Galactic Structure and Seyfert Galaxies

These flashcards cover essential vocabulary and definitions related to the structure of the galaxy, the properties of celestial bodies, and characteristics of Seyfert galaxies.

Galactic Halo

An approximately spherical region surrounding the galactic disk and bulge, characterized by low stellar density and a power-law density profile.

Power-Law Density Profile

A mathematical description of density variations with distance; for the halo, it follows 𝜗(R) ∝ R^-3.

Velocity Dispersion

A statistical measure that characterizes how fast individual stars in a halo move in various directions, helping estimate the mass of the galaxy.

Virial Theorem

A theorem used to relate the average kinetic energy of particles in a system to the average potential energy, allowing for mass estimates of celestial bodies.

Mass-to-Light Ratio

A ratio indicating the amount of mass compared to the amount of light emitted; high values suggest the presence of dark matter.

Cepheid Variable Stars

Pulsating stars whose brightness varies in a regular pattern, used to determine distances to galaxies through the period-luminosity relation.

Hubble Law

A law stating that the recession velocity of a galaxy is proportional to its distance from the observer, leading to the conclusion that the universe is expanding.

Intra-Cluster Medium (ICM)

A hot and dense gas found in galaxy clusters, often reaching temperatures of millions of degrees Kelvin.

Active Galactic Nuclei (AGN)

Extremely bright, compact regions at the cores of some galaxies, powered by supermassive black holes accreting material.

Accretion Disk

A rotating disk of gas and dust surrounding a supermassive black hole, where friction generates heat and emits radiation.

Seyfert Galaxy

A type of galaxy characterized by a bright active galactic nucleus, exhibiting narrow and broad emission lines due to energetic processes near a supermassive black hole.

Photon Sphere

A region around a black hole where light can orbit the black hole due to the intense gravitational field.