- Analyzing data from GW170817, the first kilonova ever discovered, scientists at the University of Illinois Urbana-Champaign discerned what would happen if an explosion like that ever occurred in our cosmic backyard.
- According to the study, the greatest threat would take the form of a bubble of cosmic rays that would ionize the Earth’s ozone and make the planet uninhabitable for thousands of years.
- Luckily, this is an unlikely scenario, as the binary neutron mergers that produce kilonovas are extremely rare. One has yet to be found in our galaxy.
Space is an inhospitable place—for people and planets. Stars go supernova, black holes swallow basically everything, and rogue planets careen through the galaxy, ready to dramatically disrupt stellar systems. Now, scientists are adding another doomsday scenario to this world-ending nightmare list—kilonovas.
According to scientists at the University of Illinois Urbana-Champaign, a kilonova—an explosion caused by two colliding neutron stars—located within 35 light years of Earth could bathe the planet in cosmic rays and exterminate life for thousands of years. Scientists analyzed data from GW170817, the first kilonova ever discovered, and uploaded the results of that work last week to the preprint server arXiv.
“As the awareness and understanding of powerful cosmic transients have grown, so also has the realization of their dangers,” the paper reads. “We found that cosmic rays are the most threatening emissions and are potentially lethal…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.”
Cosmic rays are energetically charged particles that bombard the Earth at all times—both from our own Sun and from distant sources throughout the universe. The cosmic ray bubble that would issue from the center of a kilonova explosion could impact planets 36 light years away. And because cosmic rays hang around longer than other types of rays rays, they’d leave planets lifeless for thousands of years.
But cosmic rays are only one threat posed by these giant space explosions. While it's less likely to hit us, the most intense threat is the two jets of gamma radiation that emitted from the kilonova. If caught in a jet’s path, the gamma rays would ionize our ozone and leave our planet susceptible to UV radiation, dooming Earth from as far as 297 light years away.
And if Earth is not in the path of this cue ball of doom, the kilonova has other options. It also issues a “cocoon” of gamma radiation in all directions that would affect planets up to 13 light years away. Damage from this cocoon could take the ozone four years to recover from—more than enough time for UV radiation to wreak havoc on the planet. Neutron star mergers also create an “X-ray afterglow” when gamma radiation hits the interstellar medium, but planets would need to be within 16 light years to be affected by that particular effect.
Thankfully, this specific cosmic doomsday scenario is highly improbable. For one, binary neutron mergers are extremely rare. Scientists estimate that for 100 billion stars, only 10 of them are destined to become binary neutron star mergers. And of the handful of kilonovae we’ve discovered, none of them are in our galaxy.
But while we might be out of the “death by kilonova” woods, dangers lurk around every cosmic corner. Even our own life-giving Sun could put us in danger. The universe is a perilous place, and we’re just trying to live in it.
Darren lives in Portland, has a cat, and writes/edits about sci-fi and how our world works. You can find his previous stuff at Gizmodo and Paste if you look hard enough.
