On February 23rd, 1987, an  explosion rocked the sky that was unlike anything anyone had seen not just in living memory, but in centuries.

If you had a keen eye and lived  in the southern hemisphere, you could step outside on a clear night and witness a bright dot that wasn’t there before. It’s as if a new star appeared.

But it wasn’t a new star, though. It was a supernova, one of the most violent events that can happen in our universe. And it was the first supernova to be visible to the naked eye since the telescope was invented!

In the decades since, researchers  have learned an astronomical amount of new science by  studying this one explosion. I’m talking right up until  2023, when they finally solved the mystery of what it left behind. [♪ INTRO] Nothing lasts forever, including stars. And the reason they’re  shining in the first place is they’re using up a bunch of  nuclear fuel inside of them.

And as anyone who has ever had to worry about surging gas prices or getting hangry  knows, fuel inevitably runs out. But while some stars like our own Sun are content to end their lives with a proverbial  whimper, others go out with a bang. A near-instant, massive explosion  that tears the star apart.

Our galaxy is supposed to have two or three of these supernovas every century. But most of the time we can’t see them from Earth. They’re often too far away, with too  much interstellar dust in the way.

That’s why the previous great supernova, one that an average person could step outside and spot without a telescope, was  seen all the way back in 1604! But luckily for astronomers,  there are super fancy telescopes that let them look at millions of other galaxies and hunt for supernovas that are  way too dim to see otherwise. And the one that happened in 1987  did happen in another galaxy.

Sure, it’s the Large Magellanic  Cloud, which is a dwarf galaxy on the Milky Way’s back porch. But it counts! And at roughly 160,000 light years away from us, the light from this supernova had 160,000 years to spread out as it traveled through space.

Which is why it was a lot less  bright than that 1604 explosion. But what it lacked in visual brilliance, it made up for as a brilliant bed-time story. Early in the morning on February 24th, at Las Campanas Observatory  high atop a Chilean mountain, astronomer Ian Shelton was developing his final photographic plate of the night.

And as he scanned the image  captured on that plate, he saw a star that didn’t used to be there. He rushed outside to check, and, to his surprise, he could see this “new star” with  his own eyes in the night sky. Of course, Shelton hadn’t  witnessed a star being born.

It was the opposite. And he  and his colleagues scrambled to get a message to the  International Astronomical Union, which involved a 100 kilometer  drive to the nearest town. Oh, and because astronomers are  so amazing at naming things, they eventually gave this once-in-many-lifetimes supernova a very catchy name… SN1987A.

Eventually, astronomers were able to pin down exactly which star in the sky went boom. It went by the name, um… this… and it was roughly 20 times more massive than our Sun. Now, being so massive, you might think it’d be able to live a lot longer than our Sun will.

But for stars, it’s actually the opposite. The more mass you’ve got, the  faster you burn through your fuel. So while our Sun is roughly halfway  through its 10 billion year lifecycle, the progenitor to SN1987A kicked the astronomical bucket at the ripe old age  of only 10 million years.

Of course, the supernova  at the end of its life was even more of a pinprick in the  greater timeline of the universe. The winds of change started about a million years before the actual explosion. The star’s core ran out of its  primary fuel source, hydrogen.

And with no way to spew out a bunch of energy, it started collapsing under its own gravity. But that near collapse actually helped the star switch over to burning the next  lightest thing available: Helium. But eventually, it ran out of helium.  So it switched to another fuel.

And this happened again and again until there was nothing left that the star could use,  and its nuclear furnace turned off. And at that point, gravity  took over one final time. In just a few tenths of a second,  the core collapsed down from being roughly Earth-sized to a sphere  the size of a small city, creating a stupendously powerful  shockwave that ripped the star apart.

And over the next few months,  that explosion released as much energy as our Sun does  over a hundred million years. In fact, it peaked in  brightness a full three months after astronomers first detected it! We’ll get back to why that happened later, but 160,000 years after that initial explosion, all that light finally reached the Earth, including Dr.

Shelton’s photographic plate. But after that momentous night  in the Chilean mountains, astronomers realized there was  another signal from the supernova that had arrived just a bit  earlier. And it was much weirder.

This episode is brought you by this months Presidents of Science Mclaren  Stanley and Charlie Stanley. How can there be two presidents? Democracy.

Maybe we should rename it. Leave your suggestions in the comments. Anyway, thank you both for being so awesome And supporting us over on Patreon.

If you, dear viewer, want to learn more about Becoming president of Science or about one of our other wonderful patron tiers, Go to Patreon.com/SciShow. In the seconds surrounding the final collapse, the nuclei in the star’s  core went through one final, sudden nuclear reaction,  which produced a burst of odd, obscure particles called   neutrinos. These fundamental particles  are infamous for having almost zero interaction  with other kinds of matter.

While a high-energy particle of light is stopped by a few centimeters of lead shielding, you’d need a wall that’s around a light year thick to stop an average neutrino. So it’s basically impossible  to capture a single neutrino in even the fanciest neutrino detector. But if you’ve got enough of them streaming through space, statistics wins out.

So in 1987, a few hours before the light of SN1987A reached Earth, neutrino observatories around the world noticed a  distinct spike in detections. Since that spike happened at  one precise moment in time, it suggested there was a sudden wave of neutrinos, generated by a single event, that  had just passed through the Earth. And the cool thing is, there was  a tiny bit of luck involved here.

Neutrinos had been known about for a few decades, but neutrino detectors were  very recent inventions. So if the supernova had  happened, like, 20 years earlier… which is nothing to the universe… we wouldn’t have picked this  part of the signal up at all! But wait, why did the neutrinos arrive before the light from the explosion?

Were the neutrinos traveling faster-than-light? Well, no. In fact, it was the other way around.

The light was traveling slower than light… or, rather, how fast light  travels in the dead void of space. Remember, neutrinos can pass through  basically anything unscathed. So as soon as they were created,  they could zip straight through the collapsing star and the  surrounding gas with nary a care.

Meanwhile, the light produced by  the supernova had to push through all that stellar matter before it  could escape into interstellar space. So to an observer on Earth, it looked like the neutrinos got a head start. And the fact that they  arrived just a few hours ahead after a journey of 160,000 years proved that neutrinos must travel  extremely close to light-speed.

In other words, SN1987A was yet another key piece of evidence supporting  Einstein’s theory of relativity. But that wasn't all we learned. SN1987A was the first major supernova in modern astronomy, even if you define “modern” as “After  people started using telescopes”.

Plus, since it was also the  1980s, scientists had a fleet of high-accuracy telescopes not just  around the world, but in space, too. So after word got out, countless people aimed their equipment at the exact same spot in space, staring down the supernova remnant  in the Large Magellanic Cloud. And over the past several decades, SN1987A has revealed a lot about how supernovas work.

For example, astronomers learned that they were generally correct about how  stars undergo core collapse. But it also showed that a few  supernova theories weren’t quite right. Remember how astronomers were able to identify the star that exploded?

Well, it was a blue supergiant,  but up until that point, astronomers had only ever attributed supernovas to their much larger cousins, red supergiants. Basically, they thought  that a collapsing blue star, like SN1987A’s progenitor,  wouldn’t be able to create the signals they were detecting  from other supernova remnants. And while it is true that most  core collapse supernovas do come from red supergiants, SN1987A  showed they don’t have to.

Astronomers also realized that before a star dies, it can eject way more matter than they thought. SN1987A’s blue supergiant  progenitor spent its last several thousand years shedding the  plasma in its outer layers. And before the big kaboom,  that debris had built up into a ring spanning about  a light-year in diameter!

When the supernova finally  happened, all that light slammed into that ring, causing  it to glow with X-ray light. And in 2010, the Hubble Space Telescope detected this ring was getting brighter, producing a structure that media  outlets likened to a pearl necklace. While this specific interaction did match what astronomers predicted would happen, some of the latest images have features that astronomers don’t quite understand, like structures that they think might be caused by what they call reverse-shock waves.

So it’s a bit of a mixed record for SN1987A confirming and denying theories about supernovas. But in 2024, the biggest mystery  of them all may have been solved. See, ever since astronomers  accepted this “new star” was in fact a newly dead star,  there’s been a debate about what exactly happened to the  star’s corpse after the explosion.

Namely, which of the two most extreme objects in the universe did the core collapse into? A neutron star, or a black hole? Both of them are observed  in other supernova remnants, so either one is possible.

But the problem is, for decades,  no one could find anything! So maybe the explosion was so  violent there was no remnant, or maybe the remnant was something completely unseen before in nature… some exotic midpoint between a neutron star and a black hole called a quark star. Or maybe it was just hiding  behind a bunch of dust.

Hints that it was probably  just a regular ol’ neutron star started trickling in a few years ago. We even covered the news over on SciShow Space. But when the JWST came online in 2022, it could use its infrared detectors to peer through all that dust with unprecedented detail.

Astronomers appear to have  finally settled the matter. According to NASA, the telescope found the tell-tale signs of a  newly-birthed neutron star. So as incredible as that stellar implosion was, it didn’t quite have enough strength to crush the core all the way down to a black hole.

Instead, the core became a hyper-dense  ball of solid nuclear matter, held up by the most extreme force in the universe. But we’ve barely scraped the surface in the treasure trove of data  that SN1987A left behind. It gave astronomers better  estimates of how far away the Large Magellanic Cloud is, how  fast the universe is expanding, and where the dust in galaxies comes from.

But perhaps most importantly, it also  fired up the public’s imagination. The supernova was even on  the cover of TIME Magazine! And I for one think it totally deserved it.

This supernova was a reminder that,  despite how fleeting our lives are to the greater cosmos, we  can see major moments of change. We live in a dynamic, evolving,  ever-changing universe. And that’s as good a reason  as any to keep looking up.

And you know what? The supernova remnant left behind will also change as time marches forward. JWST didn’t see the same shape that Hubble captured in decades past.

And whenever the next next-gen space telescope decides to take a peek,  it’ll look different again. So when our merch team had  to design our latest pin, they had to pick which version  of the supernova to go with. They went with this image inspired by the JWST.

If you’d like a tiny supernova  remnant to call your own, you can head on over to Complexly.store/SciShow  and pre-order yours today! Thanks for watching! [♪ OUTRO]