What Are the Different Types of Stars in the Sky?

Star Classification

• Astronomers categorize stars by their temperature and the elements they absorb.

  The star temperature range includes:

  • Class O and B (hot, bright)

  • Class A, F and G (medium brightness)

  • Class K and M (dim and cool).

  The star spectra range consist of:

  • Dark blue Class O and medium blue Class B

  • Pale blue Class A, white Class F and yellow Class G

  • Orange Class K and red Class M

Binary Stars

• • Many stars are binary, or double stars, that either revolve around each other, or simply appear close together from the viewpoint of Earth.

  • Eclipsing binaries are so close together, they look like one star of variable luminosity.

  • X-ray binaries contain one collapsed star (i.e. white dwarfs, black holes) linked to another star by gravity. The regular star's energy radiating onto the collapsed star generates X-rays.

Dwarfs

• The Sun is one of the smaller stars that will develop into a white dwarf, exhaust its nuclear fuels and then turn into black dwarfs. Dwarfs come in multiple colors:

  • Brown Dwarfs: stars that failed to erupt into regular stars.

  • White Dwarfs: small, dense and failing stars that are running out of fuel

  • Black Dwarfs: dead stars that don't glow

  • Yellow Dwarfs: small, main sequence stars (i.e. the Sun)

  • Red Dwarfs: cool, faint and nearly dead

Giants and Supergiants

• Giant star luminosity is 1,000 times greater than the Sun's, while supergiants glow 10 million times brighter. However, due to diminishing fuel supplies, they begin dying and eventually blow-up. Giant types includes:

  • Red Giants: fairly old, reddish-orange, increases to 100 times larger than original size

  • Blue Giants: enormous, hot, helium burning, on its way out.

  • Supergiant: largest known star-type (e.g. Rigel, Betelgeuse), become supernovas and turn into black holes.

Neutron Stars

• • Supernovas turn into neutron stars--stars that have collapsed, crushing their atoms until only the neutrons remain.

  • One teaspoon of a supernova/neutron star weighs as much as a mountain.

  • They revolve extremely fast--100s of times/second.

  • Pulsars, a type of neutron star, release radio wave pulses, like a light house beam.

Variable Stars

• • Variable stars waver in brightness, with fluctuations lasting from seconds to years.

  • Fluctuations occur at the beginning and end of star life, according to intrinsic or extrinsic variables.

  • Intrinsic variable: conditions inside the star change the brightness.

  • Extrinsic variable: external circumstances (i.e. orbiting companion stars) create the fluctuations.

  • Cepheid variables: a star's pulsating growth and shrinkage creates the variable brightness.