- Astrophysicists suggest only 10% of galaxies may support complex life due to gamma ray bursts.
- These bursts, caused by stellar explosions, could wipe out life forms beyond microbes in most galaxies.
- Gamma ray bursts kept the universe devoid of life for billions of years after the big bang.
- Recent findings challenge previous assumptions about the occurrence of gamma ray bursts.
- The study has implications for the search for intelligent life on distant planets.
The universe, with its estimated 100 billion galaxies, may be a less hospitable place for complex life than previously imagined. According to a study by astrophysicists Tsvi Piran and Raul Jimenez, only one in ten galaxies is conducive to the development of complex life akin to that on Earth.
This limitation arises from the threat posed by gamma ray bursts, powerful stellar explosions capable of obliterating life forms beyond microbial levels. Strikingly, these detonations were instrumental in keeping the universe devoid of life for billions of years after the initial cosmic explosion known as the big bang.
Gamma ray bursts come in two forms: short bursts, lasting a mere second or two, likely occurring when neutron stars or black holes collide, and long bursts, which persist for tens of seconds, arising from the demise of massive stars. Although long bursts are rarer, they release energy equivalent to approximately 100 times that of short bursts.
While a direct hit of gamma rays would not instantly eradicate life, it could trigger a chain reaction leading to the depletion of a planet’s ozone layer. In turn, this would expose the planet to lethal ultraviolet radiation from its host star, causing widespread devastation over an extended period.
Recent data challenges prior assumptions about the occurrence of gamma ray bursts. It was once believed that they would be most prevalent in regions of galaxies characterized by rapid star formation. However, current research suggests a more nuanced reality: long bursts primarily occur in star-forming areas with low levels of elements heavier than hydrogen and helium, referred to as low “metallicity” in astronomical terms.
Piran and Jimenez’s calculations, based on the Milky Way’s average metallicity and star distribution, indicate that the more potent long bursts pose the greatest threat.
Their analysis suggests that Earth’s probability of encountering a lethal gamma ray blast within the past billion years stands at approximately 50%. Some scientists speculate that such an event may have triggered the Ordovician extinction, a catastrophic event 450 million years ago responsible for the loss of 80% of Earth’s species.
The researchers further assessed the potential impact of gamma ray bursts on planets in various parts of the galaxy. Proximity to the galactic center significantly heightens the likelihood of a lethal gamma ray blast, with planets within about 6500 light-years facing a greater than 95% chance of exposure in the last billion years.
Consequently, they conclude that life’s viability primarily exists in the outer regions of large galaxies, such as our own solar system, located approximately 27,000 light-years from the galactic center.
Beyond our own galaxy, the outlook appears even more discouraging. Most galaxies are smaller and possess lower metallicity compared to the Milky Way.
Consequently, Piran and Jimenez argue that 90% of galaxies may experience an excess of long gamma ray bursts, rendering them unsuitable for sustaining life. This situation persisted for around 5 billion years following the big bang, rendering life improbable throughout the universe during that period.
While the radiation exposures discussed by Piran and Jimenez could inflict significant damage, it may not entirely eradicate microbial life. However, for more advanced life forms, it would represent a reset, requiring evolution to begin anew.
This analysis bears practical implications for the search for extraterrestrial life. The SETI Institute, which has focused its efforts on scanning for signals from intelligent life in regions with abundant stars at the center of the Milky Way, may need to redirect its attention in the opposite direction.
Gamma ray bursts could potentially render the center inhospitable to intelligent life, prompting scientists to explore the outer reaches of galaxies in their quest for cosmic companions.