BENGALURU: Astrophysicists at Bengaluru-based Raman Research Institute (RRI) have emerged as the first in the world to convincingly refute a four-year-old discovery of the most elusive and faint radio signal from the time of birth of the first stars and galaxies in the very early stages of the universe — a discovery touted as “worthy of two Nobel Prizes’’. They did this with their sophisticated radio telescope, SARAS-3, developed at RRI’s Cosmic Microwave Background Distortion Laboratory.
Astronomers from Arizona State University and Massachusetts Institute of Technology, had announced the detection of the earliest radio signal with a hydrogen signature in February 2018. They claimed to be the first to “peer” into just 180 million years after the Big Bang marked the birth of the 13.8 billion-year-old universe.
SARAS-3 radio telescope can detect faint cosmological signals
The ASU-MIT discovery using the EDGES radio telescope was considered a significant development in astrophysics as this particular radio signal — referred to ‘Cosmic Dawn Radio Signal’ — marked the presence of the earliest evidence of hydrogen in the universe. It marked the detection of the first established presence of this element which is a bedrock for the formation of stars and galaxies.
The excitement of the discovery had got the better of Abraham “Avi” Loeb, a theoretical physicist who works on astrophysics and cosmology at Harvard University, who said, “This discovery is worthy of two Nobel Prizes!” It also encouraged astrophysicists worldwide to invent new theories based on the ASU-MIT findings.
However, RRI’s findings by a team led by Prof Ravi Subrahmanyan, using the SARAS-3 radio telescope, may just steamroll all that. RRI astrophysicists said SARAS-3 radio telescope is designed to detect faint cosmological signals, especially radiation emitted by hydrogen atoms at 21-cm wavelength (1.4 GigaHertz) from the depths of the cosmos.
The researchers said the radio signal from Cosmic Dawn is expected to arrive on earth in the frequency of 50- 200 MH. SARAS-3 gave out data showing the parameters pertaining to frequency and temperature of the hydrogen-bearing radio signal were not in that range to qualify as the earliest radio signal with a hydrogen signature, explained Dr Saurabh Singh, Research Scientist at RRI who carried out rigorous statistical analysis of the SARAS-3 data.
SARAS-3 did not find any evidence of the signal claimed by the EDGES experiment. The presence of the signal, as put out by the ASU-MIT’s EDGES experiment, was then decisively rejected after a careful assessment of the measurements, according to Dr Singh. “Our findings imply that the detection reported by EDGES was likely contamination of their measurement, and not a signal from the depths of space and time,” Dr Singh said.
The unfortunate aspect of the hunt for this particular radio signal is that it is in a radio wavelength band used by numerous terrestrial communications equipment, TV and radio FM stations, which makes detecting the extra-terrestrial signal extremely difficult to detect — therefore equated to “hunting for a pin in a haystack”, because of interference from terrestrial radio frequencies which threaten to mask or mimic the radio signal with the hydrogen signature.
With the RRI’s findings proving contrary to claims of the ASU-MIT astronomers, the earliest radio signal from the Cosmic Dawn now continues to remain elusive, leaving the field open once again to hunters of this particular radio signal -- including the SARAS-3 of RRI -- and the astrophysicists’ new theories redundant. The study was published in Nature Astronomy.