GMRT, four radio telescopes detect fringes from quasar 12.3 billion light years away

Scientists obtain a fringe when data from a pair of antennae from one telescope are combined to obtain a correlated signal, while observing the same source.

astronomy GMRT
During two experiments conducted in February, astronomers detected Very Long Baseline Interferometry fringes from this distant quasar — 3C 454.3. (IE)

The Giant Metrewave Radio Telescope (GMRT), and four other international radio telescopes, successfully detected fringes from an extremely bright quasar 12.3 billion light years away.

A quasar is a galaxy that releases enormous amounts of energy and is of great interest in the astronomy community because of the powerful radio jets that are launched when matter falls into super-massive black holes.

During two experiments conducted in February, astronomers detected Very Long Baseline Interferometry fringes from this distant quasar — 3C 454.3. Scientists obtain a fringe when data from a pair of antennae from one telescope are combined to obtain a correlated signal, while observing the same source.

Longer baselines — created by a pair of antennae — allow astronomers to achieve finer and more detailed structure of the galactic source due to the larger distance separation.

For these experiments, GMRT tied up with the Medicina and Noto Radio observatories (Italy), Westerbork Synthesis Radio Telescope (The Netherlands), and the Zelenchukskaya Radio Astronomical Observatory (Russia).

The longest separation between two GMRT antennae — 30 in total — is 25 km. These two experiments, done in the 1,000-1,450 MHz band, saw the data synthesis of a large telescope offering a baseline of 6,000 km across Europe and Asia. This Very Long Baseline Interferometry (VLBI) technique improved the baseline measurements by 3 to 10 milliarcseconds.  Signals picked up by 10 of the antennae were then added into the four remaining telescope’s phased array to produce an output as high as what would be generated when all were fused into a single one, with 10 times larger collecting area.

The signal was then combined with the four European VLBI Network telescopes to give fringes on the baselines with the uGMRT. An interferometric array of radio telescopes spread throughout Asia, Europe, South Africa, and the Americas, the European VLBI Network hasbeen conducting radio astronomical observations of cosmic radio sources since the 1980s.

NCRA Director Prof Yashwant Gupta told The Indian Express that the GMRT’s participation was a leap in paving the way for similar global VLBI networks from Australia, Japan, Europe and other countries in future.

Another NCRA scientist, Prof Preeti Kharb, said the EVN-only image showed an unresolved and single source of radio emission. 

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