1. Astronomy 1020 Stellar Astronomy Spring_2015 Day-XXX

3. Expansion of the Universe Lecture Tutorial pg. 161 Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on and write complete thoughts into your LT. If you get stuck or are not sure of your answer, ask another group.

4. Making Sense of the Universe and Expansion -Lecture Tutorial pg. 151 DO THIS ONE AS HOMEWORK! Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on and write complete thoughts into your LT. If you get stuck or are not sure of your answer, ask another group.

5.  The Hubble constant H 0 is a fundamental number: It also tells the age of the universe.  We need to have distances to galaxies.  We need things inside galaxies with known luminosity to continue the distance ladder.

6.  Type I supernovae are especially good distance indicators.  Very luminous standard candles.  H 0 currently: 70 km/s per Mpc.

7. Finding H 0

8.  Knowing the luminosity of a Type Ia supernova lets you find its distance.  A Type Ia was observed in 2011 in the Pinwheel Galaxy, with a maximum brightness of 7.5 x 10 -12 W/m 2. If the maximum luminosity is 3.7 x 10 36 W, what is the distance? MATH TOOLS 19.2

9. Hubble’s Law Lecture Tutorial pg. 155 Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on and write complete thoughts into your LT. If you get stuck or are not sure of your answer, ask another group.

10. Hubble’s Law Lecture Tutorial pg. 155 Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on and write complete thoughts into your LT. If you get stuck or are not sure of your answer, ask another group.

11. Concept Quiz—H 0 and Time The value of H 0 is about 70 km/s/Mpc. Suppose it were twice as big. Compared to our current estimates, what would the age of the universe be? A.the same as now B.younger C.older

12.  It is space that is doing the expanding.  Distant galaxies have a large look-back time.  Light has a large, but finite speed; it takes 27,000 years for the light from an object 27,000 light-years away to reach us.

13.  Galaxies will be farther apart in the future.  Galaxies were closer together in the past.  If the expansion has been going on for a long time, galaxies were once very close together.  Hubble time: time when separation was zero.

14.  The Hubble time was 13.7 billion years ago.  At that time the Big Bang occurred  extremely dense point began expanding.  Galaxies are not flying away from each other.  Space itself is stretching or expanding.

15.  The redshift tells us how much the universe has expanded since a galaxy’s light was emitted.  The scale factor R U is a measure of how much the universe has expanded. Example: z = 1 means R U = 0.5. The universe was half its current size when light was emitted from this galaxy.

16.  You can calculate the time it took for two galaxies to be separated by a certain distance due to the expansion of the universe, beginning with zero separation.  If H 0 is 70 km/s/Mpc, time = 1.4 x 10 10 years. MATH TOOLS 19.3

17.  When the redshift exceeds 1, that means that mathematically the recession velocity is greater than the speed of light.  The closer z gets to 1, the more relativistic effects need to be considered.  Need to interpret the meaning in terms of the scale factor instead of the speed:  A cosmological redshift of z = 2 means that the universe was 1/3 the size it is now. CONNECTIONS 19.1

18.  Redshifts of galaxies are not due to Doppler shifts.  Instead, the light is “stretched out” as it travels through the expanding universe: cosmological redshift.  More travel = greater redshift.

19.  If all matter is in a small volume, it means conditions were very hot.  Due to expansion, temperatures dropped.  The hot, dense gas should have a blackbody spectrum.

20. Predictions have been Confirmed  As the universe expands, the light will redshift and cool.  Prediction: a Planck spectrum uniformly redshifted by the expansion of the universe to a temperature of about 5–10 K.

21.  This light was found in 1965 by Arno Penzias and Robert Wilson.  Cosmic microwave background radiation.  Form: a Planck spectrum with T = 2.73 K.  Peak at microwave wavelengths.

22.  When the universe was hot and the gas was ionized, photons were trapped with matter.  At an age of several hundred thousand years, the temperature cooled enough that protons and electrons could form neutral H atoms: recombination.

23.  At that time, light was no longer blocked from its travel by all of the matter.  The light could travel freely, and cooled by a factor of about 1,000 to about 2.7 K, as confirmed by satellite data.

24.  Before recombination, everything would have been much hotter and more dense.  At high densities, nuclear reactions occur  Big Bang nucleosynthesis.

25.  Fusion in the early universe produced mainly hydrogen and helium.  Prediction: 24 percent of matter should be helium.  In fact, this is observed!

26. The Big Bang Lecture Tutorial pg. 165 Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on and write complete thoughts into your LT. If you get stuck or are not sure of your answer, ask another group.

27. Concept Quiz— Supporting Evidence Name one fact below that on its own does not support our idea that the Big Bang happened. A.the existence of the cosmic microwave background radiation B.that 24 percent of matter is helium C.that the universe is expanding

28.  Preconceived notions cannot be built in to theories.  The data and the mathematics show the true story.  You must be able to listen to what the data tell you. PROCESS OF SCIENCE

29.  Cosmology: the study of the universe on the grandest of scales.  The universe is expanding now.  Future expansion could be faster or slower.  Expansion could halt and reverse.  Fate depends on how much matter there is in the universe.  Gravity from ordinary and dark matter slows the expansion.  Is there enough gravity to halt the expansion?

30. Critical Density  The faster the universe is expanding, the harder it is to stop it and make it contract.  The more mass there is, the more gravity there is to halt the expansion.  Express this amount needed as a ratio to the critical density.  Critical density = the density needed to almost slow the universe to a stop, but not to reverse it.   mass is the ratio of the mass density of the universe to the critical density.

31.  If  mass = 1, density is at the critical density.  Universe slows asymptotically to a stop.

32.  If  mass > 1, the expansion will stop and the universe will contract: the Big Crunch.

33.  If  mass < 1, expansion will go on forever; will slow a little from gravity.

34.  Ordinary stars and galaxies:  mass = 0.02.  Dark matter in and between galaxies increases  mass to 0.3.

35.  At the end of the 20th century, we thought we understood the expansion.  1990s: We were surprised to discover the expansion is accelerating!  2011 Nobel Prize to Perlmutter, Schmidt, and Riess.

36.  If the expansion were slowing, then the rate of expansion at earlier times should be larger than now.  Observations of Type Ia supernovae in high redshift galaxies show that the expansion was instead smaller in the past, and larger now!

37.  The expansion is accelerating, not slowing down.  This indicates that there is a type of energy in the universe that pushes on space, acting against gravity.

38.  This energy is the cosmological constant or dark energy.  Symbol:  .  Changes the universe’s possible fates since it is more difficult for gravity to reverse the expansion.

39.  We can learn about   from supernovae, galaxy clusters, or the CMB.    is about 0.7,  mass is about 0.3.  Universe is accelerating, will expand forever.

40.  If the universe’s expansion has been slowing, its age is younger than the Hubble time (13.7 billion years).  If accelerating, the age is greater.  Agrees with 13 billion year-old globular clusters.

41.  The universe has a shape.   mass +   = 1: Flat universe, infinite.   mass +   < 1: Open universe, infinite, like the surface of a saddle.   mass +   > 1: Closed universe, finite, like the surface of a sphere.

42.  The combination  mass +   is very close to 1.0. Why? This is called the flatness problem.  The CMB is almost exactly the same temperature in all directions–the horizon problem.

43.  One explanation: inflation (a very rapid expansion at extremely early times).  Smooths and flattens the early universe.

44.  Four forces govern the universe: gravity, electromagnetic force, weak nuclear force, and strong nuclear force.  Each concerns different processes and came into being at a different time.

45.  The forces are mediated by different particles.  Example: photons carry the electromagnetic force (quantum electrodynamics, QED).  Weak: 3 particles, the W +, W –, and Z 0.

46.  QED and the weak force are combined in understanding as the electroweak theory.  The strong force concerns quarks and gluons.  The ideas of electroweak + strong (QCD) = standard model of physics.

47.  Pairs of particles and antiparticles were created and annihilated in the early universe through pair production.  Particle/antiparticle type depends on temperature and energy.  Higher energy means a particle with greater mass can be created.

48.  The universe originally was full of photons, electrons, and positrons (antielectrons).  As the universe cooled, the particles and antiparticles annihilated each other.  There were slightly more particles than antiparticles, leaving matter not antimatter.

49.  In the early universe, strong force + electroweak force = grand unified theories (GUTs).  This predicts proton decay, but at a very slow rate (unobserved).  It also predicts the Higgs boson, the particle concerned with giving the property of mass to other particles, which may have been discovered in 2012 at the Large Hadron Collider at CERN.  GUTs + gravity = theory of everything (TOE), existing during the Planck era.

50.  As the universe cooled after the Big Bang: Physical forces were established. Era of photons, electrons, positrons. Matter-antimatter annihilation, leaving many photons and a little normal matter.

51. Matter and photons cooled; atomic nuclei formed (Big Bang nucleosynthesis). Neutral atoms could form and light streamed out into the universe (recombination, CMB). Galaxies and stars could form.

52.  There could be a collection of universes almost identical to ours, called multiverses.  Many theories.  An infinite universe could contain an infinite number of disjointed, observable universes (unobservable from ours).

53.  Eternal inflation is a theory suggesting that new big bangs are forever forming, creating new bubble universes with potentially different values of the fundamental constants.  Anthropic principle: We exist in our universe because it has the right properties to allow life to form.  Other multiverses might not have the right qualities for life (variances in the fundamental constants and therefore the values of the forces).