Stars Chapter 30 Pages 775-

Star A ball of gases that gives off a tremendous amount of electromagnetic energy Notice that I did not say light Stars emit all wavelengths of the electromagnetic spectrum

Analyzing Starlight Astronomers analyze stars by looking at the light they emit They use a spectrograph A spectrograph separates light into different colors or wavelengths Stars produce a display of colors and lines called a spectrum

Three types of spectra Emission or bright line Absorption or dark line—dark line shows composition and temperature Continuous

Sources of Spectra

Star classification If we look at a star with a spectroscope we see dark lines called absorption spectra These lines indicate the star’s chemical composition

The most common element in stars is hydrogen

Each chemical element has a characteristic spectra in a given range of temperatures

The colors and lines indicate the elements that make up a star

Chemical Composition Lab Use the transparency and the paper copy to identify the elements found in the “Spectra of Unknown Composition” Slide the transparency up and line the unknown spectra just above the Calcium lines Are all lines present? Then calcium is in the star List results in two columns on your 3x5 card Elements Present and Elements Not Present

Color and Stars Think of a candle Hottest part is blue Red is the cool part at the top

Examples Temperature? Composition?

Apparent Motion of Stars Time lapse photography show a circular pattern revolving around the star Polaris We know Polaris as the North Star It is located directly above the North Pole so as the Earth spins the stars appear to move

Doppler Effect The apparent shift in the wavelength of light emitted by a light source moving toward or away from a viewer

Which is closest? See how the lines shift farther to the red end of the spectrum as a star is farther away The lines are from Ca, H, Na, and Mg

parallax The apparent shift in a stars location when viewed from different locations in orbit The closer the star is, the more it appears to move

Another view of parallax

Absolute vs. Apparent Magnitude Absolute—how bright a star actually is Apparent—how bright it appears from Earth http://www.astronomynotes.com/starprop/s4.htm

Stellar Evolution Section 2 Page 781

The Hertzsprung Russell diagram –HR Diagram 90% of stars are found on a diagonal line called the main sequence Hotter on the left cooler on the right Brighter at top dimmer at bottom

Another View of the HR Diagram

Birth of Stars Nebula—interstellar clouds of gas and dust Drawn together by gravitational attraction called accretion Begins to spin as it condenses This huge ball of gas is called a protostar

Birth of a Star Part 1

Birth of a star This ball continues to be drawn together by gravitational attraction When temperatures inside reach about 10million Kelvins nuclear fusion begins This produces a huge amount of radiant and thermal energy Ignition of nuclear fuel marks the change from protostar to star

A Red Giant you know--Betelgeuse Orion

Main sequence star Most of a star’s life is spent as a main sequence star Its size, temperature, and color are relatively stable During this time it burns up its supply of hydrogen What happens next depends on the star’s size

Red Giant When the sun has burned all its hydrogen, the helium core will contract because of gravity The rise in temperature will ignite the helium in the core and the core expands to become a red giant Our sun will reach this stage in about 5 billion years

Famous Red Giants Antares

The fate of stars differs according to their size

(Low mass stars) Small stars will shrink and throw off the outer layers in rings becoming a planetary nebula The shrunken core that remains is a white dwarf There is no nuclear fusion, it is only glowing hot If it is a binary star it may form a nova, or, When the core cools it becomes a black dwarf

Medium Mass stars—like the sun Become RED GIANTS Starts to burn helium-contracts because of gravity This raises the temperature and the star expands Our sun will reach this stage about 5 Billion years from now

White Dwarf What remains after the star swells and ejects the outer layers What remains no longer burns fuel It slowly cools It is now a stellar remnant It can change color as it cools

Black Dwarf A cold, dark lump of matter that remains when a star has burned out and cooled off

Life cycle of a low mass star Nebula Protostar Main sequence Red Giant Planetary nebula White Dwarf Black Dwarf

Binary star interaction

High Mass Stars have a different fate They burn faster And Die differently

High mass stars After the main sequence, stars with a mass much greater than the sun can burn and create larger and larger elements When it gets to iron, it takes too much energy to create other elements so it collapses This causes a supernova, this is when heavier elements are made

After a supernova a high mass star may become a neutron star or a black hole if it is VERY massive

Life Cycle of a High Mass Star Protostar Main sequence Red giant or red supergiant Supernova Neutron star or black hole

Black Holes Singularity—density is infinite Event Horizon

So how does the life cycle of a high mass star differ from a small mass star? High mass burn quicker and brighter and burn out faster They also have a different fate

Groups of Stars Main sequence—diagonal line Red Giants– bright and cool Supergiants—brighter and cooler White Dwarfs—dim and hot Spectral Class OBAFGKM Oh Be A Fine Girl Kiss Me

Revisit the HR diagram Where are stars most of their lives? Where are they when they begin to die? What are they after they use up their fuel?

H-R diagram

How is the Life cycle of a high mass different???? Starts the same but burns faster and ends differently Either Supernova then Neutron star Black hole

Large Mass Stars have a different fate They end in a supernova Generate the elements of life The inner part implodes to form a super dense neutron star

The Hertzsprung Russell diagram –HR Diagram 90% of stars are found on a diagonal line called the main sequence Hotter on the left cooler on the right Brighter at top dimmer at bottom

Lab—HR diagram Study lists and answer 21.1 &21.2 Temp on horizontal Absolute magnitude on vertical Note graph lines are not equal Chart nearest stars with a (+) sign Chart brightest stars with a Show stars on both as circled + Use an * to show the sun on the diagram

Word bank for paragraph Black holes Nebula 1 million 1 thousand Light years Parsec White dwarf Magnitude Red giant Black dwarf Fusion Fission Temperature Massive Neutron star Condense Closer Super nova

Pulsars emit low frequency radio transmissions A few emit X-rays or visible light The picture to the left is a gamma ray burst animation

Extremely Massive stars Extremely massive stars that undergo gravitational collapse may become a Black Hole

Event horizon—point of no return

Gravity Lensing— or how we know where they are Image copyright © 1998 by John Chang. http://www.rdrop.com/users/green/school/detect.htm

NASA Life Cycle of Stars Review

Lab—HR diagram Study lists and answer 21.1 &21.2 Temp on horizontal Absolute magnitude on vertical Note graph lines are not equal Chart nearest stars with a (+) sign Chart brightest stars with a Show stars on both as circled + Use an * to show the sun on the diagram