Monday, April 23, 2012

Deadly Gamma radiaton on Earth? Eta Carinae

Deadly gamma ray burst might reach Earth from Eta Carinae.

Drawing of a massive star collapsing to form a black hole. Energy released as jets along the axis of rotation forms a gamma ray burst that lasts from a few milliseconds to minutes. Such an event within several thousand light years of Earth could disrupt the biosphere by wiping out half of the ozone layer, creating nitrogen dioxide and potentially cause a mass extinction.
Nicolle Rager Fuller, National Science Foundation Press Release 05-156: Gamma-Ray Burst Smashes a Record

Mass extinction on Earth?
It is possible that the Eta Carinae hypernova or supernova, when it occurs, could affect Earth, about 7,500 light years away.

It is unlikely, however, to affect terrestrial lifeforms directly, as they will be protected from gamma rays by the atmosphere, and from some other cosmic rays by the magnetosphere.

The damage would likely be restricted to the upper atmosphere, the ozone layer, spacecraft, including satellites, and any astronauts in space, although a certain few claim that radiation damage to the upper atmosphere would have catastrophic effects as well. At least one scientist has claimed that when the star explodes, "it would be so bright that you would see it during the day, and you could even read a book by its light at night".

A supernova or hypernova produced by Eta Carinae would probably eject a gamma ray burst (GRB) out on both polar areas of its rotational axis. Calculations show that the deposited energy of such a GRB striking the Earth's atmosphere would be equivalent to
  • one kiloton of TNT per square kilometer 
  • over the entire hemisphere facing the star 
  • with ionizing radiation depositing ten times the lethal whole body dose to the surface.

This catastrophic burst would probably not hit Earth, though, because the rotation axis does not currently point towards our solar system. If Eta Carinae is a binary system, this may affect the future intensity and orientation of the supernova explosion that it produces, depending on the circumstances.

No comments:

Post a Comment