Title: What if a star exploded close to Earth?
Take a look at these images. They are simply breathtaking. The more you observe them, the
more details you catch, and the more you enjoy the sight of a supernova.
Yes, what you are looking at right now is the death of a star.
All stars eventually run out of their hydrogen gas fuel and die.
How a star dies is largely determined by how much matter it contains. Stars with the
mass of our sun expand and become red giants. On the other hand, stars with high mass become
red supergiants. The supernovae are caused by these supergiants.
They destroy themselves in a huge explosion – the supernova - that, as seen from Earth,
is colorful and magnificent. But if you were to find yourself close to a supernova, you
would probably die. I mean, fair enough because in any case, the death of massive stars can
trigger the birth of other stars. You die, but someone else might be born.
In this video, however, we want to understand
if there is a minimum safety distance between us and a star that is about to become supernova:
a minimum distance that could save us.
A supernova is the spectacular explosion of
a massive star. Our sun isn’t massive enough to trigger
a stellar explosion. However, if it ever exploded as a supernova, it probably wouldn’t incinerate
the entire Earth. Instead, the resulting shock wave would extinguish the side of the Earth
facing the Sun. Basically, it would be better for you to be sleeping on the night side of
the Earth. But this is not the end of it. Everyone
would be facing serious problems. For instance, take our sun’s normal surface
temperature, about 5778 Kelvin. It’s hot as hell! Well, this temperature would feel
like Antarctica to people on Earth. Scientists estimate that the planet as a whole would
increase in temperature to roughly 15 times hotter than the normal surface temperature
of the Sun.
Basically, you would be roasted.
Moreover, when a star explodes as a supernova, material from the star is ejected at high
velocities, and this material comes from the star itself.
This process is therefore characterized
by sudden mass loss. The sudden decrease in the sun’s mass might cause our planet to
wander off into space. For sure, we would not be orbiting in the same plane or at the
same distance as our star.
Clearly, the sun’s distance, which is 8 light-minutes away, isn’t safe at all
if it were to explode in a supernova.
Fortunately, it won’t. But other stars, beyond our solar system, will. What is the
closest safe distance?
According to NASA, a supernova would have to be within 50 light-years of Earth before
we would feel its damaging effects. This is a huge distance, but why 50 and not - say
– 30 light-years? Let’s see what would happen if the supernova
exploded at this huge distance, but still not enough for us to be safe.
Were a supernova to go off within about
30 light-years of us, that would lead to major effects on the Earth, possibly mass extinctions.
This would happen because supernovae are so energetic that they emit X-rays and gamma
rays. These powerful emissions can destroy the ozone layer that protects us from solar
ultraviolet rays. These radiations could cause mutations in the earthly life. Also, radiation
from a nearby supernova could change our climate.
But this is not the end of it. More direct
effects would follow. For instance, phytoplankton and reef communities
would be particularly affected. Such an event would severely deplete the base of the ocean
food chain, which in turn means mass extinction for several species.
The good news is, there are no stars within 50 light-years of Earth poised to become a
supernova. Yay! No supernova has been known to erupt within
50 light-years in the known history of humankind. The most recent supernova visible to the eye
was Supernova 1987A, in the year 1987. But it happened at a safe distance, approximately
168,000 light-years away. This is how Hubble observed it from space:
https://www.google.com/url?sa=i&url=https%3A%2F%2Fesahubble.org%2Fimages%2Fopo9719b%2F&psig=AOvVaw0fGlkvtXE5Fp5yugDXuUE-&ust=1669188790863000&source=images&cd=vfe&ved=0CBAQjRxqFwoTCNjv5vuiwfsCFQAAAAAdAAAAABAD
This image was taken with Hubble's Wide Field and Planetary Camera 2, back in 1995.
It shows the orange-red rings surrounding Supernova 1987A in the Large Magellanic Cloud.
The glowing debris of the supernova explosion, which occurred in February 1987, is at the
center of the inner ring. Before that, the last supernova visible to
the eye was documented by Johannes Kepler in 1604, 418 years ago.
It exploded about 20,000 light-years away from us, but it shone more brightly than any
star in the night sky. It was even visible in daylight! As far as we know, it didn’t
cause earthly effects. To date, there is still no full consensus
in the scientific community on how much each of these channels contributes to the total
number of Ia supernovae we observe in the universe. But in the case of Kepler's supernova,
we tried to understand something more. We tried to reconstruct the identity of the stellar
system at the origin of the explosion through chemical and kinetic analyses of the gas and
nearby stars. Scientists concluded it was the result of a merger between two white dwarfs.
Amazing. So, we have made sure that no supernova will
explode at an unsafe distance from the Earth, so we can keep dreaming our sweetest dreams,
for now. We also said that a supernova is a very rare event to witness during your lifetime
as well. Is there any chance for our generation to
observe one of them? The estimated rate of supernova production
in a galaxy the size of the Milky Way is about twice per century. This is much higher than
the actual observed rate, implying that a portion of these events has been obscured
from Earth by interstellar dust. The deployment of new instruments that can observe across
a wide range of the electromagnetic spectrum, along with neutrino detectors, means that
the next such event will almost certainly be detected.
As for dangerous supernovae, no one really knows.
One estimate suggests there might be one dangerous supernova event in Earth’s vicinity
every 15 million years. Another says that, on average, a supernova explosion occurs within
33 light-years of Earth every 240 million years.
So you see we really don’t know. It is
something unforeseeable.
================= Hey, if you are enjoying this video, make
sure to subscribe to the channel and activate the notification bell, so that you don’t
miss any of our videos! Since we are here talking about supernovae
here, let me tell you about some stars that are actually supernova candidates.
First, you have to know there are actually two different kinds of supernovas.
There is the classic explosion associated
with so-called Type II supernovae. It has as a progenitor a very massive star
of at least eight solar masses that is at the end of its active lifetime. (These are
seen only in spiral galaxies, most often near the arms.)
The supernova detonation occurs when material falls in from the outer layers of the star.
This material then rebounds off the core, which has stopped collapsing and suddenly
presents a hard surface to the infalling gases. Unlike Type II supernovae, Type I supernovae
have a different explosion mechanism, even though we are still learning more about how
they work.
Type I supernovae can be divided into three subgroups—Ia, Ib, and Ic—on the basis
of their spectra.
Type Ia supernovae are thought to originate in binary systems consisting of a moderately
massive star and a white dwarf, with material flowing to the white dwarf from its larger
companion.
Something like 150 light years away from
our sun, there is a binary system named IK Pegasi.
It hosts the nearest known supernova progenitor candidate.
The main star in the system – IK Pegasi A – is an ordinary main sequence star, not
unlike our sun. The potential Type I supernova is the other star – IK Pegasi B.
This star is a massive white dwarf. White dwarfs are extremely small and dense,
and IK Pegasi B orbits closer to IK Pegasi A than Mercury is to our sun!
So how do we expect this explosion to take place?
When the A star begins to evolve into a red giant, it is expected to grow to a radius
where the white dwarf can accrete, or take on, matter from A’s expanded gaseous envelope.
When the B star gets massive enough, it might collapse on itself. This will be the
start of the show. And our telescope will be glad to catch it.
Another star that comes up whenever the subject turns to supernovas is Betelgeuse,
one of the brightest stars in our sky, part of the famous constellation Orion. Betelgeuse
is a supergiant star, and, as such, it is intrinsically very brilliant. Betelgeuse is
one of the most famous stars in the sky because it’s due to explode someday.
Moreover, what we know from theory is that
if a red supergiant like Betelgeuse dims drastically and turns a deeper red, a supernova is probably
imminent. What’s really interesting is that, even though Betelgeuse is not likely to explode
in our lifetimes, we observed it as it mysteriously dimmed. This fuelled speculation that the
star could be about to explode. This event would provide a spectacle the
likes of which Earthlings have not seen in centuries: the last supernova in the Milky
Way that could be observed from Earth was in 1604, and Betelgeuse is so close to our
planet that its supernova will be bright enough to be visible during the daytime for weeks.
What astronomers found later was that the dimming was likely to be caused by more mundane
mechanisms, such as a blob of unusually cold matter appearing on the surface of the star,
a cloud of dust crossing the line of sight to it, or maybe a black hole. One thing is
for sure: we weren’t witnessing the sudden explosion of a star.
However, a day will come for Betelgeuse to detonate.
It will run out of fuel, collapse under its own weight, and then rebound in a spectacular
Type II supernova explosion. When this happens, Betelgeuse will brighten
enormously for a few weeks or months, perhaps as bright as the full moon and visible in
broad daylight. Don’t worry, with it being 430 light years
away from our sun, Earthly life won’t be harmed in any way.
Hey! This video ends here! Thanks for watching! What do you think about supernovae? Let us
know in the comments below! See you next time on the channel!