Ultra-rare star collision in Milky Way could wipe out life on Earth, study finds

A potential, ultra-rare cataclysmic collision between two decaying stars in the Milky Way galaxy could strip the Earth of its protective ozone layer and induce a mass extinction of all life forms on the planet, a new study has suggested.

Until now, astronomers have observed only a handful of such neutron star collision events known as kilonovas.

Such an explosion, if it occurred in close proximity to Earth, may pose dangers to life on the planet, said scientists, including those from the University of Illinois Urbana-Champaign in the US.

The yet-to-be peer-reviewed research, posted in the arXiv preprint server, could help determine the chances of life surviving on other worlds in proximity to these star collision events.

The biggest threat from such star collisions is the burst of radiation from them, including gamma rays and an X-ray afterglow they produce, according to scientists. “Ionizing radiation from these sources can be dangerous for life on Earth-like planets when located too close,” researchers wrote in the study.

Scientists studied the possibilities of these events affecting Earth based on an analysis of what we know from the first-ever neutron star collision detected – a stellar event named GW170817.

Any living thing within the narrow range of about 297 light-years (97 parsecs) of such an explosion could get burned by powerful gamma radiation, researchers said.

If the Earth were in such a zone, scientists said the radiation may strip the Earth’s stratospheric ozone, which may take a handful of years to recover.

X-rays from the afterglow of the kilonova may be more lethal, as they tend to last longer than the gamma ray emissions, scientists said, adding however that their life-destroying effects would be within about 16 light years.

“For baseline kilonova parameters, we find that the X-ray emission from the afterglow may be lethal out to ∼5 pc and the off-axis gamma-ray emission may threaten a range out to ∼4 pc,” scientists noted.

“The greatest threat comes years after the explosion, from the cosmic rays accelerated by the kilonova blast, which can be lethal out to distances up to ∼ 11 pc,” they said.

However, the study cautioned that the findings have “significant uncertainties” and depend on the “viewing angle, ejected mass, and explosion energy”.

Due to the rarity of kilonova events, researchers also said such stellar collisions are “not important threats to life on Earth”.

“The rarity of binary neutron star mergers combined with a small range of lethality means that they are probably not important threats to life on Earth,” they said.

“We find that the mean recurrence time of lethal mergers at the location of the Sun is much larger than the age of the Universe.

“However, even if it never induced a mass extinction, a nearby kilonova event would be visible on Earth. It would likely disrupt technology soon after the merger and remain bright in the sky for over a month,” the scientists said.