super-supernova SN2007bi is an example of a "pair-instability"
breakdown, and that's like calling an atomic bomb a
"plutonium-pressing" device. At sizes of around four megayottagrams
(that's thirty-two zeros) giant stars are supported against
gravitational collapse by gamma ray pressure. The hotter the core, the
higher the energy of these gamma rays - but if they get too energetic,
these gamma rays can begin pair production: creating an
electron-positron matter-antimatter pair out of pure energy as they
pass an atom. Yes, this does mean that the entire stellar core acts as
a gigantic particle accelerator.
The antimatter annihilates
with its opposite, as antimatter is wont to do, but the problem is that
the speed of antimatter explosion - which is pretty damn fast - is
still a critical delay in the gamma-pressure holding up the star. The
outer layers sag in, compressing the core more, raising the
temperature, making more energetic gamma rays even more likely to make
antimatter and suddenly the whole star is a runaway nuclear reactor
beyond the scale of the imagination. The entire thermonuclear core
detonates at once, an atomic warhead that's not just bigger than the
Sun - it's bigger than the Sun plus the mass of another ten close by
The entire star explodes. No neutron star, no
black hole, nothing left behind but an expanding cloud of newly
radioactive material and empty space where once was the most massive
item you can actually have without ripping space. The explosion alone
triggers alchemy on a suprasolar scale, converting stars' worth of
matter into new radioactive elements.
And we saw this. This
really happened. Someday, somewhere, another massive explosion will occur and no one will be left to tweet it.
Most astronomers today believe that one of
the plausible reasons we have yet to detect intelligent life in the
universe is due to the deadly effects of local supernova explosions
that wipe out all life in a given region of a galaxy.
While there is, on average, only one supernova per galaxy per
century, there is something on the order of 100 billion galaxies in the
observable Universe. Taking 10 billion years for the age of the
Universe (it's actually 13.7 billion, but stars didn't form for the
first few hundred million), Dr. Richard Mushotzky of the NASA Goddard
Space Flight Center, derived a figure of 1 billion supernovae per year,
or 30 supernovae per second in the observable Universe!
rare stars -real killers -type 11 stars, are core-collapse hypernova
that generate deadly gamma ray bursts (GRBs). These long burst objects
release 1000 times the non-neutrino energy release of an ordinary
"core-collapse" supernova. Concrete proof of the core-collapse GRB
model came in 2003.
It was made possible in part to a
fortuitously "nearby" burst whose location was distributed to
astronomers by the Gamma-ray Burst Coordinates Network (GCN). On March
29, 2003, a burst went off close enough that the follow-up observations
were decisive in solving the gamma-ray burst mystery. The optical
spectrum of the afterglow was nearly identical to that of supernova
SN1998bw. In addition, observations from x-ray satellites showed the
same characteristic signature of "shocked" and "heated" oxygen that's
also present in supernovae. Thus, astronomers were able to determine
the "afterglow" light of a relatively close gamma-ray burst (located
"just" 2 billion light years away) resembled a supernova.
isn't known if every hypernova is associated with a GRB. However,
astronomers estimate only about one out of 100,000 supernovae produce a
hypernova. This works out to about one gamma-ray burst per day, which
is in fact what is observed.
What is almost certain is
that the core of the star involved in a given hypernova is massive
enough to collapse into a black hole (rather than a neutron star). So
every GRB detected is also the "birth cry" of a new black hole.
at the American Astronomical Society's 215th meeting, in Washington DC,
said earlier this week that new observations of T Pyxidis in the
constellation Pyxis (the compass) using the International Ultraviolet
Explorer satellite, indicate the white dwarf is part of a close binary
system with a sun, and the pair are 3,260 light-years from Earth and
much closer than the previous estimate of 6,000 light-years.
The white dwarf in the T Pyxidis system is a recurrent nova, which
means it undergoes nova (thermonuclear) eruptions around every 20
years. The most recent known events were in 1967, 1944, 1920, 1902, and
1890. These explosions are nova rather than supernova events, and do
not destroy the star, and have no effect on Earth. The astronomers do
not know why the there has been a longer than usual interval since the
last nova eruption.
Astronomers believe the nova
explosions are the result of an increase of mass as the dwarf siphons
off hydrogen-rich gases from its stellar companion. When the mass
reaches a certain limit a nova is triggered. It is unknown whether
there is a net gain or loss of mass during the siphoning/explosion
cycle, but if the mass does build up the so-called Chandrasekhar Limit
could be reached, and the dwarf would then become a Type 1a supernova.
In this event the dwarf would collapse and detonate a massive explosion
resulting in its total destruction. This type of supernova releases 10
million times the energy of a nova.
Observations of the
white dwarf during the nova eruptions suggest its mass is increasing,
and pictures from the Hubble telescope of shells of material expelled
during the previous explosions support the view. Models estimate the
white dwarf's mass could reach the Chandrasekhar Limit in around 10
million years or less.
According to the scientists the
supernova would result in gamma radiation with an energy equivalent to
1,000 solar flares simultaneously - enough to threaten Earth by
production of nitrous oxides that would damage and perhaps destroy the
ozone layer. The supernova would be as bright as all the other stars in
the Milky Way put together. One of the astronomers, Dr Edward Sion,
from Villanova University in Pennsylvania, said the supernova could
occur "soon" on the timescales familiar to astronomers and geologists,
but this is a long time in the future in human terms.
think supernova explosions closer than 100 light years from Earth would
be catastrophic, but the effects of events further away are unclear and
would depend on how powerful the supernova is. The research team
postulate it could be close enough and powerful enough to damage Earth,
possibly severely, although other researchers, such as Professor
Fillipenko of the Berkeley Astronomy Department, disagree with the
calculations and believe the supernova, if it occurred, would be
unlikely to damage the planet.
Luke McKinney with Casey Kazan