Could a gamma ray burst destroy life on Earth?

[Avalancheon]

Hm. Various initial thoughts here.

1) Per the Wikipedia page on GRBs, no observed GRB event has taken place within our galaxy. The nearest GRB so far observed was 130 million ly away. So this would seem to argue for them being very rare in a local sense or otherwise operating within limits or parameters that make an impact on Earth unlikely.

Note also that the article also talks about potential effects of a GRB on Earth and doesn't seem to be concerned with Earth being cooked or the like, but rather with environmental effects as the gamma rays are absorbed by the atmosphere and induce chemical reactions that result in smog, acid rain, and other negative stuff that could adversely (albeit perhaps temporarily) impact the biosphere.

Hi Todd, thanks for the response. This is a very important subject for me, and I welcome everyones feedback.

Gamma ray bursts used to be much more common in the past. These eruptions undoubtedly happened many times in our own Galaxy. A google search reveals that there are somewhere between 10 million to 1 billion black holes in the Milky Way alone. Why does this matter? Because black holes are the corpses of blue giants. Before these massive stars collapse and die, they will emit either a supernova or gamma ray burst.

Even if you take the lower estimate of 10 million black holes, and assume that only 1% of these are the remnants of a GRB, that still leaves you with 100,000 eruptions inside our own Galaxy. Its true that most of these would have happened early in the life of our Galaxy, which is over 13 billion years old. But even so, there were enough GRBs left over to routinely sterilise all corners of the Milky Way until now (seemingly).

You are right to point out that Brian Thomas' study had a narrow focus area, being concerned only with the direct effects of ozone formation in the aftermath of a gamma ray burst. But even here, his use of an unrealistically low energy level undermines his own conclusions.

That all said, I suppose the references you provide could be based on more recent information. However, having said that and coming to my next thoughts:

2) You talk about how much energy the Earth would be subjected to, but don't include how much energy we are starting with. So we don't have complete information to consider your argument with. If you could please add the starting amount of energy you calculated from, that would be very helpful.

3) When you did your calculations, did you take into account the Inverse Square Law?

My 2c worth,

Todd

Apologys for that, I edited my post to include that info. Gamma ray bursts typically emit 1E44 joules of energy in a jet that is 2 to 20 degrees wide. The jets emanate from their north and south poles, allowing them to irradiate large areas.

I didn't take the inverse square law into effect, for reasons of simplicity. I wasn't sure how strongly that would apply to a GRB, as their energy is highly collimated. The true energy level received by the Earth may be lower than I predicted, but its not going to be lowered to the level suggested by Brian Thomas. 

Before I ran my calculations, I figured that Thomas' numbers were off by a factor of only 50 or so. I was quite surprised to find that it was off by a factor of 760. Thats a really significant difference that limits the usefulness of his study.