A team of Indian and South African astronomers has detected a dying radio galaxy located about 3 lakh light years away.
The discovery was conclusive with the help of archival data stored at Giant Metrewave Radio Telescope (GMRT), which is operated by the TIFR-National Centre for Radio Astrophysics (NCRA), Pune.
The detection could offer newer insights in understanding the evolution of radio galaxies.
Named J1615+5452, the detection is among the fewer dying radio galaxies known so far, as they burn out very quickly in comparison to the age of the universe (3.8 billion years).
“This relatively fast degradation also makes detection very difficult, and it is achieved only at low radio frequencies that observatories like GMRT offer. We will need newer skills to detect such remnant radio galaxies,” said Ishwar Chandra from NCRA, who is the co-author of the paper ‘J1615+5452: a remnant radio galaxy in the ELAIS-N1 field’.
The characteristics of a radio galaxy are an active core, a pair of lobes, jets and hotspots. The core maintains continuous ejections of matter that fuel the Active Galactic Nuclei. After being alive, this galaxy ultimately enters a dying phase, wherein its nuclear engine switches off when the matter that fuels it, runs out.
There are two main kinds of remnant radio galaxies, the one that dies out completely and the other one, which is reborn not due to an active core, but by regaining life triggered by some external stimulus, such as re-supply of matter from a close by event like a merger.
“ J1615+5452 neither had a core nor did it showcase any typical features of an active radio galaxy when observed under low frequency. It appeared similar to a fuzzy object in the radio and the strength dropped rapidly towards higher frequencies, which confirmed that it was decaying,” said Chandra, who was part of the re-analysis of the data captured at 1400 Mega Hertz (MHz), 610 MHz, 325 MHz and 150 MHz.
The data at 1400 MHz was obtained from Karl G Jansky Very Large Array (VLA) Telescope. This discovery was corroborated by the GMRT data observed from 2011 to 2017. Of late, GMRT archival data has been re-used for making newer discoveries.
“The data used here was before the GMRT was upgraded. This shows how every bit of our data can be put to better use,” said Yashwant Gupta, director of NCRA.
When asked about the previous instances of detection of a remnant radio galaxy, Chandra said, “ So far, most detections of remnant radio galaxies have been of those that were re-born, simply because their ejections showed newly-charged particles which get detected easily. Whereas, in case of dying galaxies, the signals are diffused in nature.”
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