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cosmos has so many catastrophes in store
for our fragile little planet among the
scariest is that one day we will almost
certainly find ourselves in the path of
a gamma-ray bursts death ray the end of
the world may not be nigh but it will
come in fact there are quite a few ends
of the world on their way each one were
interesting and less avoidable than the
last and there's a good chance we can
prevent the most imminent like asteroid
strikes or at least deal with their
effects like the damage caused by
gamma-ray bursts and supernovae but the
later ones will be beyond any
conceivable technology to prevent for
example for the gradual heating and
eventual death of the Sun
hopefully our super advanced and
probably not quite human descendants
will be able to escape those by
traveling to other star systems but what
about the Milky Way's inevitable
collision with Andromeda or the final
burning out of the last stars or the
evaporation of the last black hole and
decay of the last proton the ends of the
world and of the universe will come
better to be forewarned we'll get to
each of these inevitable cosmic
catastrophes but let's start with the
one that could happen anytime a
supernova or gamma ray bursts frying our
atmosphere every hundred million years
or so a good deal of Earth's life gets
wiped out at five or six different point
in time over the past half billion years
a large fraction of species simply
vanished from the fossil record some of
these mass extinctions were due to giant
asteroid impact including the most
recent which wiped out the dinosaurs 65
million years ago but this is the most
preventable end of world scenario in
fact we've already talked about asteroid
impacts and how to deflect them however
at least one mass extinction may have
been caused by something we'll never
have the technology to stop the
Ordovician Silurian extinction 440
million years ago may have resulted from
the earth being blasted by the intense
radiation jets from a distant exploding
star it may have been caused by a
gamma-ray burst in this episode we're
going to look at the evidence that the
Oh s extinction was caused by a GRB and
we'll also figure out how long before
the next gamma-ray burst hits but first
let's go over the proposed Nereo as many
of you know a supernova is the explosion
that follows the catastrophic collapse
of a massive star at the end of its life
our Sun won't die that way but any star
more than around eight times the sun's
mass will the resulting explosion sprays
high-energy light so ultraviolet x-rays
gamma rays and neo Lightspeed particles
so at cosmic rays into the surrounding
interstellar space any planet within a
few tens of light years of a supernova
is in trouble it's even more dangerous
if the star is rapidly rotating before
it exploded in that case the powerful
magnetic fields can channel the
explosion into narrow jets that
massively focus and amplify the blast
roughly once per day the jet from such
an explosion in a distant galaxy reaches
the earth and is detected by the Swift
or Fermi satellites the observed faint
flash of gamma rays from exploding stars
can last anywhere from a couple of
seconds to a few minutes
these are long-duration gamma-ray bursts
short duration bursts that lasts less
than two seconds are caused by merging
neutron stars so how close is too close
for a GRB well the main danger of the
bursts within the Milky Way is not the
direct radiation itself essentially all
of the gamma rays and x-rays are going
to be blocked by atmosphere some extra
ultraviolet radiation will reach the
ground but not at seriously dangerous
levels instead the danger is in the long
term effects on the atmosphere gamma
rays break apart nitrogen and oxygen
molecules in the atmosphere which then
recombine into various oxides of
nitrogen those molecules are the real
killers nitric oxide catalyzes the
destruction of ozone molecules depleting
the ozone layer that protects us from
solar UV and nitrogen dioxide absorbs
visible light
reducing the energy received from the
Sun these dangerous molecules can remain
in the atmosphere for a few years and
that's potentially long enough to cause
a UV increase deadly to many species and
to initiate runaway global cooling also
they result in nitric acid rain it's
estimated that a typical gamma-ray burst
within ten thousand light years could
deplete ozone enough to cause up to a
30% increase in ultraviolet at sea level
and this is enough to devastate the most
sensitive organisms including
phytoplankton the basis of the marine
food chain and Earth's main oxygen
producer that alone is enough to cause a
mass extinction event and this could be
exacerbated by the global cooling
triggered by a few years of no.2
absorption of sunlight so why do some
scientists think that the Ordovician
Silurian extinction event resulted from
a GRB well a couple of pieces of
evidence fit nicely looking at the
fossil record there seems to be a strong
correlation between the likelihood of a
given species going extinct and the
exposure that species would have had to
ultraviolet light species in the late
Ordovician that live near the ocean
surface or in shallow water were more
likely to go extinct or went extinct
earlier than those living in deeper
water the same pattern isn't clear for
the other mass extinctions one
explanation for this unusual extinction
pattern is that deeper dwelling
organisms had more protection against
the increased UV following a gamma-ray
burst now I should mention that the oeis
extinction is definitely associated with
the beginning of an ice age scientists
agree that many of the extinctions of
that era resulted from the change in
climate the Ordovician was a very warm
period and the relatively sudden onset
of glaciation is hard to explain without
some triggering events that event may
have been
the increase in sunlight absorbing no.2
after a GRB also extinctions appear to
have started before that ice age really
got underway that fits the hypothesis of
a GRB extinction started due to the
sudden UV exposure and continued due to
climate change whether or not this
particular extinction event was due to a
gamma-ray burst we're pretty confident
that the earth does get blasted
periodically based on the rates of gr
B's we see in other galaxies and on the
population of stars in the Milky Way
it's estimated that every billion years
Earth finds itself in the path of
between 1 and 3 gr B's within 10,000
light years unfortunately there's no way
to tell whether a GRB
we point it our way until it happens the
nearest potential GRB in the brewing is
8,000 light years away so within the
danger zone this is a wolf ray star WR
104 the massive star in the last phase
of its life currently blasting off its
outer shells into a pinwheel like nebula
the exposed inner star shines several
times hotter and hundreds of thousands
of times brighter than the Sun this star
is part of a binary system and it's this
binary orbit that produces the spiraling
nebula the fact that the spiral appears
to be face-on suggests that the axis of
the entire system is pointed directly at
the earth the rotational axis of the
star will define the direction of the
jet in the event that this wolf ray star
does produce a gamma-ray burst if it
does the orientation of the system
suggests we could be rightness firing
line well no need to pack up and leave
the solar system just yet firstly WR 104
could have up to half a million years of
life in it although it's hard to tell
exactly how close a star like this is to
exploding also further observations with
the Keck telescopes indicate that the
system's orbital axis isn't pointed
directly at the earth that doesn't
necessarily mean we're safe it's a
star's rotational axis that defines the
direction of the jet but the orbital
axis of a binary system and the
rotational axis of its stars are often
correlated so we may have dodged the
bullet in this case
gamma-ray bursts a much less common than
regular supernovae and in fact regular
supernovae can do just as much damage as
a GRB however for a supernova to produce
the same effects it needs to be much
closer within 20 to 30 light years there
are definitely no stars in that range
that could explode any time soon however
the Sun isn't stationary it orbits the
Milky Way and its galactic neighbors
come and go
maybe in a few 250 million year orbits a
stellar time bomb will wander into our
vicinity however it's really the GR bees
that are most likely to eat us first and
hit us more often we should certainly
expect one in the next half to 1 billion
years even if it's not WR 104 and when
that happens
well we won't see it coming and anyway
there's nowhere in the solar system to
hide but with any luck we'll have
advanced to the stage where
geoengineering of the entire atmosphere
is possible perhaps we'll be able to
rebuild the ozone layer and clean the
bad molecules from the sky maybe we can
hold out a little longer against the
series of calamities flung at us one
after the other from outer space time
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space-time last week we talked about our
first detection of a visitor from
outside our solar system
it's a giant chunk of rock that we've
named umor more supreme 84 x us what
would happen if this thing hit us well
based on its bright
and variations in that brightness the
body is estimated to be 180 meters long
and maybe 30 meters wide now assuming an
albedo or reflectivity of 0.1 that gives
it a volume of around 130,000 cubic
meters a typical asteroidal density is
2,000 kilograms per cubic meter so that
gives it a mass of around a quarter of
billion kilograms it was moving much
faster than most solar system objects at
around 50 kilometers per second at its
closest approach to earth so it's
kinetic energy half MV squared was
around 3 by 10 to the power of 17 joules
or 70 megatons of TNT and that's greater
than the yield of tsubame the greatest
hydrogen bomb ever detonated assuming
Omaha is entirely rocky and hit the
atmosphere pretty much head-on it might
actually reach the ground before
disintegrating to deliver that energy it
would become what we call a city killer
the global effects however would be
limited pixelated donkey asks whether
there's a chance that some stars slash
solar systems will be ejected from the
galaxy when the Milky Way collides with
Andromeda well in fact yes recent
studies suggest there's a 3% chance that
the Sun will jump galaxies on Andromeda
first flyby and there's some smaller
chance that it'll miss that jump coming
up short and end up in intergalactic
space and some stars will be
slingshotted out of the galaxy by the
two supermassive black holes of
Andromeda in the Milky Way as they fall
together and what will the residents of
one of those exiled systems see well a
very dark night sky dark everywhere
except for the gigantic elliptical
galaxy milk dromeda the final result of
the merger but don't worry we have a few
billion years to come up with a better
name for that galaxy
Timothy judge points out a significant
potential error in the paper by
Portuguese watt and collaborators more
pornog translates from the Klingon more
accurately to the stone is lonely not
lonely rock let's hope the referee
caught that one before publication dog
Bihar
you