5.5 Astrophysics & Cosmology

These flashcards cover fundamental concepts and definitions related to astronomy, the evolution of stars, and cosmological phenomena.

What is a planet?

Objects with mass sufficient for gravity to make them spherical, have cleared their orbit and do not undergo nuclear fusion.

What defines a dwarf planet?

A planet whose orbit has not been cleared of other objects.

What are planetary satellites?

Bodies that orbit around a planet.

What are asteroids?

Small, unevenly shaped objects with near circular orbits around the sun.

What are comets?

Small, irregularly sized bodies made of rock, dust, and ice, orbiting the sun in eccentric shapes.

What constitutes a solar system?

A system containing stars and orbiting objects like planets.

What is a galaxy?

A collection of stars, dust, and gas, typically containing around 100 billion stars.

What are nebulae?

Giant clouds of dust and gas, and the birthplace of all stars.

What is a protostar?

A very hot, dense sphere of dust and gas formed when gravitational collapse occurs in a nebula.

What is nuclear fusion?

The process whereby hydrogen nuclei in a protostar fuse to form helium under high temperature and pressure.

What is the main phase of a star?

The stable equilibrium stage of a star where gravitational forces and radiation pressure balance each other.

What happens to low mass stars after the main phase?

They collapse, evolve into red giants, then into white dwarfs, shedding outer layers as planetary nebulae.

What prevents a white dwarf from collapsing?

Electron degeneracy pressure, which arises because two electrons cannot exist in the same state.

What is the Chandrasekhar limit?

The core mass limit of 1.44M☉ for which a white dwarf remains stable.

What occurs in the evolution of a massive star?

It expands into a red supergiant, fuses helium into heavier elements, followed by a type 2 supernova.

What are neutron stars?

Extremely small, dense stars formed when the core mass of a supernova is greater than 1.44M☉.

What is a black hole?

An object with a core mass greater than 3M☉, with escape velocity exceeding the speed of light.

What does the Hertzsprung-Russell (HR) diagram plot?

The stellar luminosity of a star against its temperature.

What happens when an atom's electron is excited?

It moves from a lower energy state to a higher energy state, requiring external energy.

What is the emission line spectrum?

A unique spectrum of colored lines produced by each element due to its distinct energy levels.

What are absorption line spectra?

Dark spectral lines present against a continuous spectrum, corresponding to specific energy levels.

What is the Doppler Effect?

The apparent shift in wavelength of waves from a source moving relative to an observer.

What does Hubble's law state?

The recessional velocity of a galaxy is proportional to its distance from Earth.

What is the Big Bang theory?

A theory describing the origins of the universe from a singularity, which has been expanding since.

What constitutes dark matter?

A type of matter that does not interact with light, making up about 27% of the universe's mass.

What role does dark energy play in the universe?

It hypothesized to fill all space and drive the acceleration of the universe's expansion.

What is the role of gravity in astrophysics?

Gravity is the force that governs the behavior of objects in the universe, influencing the motion of planets, stars, and galaxies.

What is dark energy?

A mysterious form of energy that makes up approximately 68% of the universe, thought to be responsible for its accelerated expansion.

What is the Cosmic Microwave Background (CMB)?

The remnant radiation from the Big Bang, it is a faint glow that fills the universe and provides evidence for the Big Bang theory.

What are supernovae?

Explosive deaths of stars that result in a dramatic increase in brightness and can briefly outshine entire galaxies.

What is the significance of redshift in cosmology?

Redshift is the increase in wavelength of light from distant galaxies, indicating that they are moving away from us, supporting the Big Bang theory.

What is the life cycle of a star?

The progression from stellar formation to main sequence, followed by its evolution into red giant or supergiant, and eventual death as a white dwarf, neutron star, or black hole.

What is gravitational lensing?

The bending of light from a distant object, such as a galaxy, caused by the gravity of an intermediate object, which can magnify the distant object's image.

What is the importance of spectroscopy in astrophysics?

Spectroscopy is used to analyze the light from stars and galaxies, providing information about their composition, temperature, density, mass, distance, and motion.