The Hindu : Taking a peep into the universe of the distant past

Online edition of India's National Newspaper
Monday, Aug 25, 2003

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National

Taking a peep into the universe of the distant past

By N. Gopal Raj

THIRUVANANTHAPURAM AUG. 24. The Space Infrared Telescope Facility (SIRTF) — the last of NASA's four Great Observatories — is to be launched tomorrow (Aug. 25). Like its predecessors, the Hubble Space Telescope, the Compton Gamma Ray Observatory and the Chandra X-ray Observatory, the SIRTF is expected to open new vistas for understanding the universe.

The telescope will allow the study of celestial objects which are either too cool, too dust-enshrouded or just too far away to be seen otherwise.

"The SIRTF will complete NASA's suite of Great Observatories, a programme that includes three previous missions that studied the universe with visible light, X-rays and gamma rays,'' says Ed Weiler, NASA's Associate Administrator for Space Science.

"Many cosmic objects produce radiation over a wide range of wavelengths. So it's important to get the whole picture.''

Most radiation emitted by stars, galaxies and other objects in the early universe now lies in the infrared region, which lies just beyond the red portion of visible light, which the human vision is able to perceive.

With the SIRTF, scientists will be able to look further back in space and time than was previously possible, and see the universe as it was billions of years ago, according to a NASA fact-sheet on the SIRTF.

Infrared spans a wide range of wavelengths, from the "near IR'', with wavelengths of one micron, to the "far IR'' with wavelengths of 200 microns and beyond (one micron is 1/50th the width of a human hair).

Different astronomical objects dominate distinct regions within the infrared spectrum. In the near infrared region, cooler stars such as red dwarfs and red giants glow brightly.

Astronomers will be exploiting this in their attempts to map the true distribution of stars in galaxies — a task that is nearly impossible in visible light because the brighter blue stars in a galaxy's spiral arms often drown out the older, dimmer stars in the main plane of the galaxy. Interstellar dust becomes transparent in the near and mid-infrared, allowing glimpses into star-forming regions and hearts of galaxies.

Among the science goals for the SIRTF listed in the NASA fact-sheet is the study of `brown dwarfs' — mysterious objects formed in the same way as stars but lacking the mass needed to ignite nuclear fusion. These "failed stars'' are therefore unable to shine.

A substantial amount of the mission's observing time will be spent examining circum-stellar discs of material surrounding young stars. Astronomers now think these discs are common when stars and then planets form. By observing circum-stellar discs of various ages, the mission will trace how they evolve into a mature system of planets.

The SIRTF will study processes in the birth and death of stars. Stars are born within cocoons of dust and dense molecular gas, a process mostly hidden from view at visible wavelengths.

But near IR will give astronomers a peek into this celestial birth.

The Observatory will also study the gaseous material ejected by stars at the end of their life, according to the NASA fact-sheet.

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