Science Writing

The Explosion Brighter Than The Moon

Our sun is boring.

That might seem like a harsh assessment of the object that literally keeps all life on Earth living, but it’s true. In the context of the Universe, our star is a bland, boring main-sequence that will burn steadily for a long long time.

Which is great! For us, as it means life on Earth (baring some other calamity) will continue to chug along in some form for many millions of years to come until our sun expands into a red giant and sterilises the planet.

There are more interesting stars than our Sun and a lot of time and money is being spent examining them. The James Webb Space Telescope that will replace Hubble is due to be launched next year; TESS, the Transiting Exoplanet Survey Satellite has cataloged thousands of planets and their stars over the past few years and it was a replacement for the Kepler scope that clocked over four thousand exoplanets and stars in its time.

But one of the most interesting stars in the night sky is called Betelgeuse.

You may have heard it when last year the astronomy community lit with excitement; Betelgeuse was dimming, and dimming fast. Could this be the pre-cursor to the red giant going supernova?

Telescopes all around the world locked onto the red dot on the shoulder of Orion and waited with bated breath…for nothing.

Betelgeuse didn’t explode and is still flickering steadily in the night sky as I type this.

But don’t let that fool you into thinking it is a boring star; it isn’t.

Betelgeuse is a red giant and that alone is cause for excitement. Red giants burn bright and they burn fast. In relative terms, Betelgeuse is a baby, having only been around in its current start for approximately 9 million years.

For contrast, our Sun has been chugging away for about 4.5 billion.

What makes red giants fascinating is the speed at which they burn their fuel. Betelgeuse is many times more massive than the Sun, and with that mass comes an increase in gravity.

All of Betelgeuse’s fuel is being squished and this causes the nuclear reactions within the star to occur more rapidly and with greater energy; this in turn pushes out against the gravitational force of the stars mass. With this interaction a type of balance is achieved, but because of the sheer size of red giants, the balance is short lived (relatively speaking).

When Betelgeuse burns through its hydrogen its output of energy will decrease and gravity will win out. This is a cascading reaction; the longer it continues the quicker it will occur. Gravity squeezes the red giant which begins to fuse and form heavy metals (this is where it is theorised all of the heavy elements originally were produced) but even then, the star will collapse under it’s own mass and gravitational pull.

When that happens – boom.

It rebounds back and launches light, heat, dust and elements into the abyss. It will be an explosion on a scale that Earth will never experience. Our Sun is too steady, too normal. When it begins to run out of hydrogen it will expand as it begins to form other elements, ballooning out into a red giant. The difference is, however, the mass of the sun is too little to cause the newly formed red giant to collapse in on itself. It will shrink and shed its outer layers, leaving a white hot core – a white dwarf.

So the dimming of Betelgeuse wasn’t the pre-cursor to an explosion. That won’t happen for another one hundred thousand years or so according to a study release by ANU.

What cause it then?

Betelgeuse created it’s own darkness.

Red giants are not stable and Betelgeuse is no exception. It released a huge blob of plasma into space, directed roughly at Earth, this in turn cooled and left a dust cloud that then obscured the star.

four illustrations of a red-hued star expelling gas, bringing the star into slight shadow
An illustration of the cause of the dimming of Betelgeuse in late 2019. The hot blob of plasma ejected from the star cooled and left a dust cloud that obscured the view from Earth. Credit: NASA, ESA, E. Wheatley

It’s not the most exciting explanation, I know. When Betelgeuse does go supernova the resulting light will reportedly outshine anything else in the galaxy. To us, it will be brighter than the Moon.

Unfortunately, we are unlikely to still be around to see it.

Further Reading/References

Hubble Finds Betelgeuse’s Mysterious Dimming Due to Traumatic Outburst | NASA

Supergiant star Betelgeuse smaller, closer than first thought (prezly.com)

Here’s what the supergiant star Betelgeuse will look like when it goes supernova | Space

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