When massive stars run out of fuel at the end of their lives,

they die in fantastic explosions called supernovas.

They're some of the biggest explosions out there,

and they can shine as bright as an entire galaxy.

Most of them fit neatly into one of a few categories,

depending on what they look like and what causes them.

But then, there are the peculiars,

a special group of supernovas that don't quite fit in with the rest.

These oddballs include failed explosions, extremely bright ones, slow ones,

and a whole slew of other quirky stars.

They're the ugly ducklings of the supernova family,

but their weirdness is what makes them so valuable.

Here's what we've learned from three of them.

In 2014, astronomers discovered a supernova 300 million light-years away,

and they gave it the charming name iPTF14atg.

It was part of a class called type Ia supernovas,

but it was a bit of a dud at first, kind of dim and slow.

Then, less than four days after the explosion, something really strange happened:

It gave off a flash of ultraviolet light.

No one had ever seen anything like it, but it offered a clue to a longstanding mystery.

See, we still don't really know what causes this class of supernova.

One idea says that they form when two white dwarf stars collide.

Another suggests that they happen when a white dwarf steals matter off a companion star,

which is typically too dim to see.

Eventually, the dwarf acquires enough mass to set off a thermonuclear reaction,

and blasts itself to pieces.

It's really hard to pin down the true origin story, because by the time a supernova catches anyone's eye,

it's already blown itself up, and destroyed the evidence.

But the 2014 discovery helped shed light on things.

Before this, scientists thought that if a supernova did have a companion star,

its debris should slam into that surviving companion at some point.

When it did, researchers predicted that collision would heat up nearby material so much

that it would create a flash of ultraviolet light.

So when they saw that flash for the first time in 2014, it seemed like the case was closed:

Type Ia supernovas happen in stars with companions, not in collisions.

Everybody can go home now!

Except, another team disagreed.

When they looked at data from three similar supernovas, they didn't find that ultraviolet spike.

Meaning those stars probably didn't have companions.

That kind of threw a wrench in things, but now, after more research,

astronomers think type Ia supernovas probably form in at least two totally different ways.

Some may feed off a companion, like the 2014 discovery,

while others may come from the merger of two stars.

We're still pinning down exactly how all this works,

but it's no wonder this question has been so hard to figure out!

Our next oddball supernova was spotted in 2006, and it was the brightest one astronomers had ever seen.

It was a peculiar called SN 2006gy,

and it exploded 240 million light-years away with 100 times the energy of an ordinary supernova.

And while typical explosions fade after about half a year, this one didn't.

Eight months after its detection, it was still outshining normal supernovas at their peak.

Astronomers figured that the star that blew up must have been a monster,

around 150 times the mass of our Sun.

Stars this massive are super rare in today's universe.

There are maybe a dozen of them among the Milky Way's 400 billion stars,

but that wasn't always the case.

The first stars in the universe were likely all giants,

which meant 2006gy could help us understand how they died.

Before this, scientists believed huge stars would skip the supernova stage entirely,

and collapse directly into black holes.

But 2006gy suggested that, instead,

these giants spewed their materials back into space in some of the most spectacular and energetic events ever.

That could mean these early stars played an important role in filling the universe with different elements,

which make up everything in our solar system, including us.

So thanks for sharing, giant stars!

And that brings us to our final peculiar supernova, called SN 2005E.

Astronomers spotted it in 2005, 100 million light-years away.

It blew up in the outskirts of its galaxy, where stars rarely form.

It was also about 100 times fainter than a typical supernova, and it faded really quickly.

But strangest of all, almost half of the stuff it ejected was calcium.

It spit out between 5 and 10 times as much of it as a normal supernova.

Today, we think that's because it was stealing matter from a companion star.

But instead of stealing hydrogen like in typical supernovas,

it was stealing helium from a star with helium in its outer layer, possibly another white dwarf.

When that gas ignited, it produced large amounts of calcium, along with other elements like titanium.

This discovery turned out to be really important,

because it helped astronomers figure out why there's so much calcium in the galaxy in the first place.

Calcium is the fifth-most common element in Earth's crust, and the Milky Way is full of it.

But for a long time, scientists didn't understand why.

Their models predicted there should be 50% less of it than what they actually observed.

The problem was, those models were based on the fact that almost all elements form in stars or supernovas.

And they didn't include supernovas like 2005E, because we hadn't found them yet!

This explosion was unusual at the time,

but over the next five years, astronomers found seven more that looked like it.

They realized that this appeared to be a new subcategory,

and we can likely thank these supernovas for all that extra calcium in the universe,

and for the stuff in our bones.

In the end, we have peculiar supernovas to thank for a lot more than our calcium.

These rule-breakers force scientists to question and sharpen their best hypotheses.

They also offer hints about what death was like in the early universe,

and they tell us that giant stars die in really different and spectacular ways.

It just goes to show that fitting in and being predictable is totally overrated.

Thanks for watching this episode of SciShow Space,

and a special thanks to our patrons on Patreon!

There's so much cool stuff to learn about in the universe,

and we couldn't cover it without your help.

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