Mirage in the ether: when a pulsar pretended to be a distant burst ✦
In December 2019, the CHIME radio telescope caught a periodic radio signal. It was thought to be the first fast radio burst with a clear rhythm—a burst from a distant galaxy. But it was a mirage: rain damaged the antennas, calibration went awry, and a distant explosion was mistaken for a pulsar in the Milky Way—a rotating neutron star born in a supernova explosion.
Cross-checking with archives and spectroscopy of the delay revealed the catch: the radio waves traveled through interstellar hydrogen clouds (nebulae) and cosmic dust, not emptiness. After correcting the calibration, the pulsar fell into place. Surprisingly, even the glitch couldn't hide its brightness—the pulsar shone through the incorrect settings.
The incident reminded us: even the best instruments can make mistakes. In 1967, Jocelyn Bell Burnell mistook pulsar signals for artificial ones; here a pulsar pretended to be a distant burst. Now CHIME constantly checks calibration to avoid chasing mirages.
🎯 Pulsar PSR J0248+6021 lies in a dense star-forming region, where its signal scatters like a flashlight beam in fog. That's why astronomers still debate how far away it is.