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What is a hypernova?
A
hypernova is a theoretical type of supernova
produced when exceptionally large stars collapse at the end of their
lifespan. In a hypernova, the core of the star collapses directly into
a black hole and two extremely energetic jets of plasma are emitted
from its rotational poles at nearly light speed. These jets emit
intense gamma rays, and are a candidate explanation for gamma ray
bursts. - Wikipedia
What causes hypernovae?
When a
white dwarf reaches the Chandrasekhar
limit, the maximum mass it can get, it collapses into a neutron star or
a black hole. During this breakdown the remaining carbon and oxygen
atoms go through fusion, creating a shockwave. Once that liberated
energy reaches the surface of the star, its luminosity increases
significantly and the outer layers are blown apart. This explosion is
called a supernova. These stellar detonations are so impressive that an
observer would notice a significant increase in the star's luminosity
millions of light years away. This process is similar, yet much more
violent, than that of novae. A nova is when the white dwarf doesn't
reach the Chandrasekhar limit, but incites nuclear fusion in the matter
it has accreted on its surface.
A hypernova is
the explosive result of a super massive star's core
collapsing directly into a black hole. When the collapse occurs
unshackled energy is freed at high frequencies, releasing two extremely
energetic jets of plasma emitting from its rotational poles at nearly
light speed. These jets of plasma emit gamma rays. Eta Carinae is
a
prime candidate for a hypernova.
Probably being the most massive
star
in the galaxy it tips the scale at 100-120 times the mass of our sun
and is believed to burn between 20,000° and 50,000° Fahrenheit.
Comparatively, our sun gets up to around 10,000° Fahrenheit.
Because of its mass and temperature Eta Carinae will live a relatively
short life, perhaps 25,000 years compared to a standard star's 10
billion years. Eta Carinae is between 7,000-8,000 light years away from
Earth and when it finally blows we'll know it.
*
The changing intensity of a
gamma-ray burst. On the left is an image of the gamma ray sky
showing the burst becoming the brightest object. On the right is a plot
of the changing brightness with time. The first gamma-ray burst was
seen in the year 1967 (although it was not reported to the world until
1973) by satellite-borne detectors intended to look for violations of
the Nuclear Test Ban Treaty. Credit: BATSE *
What would happen if a hypernova occurred near
Earth?
If a
hypernova were to occur within 3,000
light years from Earth it could easily wipe out all life on the planet,
even bacteria. If the Earth were within the path of one of the
energetic cones the interactions of the gamma rays in the upper
atmosphere would produce a lethal dose of highly penetrating ionized
particles, destroying life on the surface, underground and underwater.
The initial bombardment would immediately destroy the ozone layer and
detonate the atmosphere akin to that of the simultaneous discharging,
at the bare minimum, of one-kiloton of TNT per km^2, over the whole
hemisphere facing the phenomenon. Ionization, the separation of atoms
via gaining energy and losing electrons, would take place converting
the oxygen and nitrogen in the atmosphere into nitrogen dioxide. Before
covering the Earth in a black cloud comparable to that of urban smog,
the sky would burst into flames and fireballs, creating global storms
of acid rain and possibly fire. However, before all of the previous
occurred, the actual radiation would hit the surface. The radiation
energy level would be roughly around 10^4 to 10^7 eV (electron volts).
If compared to a standard medical x-ray machine's 200,000 eV (and
needing a protective lead vest), you get up to 1 million times the
radiation! Radiation affects high atomic-number elements more. The most
abundant high atomic-number elements in biological organisms are
calcium and potassium. These two elements are utilized in muscle
function, and ionizing radiation would cause extreme cramping of
muscles, making a rather stiff and painful, but quick death.
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After the initial
impact killed most surface organisms, the brief
absence of the ozone layer would allow the sun's ultraviolet rays to
barrage the Earth, reaching the depths of the oceans. Water and mud
create a buffer-zone for ionized radiation, so most amphibious eggs and
aquatic life would survive the hypernova's radiation. However,
ultraviolet radiation can penetrate tens of meters of water, so it
could harm marine organisms at these depths. Once the gamma ray and
ultraviolet ray attack is over, nuclear winter would begin due to the
nitrogen dioxide flavored atmosphere smothering the Earth and shielding
her from the sun's warming light. These same effects have been
conjectured to cause the most devastating mass extinction in our
planet's history around 440 million years ago.
How often to hypernovae occur?
The rough
estimate is every 200 million years.
That would mean the Earth is
past due by 260 million years.
How could
we be so overdue? It's fairly simple, actually. If hypernovae only
occur in massive stellar objects at least 40 times the mass of our sun,
then we're completely safe. The closest object is Eta Carinae some
7,500 light years away. Take into account its distance and the only
thing that would happen if Eta Carinae went hypernova is that
Earth-bound observers would see the increase in luminosity and
satellites in the southern hemisphere would be fried. The Earth may be
overdue by a few hundred million years, but our planets has survived
possibly several in its 4.5 billion year lifespan and now there are
none left in the neighborhood to bully us.
Fast Facts for Eta Carinae - Click for larger
Images
| Credit |
NASA/CXC/SAO |
Scale
|
Image is 100
arcsec on a side.
|
Category
|
Luminous Blue
Variable Star
|
| Coordinates (J2000) |
RA 10h 45m 04s
| Dec -59º 41' 03"
|
Constellation
|
Carina
|
| Observation Date |
September 6,
1999
|
| Observation Time |
2.8 hours
|
Color Code
|
Both - Thermal
and Intensity
|
| Instrument |
ACIS
|
| Distance Estimate |
7,000 light
years
|
Release Date
|
October 08,
1999 |
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