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AstroSat's Ultraviolet Imaging Telescope

Recently, Astronomers from the Indian Institute of Astrophysics (IIA) have spotted rare hot Ultraviolet (UV)- bright stars in Milky Way’s massive intriguing globular cluster called NGC 2808 that is said to have at least five generations of stars.
The team captured these stars using Ultraviolet Imaging Telescope (UVIT) onboard AstroSat, India’s first multiwavelength space satellite.

The team of scientists from IIA combined the UVIT data with observations made using other space missions such as the Hubble Space Telescope and the Gaia telescope along with ground-based optical observations.
These rare hot Ultraviolet (UV) bright stars, whose inner core is almost exposed, making them very hot, exist in the late stages of evolution of a Sun-like star.
It is not clear how these stars end their lives as not many of them are detected in these fast-evolving phases, making this study crucial.
With spectacular UV images of the cluster, they distinguished the hot UV-bright stars from the relatively cooler red giant and main-sequence stars which appear dim in these images.
Most of the stars were found to have evolved from a solar stage called the horizontal branch stars with hardly any outer envelope. Thus, they were bound to skip the last major phase of life called the asymptotic giant phase and directly become dead remnants or white dwarfs.
Such UV-bright stars are speculated to be the reason for the UV radiation coming from old stellar systems such as elliptical galaxies which are devoid of young blue stars. Hence, it is all the more important to observe more such stars to understand their properties.

The scientists combined the UVIT data with observations made using other space missions such as the Hubble Space Telescope and the Gaia telescope along with ground-based optical observations.
About 34 UV-bright stars were found to be members of the globular cluster. From the data, the team derived the properties of these stars such as their surface temperatures, luminosities and radii.
One of the UV-bright stars was found to be about 3,000 times brighter than the Sun with a surface temperature of about 1,00,000-K (Kelvin). The properties of these stars were then used to place them on what astronomers call the Hertzsprung-Russel (HR) diagram along with theoretical models to throw light on the characteristics of their parent stars and to predict their future evolution.

AstroSat is the first dedicated Indian astronomy mission aimed at studying celestial sources in X-ray, optical and UV spectral bands simultaneously.
The payloads cover the energy bands of Ultraviolet (Near and Far), limited optical and X-ray regime (0.3 keV to 100keV).
One of the unique features of AstroSat mission is that it enables the simultaneous multiwavelength observations of various astronomical objects with a single satellite.
AstroSat with a lift-off mass of 1515 kg was launched on September 28, 2015 to the equator by PSLV-C30 from Satish Dhawan Space Centre, Sriharikota.
In September 2020, AstroSat completed five years in orbit.

To understand high energy processes in binary star systems containing neutron stars and black holes;
Estimate magnetic fields of neutron stars;
Study star birth regions and high energy processes in star systems lying beyond our galaxy;
Detect new briefly bright X-ray sources in the sky; and
Perform a limited deep field survey of the Universe in the Ultraviolet region.