What is a galaxy group?

A collection of 3-50 galaxies gravitationally bound to each other, spanning a few million light-years A single galaxy with more than 50 individual spiral arms A collection of thousands of galaxies packed into a few thousand light-years Any two galaxies that happen to be photographed near each other in the sky

What is the Local Group?

The galaxy group containing the Milky Way, Andromeda (M31), Triangulum (M33), and about 80 total galaxies, spanning roughly 10 million light-years Just the Milky Way and its satellite galaxies The name of the 50 nearest stars to our solar system The nearest galaxy cluster containing over 1,000 galaxies

What makes galaxy clusters different from galaxy groups?

Clusters are exactly like groups but younger Clusters are much larger, containing hundreds to thousands of galaxies over 5-30 million light-years, with hot X-ray-emitting gas and large amounts of dark matter Clusters contain only elliptical galaxies while groups contain only spirals Clusters are gravitationally unbound collections of galaxies passing through the same region

What is the Virgo Cluster, and why is it significant to us?

The galaxy cluster our Milky Way will eventually merge with The nearest large galaxy cluster, about 54 million light-years away with roughly 1,300 galaxies; our Local Group sits on its outer edge A small cluster of stars inside the Milky Way visible in the constellation Virgo The cluster of galaxies that contains the quasar 3C 273

What is the hot intracluster medium?

The cool gas clouds between galaxies in a group where new stars are forming Extremely hot gas at 10-100 million degrees filling the space between galaxies in a cluster, emitting X-rays The dark matter that fills the space between galaxy clusters The interstellar medium inside the Milky Way disk

What is the Coma Cluster, and what important discovery was made using it?

A galaxy cluster about 330 million light-years away used by Fritz Zwicky in 1933 to first propose dark matter based on anomalously high galaxy velocities The largest galaxy cluster ever discovered, containing over one million galaxies A galaxy cluster inside the Local Group that orbits the Milky Way A galaxy cluster used by Hubble to discover the expansion of the universe

Why did Fritz Zwicky conclude that galaxy clusters must contain dark matter?

The cluster's X-rays were too bright to be produced by the visible galaxies alone The galaxies in the Coma Cluster were moving much faster than the visible mass could hold together — something invisible must provide extra gravitational force The cluster was bending light from behind it more strongly than expected (gravitational lensing) Individual stars in cluster galaxies were orbiting their galactic centers too fast

How large is the Local Group?

About 100,000 light-years across — same as the Milky Way About 10 million light-years across About 1 billion light-years across About 500 million light-years across

What are the three largest galaxies in the Local Group?

The Milky Way, the Large Magellanic Cloud, and the Small Magellanic Cloud Andromeda (M31), the Milky Way, and Triangulum (M33) Andromeda (M31), the Milky Way, and the Virgo Cluster Andromeda (M31), the Virgo Cluster, and Centaurus A

What type of radiation do galaxy clusters primarily emit because of their hot intracluster gas?

Visible light, because the hot gas glows like a giant fluorescent lamp Radio waves, because the magnetic fields in the gas produce synchrotron radiation X-rays, because the gas is heated to 10-100 million degrees and glows at X-ray wavelengths Infrared radiation, because the gas is cool compared to stellar surfaces