by Chris Peterson » Sun Sep 14, 2014 4:21 pm
ta152h0 wrote:how far does " nearby " have to be to not be " nearby " anymore ?
If you're talking about the Earth, a supernova within about 100 ly is near enough that its gamma emissions will have some impact on life (mostly through indirect mechanisms like modification of the ozone layer). Such events have occurred several times since complex life developed on Earth, and probably influenced life's evolutionary path.
On planets without thick atmospheres, or with smaller magnetic fields, the critical distance could be somewhat farther. Also, a farther event which had a jet axis aligned with the Earth (or other planet) could affect life.
There are currently no supernova candidates closer than 100 ly.
[quote="ta152h0"]how far does " nearby " have to be to not be " nearby " anymore ?[/quote]
If you're talking about the Earth, a supernova within about 100 ly is near enough that its gamma emissions will have some impact on life (mostly through indirect mechanisms like modification of the ozone layer). Such events have occurred several times since complex life developed on Earth, and probably influenced life's evolutionary path.
On planets without thick atmospheres, or with smaller magnetic fields, the critical distance could be somewhat farther. Also, a farther event which had a jet axis aligned with the Earth (or other planet) could affect life.
There are currently no supernova candidates closer than 100 ly.