Kind: captions
Language: en
what would happen if a star exploded
near the Earth well the nearest star to
Earth of course is the sun and it is not
going to explode but if it had eight
times the mass then it would go
supernova at the end of its life so what
would that look like well as noted by
xkcd if you held up a hydrogen bomb
right to your eyeball and detonated it
that explosion would still be a billion
times less bright than watching the sun
go supernova from
Earth that's how insanely powerful
Supernova explosions are they are the
biggest explosions in the universe when
we see Supernova in other galaxies they
are brighter than the combined light of
hundreds of billions of stars so bright
in fact that they appear to come out of
nowhere on the 8th of October 16004 the
astronomer Johannes Kepler looked up
into the night sky and noticed a bright
star he had never seen before it was
brighter than all the other stars in the
sky and about as bright as the planet
Jupiter on moonless nights it was bright
enough to cast a
shadow Kepler published his observations
of this star in a book called Della Nova
which means about a new star in Latin
Kepler thought he was witnessing the
birth of a new star but it was actually
a Stars violent death over the following
year and a half the light faded until it
was no longer visible but the name stuck
even once we learned what was really
happening in the 1930s the violent final
explosion for stars between about 8 and
30 solar masses has been called a
supernova but how exactly a star
explodes is not what most people think
for most of a star's life it exists in a
state balance in its core it fuses
lighter elements together to make
heavier ones and in the process it
converts a small amount of matter into
energy this energy is really what keeps
the star from collapsing in on itself
gravity compresses the star but that
force is counteracted by the pressure
generated by the movement of particles
inside the star and by the pressure of
photons released by Fusion so in effect
stars are propped up by their own light
if the rate of fusion drops at the
center of the star the temperature and
the pressure decrease gravity starts
winning compressing the star but this
increases the temperature and pressure
in the core which increases the rate of
fusion it's a stable self-regulating
system but there's a problem stars have
a finite amount of fuel which over time
gets used up our sun is about 5 billion
years into its 10 billion-year
lifespan there are stars dozens of times
more massive than the sun which you
would think would live much longer but
they actually use up their nuclear fuel
faster a star 20 times the mass of our
sun has a lifespan of just 10 million
years and more massive stars burn hotter
and even brighter but for much shorter
lives for 90% the life of a star the
core is only hot enough to fuse hydrogen
into
helium and when the hydrogen Runs Out
Fusion slows gravity compresses the core
and its temperature increases to 200
million de at which point helium fuses
into carbon there's enough helium to
power the star for around a million
years but as the helium runs out the
core is again compressed and heated
carbon starts fusing into neon which
lasts about a thousand years and then
neon fuses into oxygen for a few more
years then oxygen to Silicon for a few
months
and at 2.5 billion de silicon fuses into
nickel which decays into iron now at the
heart of this giant star there is an
iron core building that's only a few
thousand km
across iron is where this pattern stops
instead of liberating energy as it fuses
into heavier elements it actually
requires energy iron is the most stable
element so it actually takes energy both
to fuse it into into heavier elements
and to break it down into lighter ones
both fusion and fision reactions
ultimately end up at iron the iron core
grows but the crush of gravity becomes
greater and greater as the rate of
fusion drops when the iron core is about
1.4 time the mass of our sun which is
known as the Chandra car limit the pull
of gravity is so strong that something
totally wild happens quantum mechanics
takes over electrons run out of room to
move and they're forced into their
lowest energy states they then become
absorbed by the protons in the nucleus
in this process the protons turn into
neutrons and release
neutrinos with the electrons gone the
core collapses and fast at about 25% the
speed of light so what used to be a ball
of iron 3,000 km in diameter becomes a
ball of neutrons just 30 km across
essentially it's a neutron star with no
outward pressure to hold it up the rest
of the star caves in also falling at a
quarter of the speed of light it hits
the neutron star and bounces off
creating a huge pressure wave but this
kinetic energy isn't quite enough to
start a supernova explosion no the thing
that really kicks it off is the humble
neutrino now I normally think of
neutrinos as particles that do basically
nothing nothing I mean they interact so
rarely with matter that right now there
are a 100 trillion neutrinos passing
through your body per second it would
take a lightyear of lead just to give
you a 50/50 chance of stopping a
neutrino and that's because they
interact only through gravity and the
weak
Force but in a supernova when the
electrons are captured by the protons an
unbelievable number of neutrinos is
released around 10 to the 58 you would
think they would just fly F off at
nearly the speed of light but the core
of a supernova is incredibly dense about
10 trillion times more dense than lead
and as a result it traps some of those
neutrinos and captures their energy and
this is what makes a star go supernova a
particle that is millions of times less
massive than an electron that barely
interacts with anything is responsible
for some of the largest explosions in
the UN
Universe in that explosion only a 100th
of 1% of the energy is released as
electromagnetic radiation the light that
we can see even then Supernova have
enough energy to outshine a whole galaxy
about 1% of the energy is released as
the kinetic energy of the exploding
matter but the vast majority of the
energy is released in the form of
neutrinos and neutrinos are actually the
first signal we detect from Supernova
and that's because after they generated
in the core they can escape before the
shock wave reaches the surface where the
light that we see is generated so
neutrinos can arrive on Earth hours
before the photons giving astronomers a
chance to aim their telescopes at the
right part of the
sky I actually used to work at a
neutrino Observatory back in college and
I would work the graveyard shift between
midnight and 8:00 a.m. so if I detected
a really big increase in the nutrino
flux during my shift it was my job to
call and wake up scientists so they
could go look out for a supernova now
that never actually happened but we did
have some close calls now I need to
clarify a couple things first not all
really massive stars explode as they
collapse some form black holes instead
which means they do not go supernova and
second there's another way to make a
supernova sometimes a white dwarf star
which is incredibly dense pulls matter
off a nearby star and when its mass
reaches that Chandra sear limit of 1.4
solar masses the white dwarf collapses
creating a supernova this is actually
the type of supernova that Kepler saw in
16004 a supernova 20,000 light years
from
Earth now because the shocks are
asymmetric Supernova explain neutron
stars that can move really fast there's
a neutron star we've observed with a
velocity of 1 ,600
km/s and we think that was caused by a
very asymmetric Supernova explosion sent
it shooting off in the other direction
despite only recently learning about how
Supernova work humans have been
observing them for thousands of years
ancient Indian Chinese Arabic and
European astronomers all observed
Supernova but they are quite rare in a
galaxy like our Milky Way consisting of
a 100 billion stars there are only about
one or two Supernova per Century a
particularly amazing example is the
Supernova of 1054 when the light of a
supernova 6,500 light years away reached
the Earth and was recorded by Chinese
astronomers if we look to where that
Supernova was recorded we see the Crab
Nebula it is a giant remnant of
radioactive matter left behind by the
explosion in the thousand years since
the explosion The Remnant has grown to
11 light years in
diameter supernovas produce a lot of
cosmic rays cosmic rays are actually
particles mainly protons and helium
nuclei and they travel out at very very
nearly the speed of light have a
tremendous amount of energy so at what
distance could a supernova cause
problems for life on Earth the closest
stars to us besides the Sun are the
three stars in Alpha andari they are 4.4
light years away but stars do move
around and on average a star gets within
one lightyear of Earth every 500,000
years so what would happen if such a
star went
off yeah so within a lightyear you're
easily within a danger distance from
just the kinetic energy so I I think
even at that distance you're you're
looking at possibly blowing the
atmosphere off but we would also have
other problems to worry about supernova
create conditions that are hot enough to
fuse elements heavier than iron in the
months after the explosion these
elements undergo radioactive decay
producing gamma rays and cosmic rays
less than .1% of the energy produced by
a supernova is emitted as gamma rays
from these radioactive decays but even
this tiny percentage can be dangerous at
a few light years from a supernova the
radiation could be deadly though most of
it would be blocked by our
atmosphere now the Earth is protected
from solar and Cosmic radiation by our
atmosphere and specifically by ozone
molecules three oxygen atoms bonded
together but high energy cosmic rays
from Supernova can come down and break
apart nitrogen molecules in the
atmosphere and then these bond with
oxygen atoms which can then break apart
ozone and so we can lose a lot of our
ozone if there's too many cosmic rays
coming from Supernova events and that
can expose us to all kinds of dangerous
radiation coming in from space we
actually see an increase in atmospheric
NO3 concentrations coinciding with
Supernova
explosions a supernova within 30 light
years is rare only happening maybe once
every 1 and A2 billion years or so but a
recent article suggests Supernova could
be lethal all the way out to 150 like
years away and so those would be much
more common we actually have evidence
for a supernova that went off 150 Lighty
years from Earth 2.6 million years ago
it would have been seen by our early
human ancestors like
ostapius and we know this because there
are elements present on earth that could
only have been deposited by a recent
Supernova in sedimentary rocks at the
bottom of the Pacific Ocean scientists
found traces of iron 60 in a layer that
was deposited 2.6 million years ago iron
60 is an isotope of iron with four more
neutrons than the most common type of
iron iron 60 is really hard to make our
sun doesn't make it nor is it produced
basically anywhere else in the solar
system iron 60 is made basically
exclusively in Supernova explosions and
iron 60 is radioactive it has a halflife
of 2.6 million years so every 2.6
million years half of the sample K into
Cobalt 60 so all of the iron 60 that was
around during the formation of the earth
4 and2 billion years ago has definitely
decayed so the iron 60 that the
scientists measure is proof of a recent
Supernova scientists also measured Trace
Amounts of Manganese 53 in the same
sediments giving further Evidence
supporting the idea that recently there
was an explosion of a nearby
Supernova the Supernova that happened
2.6 million years ago wasn't C
catastrophic for our ancestors but some
researchers hypothesize that it could be
related to the mass extinction which is
seen at the pine Pline boundary in the
fossil record around the same time this
Extinction wiped out around a third of
marine megaphon the idea is that the
cosmic rays from the Supernova hit
particles in our atmosphere creating
muons which are charged particles like
the electron only more than 200 times
heavier the muon flux for years after
the Super NOA would have been 150 times
higher than normal and the bigger the
animal the larger the radiation dose it
would have received from these muons
which is why megap were so
disproportionately affected and what's
more the animals that lived in shallower
waters were more likely to become
extinct compared to the ones that lived
at depth where the water would have
protected them from muons a further
evidence for these recent nearby
Supernova comes from our place in the
Galaxy you know if you look in the space
between the stars in our galaxy on
average there are around a million
hydrogen atoms per cubic meter that may
sound like a lot but it's basically a
perfect vacuum but for hundreds of light
years in all directions around our solar
system you find there are a thousand
times fewer hydrogen atoms it's like
they've all been blown out somewhere and
our solar system is existing in this
Cosmic void inside a low density bubble
so that is evidence for maybe tens of
supernova that would have blown all this
material outwards but there are cosmic
explosions that are even more deadly
than normal Supernova gamma ray bursts
gamar Ray bursts were discovered by the
vea satellites which were looking for
Soviet nuclear tests but on the 2nd of
July 1967 the satellites detected a
large burst of gamma rays which were
coming from space there are two main
sources of gamma ray bursts mergers of
neutron stars and the core collapses of
gigantic Stars called hypernova
hypernova are caused by stars that are
at least 30 solar masses and rapidly
spinning their collapse leads to an
explosion 10 times more powerful than a
regular Supernova and it leaves behind a
black
hole the gamma ray bursts caused by
hypernova Channel most of their energy
into beams which are just a few degrees
across if there was a gamma ray burst
within 6,000 Lighty years it would
decrease the ozone level enough that it
could be catastrophic to put this
distance in context a sphere with a
radius of 6,000 Lighty years contains
hundreds of millions of stars on October
9th 2022 astronomers detected one of the
most powerful gamma ray bursts ever
measured it was powerful enough to
measurably affect how the ionosphere
bounces radio waves the effect on the
ionosphere was around the same as a
solar flare but this gamma ray burst was
located in a Galaxy 2 and2 billion light
years away astronomers speculate that a
gamma re burst could have caused the
late ordovician mass extinction which
wiped out 85% of marine species 440
million years ago there is no direct
evidence but gamma ray bursts are common
enough that it is estimated that there
has been a 50% chance that there was an
ozone removing Extinction causing grb in
the vicinity of Earth in the last 500
million years so if a supernova or a
gamma ray burst were to go off near the
earth now that would be pretty
catastrophic but in an ironic twist we
kind of owe our existence to these sorts
of explosions because 4.6 billion years
ago it was probably the shock wave from
a nearby Supernova which triggered the
collapse of a cloud of gas and dust that
gradually coalesced to form our solar
system so the Sun the Earth and all of
us wouldn't be here today without the
explosions of nearby
Stars figuring out how Supernova explode
was incredibly difficult it took a
combination of astrophysics particle
physics Computer Science and Mathematics
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