Phys 1830 Lecture 21

1. Phys 1830 Lecture 21 Upcoming Classes • Our Solar System • Solar System Formation • Second Term Test Friday Mar 6. • Covers material after previous test (pseudo-cummulative). • Topics from “how images are made” (lecture 11) through “computer simulations” (today). • Check material online for test information.

2. Cheating ... on tests, quizzes, exams, or midterms • Cheating can be spontaneous or premeditated. • You are also cheating if you allow others to look at your exam. • The Faculty of Science values academic Integrity. Cheating will not be tolerated by the Faculty of Science. • Penalties may include a minimum of: • zero in the assignment, • F-DISC in the course, • a notation written on your transcript, and/or • suspension from courses in the department or the Faculty of Science for one year.

3. Common examples of academic dishonesty that occur every term: • A student brings a calculator to the final exam. The calculator is allowed by the instructor, but the calculator cover is forbidden. • An invigilator discovers the notes and the incident is forwarded to the department Head or the Associate Dean. An act of academic dishonesty has occurred regardless of whether the notes are used by you during the exam. • Also when handing in materials you write on your exam materials near other students answer sheets this provides an opportunity for academic dishonesty. • What are the consequences of the penalties? • They may slow down the progression of your degree, costing you time and money. • They may be visible to potential employers, professional school applications, or graduate schools. • They may affect your student visa eligibility for a year or more. • Protect yourself: • Do not bring unauthorized material into the exam (e. g. notes, cell phone, calculator cover). • Resist opportunities to collaborate inappropriately or look at someone else’s paper. • If you suspect someone looking over your shoulder … Cover your paper; ask to be moved to another seat; alert the invigilator. • Review the online tutorials available through Student Advocacy: • umanitoba.ca/student/resource/student_advocacy/AI-and-Student-Conduct-Tutorials.html

4. How DO You Create a Universe? Assumptions Cosmological Model + Parameters Simulation Method Astronomical Society of Victoria: Computational Cosmology 2006

5. From this… observations! As universe expands and cools, small primordialdensity fluctuationsare amplified by gravity

6. … to this Treat dark matter & atoms as collection of points. observations! Abell Cluster 2744 (HST)

7. Cosmological Simulation • Parameters: Dark matter, etc.; number of particles, time steps, etc. • Model: Apply Newton’s law of Gravity 3) Simulation Method: the N-Body Simulation

8. N-Body Solution i (N-1) = 12 FORCE PAIRS j N*(N-1) = 13*12 = 156 CALCULATIONS N =13 particles

9. N-Body Simulations • N-bodies interacting under mutual gravitation • Generate initial distribution of positions and velocities • Calculate the forces between particles • Update the position and velocity of each particle • Repeat steps 2 and 3

10. Resolution is the Name of the Game • Ideal: • N = 100 billion stars in a galaxy • At least one simulation particle per star • Current: • Millennium Simulation (MS) • http://www.mpa-garching.mpg.de/galform/virgo/millennium/ • N = 10 billion particles in a box • MS-II focuses on smaller volume

11. 0.21 Gyr after Big Bang

12. 1 Gyr after Big Bang

13. ~5 Gyr after Big Bang

14. 13.6 Gyr after Big Bang  now

15. Visualization: Computer Simulations Input information from observations into the simulation. Evolve the simulation through time. See if the simulation and observations match. • Simulations are part of the theoretical component of the method of science. • Generate models that can be compared to observations.

16. Observations Computer Simulations Visualization CMBR Early times MS Now Clustering of Galaxies Large Scale Structure of the Universe • Input information from observations into the simulation. • Evolve the simulation through time. • See if the simulation and observations match.

17. Visualization: Example of observations and simulations that are consistent with each other. Thomas Jarrett (IPAC/Caltech) • Observations of the Cosmic Web! • Panoramic view of the entire 2MASS near-infrared sky reveals the distribution of galaxies beyond the Milky Way. • Colour coded on velocity (redshift; described later in the course).

18. Visualization: Planetary Systems Simulations  Formation of gas giant planets in a protoplanetary disks Note the spiral structure. • Assumptions: gas flows like a fluid in a disk • Model: • gravity • this uses equations from hydrodynamics (== the study of forces acting on or exerted by fluids)

19. Review • A numerical simulation • is a computer program that evolves a situation through time • uses observations as input • employs physical equations such as Newton’s law of gravity • attempts to match observations • all of the above

20. Review • To match observations the end result of a cosmological simulation should have • several hundreds of galaxies in associations • large scale structure throughout the volume modeled • a random distribution of galaxies • a & b • none of the above

21. Test up to here.

22. Planetary Systems • Animation of the evolution of a planet-forming disk. • Note the dust ring that remains in the outer parts of the system.

23. Planetary Systems: • Is the assumption of a disk a good one? • Look where stars are forming to see if there are disks

24. Planetary Systems: • HST image in centre of Orion Nebula.

25. Planetary Systems: • Protoplanetary disks are called “proplyds” for short. • Dusty disk edge-on to our view. • See radiation from a star forming.

26. Planetary Systems: • At a later stage young stellar objects in the centre of the disk will emit radiation along their poles. • The evolving Proplyd is backlit by this emission.

27. Data Subaru Telescope Yes, we see spiral protoplanetary disks. Indeed some with spiral structure. artist’s illustration

28. Do observations also show rings in the outer regions of planetary systems? • (Think of our solar system.)

29. Planetary Systems: • Evidence that a young planet formed in a “disk”! • This is first visible-light image of a dust ring around the nearby, bright young star. • The part of the ring is outside the telescope's view. The ring is tilted obliquely to our line of sight.

30. Planetary Systems: • Coronagraph used to block out the light from the bright star so they could see the faint ring. • A coronagraph uses a disk usually to block our Sun's bright surface producing an artificial eclipse.

31. Planetary Systems • Some light from the star is still visible in this image. • The ring is 133 AU from the star. • The ring’s width is 25 AU. • “The ring is tinted red for image analysis.”

32. Planetary Systems: Beta Pictoris Composite image from 2 different IR datasets acquired at the European Southern Observatory. Hubble Space Telescope’s Imaging Spectrograph • Example of an edge-on disk (warped). • Possibly a giant planet in the inner regions.

33. Planetary Systems • Simulations start with disks filled with gas and dust. • Observations motivate this initial configuration.

34. Planetary Systems & Disks -- Solar System: Looking towards the Sun Looking towards Jupiter • The orbits of the 8 classical planets also indicate that our solar system evolved out of a disk. • The planets’ orbits lay in a narrow plane. Mercury deviates the largest (with only a 7 degree tilt). • They all orbit in the same direction.

35. Planetary Systems Eagle Nebula (M16) • Assumption that planets form in disks was motivated by observations. • Is the assumption that the disk is initially very gaseous a good one?

36. Planetary Systems • Molecular Cloud with “fingers” protruding. • Evaporating Gaseous Globules = EGGs at finger tips. • Each about the size of our solar system.

37. Planetary Systems: Bok Globules in Carina Nebula • Surrounding molecular gas cloud photoevaporates leaving denser globules of rotating gas. • Material in a globule falls towards the centre via gravity. • Simultaneously, due to conservation of angular momentum, a disk consisting mainly of gas and dust forms --> proplyds.

38. Planetary Systems • Animation from Swinburne University, Centre for Astronomy and Supercomputing. • Assumption that gas dominates the initial conditions is also founded on observations. • The central condensation will become a star.

39. Planetary System Formation - Observations: • Orion is an example of a dusty, gas cloud forming planetary systems. • Distance is 1,500 ly (460 parsecs). • Proplyds and Bok Globules inform the simulations of star and planet formation.

40. Visualizations: Simulations of Planetary Systems Observations Animation based on Simulation • Observations of a planetary system with a ring and planets can be explained by a simulation. • Planetary disk simulations use: • gravity between particles, • gravity between particles and the protostar, • hydrodynamical forces • Note that the planets have cleared their orbits in the simulations.

41. Visualizations: Simulations • Two assumptions for modelling the formation of planets are: • A cloud composed of rocks collapses. This forms a disk. (The biggest rocks are the planets.) • A cloud composed mainly of gas collapses. This forms a disk. (Planets form within this disk.) • Chunks of gas tear off from molecular clouds. Photo-evaporation exposes the planets buried inside these Bok Globules.

42. Extra-solar planets == Exoplanets • More on this after we study our own Solar System

43. Solar System • The assumptions in the models of the formation of planetary systems are reasonable since supported by observations of other “solar systems”: • Gas dominates • Disks form • The models also have to match features of our own Solar System. • Why do all the planets orbit in a plane? • Why do they orbit in the same direction? • Why are some planets gaseous and others not?

44. Solar System Overview: Planet Definitions • Classical Planet • Orbits the sun. • Massive enough that is own gravity has caused its shape to be nearly spherical. • It has “cleared the neighbourhood” around its orbit of other bodies. • i.e. either by colliding with (sweeping up) the debris in the disk or by gravitationally kicking the debris out of its path (slingshot effect).

45. Solar System Overview: Planet Definitions • Examples: • Pluto • Eris (1.3 * Pluto’s mass) • Ceres (in the asteroid belt) • Dwarf Planet • Orbits the sun. • Massive enough that is own gravity has caused its shape to be spherical. • Is not a satellite of another body. (Has not cleared its neighbourhood.) Objects at Neptune and beyond are called Trans-Neptune Objects (TNO) and those TNO that are similar to Pluto are called plutoids.

46. Solar System Overview: What do you already know about the classical planets?

47. Solar System Overview: What does the class already know about the classical planets? • For each planet: • revolve & rotate in the same direction as other planets? • primarily composed of rock or of gas? # Earth Masses, # Earth radii • small or large? (i.e. closer to Earth size or Jupiter size?) • in outer region or inner region of solar system? • hot or cold? surface T in Kelvin • Lots of moons? • Any other details are welcome  (eg. Does it have rings? B field?) Note about T: -273 C = 0 K