* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Other Galaxies, their Distances, and the Expansion of the Universe
Cygnus (constellation) wikipedia , lookup
Shape of the universe wikipedia , lookup
Aries (constellation) wikipedia , lookup
Corona Australis wikipedia , lookup
Dark energy wikipedia , lookup
Space Interferometry Mission wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Modified Newtonian dynamics wikipedia , lookup
Gamma-ray burst wikipedia , lookup
Fine-tuned Universe wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Non-standard cosmology wikipedia , lookup
Flatness problem wikipedia , lookup
Physical cosmology wikipedia , lookup
Lambda-CDM model wikipedia , lookup
Observational astronomy wikipedia , lookup
Expansion of the universe wikipedia , lookup
History of supernova observation wikipedia , lookup
Chronology of the universe wikipedia , lookup
Stellar evolution wikipedia , lookup
Stellar kinematics wikipedia , lookup
High-velocity cloud wikipedia , lookup
Type II supernova wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Observable universe wikipedia , lookup
Structure formation wikipedia , lookup
Hubble's law wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Star formation wikipedia , lookup
Other Galaxies, their Distances, and the Expansion of the Universe Announcements n n n Homework # 7 starts today, and is due Thursday, December 1st. Homework # 6 is due today (11 pm). Quiz # 6 will take place on Tuesday, November 29th; n See website for information on lectures and textbook units it is based on. Reading Assignments n Units 63, 65, 73.2, 73.3, 74, 75, 76 M51 Sombrero M81 Galaxies show a huge variety of shapes and characteristics These are images obtained by my team with the Spitzer Space Telescope Some galaxies even show evidence for very violent ejection of material into the intergalactic space And some are merging with each other The merging Antennae Galaxy (NGC4038/4039) How do we `Organize all of this variety? Galaxies seem to take one of four different appearances • Spirals • Barred Spirals • Ellipticals • Irregulars This classification scheme is known as the Hubble Tuning Fork Scheme SPIRALS Spirals have a disk with dust and gas; They also show, in general, prominent spiral arms where the star formation is concentrated. We easily see the spiral arms because they contain numerous bright O and B (massive) stars which illuminate dust in the arms. However, stars in total seem to be evenly distributed throughout the disk. SPIRALS Progression from Sa to Sb, Sc, Sd, Sm depends on how tight the spiral arms are wound and how big is the bulge The tightness of a spiral galaxy’s arms is correlated to the size of its nuclear bulge Type Sa Type Sb Type Sc Variety of Spiral Arms Flocculent spirals (fleecy) Grand-design spirals (highly organized) BARRED SPIRALS Similar to spirals in many characteristics. The bar is not a spiral arm. It is made of old stars, like those in the bulge Bars of stars run through the bulges of barred spiral galaxies Type SBa Type SBb Type SBc Same progression as regular spirals: SBa, SBb, etc. ELLIPTICALS Ellipticals have no dust No cold gas No star formation Made mostly of old stars Question Given their color, do you expect elliptical galaxies to have more or less new star formation than spirals? Why? 1) ellipticals have more new star formation 2) ellipticals have less new star formation ELLIPTICALS Type E0 Type E3 Type E7 Progression from E0 (perfectly round) to E7 (shaped like a cigar) Elliptical galaxies display a huge variety of sizes and masses Giant elliptical galaxies can be 20 times larger than the Milky Way n Dwarf elliptical galaxies are extremely common and can contain as few as a million stars n IRREGULARS Irregulars do not have a specific shape; they have plenty of gas, dust and star formation Galaxies like to cluster: eg. M81 group …They like company… Galaxies also like to merge: Billions of stars all tug on each other instead of just one planet tugged by the gravity of the Sun. Galaxies fill the Universe, and are visible at great distances. Each contains hundreds of millions of stars. They can be used to trace and derive properties of the Universe itself, such as whether it is a changing or unchanging structure, the speed of change, etc. The Detail is Amazing Hubble Ultra Deep Field Determining Distances on Small Scales There is a well-tested method for measuring distances over short length scales: u Parallax - good for measuring distances to a few hundred light years Stellar Parallax (Review from a few classes ago) The baseline is the diameter of the Earth s orbit. The measurements are taken six months apart. ½ of the angle between the now location and the 6month location is called the stellar parallax. = P But what do we do about objects too far away to use the parallax method? Standard Candles n If we know an object s true Luminosity luminosity, we can Brightness = measure its distance 4 " # distance 2 by measuring its apparent brightness. An object that!has a known luminosity is called a standard candle. Survey Question You see a car on the other side of the road coming towards you with their lights on. When the car is twice as close (that is, at half the original distance), how much brighter are the headlights? 1) 2) 3) 4) 5) the same brightness twice as bright four times as bright sixteen times as bright ½ as bright So measuring distance with standard candles is easy! n Unless you worry about reality getting in the way: Dust extinction n Atmospheric extinction n Making mistakes because objects are getting dim and hard to measure n Finding a standard candle in the first place. n Reliable standard candles must be calibrated. Standard Candle #1 - Cepheid Variable Stars n n Cepheid variable stars have variable brightness that is very regular. The period of the variation can be from days to weeks – and it seems to be a reliable indication of the star’s luminosity! Cepheid Variable Stars Henrietta Leavitt (1868-1921). Luminosity=4πD2B Standard Candle #2 - Type Ia Supernova n n Always the result of a white dwarf with a mass equal to 1.4 Msun. These are some of the most energetic events in the universe – so they are very bright. Wait a moment… How can a white dwarf (the stellar remnant of a low mass star) become a supernova? n It can, if it has a companion (that is, it is in a binary star). n When the companion becomes a red giant, some of its mass flows to the white dwarf, increasing its mass. If the mass increases sufficiently (up to 1.4 Msun), the WD will explode as supernova! Type Ia (white Dwarf) SNa n n n The peak luminosity of a Type Ia supernova is very high They are visible from the deepest cosmological reaches Type II Snae are explosions of massive stars Standard Candle #2 - Type Ia Supernova n All type Ia supernovae have the same luminosity (more or less), so this is our best standard candle yet since they are so bright we can measure the distances to things that are very far away! Supernova 1998ba 2011 Nobel Prizes: Saul Perlmutter Brian Schmidt Adam Riess Type 1a Supernovae show that the Universe is accelerating! Survey Question For an object to be a true standard candle, all occurrences of the object must have the same _______? 1) 2) 3) 4) 5) brightness distance age luminosity mass Hubble s Discovery In the 1920s, Edwin Hubble used the distance ladder (based on Cepheid variable stars) to measure the distances of about 50 galaxies. n This work proved that the Andromeda galaxy was not part of the Milky Way. n Hubble and his staff then measured the redshifts (remember the Doppler Shift) of the galaxies. They were shocked with what they found. n Velocity Hubble’s distance/velocity data Distance The further away is a galaxy, the faster it s moving away from us. Hubble's Law" V = H0D Hubble's Data Modern Data The further away is a galaxy, the faster it s moving away from us. Hubble s Law v = H0d A constant: ~70 km/s/Mpc Velocity that the galaxy is moving away from us. The distance to the galaxy Distance to a galaxy V = H0D Ho = 73 km/s / Mpc. The receding velocity causes the redshift of spectral lines, which can be used to estimate distances to distant galaxies that follow the Hubble's law: D = V/H0. e.g., for a galaxy with V =7300 km/s, D=100 Mpc The Universe is expanding…. Isn t this at odds with our notion that Earth isn t special? n Not exactly. Try the balloon analogy or the loaf of bread with raisins… The Age of the Universe n The reciprocal of H0 is the age of the universe (if the universe has been expanding at the same rate since it was born). 1/H0 ~ 13.7 billion years n n This is in remarkably good agreement with the age inferred from measuring the age of the oldest globular clusters. This age has been confirmed by other, recent experiments that we ll talk about in the next few lectures. How Big is the Universe? The Universe we can observe is as big as the age of the Universe multiplied by the speed of light: Runiverse = c x age = 4.2 x 109 pc = 4200 Mpc