However, it takes at least 30 ppb of ozone to increase the risk of death due to respiratory failure in humans. Thomas and his team of researchers used computer models to determine that the amount of ozone present in the lower atmosphere following a GRB concentrated on the South Pole is around 10 parts per billion (ppb) and this amount varies with the seasons. A burst at the South Pole fits in with theories of the Ordovician extinction because the measured extinction rates match the models that predicts latitude-dependent biological damage. This is because the radiation produces chemical changes in the middle atmosphere, and atmospheric transport from this region is mainly towards the pole making the effect of the GRB most extreme in this location. “When the radiation enters the atmosphere over a pole, the depletion is concentrated there instead of spread around the globe.” “A GRB could happen over any latitude or time but we chose the South Pole mainly to look at a very high depletion case,” explains Thomas. But would the ground-level ozone created after a GRB pose a longterm biological threat? Thomas and his colleague Byron Goracke investigated the severity of this ground-level ozone and its potential effects on life using an atmospheric model to simulate a particular case of a GRB occurring over the South Pole. We see this kind of ozone on hot, polluted days when smog alerts warn us to stay indoors for health reasons. As the UV rays penetrate the planet’s surface they would break apart oxygen molecules and ground-level ozone would form, according to Washburn University astrophysicist Brian Thomas. But a GRB or supernova would quickly eviscerate that layer. Normally, the ozone layer in the upper atmosphere shields the Earth’s surface from harmful ultraviolet light. The research was funded by the Exobiology and Evolutionary Biology element of the NASA Astrobiology Program. Both GRBs and supernovae are usually observed in distant galaxies, but can pose a threat if they occur closer to home, where they can strip the Earth’s upper atmosphere of its protective ozone layer leaving life exposed to harmful ultraviolet radiation from the Sun.Ī new paper, titled “Ground-Level Ozone Following Astrophysical Ionizing Radiation Events – An Additional Biological Hazard?” published in the journal Astrobiology took a look at the ramifications of a nearby GRB or supernova and the effects on life. Supernovae are stellar explosions that also can send harmful radiation hurtling towards Earth.
The recent discovery of a short gamma-ray burst counterpart to a gravitational wave detection (GW 170817) brings the promise of a completely new avenue to explore and constrain the dynamics of gamma-ray burst blast waves.Gamma ray bursts ( GRBs) are the brightest electromagnetic blasts known to occur in the Universe, and can originate from the collapse of the most massive types of stars or from the collision of two neutron stars. Over the past years significant progress has been made both observationally and theoretically/numerically in our understanding of these blast waves, unique in the universe due to their often incredibly high initial Lorentz factors of 100-1000.
Ultimately the blast wave spreads sideways and slows down, and the dominant afterglow emission shifts from X-rays down to radio. A massive ejecta is released and potentially fed by ongoing energy release from the burster and a forward-reverse shock system is set up between ejecta and ambient density. Initially, the blast waves are confined to the dense medium surrounding the burster (stellar envelope or dense wind), giving rise to a jet-cocoon structure. These are responsible for the afterglow emission from which much of our understanding of gamma-ray bursts derives. The various stages of baryonic gamma-ray burst (GRB) afterglow blast waves are reviewed.