Dangerous Space
This is the text version of the interactive 3D documentary. 한국어
Danger ranking › Extreme objects
SGR 1806-20
Extreme objects #2 · In 2004, a flash from tens of thousands of light-years away shook Earth’s upper atmosphere
View in 3D- Name
- SGR 1806-20
- Type
- Magnetar (neutron star with an extreme magnetic field)
- Size
- About 20 km across
- Distance
- about 28,000 light-years from Earth · light takes 28,000 years (The estimate varies a lot (about 20,000–50,000 light-years))
The story in 1 scene
A flash from tens of thousands of light-years away
On 27 December 2004, a magnetar in the direction of Sagittarius let out a giant flare. In just over 0.2 seconds it released as much energy as the Sun gives off in more than 100,000 years. Its gamma rays disturbed the ionosphere, the top layer of Earth’s atmosphere.
Why?A magnetar is a neutron star whose magnetic field is about a thousand trillion times stronger than Earth’s. When the field twists the star’s crust until it cracks, a giant flare bursts out.
What nextIt was tens of thousands of light-years away, so Earth wasn’t harmed. If the same flare had happened within a few dozen light-years, the ozone layer would have been badly damaged.
See this scene in 3D →Sources
Impact-threat rankings and probabilities follow NASA/JPL’s Sentry risk table (as of 2026-11-04). The other categories are editorial rankings using the published criteria. Distances to stars can carry large uncertainties.