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Introducing ... Superdupernovas
By Ron Cowen
Blue, brilliant and bizarre. That’s how
astronomers describe six supernovas
that form a brand new class.
Like other supernovas, these oddballs are stellar explosions that produce
spectacular light shows as their glowing
debris roils the gas around them. But
unlike known supernovas, these newly
discovered objects emit much of their
light at ultraviolet wavelengths and
bear no trace of hydrogen, an element in
abundance in most other stellar blasts.
The very existence of these explosions
defies ready explanation, says astronomer Robert Quimby of Caltech. He and
his colleagues describe the findings
online June 8 in Nature.
The new class consists of four super-
novas that the team recently discovered
and t wo others that have baffled astrono-
mers in the years since they were found
(SN: 7/18/09, p. 9). None of the six are
extremely remote, but members of this
new class are so bright that they should
be visible from more than 12 billion light-
years away. Some might serve as new
probes of distant galaxies that would
otherwise be too faint to be observed.
energy into a power source that boosts
the brightness of the supernova.
The second possible explanation
is that just years before one of these
stars explodes, it expels a huge bubble
of hydrogen-poor material. When the
explosion erupts, the expanding debris
rams into the previously cast-off material, boosting the brightness.
Stars with helium envelopes that long
ago ejected their outer shell of hydrogen
are already known, says McCray. If such
a star ejected its helium envelope before
exploding, “that would do the trick” to
explain the brightness, he notes.
Ultraviolet observations could identify a host of elements in the explosions
and might indicate which of the two proposals is correct, Quimby says. A large
amount of unburned carbon and oxygen,
for example, would favor the model in
which debris from the explosion runs into
a bubble of previously ejected material.
With large sky surveys — such as the
Palomar Transient Factory that Quimby’s
team used — finding thousands of supernovas, it’s no surprise that astronomers
have discovered some brilliant oddballs,
says theorist Stan Woosley of the University of California, Santa Cruz. s
Black hole jets, now in HD
astronomers have produced the sharpest images ever of twin
jets racing outward from a galaxy’s central black hole. Generated
using nine radio telescopes arrayed across the southern Hemisphere, the images reveal features just 15 light-days across in
the heart of the galaxy centaurus a (galaxy shown at left). at its
core, the galaxy contains a black hole as massive as 55 million
suns. the new images home in on a region around the black
hole that is less than 4. 2 light-years across —smaller than the
distance between the sun and its nearest star—says roopesh
Ojha of Nasa’s Goddard space Flight center in Greenbelt, Md.
Ojha and colleagues describe their findings in the June
Astronomy & Astrophysics. the team combined data from the radio
telescopes to achieve resolution equivalent to that of a single
superdish about 80 percent of earth’s diameter. the images
reveal for the first time just how close to a black hole a jet can
form, a constraint that must now be incorporated into models of
how such jets are generated, Ojha says. — Ron Cowen