This SciShow Space video is  supported by you, enjoy our  beautiful new moon-themed  calendar.

You can look at  Earth’s moon any day, but with  this calendar you can gaze  at the moons of other planets  all year long. You can find it,  now at a discount, for a limited time at  ComplexlyCalendars.com. [♪ Intro]  It’s not every day you see a  star explode.

Unless you’re an  astronomer studying supernovas,  and then you very well  might. When you look at the  whole universe, they’re a  common cosmic catastrophe.  And some can outshine an  entire galaxy. So it’s a good  thing that they’re happening  well away from our solar  system.

While a few prominent  supernovas have been witnessed without the aid of telescopes, astronomers have used this   invention to learn more about exactly how   stars die spectacularly. And they’ve learned that there’s   more than one way to do it. So let’s dive into five of the   most explosive ways a star can end its life.

On February 23,   1987, humanity witnessed a supernova on the Milky Way’s   cosmic porch. Supernova 1987A, as it’s known,   happened a mere 170,000 light years away, in a dwarf galaxy   called the Large Magellanic Cloud. As the closest observed   supernova in nearly four centuries,   it was visible to the naked eye for months.

And astronomers have been watching it through their  telescopes ever since. Most  agree that 1987A began as a  regular, blue supergiant star  about twenty times the mass  of our Sun. Like all stars, it  spent most of its life fusing  lighter elements into heavier  ones, creating light in the  process.

But after ten million  years or so, it had run out of  fuel. There were still plenty  of atoms hanging around, but it  wasn’t hot enough to fuse those elements, too. So the fusion engine shut down,   and the entire star started collapsing in on itself.

With   the pressure of that contraction, temperatures at the core got   hot enough for the fusion furnace to ignite once more.   At least for a little while, until it ran out of fuel again. For a blue   supergiant, this cycle happens a few times,   until the core is filled with iron. And iron just so happens to be a special   tipping point for stars.

Smaller atoms give off energy   by fusing together. Bigger atoms give off energy   by breaking apart. But giant stars have no good way to get energy from iron itself.  Instead, as the star’s mass  descends upon the core one  final time, the iron is  squeezed so tightly that physics  becomes a little fuzzy.

Protons  and electrons start merging  to form neutrons. The rest of  the falling gas bounces off  this new neutron core and  explodes outward, propelled by  a torrent of light and other  particles into interstellar space.  The catastrophic result is what  astronomers call a Type II,  or core collapse, supernova.  In a fraction of a second,  1987A released more energy  than our Sun will put out in  its entire ten billion year lifetime.  But in destruction, there is  the opportunity for creation.  The expanding clouds that  these supernovas leave behind  are filled with the elements  that can construct a planet,  as well as the curious  inhabitants that call it  home. When people describe a  supernova, they often describe  a core collapse scenario  like what happened to 1987A.  Sometimes the explosion  leaves behind a super dense  neutron star, and sometimes  it’s a black hole.

But a collapsing  core isn’t the only way for  a star to go boom. It’s just  the simplest, which makes it  nice for summarizing what  happens when big stars die. But  scientists love edge cases.

And boy, do supernovas have some weird ones. On July 4, 1054, a new star  appeared and was so bright,  you could see it during the  day for nearly a month. At  night, you could see it for the  next two years.

Today, we  know this was the supernova  that produced the Crab Nebula and the neutron star pulsating at its heart, roughly   6500 light years from Earth. Astronomers spent years thinking   that it was just another core collapse supernova,   like 1987A, but there was one notable problem: the original   star wasn’t massive enough. Estimates put it somewhere   between eight and ten times the mass of the Sun, which is big,   sure, but not big enough for the core to build   up iron.

It should have stopped when there was mostly oxygen, neon, and magnesium  surrounded by a sea of  free-flying electrons, which serve  as a sort of scaffold to help  support the stellar core from  collapsing further. And that  mixture shouldn’t have blown  up with an energy equivalent  to 1987A. So astronomers  put their heads together  and realized something very  special had happened.

If the  star contained just the right  amount of oxygen, neon,  and magnesium, the neon and  magnesium would absorb some  of those free electrons into  their nuclei faster than they  released them back into the  star. In other words, they  removed pieces of stellar  scaffolding over time. And  eventually, the crushing force of  gravity won out.

All of a  sudden, the collapsing core  became hot enough for one  last frenzied round of fusion,  leading to an iron core, neutron  star, and ultimately what  astronomers call an  electron-capture supernova. This  kind of supernova was first  predicted in the 1980s, but it  took until 2018 for astronomers  to observe one in action,  and prove they were possible.  After that, they could finally  solve the mystery of 1054,  including why it shined so bright  for so long. It was an  electron-capture supernova, and  appeared brighter than normal  because the light from its  explosion lit up the clouds of  gas that the star had thrown  off before it died.

All the  supernova’s light bounced around  that gas like a hall of mirrors,  escaping over time instead of  all at once. Electron capture  supernovas are a twist on the  usual core collapse model.  But some supernovas go to  much greater lengths to stand  out from the pack. Take our  next entry: Supernova 2007bi.  It happened about 1.6 billion  light years away, and it first  caught astronomers’ attention  because it wasn’t the typical  flash in the pan.

It brightened  over about two months, and  then it just stayed there. A  year and a half later, it was  barely any dimmer. But there  was another oddity.

Certain  elements had gone missing.  Before a supernova’s light  can reach us, it has to travel  through layers of gas its star  lost to space. And by passing  through layers made of different  elements, the light records  the overall composition of  what it had to travel through.  Typically, that tends to be  mostly hydrogen and helium. But  2007bi’s light didn’t show the  presence of either element.  Instead, it was marked by  layers of heavier elements like  oxygen, sulfur, and nickel,  four whole Suns’ worth of  radioactive nickel.

Based  on how much of these heavy  elements came out of the  explosion, astronomers estimate  that the original star must  have been about two hundred  times more massive than the  Sun. And to explain the weird  pattern in its light, they think  2007bi was one of the first  conclusive examples of a  pair instability supernova.  When such a massive star  nears the end of its life, the  fusion in its core creates  particles of light that are more  energetic than usual. In fact,  this light has so much energy  that it can randomly transform  into matter.

Each particle of  light turns into a pair of  subatomic particles, like electrons  and positrons. And that matter  doesn’t transfer heat as well  as light does. So all of a  sudden, the temperature in the  core starts dropping.

And the  core starts shrinking. It keeps  shrinking until it can literally  shrink no more. The atoms get  shoved so close together, they  fuse rapid-fire into iron,  leading to an explosion so  powerful that the core is blown  to smithereens, leaving  nothing behind. 2007bi was so  violent, the star kind of got  turned inside-out.

That would  explain the lack of a hydrogen  and helium signal in the light  we see from

Earth: The heavier  layers swapped with them,  concealing their presence.  2007bi was wild, one of the  largest explosions humans  have ever measured. But that’s  not the most extreme kind of  pair instability out there. The  supernova 2016aps is in the  running for the brightest  supernova ever detected, when  you account for distance.  That title is hard to define,  so the belt is always changing  hands. But all told, it  released about fifteen times the  energy our Sun will emit over  its whole lifetime.

To shine so  brightly, it must have been  surrounded by a dense cloud of  hydrogen, probably at least  a few dozen Suns’ worth. All  that gas would help trap the  light and matter bouncing  around inside, instead of  letting it spread out and cool  everything down. If you’re  keeping track, that’s a lot like  what happened with the supernova in 1054.

To some astronomers, the story stops there.   Having lots of gas around a big, exploding   star keeps the party going longer than you’d expect. Meanwhile,   other astronomers think there must have been more to the story. One team  proposed it was thanks to pair  instability, like we saw with  2007bi.

But because the star  behind 2016aps wasn’t as  massive as the one behind  2007bi, it took time for the  catastrophe to build up. Instead  of happening all at once,  light would have transformed  into pairs of subatomic  particles in fits and starts,  maybe over hundreds or  thousands of years. After a  series of super-bright flashes  that each had as much energy  as a typical supernova, one  final bout of pair production  would have done everything in.  Astronomers call it a pulsational pair instability  supernova.

It’s the extreme  version of an already extreme  cosmic event. We’re lucky  2016aps happened three billion  light years away. But for our  final entry, we need to bring  things back a lot closer to  home.

In 1006, astronomers  around the world saw what  was possibly the brightest  supernova in recorded history.  At its peak, it outshone  every star and planet in the  night sky, and it remained  visible for two and a half  years. In the 1960s, astronomers  finally found the nebula that  this explosion produced. It’s  called “Supernova Remnant  SN 1006” and it’s about 7100  light years from us.

That name  isn’t as cool as “the Crab  Nebula”, but its origin story  sure is. Because the supernova  of 1006 involved two stars,  not one. Okay, technically one  of those stars was a white  dwarf: the core of an already  dead star that wasn’t massive  enough to go supernova on  its own.

But if a white dwarf  gets a little help from a friend,  it can jump over that hurdle  spectacularly. When a white  dwarf explodes, it produces  a Type Ia supernova. And the  key to blowing up white dwarfs  is they have to break one  very important rule.

White  dwarfs can only get so heavy,  about 1.4 times the mass of  the Sun. If one happens to  exceed that limit, it suddenly  kicks off a round of nuclear  fusion that eventually leads  to a massive explosion that  leaves nothing behind.  Astronomers know the supernova  of 1006 was within the Milky  Way, and based on the light it  produced they’re confident it  was a Type Ia. But we don’t  know what the other star looked  like.

It could have been a  case of cosmic vampirism,  where the white dwarf siphoned  off enough gas from a nearby  companion star that it tipped  the scales and exploded. But  the other object could have  also been another white dwarf,  and the two overshot the  1.4 solar mass limit by smashing into one another.  Astronomers lean toward it  being another white dwarf  because they can’t find a star  near the remnant nebula that  looks like it could have been  the companion, but no one’s  sure. What they do know is  that, given how dramatic the  death was, and how close it  happened to Earth, humanity  is unlikely to witnessan  explosion as bright as 1006 for a  very long time.

Is this the  most extraordinary kind of  cosmic explosion humanity has  ever witnessed? Only time,  and more research, will tell.  But space is awesome, so we  shouldn’t be surprised when  another supernova comes  along with an even more  complicated origin story that  brings us another step closer to understanding the universe we live in. And to understand   this incredible universe just a   little bit better, you can learn a new moon fact every month with your own SciShow Space wall  calendar.

The people who  made this video also made a  high quality 2023 calendar full  of beautiful images, science  related holidays, and  mesmerizing moon blurbs. Travel  from Jupiter’s Europa to  Neptune’s Triton and Saturn’s  Hyrerion all in one year. You  won’t find a shuttle making  the same trip!

And with the  year ending incredibly soon,  you’ll need a 2023 calendar  ASAP. You can get yours now  for a 25% discount at  ComplexlyCalendars.com or the link  in the description down below.  Thank you so much for your  support by watching to the  end of this video and by  ordering your calendar today. [♪ Outro]