Type: Prelims Only

Introduction

• Astronomers have triumphantly uncovered a rare class of stars, known as helium stars, after a decade-long quest.
• Led by Dr. Maria Drout from the University of Toronto, astronomers embarked on a collaborative mission to decipher the mysteries of these elusive cosmic entities

Helium Stars: An Overview

• Helium stars, also known as helium-burning stars, are a stage in the evolution of certain types of stars.
• These stars are typically more massive than the Sun and have exhausted the hydrogen fuel in their cores, leading to a contraction and subsequent heating of the core.
• As a result, helium fusion begins in the core, where helium nuclei fuse to form heavier elements such as carbon and oxygen.
• This fusion process releases energy, causing the star to expand and become more luminous.
• Helium stars represent an intermediate stage in stellar evolution between main-sequence stars and later stages such as red giants or supernovae.

Key Findings and Insights

• Spectral Analysis: Rigorous spectral analysis conducted from 2017 to 2024 unveiled distinct classes of helium stars based on hydrogen content, providing profound insights into their evolutionary trajectories.
• Computational Modeling: Advanced computational modelling techniques yielded crucial data on surface temperatures and gravitational forces, enriching our understanding of helium stars’ properties.
• Surface Conditions of Class 1 Stars: Further investigations into Class 1 helium stars revealed intriguing surface conditions. The team utilized computer modelling to determine surface temperature and gravity, finding them to be approximately 20 times hotter than the Sun and possessing surface gravity about 1,000 times stronger than Earth’s.

Significance of the Findings

• Hydrogen-Deficient Supernovae: A pivotal breakthrough in the discovery of helium stars was the elucidation of hydrogen-deficient supernovae, perplexing phenomena that puzzled scientists for decades.
• Binary-Star Interactions: Gravitational interactions within binary star systems played a crucial role in unmasking the helium-rich surfaces of these stellar anomalies.

Implications for Astrophysics

• Cosmic Laboratories: Helium stars serve as invaluable cosmic laboratories, offering unprecedented opportunities to explore the intricacies of stellar evolution and binary star dynamics.
• Frontiers of Research: Their discovery opens new frontiers in astrophysical research, unraveling mysteries surrounding heavy element formation and gravitational wave generation.

Introduction

• Indian Space Research Organisation (ISRO) has achieved a significant breakthrough in its quest for human spaceflight with the successful human rating of its CE20 cryogenic engine.
• The ground qualification tests, conducted at the High Altitude Test Facility at ISRO Propulsion Complex, Mahendragiri, have been successfully completed, validating the CE20 engine for the Gaganyaan programme.

About CE20 Cryogenic Engine

• It has been designed and developed by the Liquid Propulsion Systems Centre (LPSC), a subsidiary of ISRO.
• It is the first Indian cryogenic engine to feature a gas-generator cycle.
• It is one of the most powerful upper-stage cryogenic engines in the world.
• This engine develops a nominal thrust of 186.36 kN in vacuum.

Key Highlights of Ground Qualification Tests

• Thorough Evaluation: The CE20 engine underwent extensive testing, including evaluation under nominal and off-nominal conditions related to thrust, mixture ratio, and propellant tank pressure.
• Hot Firing Tests: Four engines underwent a total of 39 hot firing tests, accumulating a cumulative duration of 8,810 seconds, surpassing the minimum human rating qualification standard requirement of 6,350 seconds.

Update on First Unmanned Gaganyaan (G1) Mission

• Mission Objectives: The Gaganyaan project aims to demonstrate India’s human spaceflight capabilities by launching a crew of three members into a 400 km orbit for a 3-day mission, followed by a safe return to Earth with a landing in Indian sea waters.
• Acceptance Tests: ISRO has completed the acceptance tests of the flight engine designated for the first unmanned Gaganyaan (G1) mission, scheduled tentatively for the second quarter of 2024.
• Engine Specifications: The flight engine, which will power the upper stage of the human-rated LVM3 vehicle, boasts a thrust capability of 19 to 22 tonnes and a specific impulse of 442.5 seconds.

Introduction

• Recent findings published in the journal Nature suggest that beneath the icy shell of Mimas, there lies a potential liquid ocean, challenging previous assumptions about the moon’s composition and internal dynamics.

About Mimas

Astronomical Insights

• Potential Liquid Ocean: Scientists analyzed Mimas’s orbital motion using data from NASA’s Cassini spacecraft, concluding that the moon’s oscillations indicate the presence of either an elongated silicate core or a global ocean.
• Librational Model: Calculations based on Mimas’s librations and orbital changes reached a deadlock, prompting consideration of a subsurface ocean. Theoretical models incorporating viscoelastic outer layers and hydrostatic interior interfaces suggested an ice shell thickness of 20-30 km.
• Surface Heat and Eccentricity: Estimates indicate surface heat release of approximately 25 milliwatts per sq. m, expected to reduce Mimas’s eccentricity by half in 4-5 million years. Simulations suggest the ocean may have formed 2-25 million years ago, with potential hydrothermal activity.

Implications and Findings

• Comparative Analysis: Similarities between Mimas and Enceladus, another Saturn moon with a global ocean, hint at potential hydrothermal activity despite surface differences.
• Ice Shell Composition: The viscoelastic nature of Mimas’s outer icy layer and hydrostatic interior interfaces align with observations, supporting the theoretical ice shell thickness determined through calculations.