February 6, 2013
Supernova Observation Helps Scientists Make Better Forecasts
Lee Rannals for redOrbit.com - Your Universe Online
New observations have led to a better understanding of supernovae, which could one day lead to even better forecasts for the cosmic events.Type II supernovae form when a massive star collapses, sending off a giant explosion from the dying star. Having a better way to predict these events would allow astronomers to study them in their earliest stages.
Astronomers wrote in the journal Nature this week that they have observed an energetic outburst from a supernova called SN 2010mc, witnessing a remarkable mass-loss event about a month before the explosion.
“What is surprising is the short time between the precursor eruption and the eventual supernova explosion -- one month is an extremely tiny fraction of the ten-million-year lifespan of a star,” said Carnegie Institution's Mansi Kasliwal.
Models showed that there was just a 0.1 percent chance that the outburst was due to random chance, which gives astronomers evidence that it and the explosion are related. These outbursts are two orders of magnitude more likely to occur in the immediate run-up to the star's explosion, than at other times in a star's life.
Several models of the supernova-creation process predict pre-explosion outbursts, but it has been difficult for scientists to see this process directly.
When the team compared their observations to three proposed models for the mechanism by which this mass is ejected, they found one model to be the best match. This model shows that the high velocities lend credence to the idea that the mass is driven out to the envelope that forms the star's atmosphere by the propagation and dissipation of excited gravity waves.
“Our discovery of SN 2010mc shows that we can mark the imminent death of a massive star. By predicting the explosion, we can catch it in the act,” Kasliwal said.
Type II supernovae show very broad emission lines, indicating expansion velocities of many thousand miles per second, and some have relatively narrow features in their spectra. The supernova observed by the team was a narrow feature type, or Type IIn.
Some supernovae appear to change their types, showing lines of hydrogen at early times, but over weeks become dominated by lines of helium, which can be described as Type IIb supernovae.
Supernovae could actually be as far as 3,000 light-years away from Earth, but could have noticeable effects on our planet's biosphere. Having a better understanding of these cosmic eruptions will enable scientists to also better understand how they may affect our own planet one day.
One theory as to what killed nearly 60 percent of the oceanic life on Earth says that gamma rays from a supernova induced a chemical reaction in the upper atmosphere, converting molecular nitrogen into nitrogen oxides, depleting the ozone layer enough to expose the surface to harmful solar and cosmic radiation. This extinction is known as the Ordovician-Silurian extinction.