Cosmic Radio Pulses: Echo of the Expanding Universe ✛ ✎ ✦
Radio bursts are cosmic echoes. Ultrafast radio wave outbursts, passing through hot, rarefied gas in interstellar space, are delayed more the longer their journey. This delay is like an echo from a distant wall: the farther away, the later the response.
By matching the delay with the stretching of light, scientists measured the expansion rate of the Universe — a value first determined by Edwin Hubble. Today, two main methods, from supernova explosions and the ancient relic radiation, give different numbers: 73 and 67 (km/s per 3 million light-years). Adam Riess and the Planck satellite disagree, while fast radio bursts offer an intermediate value of about 69, easing the “Hubble tension.”
The bursts themselves originate from neutron stars with extreme magnetic fields. Every second, hundreds of such bursts occur somewhere in space: we only catch a tiny fraction of this echo. In the future, by accounting for the bending of the signal's path by gravity and using computer simulations, astronomers plan to use radio bursts to precisely measure dark energy — the force accelerating the universe, suspected since Vera Rubin observed galaxy rotation.
The energy of a typical fast radio burst equals what the Sun emits over several days, yet the burst lasts only a few milliseconds.
Carl Sagan's novel 'Contact' explored the idea of receiving radio signals from aliens; when fast radio bursts were discovered, they too were suspected of artificial origin.