exploding in a galaxy far, far away

No, Lewis Carroll’s The Walrus didn’t say that, but it’s never a bad time to talk about a supernova. And now is an especially good time, because someone has just… well, how do I say it? exploded? But a supernova doesn’t explode. Stars explode to make a supernova. So the supernova just… happens.

And yet a word like “happen” cannot capture the cataclysmic, earth-shattering nature of this event. In fact, when our Sun turns into a supernova, the Earth will indeed be disintegrated. This adjective is accurate. So I’m not going to hang around waiting for this to happen, a few billion years from now.

But the time has also come to get serious. You’ve heard the term “supernova”. You may have heard of the supernova that Koichi Itagaki, a Japanese amateur astronomer, detected only a week ago. It was also later seen on images taken a few days earlier. Late on 19 May, a team of astronomers used a telescope in Spain to confirm the sighting of Itagaki. They classified it as a “Type II” supernova – one formed from the violent explosion of a star that is 10 to 50 times more massive than our Sun. It has a name: SN 2023ixf.

Any supernova is exciting news. But it has caught the attention of the world’s astronomers for a few reasons.

First, it is relatively easily seen even through small amateur telescopes. It’s also very easy to spot in the night sky – very close to Ursa Major or the Great Bear, the familiar constellation that looks like a giant question mark. In fact, if I were not in Bombay when I write this, and were instead somewhere far away with dark skies, I think I would be able to see SN2023ixf through my telescope, at least as a tiny dot in the northern sky. in the form of.

Second, it’s in an arm of the Pinwheel Galaxy, known as M101. It’s a spiral galaxy that’s facing us, so we can see the whole spiral through a telescope, so the pinwheel is always a photogenic, always gorgeous sight.

Third, Pinwheel is only about 21 million light-years away, meaning that SN2023ixf is the closest supernova we’ve discovered in five years.

So what are supernovae, and why should we care about them? In a very real sense, I’m writing this and you’re reading this because of some old supernova. Stars consist of various elements, including carbon, which is fundamental to life. But as the great Stephen Hawking once wrote:

“… that carbon is still far from forming the kind of ordered aggregates of chemical compounds that can enjoy a glass of Bordeaux … or ask questions about the universe. For the existence of beings such as humans, Carbon must be transferred from inside the star to friendly neighbourhoods. This is accomplished when the star, at the end of its life cycle, explodes as a supernova, spewing out carbon and other heavy elements that later form a planet. are condensed in.”

So the short version of what just happened in the Pinwheel Galaxy: A massive star ran out of fuel, and bang! We have the supernova SN2023ixf.

Should be clear about that phrase “just happened” though. It would be more accurate to say that we just witnessed the explosion, as it actually happened some time ago. Exactly 21 million years ago. Remember that the Pinwheel is light years away, meaning it takes years for light from there to reach us on Earth. So when this star exploded and released the carbon into space, it also sent shootings of light into space. After 21 million years, some of that light reaches us on Earth, and we see the “supernova”.

Let’s also be clear: The sight of this eruption is nothing like what we see here on Earth — no giant mushroom clouds, no rocks flying everywhere. I mean, it’s unimaginably more powerful than what we see on our planet. But it’s also so unimaginably distant that all we can actually detect is a bright point of light where there was none before. This is typical of supernova sightings. Of course the star that became SN2023ixf was in that location, but the Pinwheel Galaxy is too far away for us to see a distinct star there. until it became a supernova. Thus Itagaki discovered SN2023ixf.

Think for a moment what is implied here. We have never seen the star itself because it is so far away. But Itagaki saw it in the throes of its death, when it turned into a supernova. He found it with a telescope, of course, but still – it’s visible now. This means astronomers have been able to calculate its “apparent magnitude”, a measure of how bright it appears to us.

A few lines to explain the idea of ​​magnitude: On this scale, the lower the number, the brighter the object in our night sky. The brightest star we can see, Sirius or the Dog Star, has a magnitude of -1.33; Polaris, the North Star, is at magnitude 2.0; Venus, at its brightest, reaches −4.6; And the faintest stars we can see with our naked eye have a magnitude of 7.2. To put all of this into perspective, one unit of magnitude means a brightness factor of about 2.5. So Polaris, 3.33 magnitudes less than Sirius, is 3.33 x 2.5 = 8.3 times fainter than Sirius. Similarly, Venus is 8 times brighter than Sirius.

So on this scale, SN2023ixf has a magnitude of 10.8. Maybe it doesn’t affect you much. But it probably will: it’s about the magnitude of Messier 102, which is about twice as far away from us as SN2023ixf. But get this: Messier 102 is a galaxy containing about 100 billion stars. So this obscure distant star turns into a supernova that is as bright as the entire Milky Way.

Really, think about it for a moment.

In fact, the last known supernova in our own Milky Way galaxy, SN1604 in 1604, was brighter than all the stars in the sky for several months. At an estimated magnitude of -2.25, it was twice as bright as Sirius.

If SN2023ixf were in the Milky Way instead of the Pinwheel, it would probably be as spectacular a sight as SN1604 would have been 400 years ago. If it were in our solar system, though… let’s say, you wouldn’t be reading this.

Dilip D’Souza, once a computer scientist, now lives in Mumbai and writes for his dinner. His Twitter handle is @DeathEndsFun.

Updated: May 25, 2023, 10:27 PM IST