Astronomers have captured the earliest minutes of two exploding
stars, and for the irst time seen a shockwave generated by a star’s
collapsing core. “It’s like the shockwave from a nuclear bomb,
only much bigger and no one gets hurt,” said Dr Brad Tucker of
The Australian National University.
Stars explode when their fuel runs down and the core collapses.
The resulting supernova explosion is brighter than the rest of its
galaxy, and shines for some weeks.
Supernovae are so bright that they can be seen in distant
galaxies, but very little is known about the early stages of these
explosions.
As the core of a supernova collapses to form a neutron star,
energy bounces back from the core in the form of a shockwave that
travels at 30–40,000 km/s and causes the nuclear fusion that
creates heavy elements such as gold, silver and uranium.The new study, published in theAstrophysical Journal
(http://tinyurl.com/zfplud3), reports the explosions of two red
supergiants. The astronomers only saw a shockwave in the smaller
star, which has a radius 270 times that of the Sun. The shock-
wave was observed as a peak in the light emitted from the explo-
sion in the irst few days.
While a shockwave could not be detected in the second star, a
large supergiant with a radius 460 times larger than the Sun, Tucker
said that it must have existed. “The star was so large that the shock-
wave did not travel all the way to the surface,” he explained.
The observation will help astronomers ine-tune their under-
standing of how the size and composition of a star affects the
early moments of its death. “Supernovae made the heavy elements
we need to survive, such as iron, zinc and iodine, so we are really
learning about how we are created,” Tucker said.6 | MAY 2016
Increasing exposure to outdoor light can
stave off an “epidemic” of short-sightedness
among children, according to research
published in Investigative Ophthalmology &
Visual Science(http://tinyurl.com/hqynqu2).
A/Prof Scott Read of Queensland
University of Technology’s School of
Optometry and Vision Science said that
children need to spend more than an hour
and preferably at least 2 hours per day
outside to help prevent the development andprogression of myopia. Read explained that it
wasn’t “near work” on screens that caused
myopia, but a lack of adequate outdoor
light. While screens are leading children to
spend more time indoors than in previous
years, the research shows they are not the
direct cause of the increased incidence of
myopia.
The QUT study measured children’s eye
growth, with study participants wearing
wristwatch light sensors to record lightexposure and physical activity for a fortnight
during warmer and then colder months to give
an overall measurement of their typical light
exposure.
“Children exposed to the least outdoor
light had faster eye growth and hence faster
myopia progression,” Read said.
In February the Brien Holden Vision
Institute predicted that half the world’s
population will be short-sighted by 2050,
with 10% of the world’s population at risk of
blindness.An Hour a Day Keeps Myopia at Bay
BROWSEFor the first time, a supernova shockwave has been observed in the visible spectrum as it reaches the surface of a star called KSN
2011d. It took 14 days for the explosive death of this star to reach maximum brightness, but the initial shock breakout lasted only
20 minutes. Credit: NASA Ames/W. StenzelAstronomers Glimpse Supernova Shockwave