StarsStars

What is a star? Objects that heat and light the planets in a system A ball of plasma held together by its own gravity –Nuclear reactions (fusion) occur in stars (H  He) –Energy from the nuclear reactions is released as electromagnetic radiation

Stars are born with a specific mass Mass is the main factor in determining the star’s brightness, temperature, expected lifetime, type of death, and spectra. Classified according to their spectra

Astronomers realized that large numbers of stars exhibit a small number of distinct patterns in their spectral features.

Spectral lines are caused by different elements present in a star Overall spectrum is strongly related to the surface temperature of the star Stars are categorized into classes by: 1.Strength of the spectral lines 2.Shape

The 7 classes of stars are: O B A F G K M From O M: 1.Stars decrease in temperature 2.Stars generally become less massive (smaller)

O B A F G K M Oh Be A Fine Guy/Girl, Kiss Me! One Bug Ate Five Green Killer Moths

The Hertsprung-Russell or H-R diagram reveals that about 90% of all stars lie along a smooth diagonal curve called the main sequence with hot, luminous stars in the upper left and cool, dim stars in the lower right. Not all stars fall on the main sequence. Stars below the main sequence are called white dwarfs and those above it are called giants.

Since hotter stars are bluer, and cooler stars are redder, a White Dwarf is hotter than a Red Giant.

Color:blueColor: blue Temperature: 28, ,000 KTemperature: 28, ,000 K Size: very large and massiveSize: very large and massive Spectra: ionized helium, ultraviolet continuumSpectra: ionized helium, ultraviolet continuum Examples: 10 Lacertra, Zeta Puppis, and Iota Orionis AExamples: 10 Lacertra, Zeta Puppis, and Iota Orionis A The rock stars of the universe-they live fast and die young!

Color:blueColor: blue Temperature: 10, ,000 KTemperature: 10, ,000 K Size: large and massiveSize: large and massive Spectra: neutral helium lines,some hydrogenSpectra: neutral helium lines,some hydrogen Examples: Beta Centauri, Rigal, SpicaExamples: Beta Centauri, Rigal, Spica B stars are relatively rare, comprising only 0.1% of main sequence stars.

Color:whiteColor: white Temperature: 75, ,000 KTemperature: 75, ,000 K Size: moderate sized, very luminousSize: moderate sized, very luminous Spectra: strong hydrogen lines, ionized metalsSpectra: strong hydrogen lines, ionized metals Examples: Alpha Canis Majoris (Sirius) and Alpha Lyrae (Vega)Examples: Alpha Canis Majoris (Sirius) and Alpha Lyrae (Vega) A stars are amongst the most common naked eye stars.

Color: white-yellowColor: white-yellow Temperature: 6, ,000 KTemperature: 6, ,000 K Size: 1.2 to 1.6 times bigger than the SunSize: 1.2 to 1.6 times bigger than the Sun Spectra: weak hydrogen lines, strong Calcium and other ionized metalsSpectra: weak hydrogen lines, strong Calcium and other ionized metals Examples: Canopus, ProcyonExamples: Canopus, Procyon Often used as targets for extrasolar planet searches and SETI programs.

Color:Color: yellow Temperature: 5,000- 6,000 KTemperature: 5,000- 6,000 K Size: 0.8 to 1.1 times the mass of the SunSize: 0.8 to 1.1 times the mass of the Sun Spectra: weak hydrogen lines, neutral and ionized metalsSpectra: weak hydrogen lines, neutral and ionized metals Examples: Alpha Centauri A, CapellaExamples: Alpha Centauri A, Capella The best known example of a G star is our SUN!

Color: orangeColor: orange Temperature: 3,500- 5,000 KTemperature: 3,500- 5,000 K Size: smaller and cooler than the SunSize: smaller and cooler than the Sun Spectra: faint hydrogen lines, strong neutral metallic linesSpectra: faint hydrogen lines, strong neutral metallic lines Examples: Alpha Boötis (Arcturus) and Alpha Tauri (Aldebaran)Examples: Alpha Boötis (Arcturus) and Alpha Tauri (Aldebaran) Also used as targets for extrasolar planet searches like project Ozma in 1960.

Color: redColor: red Temperature: 2,500- 3,500 KTemperature: 2,500- 3,500 K Size: range from (main sequence- supergiants) times the mass of the SunSize: range from (main sequence- supergiants) times the mass of the Sun Spectra: strong metallic lines and wide titanium oxide bandsSpectra: strong metallic lines and wide titanium oxide bands Examples: Antares and BetelgeuseExamples: Antares and Betelgeuse Most common class by number of stars, since 90% of all stars are red dwarfs.

Types of Stars Classification ClassTemperatureColor O20, ,000 KBlue B10,000 – 30,000 KBlue-white A7,500 – 10,000 KWhite F6,000 – 7,500 KYellow-white G5,000 – 6,000 KYellow K3,500 – 5,000 KOrange M2,000 – 3,500 KRed

Life Cycle of Stars

Life Cycle of Stars 1.Begin their lives as clouds of dust and gas called nebulae 2.Gravity may cause the nebula to contract 3.Matter in the gas cloud will begin to condense into a dense region called a protostar 4.Protostar continues to condense, it heats up –Eventually reaches a critical mass and nuclear fusion begins. 5.Begins the main sequence phase of the star –Most of its life is in this phase

Life Cycle of Stars Life span of a star depends on its size. –Very large, massive stars burn their fuel much faster than smaller stars –Main sequence may last only a few hundred thousand years –Smaller stars will live on for billions of years because they burn their fuel much more slowly Eventually, the star's fuel will begin to run out.

Life Cycle of Stars Will expand into what is known as a red giant Massive stars will become red supergiants This phase will last until the star exhausts its remaining fuel At this point the star will collapse

Life Cycle of Stars Most average stars will blow away their outer atmospheres to form a planetary nebula (ionized gas emission) Cores will remain behind and burn as a white dwarf until they cool down What will be left is a dark ball of matter known as a black dwarf

Planetary Nebula White Dwarf

Nebulas

Life Cycle of Stars If the star is massive enough, the collapse will trigger a violent explosion known as a supernova Supernova = stellar explosion that briefly outshines an entire galaxy, gives off as much energy as the Sun over its entire life span, before fading from view over several weeks or months

Cassiopeia Supernova Remnant

Life Cycle of Stars If the remaining mass of the star is about 1.4 times that of our Sun, the core is unable to support itself and it will collapse further to become a neutron star Neutron star = star remnant that results from collapse of a massive star after a supernova –Densest and smallest stars known –Can have a mass of about two times that of the Sun

Life Cycle of Stars