One of the most cataclysmic events in the universe: When a massive star
bigger than our Sun reaches the end of its life,
it creates a supernova. A powerful explosion destructive on a scale almost beyond human
imagining. And sometimes so powerful they can be seen by the naked eye from Earth.
Scientists thought they understood this phenomenon,
but recent discoveries have revealed not one, but two new kinds of supernova.
But just how powerful is a supernova, and could the Earth one day be destroyed by the blast
from one? Get ready to be surprised by the answers to this and more...
Stars like our Sun shine because of thermonuclear fusion by fusing light atoms in their cores to
make heavier atoms. Eventually, all stars run out of the raw materials needed for fusion.
If this happens, and the star is big enough, it will explode as a supernova.
Supernovae were first discovered in 185 A.D. when Chinese astronomers suddenly saw a strange ‘guest
star’ appear in the night sky, and it stayed visible in the sky for the next eight months.
It was the first-known observation of a supernova in human history.
But there have been other sightings from here on Earth.
In the year 1006 A.D. a staggeringly bright star exploded in the constellation Lupus,
and could be seen brightly in Earth’s skies. Current astronomers say it would have been 16
times brighter than Venus; the brightest object in our night skies besides the Moon. In fact,
this supernova became so bright that it was visible in the skies during the day!
The most recent supernova visible to the eye was Supernova 1987A in the year 1987.
But are we going to get to see another one? We’ll get to that in a moment.
If you want an idea of what these might have looked like, the Hubble Telescope
recorded a supernova in the spiral galaxy NGC 2525, which is 70 million light years away.
Hubble began observing the star from February 2018 to 2019. The supernova first appears as
a blazing star located on the galaxy's outer edge, and outshines even the brightest stars
before fading. This star exploded 70 million years ago when the dinosaurs still roamed the Earth,
yet it took all this time to see it as the light from the massive explosion finally reached us.
Since their discovery, there were thought to be only two different types of supernova;
a type 1-A thermonuclear, and type II iron-core collapse.
A thermonuclear supernova, or Type One-A is the result of an explosion of a white dwarf
star in a binary system at least [8-times the mass of the Sun] after it becomes too
massive to support itself after siphoning material from a nearby companion star.
Matter piles up on the white dwarf’s surface, and once it reaches a certain mass limit,
a runaway thermonuclear explosion rips the white dwarf apart.
The iron-core collapse variety of supernovae are the ones that most people are familiar with. This
happens when a massive star, one at least [10 times the mass of the Sun] runs out of nuclear
fuel. As molecules fuse inside the star, it can no longer support its own weight, and
gravity causes its iron core to collapse leaving behind either a black hole or a neutron star.
Astronomers thought these were the only two ways a supernova could happen.
But now, a worldwide team of scientists from UC Santa Barbara have discovered a new type
of supernova 31 million light years away in the galaxy NGC 2146 using the Las Cumbres Observatory.
This new type of stellar explosion is called an electron-capture supernova.
In an electron-capture supernova, some of the electrons in the oxygen - neon - magnesium core
get smashed into their atomic nuclei...or electron capture. This removal of electrons causes the
core of the star to buckle under its own weight and collapse, resulting in a massive explosion.
But recently, another new kind of supernova was discovered.
A team of astronomers were going over data from the Very Large Array Sky Survey from 2017,
when they were surprised to learn that a black hole had caused a supernova!
The explosion was triggered when a dead-star companion, either a black hole or neutron star,
plunged into a nearby star’s core. This black hole or neutron star slammed into the massive star,
and as it traveled through the star, ejected a spiral of material from the star's atmosphere.
As it reached the core of the star, material rapidly fell onto the stellar corpse that
launched a pair of x-ray jets at nearly the speed of light, and set off the explosion.
This is the first time a collision-triggered supernova has ever been recorded.
And if you’re curious how fast the particles from one of these explosions can travel,
NASA's Chandra X-ray Observatory has tracked the debris from a supernova explosion witnessed by
Johannes Kepler in 1604, when a dying star 20,000 light years from Earth tore itself apart. Now more
than 400 years later, the NASA probe found debris still racing through space at more than 32-million
kilometers per hour or [23-million mph]! That’s about 25,000 times faster than the speed of sound!
Now since you know a little about these powerful stellar explosions, one might
wonder what would happen if the Earth was ever caught in the path of a supernova explosion.
If our Sun exploded as a supernova, the shockwave might not destroy the whole Earth,
but the side of the planet facing the Sun at the time of the explosion would burn and boil away.
The entire planet would increase in temperature 15 times hotter than the surface of the Sun.
Not only this, but the Earth would not stay in its orbit because of the sudden
decrease in the Sun’s mass, and our planet would wander off into space.
Fortunately, our Sun is far too small and doesn’t have enough mass to go supernova.
But let’s consider the explosion of a star besides our Sun, one that is close enough to create some
big problems here on Earth. Astronomers say that a star within 30 to 50 light years away
could be devastating to the planet. If a star went supernova close enough to us,
X-rays and more energetic gamma-rays from the explosion would destroy the ozone layer that
protects us from solar ultraviolet rays. It is possible that it could also ionize nitrogen and
oxygen in the atmosphere which would form huge amounts of smog-like nitrous oxide.
Phytoplankton and coral reefs would be affected and most organisms would be killed off by the
radiation and severely deplete the base of the ocean food chain. It is possible the
supernova might leave surface and ocean life relatively intact. However, the planet would
be showered with gamma rays and other high-energy radiation which could cause mutations in earthly
life. There would definitely be mass extinctions of entire species of plants and animals.
So has the planet Earth ever been hit by the waves of a supernova?
It turns out scientists have found clues on our planet that show our entire solar
system has actually flown through the debris fields of a supernova in its ancient past.
In fact, the whole solar system has been flying through the debris fields of a supernova for
the last 33,000 years! In fact, a supernova carved out the Local Bubble, as it's called,
that the entire solar system rests in. Aside from the holes that supernovae have blasted
out of the Milky Way, they also left traces on our planet on the ocean floor in the form of Iron-60:
a radioactive isotope of Iron which we know can only be created by an exploding star.
But no supernova has been known to happen at this close a distance in the known history of mankind.
So what are the chances of you seeing a Milky Way supernova in the skies from Earth
in the next 50 years? For those people in the southern hemisphere,
where more of the galaxy can be seen in the night sky, there is a 20-50%
chance of seeing a blast from a supernova with the unaided eye.
One star which could go supernova any day now is Betelgeuse in the constellation Orion the Hunter.
Betelgeuse is one of the largest stars known and is a bright red dot marking Orion’s shoulder.
This star is a dying red supergiant with a diameter roughly 950 times larger than our Sun,
and either today, tomorrow, or 100,000 years from now, it’s going to explode
giving humanity a celestial fireworks show. In 2019, Betelguese started to dim dramatically
giving way to the idea the star could have reached the end of its life.
Astronomers aren’t 100% sure how the supernova will play out, but they all agree that there
would be an intense light in the sky that would rival a full moon and cast shadows at night,
and yes, you would be able to see the supernova in the sky during the day.
It sounds a little scary to say you’ll see the massive explosion,
but there is no need to worry about this supernova wiping out life on Earth because Betelguese is far
outside the supernova kill range of 30 to 50 light years, and sits roughly 724 light years away.
Only animals that use the moon for navigation would be confused since
adding another light in the sky as bright as the moon could be disruptive to them.
But if Betelguese doesn’t explode within our lifetimes, you still have a chance of
witnessing a supernova with the naked eye, and it will be the first naked eye nova in decades.
There is a double star just off the left wing tip in the constellation of Cygnus the Swan.
Astronomers are seeing the orbits of these two stars speeding up, which means they are getting
closer and will merge together sometime around the year 2022...which is just around the corner.
This star system lies 1800 light years away, but it should be visible with the naked eye,
and its brightness will be second magnitude matching the brightness of the stars of the
Big Dipper. And if you have a telescope, then you’re really going to see something cool.
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