Cosmology and Astrophysics Quiz

The branch of physics that studies the universe's origin, evolution, and fate, drawing knowledge from astrophysics, observational astronomy, General Relativity, and particle physics.

The standard model of modern cosmology, assuming the universe is isotropic and homogeneous with a Big Bang origin.

The distance between stars, usually expressed in parsecs (pc).

A collection of billions of stars, gas, and dust held together by gravity.

Groups of galaxies bound together by gravity.

Groups of clusters of galaxies, forming larger structures in the universe.

Large empty regions between superclusters of galaxies.

The observation that galaxies are moving away from each other at speeds proportional to their distance.

The redshift of a galaxy is a measure of how much its light has been stretched due to the expansion of the universe. It is calculated as the difference between the observed wavelength of a spectral line and the rest wavelength of the same line, divided by the rest wavelength.

The 21-cm emission line is a spectral line emitted by neutral hydrogen atoms. It is a very important tool for studying the distribution of neutral hydrogen in the universe.

Cepheid variables are stars that pulsate at a rate that is directly related to their absolute brightness. By measuring the pulsation period of a Cepheid variable, we can determine its absolute brightness, and then use its apparent brightness to calculate its distance.

Photometry measures the brightness of an object, while spectroscopy measures the detailed spectrum of light emitted or absorbed by an object. Spectroscopy can reveal the composition and motion of the object.

A graph plotting the luminosity of stars against their surface temperature, with stars categorized into main sequence, giants, supergiants, and white dwarfs.

A plot showing the change in apparent magnitude (brightness) of a variable star over time.

A relationship between the period of a Cepheid variable star and its luminosity, used to measure distances to galaxies.

The expansion of space itself, causing light from distant objects to be stretched to longer wavelengths, leading to a redshift.

A model proposing that, on large scales, the universe is homogeneous and isotropic, meaning it appears the same in all directions and locations.

The universe is expanding, but galaxies within clusters stay bound due to their mutual gravitational attraction.

Using Hubble's law, we can estimate the age of the universe by calculating the time it took for galaxies to reach their current distances.

The distance light can travel in 13.4 billion years, defining the observable universe.

The event where the universe was incredibly dense and began expanding, marking the origin of the cosmos.

Hubble's law only applies to large-scale movements governed by the cumulative gravitational force of evenly spread matter.

The expansion of the universe doesn't violate the speed of light because it's space itself stretching, not objects moving.

A faint afterglow of the Big Bang, observed as microwave radiation from all directions.

The presence of Helium in the universe, which is more than expected from star formation, is a key evidence of the Big Bang.

Photons from the early universe have undergone a redshift due to the expansion of the universe, resulting in their energy being lowered and wavelength increased.

A measure of the energy density of dark energy relative to the critical density of the universe. It is a dimensionless quantity that quantifies the contribution of dark energy to the total energy budget of the universe. Its estimated value is around 0.76.

The observation that the expansion of the universe is accelerating, meaning that the rate at which galaxies are moving apart is increasing over time. This is attributed to the repulsive effect of dark energy.

The theoretical model of the universe where its expansion is accelerating due to the presence of a constant energy filling space called dark energy, consistent with observations of distant supernovae.

The theory that a hypothetical energy filling the universe uniformly contributes to its accelerating expansion. This is one of the candidates for dark energy, but the precise nature of this constant energy remains a mystery.

The redshift of a galaxy is a measure of how much its light has been stretched due to the expansion of the universe. It is calculated as the difference between the observed wavelength of a spectral line and the rest wavelength of the same line, divided by the rest wavelength.

The velocity at which a galaxy is receding from us due to the expansion of the universe. It is calculated using the redshift of the galaxy and the Hubble Constant.

The expansion rate of the universe, describing the speed at which galaxies are moving apart due to the expansion of space. It is estimated to be approximately 70 km/s/Mpc, meaning that for every megaparsec (Mpc) further away a galaxy is, it is moving approximately 70 kilometers per second faster.

The distance to a galaxy or other celestial object, often determined by combining its recession velocity with the Hubble Constant.

The Cosmic Microwave Background (CMB) is a faint afterglow of the Big Bang, a uniform radiation bath filling the entire universe. It acts as a time capsule, offering insight into the universe's early state and evolution.

The CMB spectrum closely matches that of a blackbody, indicating it originated from a very hot, dense state. This provides strong evidence for the Big Bang theory.

Tiny temperature variations in the CMB, called anisotropies, reveal regions of slightly higher and lower density in the early universe. These variations ultimately led to the formation of galaxies and large-scale structures we see today.

Regions of the CMB with higher density gave rise to galaxies, while regions with lower density became voids. This pattern reflects the initial clumpiness of matter in the early universe.

Measuring the angles of a triangle formed by distant objects allows us to deduce the curvature of space. If the angles sum to less than 180 degrees, space is hyperbolic (curving outwards). If the angles sum to 180 degrees, space is flat. If the angles sum to more than 180 degrees, space is spherical (curving inwards).

The measurement of space curvature involves placing powerful light sources and detectors at the vertices of a triangle, with sides spanning billions of light-years, to determine the sum of its angles.

The shape of the universe is determined by its curvature. A hyperbolic universe is infinite and open, while a spherical universe is finite and closed. A flat universe represents an intermediary state between these extremes.

Observations reveal that the universe is nearly flat, indicating its overall curvature is very close to zero. This implies that it will continue to expand indefinitely but at a slowing rate due to gravity.