Blog #1 (Astrophysics)


Author: Avinanda Chakraborty

The Karl G. Jansky Very Large Array (VLA) is a radio interferometer operating in the centimetre-wavelength range being used for radio astronomy observations. It is located in central New Mexico on the Plains of San Agustin, around 50 miles (80 km) west of Socorro. The VLA is a Y-shaped array consisting of twenty-seven 25-meter radio telescopes. David S. Heeschen was the main person for the development of VLA, who is also noted as having “sustained and guided the development of the best radio astronomy observatory in the world for sixteen years”.The VLA project was started in early 1973 and was formally inaugurated in 1980. The Array Operations Center (AOC) serves as the headquarter for the VLA which is a component of National Radio Astronomy Observatory (NRAO)

Radio Astronomy and Radio Telescopes: If we are talking about VLA telescopes, we have to know about radio astronomy a little bit. Pioneers of the radio astronomy are Karl Jansky, who first discovered the radio signal from extra-terrestrial objects (1933) and Grote Reber, who has used the parabolic reflecting antenna as a radio telescope (1937). The driving force for radio astronomy in India was Govind Swarup,Kalyan Radio Telescope (1965) at the Kodaikanal Observatory was the first among the radio telescopes in India. Ooty Radio Telescope (1970) and GMRT (1990) are the few others

Working Principal : The VLA is a radio interferometer (an astronomical interferometer is an array of separate telescopes, mirror segments, or radio telescope antennae that work togeth- er as a single telescope to provide higher resolution images) which is operated by multiplying the data from each pair of telescopes together to form the interference pattern. The structure of those interference patterns and how they change with time as the earth rotates, reflect the structure of radio sources on the sky. We can take the patterns and make the maps by using Fourier transformation techniques (Fourier transformation is a mathematical operation that decomposes a function of time i.e., a signal into the frequencies).

CHARACTERISTICS : The radio telescope comprises 27 independent antennae, each of which has a dish diameter of 25 meters (82 feet) and weighs 209 metric tons (230 Short tons) and its total collecting area is 13,250 m2.(142,600 sq. ft). Each of the massive telescopes is mounted on double parallel Y-shaped railroad tracks, so that the radius and density of the array can be adjusted to balance between its angular resolution and its surface brightness sensitivity. The angular resolution that can be reached is between 0.2 and 0.04 arc seconds. The frequency coverage is 74 MHz to 50 GHz (400 to 0.7 cm). A, B, C, D are the four commonly used configurations of VLA, A is the largest and D is the tightest, D is the configuration when all the dishes are within 600 m of the center point. In every 16 months, the observatory normally cycles through all the various possible configurations (including several hybrids); the antennae are moved every three to four months.

Author: Avinanda Chakraborty

OBSERVATIONS: The Very Large Array is widely-used most versatile radio tele- scope in the world. It can map large-scale structure of gas, molecular clouds as well as pinpoint ejections of plasma from supermassive black holes. It is the world's first colour camera for radio astronomy. To keep tabs on robotic spacecraft exploring the Solar System, NASA and ESA have used the VLA also as a high- precision spacecraft tracker.

  1. Ice on Mercury: In 1991, using a radar system consisting of NASA's 70-meter (230-foot) dish antenna, planetary scientists studied Mercury at Goldstone, California, equipped with a half-million-watt transmitter, and the VLA was used as the receiving system. The VLA was configured to map Mercury with detail down to 100 meters across.

  2. Supermassive Black Hole or Galaxy First? In 2011, VLA dwarf galaxy discovery is a strong indication that supermassive black holes formed before the buildup of galaxies. This is a critical piece of the galaxy-making riddle unrevealed!

  3. Micro Quasars: In the Spring of 1994, time series of VLA observations showed that a pair of objects ejected from an X- ray emitting object called GRS 1915+105 were moving apart at super speeds.This was the first time that this type of jet action had been detected in our own Galaxy.

  4. Centre of our Galaxy: In 1983, a team of observers used the VLA to make an image of the Galactic Center that revealed for the first time a “mini-spiral” of hot gas lurking there.

  5. Gravitational Lens: Optical observers discovered the first gravitational lens in 1979, and the VLA quickly was used to confirm the discovery. The fourth known gravitational lens was discovered with the VLA.




  2. National_Radio_Astronomy_Observatory



Video Source: NRAO