Astronomy

The Legacy Of Raman – A Unique Radio Dish

red, blue and orange stars.

A profound discovery with simple equipment was the hallmark of the great scientist, C.V. Raman. It is refreshing to see the flowering of this tradition in the radio astronomy programmes of the Raman Research Institute (RRI), Bangalore. India has been exploiting low frequencies to study radio waves from celestial sources. Even as the world moves over to higher and higher frequencies, there has been a rekindling of interest in the physical phenomena that can be detected at low frequencies.

In the area of low frequency radio detection, RRI has gained considerable experience. Its scientists have imaged the entire radio sky at 34.5 MHz using dipole arrays, studied supernova remnants and observed a lot of pulsars at low frequencies. RRI has built its own control systems and receivers.

Recently, the RRI scientists have designed and installed a unique 12-metre dish at Gauribidanur. The new dish is a pre-formed parabolic device. It has a central hub from which stainless tubes go out and are bent inward. As in an umbrella, the tubes provide the structure its tension and strength. The design makes the dish take on the shape of a parabola which can withstand high winds and gravity. Moreover, the dish can operate across a wide range of frequencies: 300 MHz to a few giga hertz. The RRI scientists have already operated it at 2 GHz. The design is considered the fist-ever for radio telescopes. Its efficiency and relatively low cost make it a good candidate for many projects at home and abroad.

RRI has plans to build three 15-metre radio dishes and as many dipole arrays for catching high and low radio frequencies, respectively at Gauribidanur. This again would be the fist step in the RRI’s plan to set up a set of 50 such receivers, consisting of both dishes and arrays in a place yet to be chosen in the northern hemisphere. A portable evaluation kit is also being readied to test the radio pollution levels of possible areas. The dishes would be made in such a way as to withstand climate changes and wind speeds for over 15 years. The project is open to participation by foreign scientists as well.

International Participation

In a significant development, RRI has become a partner in the MIRA (Mileura International Radio Array), Widefield Array (MWA), a revolutionary new type of radio telescope, taking shape in the remote outback of Western Australia. RRI will be involved in jointly designing the components of the Array.

MWA consists of 512 inexpensive radio ‘titles’ (with each tile having 16 dipoles that can be electronically steered) observing in the frequency range of 800 to 300 MHz. This is in sharp contrast to the highly sophisticated computer hardware and software traditionally used. The other partners in the project are a consortium of Australian universities, Massachusetts Institute of Technology and the Harvard Smithsonian Centre for Astrophysics.

Besides MIRA, the other project is called MIRANDA, comprising thirty 12-m diameter telescopes—working between 700 and 1800 MHz—to function as an international facility. Its key areas of science are: an all-sky survey for 500,000 hydrogen-rich galaxies to understand the evolution of gas in the early Universe; a deep survey to detect 10 million objects for understanding radio sources and for cosmology tests and to study magnetic fields in our galaxy and elsewhere and survey for pulsars.

MIRA is in part a pathfinder for a huge international astronomy project, the Square Kilometer Array (SKA) radio telescope. It is an international collaboration of 17 countries in planning the giant telescope. The decision on its location, (Australia and South Africa are short listed) is expected arI ound 2011. India hopes to be actively involved in the design and construction of the Array. The SKA will address frontier-area in cosmology

radio dish graphic design

Science Goals of the SKA: Study of the Universe in the so-called Dark Age

The Universe, initially filled with ionized gas, becomes neutral and opaque. Some 500 million years after the Big Bang, the predominantly neutral hydrogen in the Universe was ionized again and this re-ionisation ends the Dark Age at one billion years (corresponding to a red-shift of 6.5) and the Universe becomes transparent again leading to the formation of the fist luminous objects. (Ionisation is the gain or loss of electrons—loss being the more common process in the astrophysical environment; it converts an atom into a positively charged ion.)

In this process, neutral hydrogen glows at 21 cm and thus the early Universe can be identified at low radio frequencies. In the Universe, 90 per cent of hydrogen is in a neutral stage i.e. it contains an electron and a proton and emits at 21 cm once in 10,000 million years. SKA can map out the complete processing occurring during the epoch of re-ionisation showing the first assembly of galaxies and black holes.

  • Search for Earth-like planets.
  • Origin and evolution of cosmic magnetism
  • Evolution of large-scale structures in the cosmos.

Going by the historical records, SKA’s two orders of magnitude increase in sensitivity of its instruments is likely to reveal new cosmic phenomena.

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