2 Big Bang theory – Origin of the Universe Big Bang marks the inception of the universeOccurred about 13.7 billion years agoAll matter and space was createdNot a huge explosion that hurled matter in all directions. Technically, there was no “bang”Technically, matter is not moving outward in all directions. Reality: space expands
3 Big Bang EvidenceDistant galaxies are moving away from each other – Doppler Red Shift. Hubble (1929) – the farther away the galaxy is the faster it is moving away.Cosmic Microwave Background Radiation – Penzias & Wilson (1965). Left over radiation from the “explosion”
5 Expansion Evidence for Big Bang Electromagnetic Energy - Type of energy given off in the form of transverse wavesDifferent types of electromagnetic energy are distinguished by their different wavelengths
7 Electromagnetic Spectrum – humans can only see one part of spectrum – visible light
8 Expansion Evidence Most stars are made of Hydrogen & Helium gas. Elements that emit specific wavelengths within the electromagnetic spectrum.The spectral line pattern can be used to identify the star rather like a fingerprint or bar code.
9 Red Shift – Blue ShiftIn 1929, Edwin Hubble observed that spectral lines emitted by stars in distant galaxies were considerably Red shifted.If a galaxy or star were moving toward the earth, the spectral lines would show a blue shift.When scientists look at the spectrum of radiation emitted by stars in far away galaxies they noticed the positions of the characteristic wavelengths are shifted to the shorter (blue light end of spectrum) or longer (red light end of spectrum) wavelengths depending on whether the star is coming towards you or moving away.In 1929, Edwin Hubble observed that spectral lines emitted by stars in distant galaxies were considerably Red shifted.
11 Shifting of Wavelengths is called the Doppler Effect Change in the wavelength of light emitted by an object due to its motionMovement toward “squeezes” the wavelengthShorter wavelengthLight shifted toward the blue end of the spectrumMovement away stretches the wavelengthLonger wavelengthLight shifted toward the red end of spectrum
13 RED SHIFT – BLUE SHIFTThe greater the degree of shift of the spectral lines, the faster the object is moving awayThe star light DOES NOT appear red or blue (it still appears as white light from the star)The “bar code” for each element either shifts to the shorter wavelength blue end of the spectrum or to the longer wavelength red end of the spectrum
15 What is the best inference that can be made concerning the movements of Galaxies A, B, and C?
16 Structure of the Universe Hubble Telescope allowed scientists to infer the structure of the universeA GALAXY is a collection of billions of stars held together by gravityOver l00 billion galaxiesspiral – elliptical - irregular
24 Understanding Stars Grouping of stars and the classification system has changed over time with more advanced tools
25 STELLAR SPECTRAL CLASS Grouping the stars based on their temperatures
26 Each class of star has a unique pattern of lines (“bar code”) to identify it. HydrogenHydrogenHydrogenSodium“Hottest”“Coldest”
27 Hertzsprung-Russell Diagram Comparing temperature and brightness for various stars
28 Hertzsprung-Russell Diagram aka Luminosity and Temperature of Stars Diagram – NOT A MAP DIAGRAM IS A USEFUL WAY TO FOLLOW CHANGES THAT TAKE PLACE AS THE STARS LIVE OUT THEIR LIVESDiagram is made by plotting (graphing) each star's LUMINOSITY (brightness) and TEMPERATURE (as reflected by color) COMPARED TO THE SUNIt is readily apparent that the H-R Diagram is not uniformly populated, but that stars preferentially fall into certain regions of the diagram. The majority of stars fall along a curving diagonal line called the main sequence but there are other regions where many stars also fall.
31 Which groups of stars are the SMALLEST and DIMMEST?
32 Schematically, stars fall into regions shown below with respect to the sun.
33 Most stars are on the Main Sequence because that is where they spend most of their lives Our sun is an average main sequence starLuminosity of 1Temperature 5500°C – yellow in colorConsider stars cooler than, but brighter than the sun. These must be very large stars (Red Giants), whereas stars bluer than the sun but less luminous must be quite small ( White Dwarfs).We will see that the H-R Diagram is an extremely useful way to follow the changes that take place as a star evolves. Most stars are on the Main Sequence because that is where stars spend most of their lives, burning hydrogen to helium through nuclear reactions. As stars live out their lives, changes in the structure of the star are reflected in changes in stars temperatures, sizes and luminosities, which cause them to move in tracks on the H-R Diagram.
34 What color stars are hottest? Coldest? Red Super Giants Red GiantsMAIN SEQUENCECOLOR AND TEMPERATURE ARE RELATED!White Dwarfs
35 Star Formation A star is born when nuclear fusion starts. Gravity pulls hydrogen atoms together. As trillions of hydrogen atoms are compressed the temperature increases.Once the temperature reaches ~15 million ºC, nuclear fusion begins and a star is born.
36 Space is filled with the stuff to make stars – mostly hydrogen gas. Image of the pillars of creation inside the crab nebulaColumns of hydrogen gas and dust that is the beginnings of stars
37 At 15 million degrees Celsius in the center of the star - nuclear fusion begins
39 As long as the forces of gravity and thermal pressure are balanced, the star exists on the main sequence.
40 Life Cycle of Stars – Depends upon their original mass After they spend their life as main sequence star ….Sun size > expand to red giant in about 5 billion years > white dwarf > black dwarfSuper giant > supernova >very high mass – black holehigh mass – neutron star
43 Star Life Cycle: Stars are like humans Star Life Cycle: Stars are like humans. They are born, live and then die.Takes about 1-3 yearsProtostar takes 10 million yearsNebula – cloud Protostar – new, justof gas and dust forming star
44 Main Sequence (like the sun) Red Giant (Betleguise) – once the star runs out of hydrogen and the balance of forces is upset.Main Sequence (like the sun)From start to finish in main sequence takes about 11 billion yearsFrom the finish of the main sequence – red giant takes about 100 million years
45 DEPENDING ON THE ORIGINAL MASS White Dwarf: Smaller stars Supernova: Star thatshrink and cool and has died an explosiveeventually become cold death.black dwarves.This takes about 10,000 years from the end of red giant stage
46 Star Dies – Star casts off shell Star Dies – Star casts off shell . It creates nebula that can take a variety of shapes – Ant Nebula