Sky survey of stars: How PASIPHAE instrument would help scientists look into sudden expansion of universe

Scientists believe that the universe, soon after its formation, went through a phase where it expanded at a rapid pace, before slowing down. (Representational image)

PASIPHAE: As the scientific community across the world is looking to find answers behind the origin of the universe, an Indian astronomer is leading the development of an important instrument that is slated to be used for a sky survey to study the stars. According to a report in IE, the instrument development project is being backed by several of the leading institutions in the world. This indicates the growing stature of India in terms of its capability of building complex instruments for astronomical studies and research. The project is called Polar-Areas Stellar-Imaging in Polarisation High-Accuracy Experiment or PASIPHAE, which has been named after Greek Sun God’s daughter. This instrument would aid scientists in their study of polarisation in light coming from innumerable stars.

Two high-tech optical polarimeters would be used to simultaneously study the northern as well as the southern skies during the survey, the report said. The focus would be to capture starlight polarisation of very faint stars. These stars are very far away and therefore, their polarisation signals have not yet been studied in a systematic way. The GAIA satellite measurements would help in ascertaining the distances between these stars and the Earth.

With the help of these data and a novel polarimeter called the Wide Area Linear Optical Polarimeter or the WALOP, scientists would undertake a magnetic field tomography mapping of very large areas of the sky, the report added.

Scientists believe that the universe, soon after its formation, went through a phase where it expanded at a rapid pace, before slowing down. However, there is no direct evidence of such an inflationary expansion. Experts are of the view that a definitive consequence of this inflation is that some fraction of the Cosmic Microwave Background or CMB radiation should have left traces in a specific type of polarisation called the B-mode signal. But previous attempts of tracing this polarisation have largely failed due to the Milky Way’s high emission of polarised radiation. Apart from this, the high amount of dust cloud clusters also scatter and polarise starlight.

Scientists have compared trying to study the CMB radiation polarisation signal through the galaxy’s emission currently to trying to look at faint stars during the day.

This is where the PASIPHAE comes in. The instruments would calculate the polarisation of starlight over large portions of the sky, and then, with the help of distance measurements from GAIA, a three-dimensional model of galactic dust and magnetic field structure would be created. With this, the polarised foreground light due to the galaxy could be removed so that scientists could look for the B-mode signal.