In a first, a team of Indian astronomers has discovered some sources in the universe capable of emitting radio waves in a never-before-known mechanism, using the Giant Metrewave Radio Telescope (GMRT) located at Khodad in Junnar, about 80 km from Pune.
The team, led by TIFR-National Centre for Radio Astronomy (NCRA), which operates the GMRT, said they found a rare source named ‘Extremely Inverted Spectrum Extragalactic Radio Sources’. This discovery, according to the team, could open up avenues for further studies regarding an alternate theory suggesting radio sources to be powered outside the power law.
“In case of special cluster sources, the magnetic flux drops to low frequencies and capturing this sudden fall is extremely challenging. This was possible only due to the high sensitivity of the GMRT and its low range feature. We took accurate measurements as such emissions were captured at frequencies around 150 MHz (megahertz),” senior NCRA scientist Ishwar Chandra told Media.
Radio galaxies are a small subset of galaxies that emit exceptionally powerful emissions at radio frequencies. Up until now, astronomers believed that all these sources emitted radio waves due according to the power law. But a section of scientists, including astronomer Mark Henry from Cambridge University in 1967, had proposed that not all sources were powered as per this law. “So, if a radio spectrum was found declining at a speed larger than +2.5, it was ruled out under the power law. But now, there is an alternate theory and it will begin to emerge as we can confirm that not all sources need to be classified under the power law. However, the number of such sources is still small,” said Chandra.
The NCRA team, comprising Gopal Krishna from Aryabhatta Research Institute of Observational Science; Mukul Mhaskey, Surajit Paul and Sameer Salunke from Savitribai Phule Pune University; Pratik Dhabadhe from Inter University Centre for Astronomy and Astrophysics; Sandeep Sirothia from Square Kilometre Array, South Africa, and former scientist at NCRA, is presently involved in an advanced study in tracing more such sources using the upgraded GMRT (uGMRT).