Astrophysics and Cosmology

The Twin Paradox is a famous thought experiment in special relativity where one twin travels at high speed and returns younger than the other. It demonstrates time dilation, not gravitational motion or classical mechanics.

A black hole appears black because its gravitational pull is so strong that nothing, not even light, can escape from it. All light that approaches the event horizon gets absorbed into the black hole. This is why we cannot see black holes directly - we can only detect them through their effects on surrounding matter.

Einstein's General Theory of Relativity (1915) provides the theoretical framework for understanding black holes. The theory describes how massive objects warp spacetime, and extreme curvature can create black holes where escape velocity exceeds light speed.

Stars can end their lives as black holes when they have sufficient mass (typically >20 solar masses) and undergo gravitational collapse after supernova explosions. Planets, comets, and asteroids lack the required mass.

A star needs approximately 1.5 to 3 times the mass of the Sun to potentially form a black hole after its death. Stars with less mass typically become white dwarfs or neutron stars.

The event horizon is the boundary surrounding a black hole, beyond which nothing can escape - not even light. It marks the 'point of no return' where the gravitational pull becomes so strong that escape velocity exceeds the speed of light. Option D is a reference to a film, not a physics concept.

According to the no-hair theorem, black holes are characterized by only three properties: mass, electric charge, and angular momentum. Linear momentum is not a fundamental property used to describe a black hole's state. A black hole can have momentum through its motion, but it's not one of its defining intrinsic properties.

Gravitational microlensing occurs when a black hole passes between Earth and a distant star, causing the star's light to bend and brighten temporarily. This effect allows detection of isolated black holes that aren't actively accreting matter. Black holes themselves don't emit visible light, making direct observation impossible, but their gravitational effects betray their presence.

Subrahmanyan Chandrasekhar calculated the Chandrasekhar limit (~1.4 solar masses) - the maximum mass for a white dwarf star before gravitational collapse into a neutron star or black hole. Schrodinger, Feynman, and Einstein made different contributions to physics.

At a singularity, density and spacetime curvature become infinite according to general relativity, but temperature does not necessarily become infinite. The concept of infinite temperature at a singularity is not a standard prediction of classical general relativity.

Nearly every large galaxy, including our Milky Way, has a supermassive black hole at its center. These range from millions to billions of solar masses. Our galaxy's Sagittarius A* is about 4 million solar masses. They power galactic centers and influence star formation.

General relativity, proposed by Einstein in 1915, describes gravity not as a force but as the curvature of spacetime caused by mass and energy. The theory states that the laws of physics are the same for all observers regardless of their motion. It explains gravitational phenomena as objects following the curved geometry of 4-dimensional spacetime. This framework successfully predicts black holes, gravitational lensing, and the expanding universe.

A naked singularity is a hypothetical gravitational singularity without an event horizon. Unlike black holes, which hide their singularities behind event horizons, a naked singularity would be visible from outside. This concept challenges the Cosmic Censorship Hypothesis, which proposes that all singularities must be hidden behind event horizons. Naked singularities remain theoretical and have not been observed.