Gamma ray bursts (GRB) and distribution of life

[marcus]

Gammaray bursts (GRB) may affect the prevalence of life in various different regions of the galaxy.
http://arxiv.org/abs/1409.2506
On the role of GRBs on life extinction in the Universe
Tsvi Piran, Raul Jimenez
(Submitted on 8 Sep 2014)
As a copious source of gamma-rays, a nearby Galactic Gamma-Ray Burst (GRB) can be a threat to life. Using recent determinations of the rate of GRBs, their luminosity function and properties of their host galaxies, we estimate the probability that a life-threatening (lethal) GRB would take place. Amongst the different kinds of GRBs, long ones are most dangerous. There is a very good chance (but no certainty) that at least one lethal GRB took place during the past 5 Gyr close enough to Earth as to significantly damage life. There is a 50% chance that such a lethal GRB took place during the last 500 Myr causing one of the major mass extinction events. Assuming that a similar level of radiation would be lethal to life on other exoplanets hosting life, we explore the potential effects of GRBs to life elsewhere in the Galaxy and the Universe. We find that the probability of a lethal GRB is much larger in the inner Milky Way (95% within a radius of 4 kpc from the galactic center), making it inhospitable to life. Only at the outskirts of the Milky Way, at more than 10 kpc from the galactic center, this probability drops below 50%. When considering the Universe as a whole, the safest environments for life (similar to the one on Earth) are the lowest density regions in the outskirts of large galaxies and life can exist in only ~ 10% of galaxies. Remarkably, a cosmological constant is essential for such systems to exist. Furthermore, because of both the higher GRB rate and galaxies being smaller, life as it exists on Earth could not take place at z>0.5. Early life forms must have been much more resilient to radiation.
6 pages, 4 figures.

Tsvi Piran has impressed me over the years as being a very able researcher in a broad range of subjects. I am not sure I can always follow his reasoning (e.g. about the cosmological constant in this case) but still want to pay attention. Maybe other people an provide some comment and perspective on this.

 

[Chronos]

I always wonder how relevant GRB beaming/alignment with jets is to the probability of an extinction level event on life bearing planets. I'm sure this was taken into account by Piran, but, still seems like a reasonable question.

 

[vociferous]

This is an interest of mine. Thank you for the link.

 

[BWV]

Was going to post on this & found this topic - the relevance is that this is hopeful news in regards to the Fermi Paradox, i.e. a past period of GRBs plus galactic geography is the great filter

have not read the paper, but this synopsis (http://physics.aps.org/articles/v7/124) mentions that GRBs may have made much of the Universe unfriendly to life until about 5 billion years ago. So that would a) make us an early intelligent species and b) eliminate a huge chunk of the current galaxy as a potential home for other intelligent species

 

[mfb]

The early Earth with life did not even have such a layer (or molecular oxygen in the atmosphere at all), so this is applicable to more recent developments (in particular, land-based life) only.

How can a GRB destroy the 50% of ozone that are shielded by Earth?

 

[Chronos]

Agreed mfb, the Earth did not even have significant oxygen content much before a couple gy ago, so the question is moot.