No ET, radio calls from faraway galaxy are just ‘ordinary physics’

ASTRONOMERS HAVE traced a series of brief, enigmatic bursts of radio waves to a galaxy far, far away and indeed a long time ago — some 3 billion years or so.

But much as you might be hoping or dreading it to be true, this is probably not E.T. “We think we can explain it with ordinary physics,” said Shamibrata Chatterjee of Cornell University, lead author of a paper published last week in the journal Nature, which details the search for the source of the radio waves known as “fast radio bursts” — intense pulses of radiation from the sky lasting only a few milliseconds. He also spoke at a news conference sponsored by the American Astronomical Society in Grapevine, Texas.

Most likely, Chatterjee said in a telephone interview, the bursts could be caused by weird reactions between a neutron star — the dense spinning magnet left behind by a supernova explosion — and the debris from that explosion. Or perhaps from some unexpected quirk of a supermassive black hole in the centre of the galaxy, a dwarf assemblage of stars some 3 billion light years away in the constellation Auriga.

But there are problems with both explanations, Chatterjee added.

Fast radio bursts were discovered in 2007 in data recorded earlier by the Parkes radio telescope in Australia. Because they are so short and until recently have never been seen to repeat, they were hard for astronomers to study. Usually, astronomers notice them after the fact. Moreover, radio telescopes have poor angular resolution, making it impossible to determine exactly what star or distant galaxy they came from.

The radio emissions, Chatterjee said, resemble blasts from pulsars — spinning neutron stars that emit clock-like pulses of radiation, and whose discovery in 1968 elicited speculation about little green men. But the radio waves arrive on Earth dispersed or spread out in time by wavelength, which implies they’ve travelled from far outside our galaxy. That great distance also implies that they are enormously more powerful than pulsars in our galaxy, adding to the mystery of what they are and raising the question of why they are not seen within the Milky Way.

In all, only 18 fast bursters have been spotted since they were first recognized. If extrapolated to the whole sky, that means 5,000 to 10,000 of these flashes should happen every day. Where are they? Lacking much evidence to the contrary, astronomers theorised that the bursts resulted from apocalyptic events like collisions of neutron stars.

The big break came in 2012 when the burst known as 121102 — after November 2, 2012, the date it was observed — repeated itself. Subsequently, the Very Large Array of telescopes in New Mexico and the Arecibo radio telescope in Puerto Rico recorded nine bursts over 83 hours of observing time and a terabyte of data during a 6-month period in 2016.

Scientists were able to pinpoint the location of the burst to a faint dwarf galaxy in the Auriga constellation. A group of scientists led by Shriharsh Tendulkar of Mcgill University then used the eight-metre Gemini North telescope on Mauna Kea in Hawaii to observe the galaxy and measure its distance.

That distance, 3 billion light years, confirmed the original supposition that the fast bursts come from far, far away. “The host galaxy is puny,” Tendulkar said during the news conference in Grapevine. That dwarf galaxy is only a hundredth of the mass of the Milky Way.

But, mused Chatterjee: “The only one that repeats is from 3 billion light years. Where are all the nearby ones?” He noted that they should be even brighter, saturating our radio receivers. “It’s very curious.”

THE NEW YORK TIMES

Thinkstock That dwarf galaxy from where the radio signals came is only a hundredth of the mass of the Milky Way (above).