Unit 2- Stars

Stars Earth circles the sun (star). Billions in space To measure distances between stars we a distance measurement called the Light- year.

Light-Year 1 light-year is the distance light travels in one year. Light moves at 300,000 km/sec That’s 186,000 mile/sec Nearest star is 4.3light years away

Binary Stars Most stars are found in pairs that revolve around each other

Nova A star getting suddenly brighter Occurs in a binary star system Gases from one star are pulled into the other. Causes a nuclear explosion.

Nebula Gas and dust clouds in space. Most can’t be seen If they reflect light from nearby stars they can be seen Probably the birthplace of new stars

Activity on the Sun Storms on the sun: Prominences Solar Flares Sunspots

Prominences- Loops or arches of gas that rise from the chromosphere

Solar Flares- Bright bursts of light, huge amounts of energy released

Sunspots- Dark areas on the suns surface in the lower atmosphere

Stars Characteristics Are formed by the same forces Have different Size Composition Temperature Color Mass Brightness

Size 5 main categories Medium sized - like our sun from 1/10 size of sun to 10 times it’s size Giant stars- 10 to 100 times bigger than the sun Supergiant stars- 100 to 1000 times bigger than the sun

Size White dwarfs- smaller than 1/10 the size of the sun Neutron stars - smallest stars - about 16 km in diameter

Composition of Stars Determined with a spectroscope by the colors of light it gives off The lightest element Hydrogen makes up 60 - 80 % of a star Helium is second most 96-99 % is hydrogen and helium rest is other elements

Temperature Color also indicates temperature hottest surface 50000 °C Coolest 3000°C

Brightness Magnitude - measure of brightness Apparent magnitude - how bright it looks from earth Absolute magnitude - how bright it really is Variable stars - brightness changes from time to time

Hertzsprung-Russell Diagram Found that as temperature increased, so did absolute magnitude(brightness) 90% of stars followed this pattern Called main sequence stars Other 10% were once main sequence stars but have changed over time

Distance to Stars One method is parallax Apparent change in position as the earth goes around the sun Parallax works only to 100 light-years

Why Stars Shine Stars are powered by nuclear fusion Hydrogen atoms join to form helium Because gravity pulls the atoms in the core so close together Energy from sun is emitted as either light, heat, UV or x- rays

Corona- Outermost layer Temp=1,700,000ºC Few particles Chromosphere- middle of atmosphere Temp =27,800ºC 1000’s of km thick

Photosphere- Temp=6000ºC 550 km thick Surface of the sun Core- 1,000,000ºC 15,000,000ºC

Nebulae Huge cloud of gas and dust in space Used to form new stars

Star Life Cycles Stars change over time New stars form from nebulae Gravity pulls the dust and gas together Mostly hydrogen Forms a spinning cloud

Star Life Cycle When the temperature reaches 15,000,000 °C fusion begins Makes a protostar - a new star What determines the life cycle of the star is how much mass it starts with.

Medium-Sized stars Shine for a few billion years as hydrogen turns to helium. Helium core shrinks and heats up Outside expand and cool Gives off red light Becomes red giant

Medium-Sized Stars Helium in core turns to carbon Last of hydrogen gas drifts away to become a ring nebula or a planetary nebula. When last of helium is used up the core collapses and becomes a white dwarf Incredibly dense- a teaspoon will weigh tons

How long It depends on the mass. Smaller stars take longer From a few to 100 billion years for medium sized stars The sun will take about 10 billion years

Massive Stars Start with at least 6 times the mass of the sun. Become red giants The helium in the core becomes carbon and gets hotter. Carbon atoms fuse to form oxygen, nitrogen and iron

Death of Stars Stars become black dwarfs, neutron stars or black hole depending on its mass. 3 Categories: Sun-like Stars Huge Stars Giant Stars

Sun-like Stars Up to 1.5 times the mass of the sun

Huge Stars 1.5-3 times mass of the sun

Giant Stars Over 3 times the mass of the sun

Black Dwarf White dwarf- staple star; no nuclear fuel When all fuel is released turns into a black dwarf

Neutron Stars Stars that start out up to 2-8 times the mass of the sun The core of the exploding star collapses and becomes a neutron star. (Protons and Electrons combine to form neutron.) As massive as the sun, but only 16 km across. Give off pulses of radio waves If these radio waves come in pulses it is called a pulsar

Black holes If the star was bigger than 30 times the mass of the sun The left over core becomes so dense that light can’t escape its gravity. Becomes a black hole. Grab any nearby matter and get bigger As matter falls in, it gives off x-rays. That’s how they find them