Star Properties

Where do stars come from?

• Stars form in a cloud of dust and gas in space called a nebula.

How do stars form?

1. A force from outside the nebula causes the cloud to condense into stars. – Example: a shockwave

2. Gravity causes the particle in the cloud to contract.– This causes and increase in temperature.

3. As the cloud becomes larger and its temperature increases, certain parts of the cloud will begin to glow.4. The glowing sections of a cloud are called stars.

What are stars made of?

• Hydrogen – 69%• Helium – 29%• Heavy Metals and other gasses (oxygen,

carbon, nitrogen, sodium) – 1-2%

How hot are stars?

• We can tell the approximate temperature of a star by looking at its color.

• 30,000°C = Blue• 3,000°C = Red• Our Sun = 5,500°C

Key terms related to star distance:

• Parallax – the apparent shift in star position.• Astronomical Unit (AU) – the mean distance

between the Earth and the Sun. (150 million km or 93 million miles)

• Light Year – the distance light travels in one year. (9.5 trillion km)

Key terms related to star distance:

• Apparent Magnitude – how bright a star appears to be to an observer on Earth (adjusted to the value it would have in the absence of the atmosphere). The lower the magnitude, the brighter the star. Our sun is -26.7 apparent magnitude.

• Absolute Magnitude – the brightness of a star if the star where the same distance from Earth.

Key terms related to star distance:

• Luminosity – the brightness of a star, due to energy given off.

• Seasonal Constellations – constellations change position in the night sky throughout the year due to Earth’s movement around the sun.– Orion = seen in winter– Lyra = seen in summer

Life Cycle of StarsNebula

Main-sequence star

Red Giant

White Dwarf

Black Dwarf

Supergiant

Supernova

Neutron Star Black Hole

Increasing Mass

Incr

easi

ng T

ime

NebulaA dark cloud of dust and gas.

Life Cycle of StarsNebula

Protostar

Main-sequence star

Red Giant

White Dwarf

Black Dwarf

Supergiant

Supernova

Neutron Star Black Hole

Increasing Mass

Incr

easi

ng T

ime

Protostar

• Forms at the center of a shrinking spinning nebula

Life Cycle of StarsNebula

Protostar

Main-sequence star

Red Giant

White Dwarf

Black Dwarf

Supergiant

Supernova

Neutron Star Black Hole

Increasing Mass

Incr

easi

ng T

ime

Main-Sequence Stars

• Second, longest and most stable stage in the life of a star.

Life Cycle of StarsNebula

Protostar

Main-sequence star

Red Giant

White Dwarf

Black Dwarf

Supergiant

Supernova

Neutron Star Black Hole

Increasing Mass

Incr

easi

ng T

ime

Red Giant

• Third Stage, star expands greatly and cools• 10 times bigger than the sun

Life Cycle of StarsNebula

Protostar

Main-sequence star

Red Giant

White Dwarf

Black Dwarf

Supergiant

Supernova

Neutron Star Black Hole

Increasing Mass

Incr

easi

ng T

ime

Red Supergiants

• Third stage, star expands greatly and cools.• 100 times bigger than the Sun

Life Cycle of StarsNebula

Protostar

Main-sequence star

Red Giant

White Dwarf

Black Dwarf

Supergiant

Supernova

Neutron Star Black Hole

Increasing Mass

Incr

easi

ng T

ime

White Dwarfs

• Small, hot, dim star.

Life Cycle of StarsNebula

Protostar

Main-sequence star

Red Giant

White Dwarf

Black Dwarf

Supergiant

Supernova

Neutron Star Black Hole

Increasing Mass

Incr

easi

ng T

ime

Black Dwarf

• Dead stars• None actually found in existence.

Life Cycle of StarsNebula

Protostar

Main-sequence star

Red Giant

White Dwarf

Black Dwarf

Supergiant

Supernova

Neutron Star Black Hole

Increasing Mass

Incr

easi

ng T

ime

Supernova

• The explosion of a star.– Most famous = 1987, Large Magellanic Cloud. The

explosion produced subatomic particles called neutrinos.

• First recorded by the Chinese in 1054 A.D.– Outer shell became the Crab Nebula – part of

Taurus the Bull constellation

Life Cycle of StarsNebula

Protostar

Main-sequence star

Red Giant

White Dwarf

Black Dwarf

Supergiant

Supernova

Neutron Star Black Hole

Increasing Mass

Incr

easi

ng T

ime

Neutron Star

• Mass of remaining material from a supernova explosion.

• Can become a pulsar.– Fastest pulsar was 642 times a second. (called

millisecond pulsars)

Life Cycle of StarsNebula

Protostar

Main-sequence star

Red Giant

White Dwarf

Black Dwarf

Supergiant

Supernova

Neutron Star Black Hole

Increasing Mass

Incr

easi

ng T

ime

Black Holes• Called an invisible star.• Caused by the strong gravitational pull of the star.• Produces no light.• Instead they are seen indirectly by the energy

given off by a nearby visible star.• Conditions for Black Hole Classification:– X-rays must come from an area where one star is visible

and another is invisible.– The invisible star must have a mass 3 times larger than

the sun.– Telescopes must be able to detect it.

Galaxies

• There are billions of galaxies in the universe.• Galaxies contain billions of stars.• Milky Way has around 100 billion stars.

Three Main Types of Galaxies

• Spiral• Elliptical• Irregular

Spiral• Central nucleus• Flattened arms of stars that spiral around the

nucleus• Contains millions of young stars, gas and dust

Elliptical

• Spherical (football shaped) to flattened disks

• No arms• No young stars• Very little dust or gas

Irregular

• Smaller and fainter than other types of galaxies

• Stars are spread out evenly

• Very uncommon

Quasars• Discovered in 1961• Most luminous objects in the universe• Most distant objects observed in the universe• A star like object that radiates light and radio

waves at very high rates.– Scientists believe quasars are whole galaxies in the

early stage of development.

Quasar PKS 1127-14510 million light years away

Big Bang

• All the matter and energy in the universe was concentrated in an extremely small volume.

• Approximately 13.8 billion years ago the Big Bang occurred and forming a large expanding cloud.– Subatomic particles to what exists today.

• Most widely accepted theory explaining the formation of the universe

Big Bang (cont.)

• Evidence of the Big Bang– 1929, Edwin Hubble related the origin of the

universe to the Doppler Effect– Doppler Effect – measures the shift in wavelength

on the electromagnetic spectrum.• Redshift = bodies are moving away from each other =

increase in wavelength– Redshift is happening in the universe now.

• Blueshift = celestial bodies are moving towards each other = decrease in wavelength