Gamma-Ray Bursts, Mass Extinctions And Goldilocks’ Search For A Home
The Universe is a hostile place: space debris, magnetic fields, radiation, etc, all conspire to produce a challenging environment for life to thrive. However, as we sit here and read this article we remind ourselves that life is resilient, and where environmental niches can be found biology will take root and blossom.
So, where are the cosmic sweet spots? Where are the cosmological ‘Goldilocks zones’, just right for life to eke out a relatively comfortable existence?
New research from Professors Tsvi Piran and Raul Jimenez propose that Gamma Ray Bursts (GRBs) could provide the defining parameter: ‘as a copious source of gamma rays, a nearby galactic gamma ray burst (GRB) can be a threat to life’, highlights the team from their recently published review letter.
GRBs are triggered by high energy supernova events that occur predominantly in low metallicity, hydrogen/helium rich, galaxies—however, GRBs are possible at the centre of Milky Way type galaxies although with much lower probability. The team point out that because stellar density is much higher within 4 kpc of the galactic centre there is a 95% chance of planetary systems experiencing a lethal GRB, meaning life is highly improbable within this region. At d ≥ 10 kpc from the centre chances drop to 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’.
Even with these lower probabilities major extinction events may have occurred in the past due to high powered GRBs: ‘There is a very good chance (but no certainty) that at least one lethal GRB took place during the past 5 gigayears close enough to Earth as to significantly damage life’, said the team; also, ‘there is a 50% chance that such a lethal GRB took place during the last 500 million years, causing one of the major mass extinction events.’
To further compound the GRB issue: due to the low metallicity and reduced sizes of high red shift galaxies (z > 0.5) life as we know it is highly unlikely to exist at these vast cosmological distances—this greatly reduces our existential search area by a considerable margin.
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