Astronomy chp14-16 test

Galaxy

a system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.

Galaxy Cluster

a gravitationally bound grouping of galaxies, ranging from hundreds to tens of thousands

Hubble’s law

The observation that galaxies are moving away from each other.

Look-Back Time

The time elapsed between when we detect the light vs when it was originally emitted by the source. (How far back are we looking at this object).

Redshift

An increase in wavelength. Showing us that an object is going further away.

Blueshift

A decrease in wavelength. Showing us that an object is coming closer.

Quasar

An extremely luminous active galactic nucleus. Emitting large amounts of energy.

Supermassive Black hole

Black holes with a mass above 100,000 solar masses.

Normal matter

Normal matter consists of the atoms that make up stars, planets, human beings and every other visible object in the Universe.

Dark matter

Matter that is not visible but helps shape the cosmos

MACHO

Massive Compact Halo Object – could help explain dark matter.

WIMP

Weakly interactive massive particles – hypothetical particles that help explain dark matter.

Hubble time

The time it took for the universe to expand to its present size. Estimated 13.8 billion years.

Big bang theory

How the universe began.

Dark energy

The proposed source of why the universe is expanding and accelerating

Cosmic microwave background

Radiation that fills all space in the observable universe

Density

How much matter is in an object. Mass / Volume

String theory

A theoretical framework in which subatomic particles are made up of vibrating strings.