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Spaghetti Scenarios · Global risk

Nearby gamma-ray burst

A stellar explosion within our galaxy fires a narrow beam of gamma rays, the most intense radiation in the universe. If Earth were in its path and the explosion relatively close, it would destroy much of the ozone layer and leave the surface exposed to the Sun's ultraviolet radiation.

Satellites detect gamma-ray bursts almost daily; one dangerous to life would have to happen within our galaxy and point straight at us.

Catalog of nearby candidate stars and their orientation

~42°

is the tilt measured in 2026 for the most studied candidate star, about 8,500 light-years away. In 2008 it was thought to face us almost head-on (less than 16°); a burst would only be dangerous if Earth were within about 12° of its axis.

▲ Two studies (2024 and 2026) find it tilted 42–45°

At what distance would it be dangerous?

Distances in light-years. A burst would only harm life on Earth if it happened within our galaxy, very close in cosmic terms, and pointed toward us. The scale is logarithmic.

Danger from a short burst~650
Danger from a long burst (most of those detected)~6,500
Most studied candidate star~8,500
With a margin of about ±2,300 light-years.
Diameter of our galaxy~65,000

Logarithmic scale: each step is ten times the previous one.

'Danger' = loss of about a third of the ozone layer, according to peer-reviewed studies.

What we know about the bursts

~240bursts a year are detected by the Fermi space telescope
×70brighter than any other was the burst of October 9, 2022
1 every 10,000 yearsis the estimated frequency of a burst as bright as that one
50%probability that a lethal burst has hit Earth in the last 500 million years (2014 study)

Where does the candidate star point?

Estimated tilt of the candidate binary star relative to our line of sight. The larger the angle, the less directly it faces us. A burst would be dangerous if Earth were within about 12° of its axis.

Images (2008)less than 16°
Spectra (2024)~45°
It could be only ~34°.
Dust eclipses (2026)~42°
Margin of about ±14°.

Gamma-ray bursts: from hypothesis to monitoring

  1. ~440 million years agoOrdovician extinction: about 60% of marine invertebrates die. One hypothesis, without direct proof, proposes that a nearby burst triggered it.
  2. Late 1960sU.S. military satellites monitoring nuclear tests discover the bursts by chance.
  3. 2004Swift, a satellite dedicated to these bursts, is launched (November 20).
  4. 2008The Fermi telescope is launched (June 11). A study suggests the most studied candidate star faces us almost head-on.
  5. 2022The brightest burst ever recorded arrives (October 9).
  6. 2024Twenty years of spectra show that the candidate is tilted about 45°.
  7. 2026Another method confirms that the candidate is tilted about 42°.

Scenario profile

ImpactCatastrophic (5)
NegligibleMinorModerateMajorCatastrophic
ProbabilityRemote (1)
RemoteUnlikelyPossibleVery likelyAlmost certain
Confidence in the evidenceMedium
LowMediumHigh
WhenGeological timescales
Where it leadsCollapse / Extinction
ReversibilityIrreversible on a human scale
Score5

Nearby gamma-ray burst

Impact
Catastrophic (5)
Probability
Remote (1)
Timeframe
Geological timescales
Score
5
Confidence
Medium
Reversibility
Irreversible on a human scale
Classification
Astronomical

Signals to watch

  • Catalog of nearby candidate stars and their orientation

Possible human action

  • None directly today; it strengthens the case for advancing as a civilization