During an after-dinner stroll on a cool autumn evening in 1572, the great Danish astronomer Tycho Brahe was stopped in his tracks by the sight of a blazing new star in the constellation Cassiopeia. Tycho knew every star in the sky since his youth, and he lived in a time when many thought the heavens never changed. So when he saw this new star, he was, as he later wrote, “so astonished at this sight that I was not ashamed to doubt the trustworthiness of my own eye.”
Tycho was amazed by what’s now called a supernova, a massive exploding star which for a few weeks can outshine an entire galaxy. It’s a sight you should see for yourself, as luck allows, which is why it tops our celestial “Bucket List for Backyard Stargazers”…
Tycho had no way of knowing the nature of this new star. It would take more than 350 years before astronomers figured out enough physics to understand supernovae and the critical role they play in the creation of new stars, planets, and, well… you (more on this in a moment).
Now we know Tycho’s supernova was likely a small white dwarf star that suddenly blew itself to bits in a planet-sized nuclear explosion after taking on too much mass from a close companion star. This is known as a Type Ia supernova.
A multi-wavelength image of the remnants of Tycho’s 1572 supernova.
And there’s another type… the Type II supernova. This is a massive star that runs out of fuel and suddenly collapses upon itself, crushing its innards into a dense, scorching brew of radiation and atomic particles before rebounding outwards to release light and radiation and matter.
Both types of supernova create more energy in a few weeks than our Sun creates in its entire lifetime. Visible light is released, along with neutrinos and atomic and subatomic particles at high speed. The dangerous X-rays and gamma rays from a supernova would destroy or degrade life (as we know it) on any planet within an astonishing 50 light-year radius.
But while they are fearsome events, you would not be here if not for supernovae.
Long before it explodes, a big star turns hydrogen and helium into carbon and oxygen and many heavier elements all the way up to iron. This material is blasted out during the supernova explosion into the space between the stars.
What’s more, as the star collapses, neutrons get smashed into atomic nuclei to create and release all the naturally occurring elements heavier than iron, right up to uranium and beyond. The iron in your blood and your frying pan, the gold and silver in your jewelry, the copper and zinc and tantalum in your computer, were all created and released during long forgotten supernova explosions billions of years ago.
Now… how do you get to see one of these awesome beauties?
Supernova 1994D in the galaxy NGC 4526
Well, they are quite rare… about one every 50-100 years in the Milky Way on average. While many of the stars we see in the night sky will blow up as supernovae, none has been seen in our galaxy since 1604. So we are way overdue. Most stars, including the Sun and nearby stars, are too small to explode in this way.
Here’s a short list of nearby stars that will one day detonate as Type II supernovae: Betelguese in Orion, eta Carinae, rho Cassiopeiae, Spica, and Antares and Shaula in Scorpius. Astronomers don’t know when any of these stars will blow… it might be next week, it might be a million years. But all will one day shine bright enough to see in our daytime skies and cast shadows by night for weeks before fading away. And though no star is close enough to be dangerous to us, gamma rays and neutrinos from nearby supernova will be detected on Earth.
Your best bet to see a supernova lies in looking at other galaxies. The last naked-eye supernova occurred in 1987 in a nearby dwarf galaxy, the Large Magellanic Cloud. At least one extragalactic supernova is discovered with large telescopes every year in more distant galaxies. Some are discovered by amateur astronomers, including a recent discovery by a 10-year-old Canadian girl who found the star in an image taken with a large telescope.
Occasionally, these extragalactic supernovae are bright enough to see in a small telescope. A supernovae bright enough to see with binoculars or a small telescope will surely be announced on the news, or in these pages, so stay tuned and you’ll get your chance
And keep an eye on Betelguese, Spica, and Antares… you just never know. While you’re waiting for the “big one”, you can gaze at scattered remnants of supernovae that are visible in small telescopes, including the Crab Nebula and the Veil Nebula. Most are beautiful sights in their own right.
Publisher’s Note: I hope you liked the “Bucket List” series. I know they take longer than a minute to read, but what the heck. I’ll be posting a downloadable PDF with all ten of these articles on the website in the next several days. Please share it with your astronomy club and stargazing friends. And start crossing each sight off your own list as time and good fortune allow.