stars close up, but we have seen them from afar. X-ray images have been taken that