What Happens During a Supernova?

Supernovae are the spectacular deaths of giant stars -- and they create the elements that make up our universe. Learn how they work and what we learn from them in this episode of BrainStuff, based on this article: https://science.howstuffworks.com/supernova.htm/printable

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff,
Lauren Vogelbomb. Here humans are born, then we grow and die.
Our life cycles are basically the same as those of
the massive stars twinkling in the night sky. If we

(00:22):
exploded in a blaze of glory at the end of
our time when the cosmosis, most colossal stars go out
with a bang. The immense interstellar explosion is known as
a supernova, while smaller stars simply fizzle out. The death
of an astronomical heavyweight is a showstopper. It spent its

(00:42):
life cannibalizing its own inerds for fuel and sometimes the
intererds of a solar neighbor. When there is nothing left
for it to consume, it collapses in on itself and
then explodes outward and a depth knell that outshines other
huge stars and sometimes entire galaxies for days, weeks, or
even months. Some are so bright that they can be

(01:04):
seen with a simple set of binoculars. A supernova should
statistically detonate once every fifty years or so in a
galaxy the size of our Milky Way, So how do
you spot one? Identifying a new point of light as
a supernova as opposed to a high flying aircraft or
a comet, may be easier than you think. The stars

(01:27):
about to go supernova change color from red to blue
due to their increasing temperatures, and supernova maintain some blue
color due to the Doppler effect. The light from their
explosions moves towards us so fast that it appears blue plus.
Unlike a comet or commercial airplane, a supernova won't waver

(01:48):
from its position. But how do stars self destruct so spectacularly?
Let's talk about a giant stars life cycle. A giant
stars starts out when gas and dust buckle under an
assertive gravitational pull to form a baby star. As the
material at the center of a fledgling star heats, it

(02:10):
attracts more interstellar gas and dust. This growth phase can
take up to fifty million years, followed by another ten
billion years of shiny adulthood. Stars are fueled by the
nuclear fusion of hydrogen into the slightly denser and heavier
element helium. The fusion takes place in the star's core,

(02:31):
and the energy it produces flows outward, creating the star's
observable glow and preventing the heavy core from collapsing in
on itself. When a star starts running out of hydrogen
to fuse into helium, it's the beginning of the end.
With less energy radiating outward, the core begins to collapse,
causing its temperature to spike. Hydrogen fusion continues only in

(02:54):
the star's outer layers, which causes it to expand it
becomes a red giant. A red giant will lose its
outer layers, either by consuming them or releasing them into
space to become a white dwarf. A white dwarf with
enough mass will eventually go supernova. Its core will collapse,

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resulting in an explosion that can't compare to any we
might experience on Earth, unless we were to bundle a
few Octilian nuclear warheads and detonate them all at the
same time. Our own Sun isn't big enough to go
out with such a bang, but stars that are are
separated into two supernova classes, type one and type two.

(03:38):
Astronomers learn a lot about stars from the colors of
life that they emit. Using a device called a spectrograph,
they can get a clear picture of exactly what elements
are burning inside a star. In the nineteen forties, astronomers
noticed that some supernova type one do not contain hydrogen,
but the others do. Those are type two. In the

(04:00):
nineteen eighties, as observational technology improved, scientists further divided type
one supernova into three subcategories, Type one A, which contains
silicon in their spectra, Type one B, which contain helium,
and type one C, which contain neither. The stars lose
elements when stellar winds rip their outer layers away long

(04:22):
before they go supernova. A Type one A supernova work
differently than all the other types. A Type one A
supernova results from a white dwarf that's part of a
binary system, that is, one that shares an orbit with
another star and was about twice the size of our
Sun during its life. The white dwarf's mass allows it

(04:44):
to fuse elements slightly heavier than hydrogen, so it has
a stable core of carbon and oxygen. Left to its
own devices, this white dwarf would eventually decay into a
black dwarf, but since it's not alone, it has access
to resources that other stars don't. The more massive of
the two stars acts like an opportunistic sibling, using its

(05:07):
gravitational pull to steal matter from the other star. This
gluttonous star grows until it exceeds what's called the Chindra
Shaykhar limit, after the guy who discovered it. It's a
mass of one point four times that of our self,
otherwise known as one point four solar masses. At this size,
the white dwarf suddenly has enough heat and pressure in

(05:30):
its core to fuse carbon, and all of that carbon
fuses at once, like a thermonuclear bomb going off, blowing
the star to bits. It leaves behind a gaseous remnant
that's symmetrical in shape and contains a great deal of
iron created in the heat of the explosion. Because type

(05:51):
one A supernovae all explode at the same point in
their stellar deaths, they all peak at almost exactly the
same brightness. It's so consistent that type one A supernova
are also called standard candles. Once astronomers find one in
a region of space, they can use it as a
baseline with which to compare and learn about other objects

(06:12):
around it. Type one, B, one C, and type two supernova,
despite showing different elements in their spectra, all explode the
same way. They start out so huge, possibly eight times
the size of our Sun that they cannibalize themselves to
the point of collapse. A white dwarf eventually created from

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a star that massive, has so much heat and pressure
inside its core that lighter elements keep fusing into increasingly
heavy elements instead of flying off into space. This produces
enough radiating energy to support the star's increasing weight until
iron forms. The fusion of iron into heavier elements actually

(06:57):
uses energy rather than giving it off, so when iron
begins to fuse, the star's outer layers lose their support
and begin to fall inward. To understand the huge explosion
that results, you have to know what's going on with
the star's tiniest particles. When a white dwarf is massive

(07:18):
enough to fuse the iron in its core, those iron
atoms are incredibly hot and densely packed, squashed together like
sweaty clowns stuck in a circus car. Their sub atomic
particles collide and the iron atom's nuclei split, leaving behind
helium nuclei plus a few leftover neutrons, and absorbing a

(07:38):
lot of energy in the process. That energy was holding
the star's core up, so without it, the core starts
shrinking rapidly. It goes from a diameter of some five
thousand miles to only twelve miles real Suddenly that's about
eight thousand kilometers to just nineteen. This creates temperature somewhere

(08:00):
in the region of one hundred and eighty billion degrees
fahrenheit or one hundred billion degrees celsius, though at that
point who's really counting. The heat causes protons and electrons
to fuse together, canceling each other out to become neutrons
and expelling a bunch of neutrinos in the process. The
neutrinos can escape, so they do, leaving the core with

(08:21):
even less energy to hold itself up. The core contracts
as much as it physically can, but the star's outer
layers keep falling inward even after there's no more room.
That's when they rebound in that enormous explosion. All of
that took a lot of words to explain, but it
can happen in as little as a quarter of a second.

(08:45):
The explosion is hot enough to fuse elements far heavier
than iron, and it releases these elements in a gaseous
cloud that will become an asymmetrical remnant around the remaining
solid core. What happens next depends on how massive the
original star was. If its inner core was less than
three solar masses, it creates a neutron star with a

(09:08):
core about as dense as an atom's nucleus and a
powerful magnetic field. If its magnetic field creates lighthouse style
beams of radiation that flash toward Earth as the star rotates,
it's called a pulsar. But when a star with the
core equal to three solar masses or more explodes, that
can result in a black hole. A scientist's hypothesize that

(09:31):
black holes form when gravity causes the stars compressed inner
core to continually sink into itself. A black hole has
such powerful gravitational force that it can drag surrounding matter,
even planets, stars, and light itself into its mall, all
of their powers of destruction. Aside, a lot of good
can come of a supernova, and by tracking the demise

(09:54):
of particular stars, scientists have uncovered ancient astronomical events and
predicted future changes in the uns. And by using type
one A supernova as standard candles, researchers have been able
to map entire galaxies distances from us and determine that
the universe is in fact expanding ever more rapidly. But

(10:15):
of course, exploding stars leave more than just an electromagnetic
signature behind. They also produce cosmic debris and dust. Type
one a supernova are thought to be responsible for the
large amount of iron in the universe, and all of
the elements in the universe that are heavier than iron,
from cobalt to rent genium, are thought to be created

(10:37):
during core collapse supernova explosions. After millions of years, these
remnants commingle with space gas to form new interstellar life
baby stars that mature, age and may eventually complete the
circle of life by becoming a supernova themselves. Today's episode

(10:59):
is based on article how supernova works on HowStuffWorks dot com,
written by Laureel Dove. Brain Stuff is production of iHeartRadio
in partnership with how stuffworks dot Com and is produced
by Tyler Klang. For more podcasts my heart Radio, visit
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