Friday, December 18, 2015

ASTROSAT vs The Giant Hubble

A TV program on the legendary Hubble Space Telescope, HST (Hubble's Cosmic Journey, National Geographic), prompted me to write this piece on the recently launched Indian space telescope called ASTROSAT.  The purpose of Hubble Space Telescope is to break the barrier of 1-arc second seeing limit (full moon is about 1,800 arc-seconds across) from the ground which arises due to the atmospheric disturbances. NASA had achieved this by a mammoth effort of grinding a 2.4-meter glass to the curvature accuracy of 1/800,000 th of an inch and placing the school bus size object weighing 11,110-kg in 550-km orbit. ASTROSAT is India's  multi-wavelength telescope geared to look at the stellar objects primarily in UV, X-ray regions of the EM spectrum. In that TV program, the sweet voice of John Grunsfeld conveying his strong bond he had created in repairing the Hubble more than one time. Hubble is the most sophisticated optical experiment of humans in the space which has been working for 25-years and is going great guns.

In the back drop of this legacy; enters here,  the young-aspiring Indian beauty, ASTROSAT. In a typical Indian style of small-simple but effective, this telescope carries the same heritage as that of the Indian Chandrayaan-I (moon  mission) and MOM (Mars mission).  The idea of Indian scientists is to perform front line research from the existing experience in the country (X-ray astronomy); and hence majority of the hardware which went into is in the X-ray regime of EM spectrum. Considered to be a small size (in comparison to others) space telescope, it weighs 1513-kg at the time of lift off; it is basically a multi-wavelength telescope in a near equator orbit of around 650-kms radius.

Apart from performing the deep field survey of the Universe in the UV region; ASTROSAT's wish list covers a wide range of phenomenon which are taking place in the universe:
a. studying the high energy processes of binary star system (neutron star-black hole),
b. estimation of magnetic field of neutron stars,
c. look for star birth region beyond our galaxy,
d. detecting the new briefly appearing bright x-ray sources in the sky.

If I could drift a bit beyond the popular level flow of this presentation; here is the list of payloads, the instruments which are very well thought over and put together by the host of Indian research institutes: TIFR, IIA, IUCAA, PRL and RRI.

Credit: ISRO
The details given above emphasises that the Optical and UV region is covered by a single detector; great efforts have been put to cover a very wide range of X-ray based 4-instruments.

As they say, the proof of the pudding is in eating.... the ASTROSAT has come out with a flying colours as soon as its eyes were made to open.

On 17th November, when the Swift observatory of NASA made its 1000th observation of Gamma Ray Burst (GRB), the ASTROSAT's CTZI indeed picked the same object and hence the sweet news of success to the eagerly waiting Indian scientists. The observations are reported here .


Comparing Hubble Telescope with the ASTROSAT would be like comparing the legend Carl Lewis to that of a young athlete or in Indian terms, comparing Sachin Tendulkar to a Ranji trophy player. Without offending anyone, I must also add that both of these sport legends have indeed followed the same nascent stages. Hubble is a huge optical telescope to peek deep into the dark patches as seen from the ground telescopes. This was possible due to the avoidance of atmospheric disturbances. Where as, ASTROSAT is a multi-wavelength observing telescope; may not be huge in size but carries a state-of-the art X-ray detectors and a combined UV-Visible detector in aiming the similar deepest in-accessible "dark regions". With the success of operation of most of the detectors, it is only the time which is going to unravel the worthiness of all the hard work of Indian scientists. Best of luck INIDA..... 

Hubble Space Telescope

As has been referred here, Hubble is a legend in opening the eyes of humanity into the darkest regions of skies. Hubble basically is an optical observatory with an viewing ability of better than 0.1-arc second, having the 3-different types of sensors: i. Camera, ii. Spectrograph and iii. Photometer. A daring 5-space walks had fixed the flaw in achieving the intended goals of Hubble imagery; a total of 4-repairing attempts have kept the instrument in its best abilities.

Here is the summary of few greatest achievements of Hubble:
  • Identification of dark matter which is otherwise invisible and comprises around 23% of the entire universe could be modelled into 3-D from the observations of Hubble
  • Hubble discovered 2-new moons of Pluto : Nix, Hydra
  • Identification of star forming regions, e.g. Orion nebula
  • Picking up gamma ray bursts (GRB) and resolving the mystery around them
  • Capturing the famous collision of comet Shoemaker-Levy with planet Jupiter
  • Helped to identify the dark energy which is responsible for expansion of universe
  • Super massive black holes may be lurking in many galaxies that have bulge of stars at the centre
  • Observing the atmosphere of exo-planet (in Visible)
The list goes on.... and is still counting.....

The humble : ASTROSAT

The unique capabilities of ASTROSAT lies in its multi-wavelength capabilities of observing stellar objects.
  • The Large Area X-Ray Proportional Counter (LAXPC) stands out among all the available space telescopes (RXTE, HEXTE, SAX); by offering almost 3-times larger area at 40-keV energy x-rays.
  • The LAXPC will also offer best timing studies; helping the observers to study the strong gravity regions around neutron stars and stellar mass black holes
  • LAXPC will also serve  as a complimentary instrument for the present/upcoming spectroscopic observations (Chandra, XMM-Newton, NuSTAR, ASTRO-H)
  • Sensitive hard X-ray spectroscopy
  • Wide spectral coverage : UV, 0.3-150 keV

RXTE : The Rossi X-ray Timing Explorer
HEXTE : High Energy Timing Experiment
SAX: Beppo SAX, Italian Dutch Satellite for X-ray astronomy
MOM: Mars Orbiter Mission

Lunar water; Who dunit ??