What is a Supernova? Yes, It's Truly "Super" Cool.


The Crab Nebula is what’s left of a massive star in our Milky Way; astronomers saw the supernova in the year 1054.

Photo Credit

What is the biggest explosion we've ever seen?

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What is the biggest explosion that we humans have ever seen? It’s the supernova! Bob Berman’s newest piece is about supernovas, a truly super phenomenon with “star power.”


Any word that begins with “super” is supposedly remarkable. But it’s not always true.  Some are visual duds, like the “supermoon” the media frequently hypes. Most look no different from every other Full Moon, despite trolls photoshopping them to seemingly fill the sky. We also have fictitious ultra-entities like Superman, who still use phone booths as changing rooms even though they neither exist nor were ever legal for that purpose. That leaves us with only a few genuine items possessing that superlative, like superstars and the Super Bowl.

But one example never disappoints—the supernova. 

What is a Supernova?

This is the biggest explosion that will ever light up the modern universe. Every blast is the extremely bright, super-powerful explosion of a star. It’s so bright that supernovas can be seen across the universe; they outshine their entire galaxies for a few days or even months.

How Rare is a Supernova?

An exploding star happens around once a century in each of the hundreds of billions of galaxies in the cosmos. If it’s near enough, we see a “new” star that is so bright it outshines every other star and can even remain visible in daylight. That actually happened in 1008, 1054, 1572, and 1604.

If a very nearby star goes supernova, it can genetically alter or possibly even destroy life on Earth. Even a fairly distant one often leaves visible wreckage that makes us telescopically gawk at what very much resembles a disastrous event. 

On top of all that, the most common supernovae brighten to about the same brilliance level as every other, which provides a reliable way of measuring cosmic distances. Absolutely, the “super” is fully deserved.

So let’s understand them, since even their facts are supercool. And yes, you can pluralize them by using either supernovas or supernovae; both are correct. (I prefer the latter with that “..VEE” ending whose nerdy aura can make geeky people fall in love with you.)

Astronomical Jargon

Let’s momentarily digress to ponder the subset of astrophysicists who uphold science’s longstanding tradition of making laypeople feel like idiots whenever possible.

  •  For example, when physicians write a prescription to take a pill three times a day, they could have written “3xD.” But since that might have let you catch on to its actual meaning, they instead write “tid,” which stands for “ter en die,” which is Latin for three times a day, and bingo, mission accomplished, since your doctor knows that no electrical signal will traverse your brain if he employs a language spoken in no country on the planet.
  •  Astrophysicists find such obfuscation similarly alluring, so when bodies resembling Pluto were found in its vicinity, and astronomers initially termed them “Plutoids,” the IAU, the organization that officially names celestial objects, basically said, “We’ll call them Kuiper Belt Objects!”  And that was okay for a few years, until too many people learned how to pronounce Kuiper (it’s KY-per), and then the Plutoids were again renamed to become KBOs permanently. 
  • Similarly, using the light-year to express distance proved too easy for the public. So, instead, the pointlessly similar distance of 3 ¼ light-years, called the “parsec,” whose usefulness ends at just a few hundred lightyears, nonetheless got promulgated; nowadays, galaxy distances are solely expressed as megaparsecs. Light-years have now vanished from astronomy journals. Along with the public’s ability to visualize celestial distances.

Types of Supernovas

This digression is meant to help appreciate how astronomers then did a very strange thing. When, nearly a century ago, they discovered there are two different kinds of supernovae, they somehow got confused and neglected to give them unrelated, unpronounceable terms. 

Instead, astronomers called them “type 1” and “type 2” supernovae. How such a logical structure managed to materialize remains an enigma, but we’ll happily accept it, along with a single necessary clarification: 

  1. A Type 1 supernova is brighter, and involves two stars orbiting each other.
  2. A Type 2 supernova befalls a single heavy star in its old age.

Memorize that, and you’ll grasp the main supernova story. 

What Causes Supernovas?

Consider Betelgeuse, the supergiant star in Orion’s left shoulder. It’s heavy, massive, and old. It has nearly used up the hydrogen fuel in its core. When enough of that is gone, which won’t be too long now, the outward push of the core’s energy won’t be able to hold back the crushing, infalling gravitational weight of the rest of the star. When all of Betelgeuse’s enormous mass implodes inward, it’ll suddenly increase the core temperature so that new reactions instantly happen, making the whole star wreck itself in a titanic explosion. If you call this a type 2 supernova, you win the prize.

Now consider another big star, but this one is orbiting a tiny, dense white dwarf. The dwarf’s gravity is huge, so it keeps pulling the big star’s “stellar wind” material to its surface. When enough accumulates like an ultradense layer of pond scum, it all ignites in a fusion bomb that destroys both stars. It’s a type 1 supernova, the brightest kind.

This wreckage flying apart at 1,000 miles per second is a supernova still in progress. It blew up near the Pleiades star cluster on the 4th of July in 1054. At its center is a faint star close to the lower right of a slightly brighter one, which is the original star that exploded. It is now an ultradense pulsar spinning 30 times a second.
Credit: Former Woodstocker Bill Rouady, taken last week in Virginia.

The Next Supernova

Now, we’ve gained enough celestial knowledge to decide whether we want bad news or good news. 

The bad news: We’d all love to see a brand new super bright star appear one night, casting shadows. It’s been 420 years since we last saw that, so we’re kind of overdue. I even led a group to near the equator in 1987 to observe a medium faint-looking one in a nearby galaxy, the first naked-eye supernova in four centuries. But as for a super-brilliant lighthouse that casts shadows around your home, no potential stars seem genuinely on the edge. Well, maybe Betelgeuse. It’s a good candidate, but it could pop tomorrow or, more likely, in ten thousand years.

Will Our Sun Go Supernova?

The good news: Our Sun is neither a double star nor a massive old one. It cannot “go supernova” as either a type one or a type two. Can’t pop, won’t pop, not ever. We’re safe from oblivion. 

The nearest heavy sun is the Dog Star Sirius, 8.65 light-years away. But it’s not heavy enough, being just 2.4 times our sun’s weight, which we think is at least five times too skimpy. Even Roberto Duran denigrated it by saying, “No mass, no mass.” 

But Sirius does have a white dwarf companion, popularly called “the Pup.” So there’s always a bit of hope it’ll someday escape from its current well-behaved kennel and transform our sky and Earth as if ripping up the neighborhood garbage.

See more of the Universe’s Big Bangs!

About The Author

Bob Berman

Bob Berman, astronomer editor for The Old Farmer’s Almanac, covers everything under the Sun (and Moon)! Bob is the world’s most widely read astronomer and has written ten popular books. Read More from Bob Berman

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