The excitement over 2018 claims of discovery of light from the universe’s first stars (cosmic dawn) seems to have hit a roadblock in Bengaluru. City-based Raman Research Institute on Monday claimed their experiments have refuted claims by Arizona State University (ASU) and Massachusetts Institute of Technology (MIT) that they discovered the elusive radio signals from the cosmic dawn. The findings were published in the journal Nature Astronomy on Monday night, which had also published the earlier claims of discovery in 2018.
The elusive radio signal is a theoretical prediction of a dip in the brightness of the spectrum due to the interaction of hydrogen gas and Cosmic Microwave Background radiation at different temperatures at cosmic dawn. For decades now, scientists have been experimentally trying to observe and capture this signal, to hopefully reverse engineer and study the formation of the first stars after the big bang, a phase about which very little is known.
ASU and MIT, using data from their EDGES radio telescope mounted in Western Australia, claimed to have finally discovered the elusive signal in February 2018. However, the observed dip was twice over what was theoretically predicted, disrupting the widely accepted cosmological model of the universe. Hailed by many as revolutionary, this claim led to several new theories like early galaxies before cosmic dawn and dark matter interactions in an attempt to explain this variation. Since then, over 10 experiments across the world have been trying to cross verify this discovery.
In an initiative led by former RRI director Prof. Ravi Subrahmanyan and Prof. N. Udaya Shankar, CMB Distortion Laboratory, RRI-developed highly sensitive radio telescope SARAS has been trying to detect the elusive cosmic dawn signal for nearly 15 years now, without success. Post the 2018 claim of its discovery, SARAS 3 was deployed at Dandiganahalli Lake near Bengaluru and the Sharavathi backwaters in January and March 2020 to cross verify these claims. “For the first time, we deployed the radio telescope on a water surface to cut out contamination by radio signals emanating from the ground and had very good results,” said research scientist Dr. Saurabh Singh, who presented the findings to the press on Monday.
“After a rigorous statistical analysis, SARAS 3 did not find any evidence of the signal claimed by the EDGES experiment. The presence of the signal is decisively rejected after a careful assessment..”, said a statement from RRI. It further said this finding implied that the detection reported by EDGES was likely a contamination of their measurement and not a signal from the depth of space and time, RRI said. Dr. Singh said RRI could refute the EDGES signal with “95% accuracy”.
Detecting the elusive cosmic dawn signal is a herculean effort as the “faint signal is buried in the sky radio waves coming from our own galaxy Milky Way, which are a million times brighter and are in the same wavelength band by terrestrial communication equipments”, making removing contamination the cornerstone of the experiment.
The findings of SARAS 3 “re-establishes the prevailing cosmological model of the cosmos”, RRI said in its statement.
Prof. Udaya Shankar said RRI now intends to deploy SARAS 3 in the relatively less radio wave contaminated Ladakh, Himalayas for a longer period of time in an attempt to detect the radio signal from cosmic dawn. A project to deploy the telescope in the moon’s orbit in an attempt to detect the radio signal from the far side of the moon, one of the most uncontaminated zones in the universe, is in its initial stages.
