Thursday, 15 March 2018

11. Very Large Array

Very Large array (VLA) is situated in New Maxico, USA and is operated by NRAO (National Radio Astronomy Observatory).

The red dot is showing position of VLA on earth
Very Large Array is a collection of 27 radio telescopes, each 25m in diameter. They are distributed in a Y-configuration and each of these telescopes can be moved along the railroad tracks. In 2012 it was renamed as Karl J. Janskey Very Large Array after Karl Guthe Jansky who built his own 14.6m rotatable antenna and later in 1931 discovered radio waves coming from the center of our galaxy.

Very Large Array 
APOD May 14, 2006
Credit: Dave FinleyAUINRAONSF
VLA had been used for SETI (Search for Extraterrestrial Intelligence).
We know that our galaxy - Milky Way is the second largest in the Local Group, the first and third are M31 (Andromeda galaxy) and M33 (Triangulum galaxy) respectively. So astronomers pointed the VLA telescopes to look for radio signals of 21cm from these two galaxies but they didn't find any.

VLA radio telescopes also discovered the first Einstein Ring gravitational lens. In gravitational lensing, when a heavy object comes in front of a star, galaxy or quasar it bends the light coming from them and thus distorts is totally. Sometimes it forms a ring and sometimes multiple images. And the first Einstein Ring was made because the image of a quasar was bent by a galaxy in between.

Tuesday, 13 March 2018

10. Australia Telescope Compact Array (ATCA)

Australia Telescope Compact Array or ATCA is located in Australia and is operated by CSIRO.

The red dot on the right end of Australia shows the position of the radio telescopes.

ATCA has six 22m diameter antennas to detect radio waves from space.
Radio waves have the frequency range of 3kHz to 300GHz. These radio telescopes have parabolic dishes to reflect the radio waves to receiver.
The dish of the radio telescope is usually not solid because it would be a waste of money and time to build one. Radio waves can easily get reflected from a mesh just like from a solid surface because of their longer wavelengths.

Another difference that is seen between Radio and optical telescopes is that radio telescopes are usually an array of antennas working together just like ATCA has six Radio antennas.

One of the radio antennas at Australia Telescope Compact Array
The size of these antennas is big because a larger collecting area can help in detecting more faint sources.

Image credit: X-ray: NASA/CXC/Univ. of Hertfordshire/M. Hardcastle et al.; Radio: CSIRO/ATNF/ATCA

The above image is showing the enormous jet of energy released by the Supermassive black hole. It's a composite image showing the data from Chandra X-ray Observatory in blue and the radio data from ATCA in red.

Sunday, 11 March 2018

9. Fermi Gamma Ray Space Telescope

Fermi Gamma Ray Space Telescope orbits around Earth once per 95 minutes.

Fermi Telescope was launched on 11 June, 2008. And this year it completed 10 years in orbit. Previously it was called Gamma-ray Large Area Space Telescope (GLAST) but later in 2008 it was renamed to honour physicist Enrico Fermi.

It has two instruments on board-
1. Large Area Telescope (LAT)
2. Gamma-ray Burst Monitor (GBM)
Both of these instruments also contain many subsystems.

Fermi has detected the most distant Blazars that are 2.1 billion years old!

Friday, 9 March 2018

8. Suzaku Observatory

Suzaku was an X-ray observatory in a 96 minute orbit around earth.

Suzaku was launched on July 10, 2005. Before its launch it was known as ASTRO-E2. And it was the second launch mission of ASTRO-E observatory which was lost on 10th Feb, 2000 due to rocket failure which crashed into ocean with its payload.

The instruments on board Suzaku are-
1. X-ray Telescope (XRT)
2. X-ray Spectrometer (XRS)
3. X-ray Imaging Spectrometer (XIS)
4. Hard X-ray Detector (HXD)

Suzaku detected chromium and manganese elements in the intergalactic space - the space between galaxies of Perseus Cluster. The gas in cluster was very hot thus emitting X-rays. Suzaku's instruments detected these X-rays and split them into its component wavelengths. As every element has a different spectrum, the two atoms were identified.

This video describes more details about the discovery-

The mission was deactivated on 2nd September, 2015.

Wednesday, 7 March 2018

7. Swift Observatory

Swift observatory is in a 95.74 minute orbit around earth. Its NASA's Multi-wavelength space telescope.

NASA E/PO, Sonoma State University/Aurore Simonnet

It was launched on 20th November, 2004. Swift is named after a small bird. One of its mission is to detect Gamma Ray Bursts and their afterglows in X-ray and visible light. For this, there are three instruments on board Swift -

1. Burst Alert Telescope (BAT)
2. X-Ray Telescope (XRT)
3. Ultraviolet/Optical Telescope (UVOT)
Swift detects ~100 GRBs per year.

This year in January, Swift was renamed as Neil Gehrels Swift Observatory to honour Cornelis A. Neil Gehrels, an astrophysicist who left us on February 6, 2017.

It was the first image captured by the UVOT instrument - the pinwheel galaxy in UV and visible light.

Tuesday, 6 March 2018


Rossi X-Ray Timing Explorer (RXTE) was a spacecraft in low-earth circular orbit of 90 minutes.

RXTE was launched on December 30, 1995. Its mission was to study time variation of astronomical X-ray sources. The spacecraft was named after an Italian physicist Burno Benedetto Rossi.
The mission was deactivated on 5th January, 2012 after working for 16 years and 6 days.

RXTE solved one of the deepest mysteries in Astronomy.

It was known through observations that the galactic plane glows in X-rays whose brightness increases towards the galactic center.

Other observatories like Chandra and XMM-Newton were not able to give details of what's causing the glow. So, it was assumed by astronomers that the X-rays were coming from hot, diffuse Interstellar gas.

RXTE had mapped the X-ray background for 10 years since February, 1996. And NASA's another satellite COBE (Cosmic microwave Background Explorer) in early 1990s had also mapped the near-Infrared glow from our galaxy. The data from two satellites were matched.

Credit: NASA/RXTE-COBE/Revnivtsev et al.

As lots of individual stars glow in near-Infrared, it was suggested that X-ray emission in the galactic plane came from cataclysmic variables (a binary system with a star and a white dwarf).

White dwarfs are cores of dead stars and if they are in a binary, they will accrete gas from their companion star. Due to this process very high energy X-rays are released.

(New Map of Milky Way Reveals Millions of Unseen Objects - March 2006.

Monday, 5 March 2018


ESA's INTEGRAL (INTErnational Gamma Ray Astrophysics Laboratories) is orbiting in a highly elliptical orbit around Earth. And it takes three days to orbit once around Earth.

Credit: ESA/ D. Ducros

INTEGRAL was launched on 17th October, 2002. Its mission is to study black holes, neutron stars, pulsars, active galactic nuclei, Supernovae, Gamma Ray Bursts etc.

It's the most sensitive gamma-ray Observatory ever launched. To detect Gamma rays from the objects in the universe an instrument needs to go in space because Earth's protective layer prevents them from reaching the ground.

INTEGRAL can observe objects in gamma-rays, X-rays and visible light. There are two detectors on INTEGRAL to detect gamma rays from space - an imager (IBIS - Imager on-board INTEGRAL) and an spectrometer (SPI - Spectrometer on INTEGRAL). Other two instruments are JEM-X (Joint European X-ray Monitor) and OMC (Optical monitoring Camera). OMC can detect stars with visual magnitude up to 19.7. It's a standard optical refractor with 5-cm lens and a CCD of 2055×1056 pixels in the focal plane.

On 14th August, the merger of two neutron stars that triggered the LIGO detectors fifth time also triggered the instruments on board INTEGRAL. And It was recorded as a 2 second gamma-ray-burst prior to the gravitational wave detection.

It became the first event to be observed in gravitational waves and in electromagnetic spectrum by lots of ground based and space based Telescopes in addition to the LIGO detectors.