PASIPHAE

Polar-Areas Stellar-Imaging in Polarization High-Accuracy Experiment (PASIPHAE) is an international collaborative sky surveying project.
Aim: To study the polarization in the light coming from millions of stars.

A light wave that is vibrating in more than one plane is referred to as unpolarized light.Polarized light waves are light waves in which the vibrations occur in a single plane.A polarimeter is an optical instrument with which one can accurately measure the angle by which the polarization of light is rotated.

The survey will use two high-tech optical polarimeters to observe the northern and southern skies,
It will focus on capturing starlight polarization of very faint stars that are so far away that polarization signals from there have not been systematically studied yet.
The distances to these stars will be obtained from measurements of the GAIA satellite.

Global Astrometric Interferometer For Astrophysics (GAIA) is a space observatory of the European Space Agency (ESA), launched in 2013. The spacecraft is designed for astrometry: measuring the positions, distances and motions of stars with unprecedented precision.The mission aims to construct by far the largest and most precise 3D space catalog ever made, totalling approximately 1 billion astronomical objects, mainly stars, but also planets, comets, asteroids and quasars, among others.

By combining these data, astronomers will perform a maiden magnetic field tomography mapping of the interstellar medium of very large areas of the sky using a novel polarimeter instrument known as WALOP (Wide Area Linear Optical Polarimeter).
- Interstellar medium (ISM) is the matter and radiation that exist in the space between the star systems in a galaxy.
- Tomography is the representation of a cross section of solid object using X-rays.

Why is PASIPHAE important?

Since its birth about 14 billion years ago, the universe has been constantly expanding, as evidenced by the presence of Cosmic Microwave Background (CMB) radiation which fills the universe.

The Cosmic Microwave Background (CMB) is the cooled remnant of the first light that could ever travel freely throughout the Universe. This 'fossil' radiation, the furthest that any telescope can see, was released soon after the 'Big Bang'. Scientists consider it as an echo or 'shockwave' of the Big Bang.

Immediately after its birth, the universe went through a short inflationary phase during which it expanded at a very high rate, before it slowed down and reached the current rate.
However, so far, there have only been theories and indirect evidence of inflation associated with the early universe.
Consequence of the inflationary phase - A tiny fraction of the CMB radiation has its imprints in the form of a specific kind of polarisation(known scientifically as B-mode signal).
All previous attempts to detect this signal met with failure mainly due to the difficulty posed by our galaxy, the Milky Way, which emits copious amounts of polarized radiation.
Besides, it contains a lot of dust clouds that are present in the form of clusters.
When starlight passes through these dust clouds, they get scattered and polarised.
In a nutshell, the galactic emission is so bright that the polarisation signal of CMB radiation is lost.

The role of Pasiphae

The PASIPHAE survey will measure starlight polarization over large areas of the sky.
This data along with GAIA distances to the stars will help create a 3-Dimensional model of the distribution of the dust and magnetic field structure of the galaxy.
Such data can help remove the galactic polarised foreground light and enable astronomers to look for the elusive B-mode signal.

What is WALOP?

It is an instrument, when mounted on two small optical telescopes, will be used to detect polarised light signals emerging from the stars along high galactic latitudes.

Previous Robopol Experiment

RoboPol experiment survey during 2012-2017 was the predecessor of WALOPand it has a much smaller field of view in the sky.
But both WALOP and its predecessor RoboPol share the single shot photometry principle.

Photometry, in astronomy, is the measurement of the brightness of stars and other celestial objects (nebulae, galaxies, planets, etc.). Such measurements can yield large amounts of information on the objects’ structure, temperature, distance, age, etc.

Watch this video for better understanding: https://youtu.be/OQVXNSmgQ3E