All scenarios / Space
Gamma‑Ray Burst
A dying star a few thousand light-years away ruins our ozone.
What it is
A gamma-ray burst is the most powerful explosion known in the universe, usually from a collapsing massive star or merging neutron stars. If one went off within a few thousand light-years of Earth and was aimed at us, it could strip away much of the ozone layer and expose life on the surface to harmful ultraviolet radiation.
Why it ranks where it does
Some scientists have suggested that a nearby gamma-ray burst could have helped trigger the Ordovician mass extinction about 440 million years ago, though that's unproven. Dangerous bursts close enough to matter are extremely rare, and no candidate star nearby is known to be pointed at Earth.
Evidence on the board
- No candidate star nearby is aimed at us.
What the experts say
Toby Ord puts the existential risk from all stellar explosions at about 1 in 1 billion per century, one of the smallest numbers on our board.
Could we survive it?
A gamma-ray burst lasts only seconds to minutes, so only the hemisphere facing it would take the direct hit. The lasting damage would come from ozone loss, which models suggest could take years to recover. Life in the oceans and underground would be partly shielded. Astronomers have also noticed that our galaxy's most dangerous bursts tend to come from low-metal, star-forming regions, which are mostly found far from the Sun. Our cosmic neighborhood is a fairly quiet place to live.
What would move the number
Up
- The discovery of a nearby star close to collapse with its rotation axis aimed at Earth
Down
- Further surveys that rule out nearby candidates
Live signals we track
The baseline above is set from the evidence as of October 13, 2026. On the live board, your browser adjusts it in real time using these feeds. Chatter can only nudge a score in proportion to its evidence, so attention alone can't make an unlikely scenario look likely.
- Public attention: daily Wikipedia pageviews for Gamma-ray burst
- Online chatter: Hacker News stories mentioning "gamma ray burst" this week vs. the prior eight weeks
Sources
- NASA Astrobiology: How deadly would a nearby gamma-ray burst be?
https://astrobiology.nasa.gov/news/how-deadly-would-a-nearby-gamma-ray-burst-be/ - Space.com: Gamma-ray bursts and mass extinction
https://www.space.com/27948-gamma-ray-burst-mass-extinction.html - 80,000 Hours: Toby Ord's existential risk estimates
https://80000hours.org/articles/existential-risks/
Baseline scores are an editorial threat index from 0 to 100 that combines current reporting with published expert estimates. They're meant for comparing risks, not as actuarial forecasts. See how the numbers work.