2013 North Carolina Science Olympiad Coaches Institute. Astronomy (C) Don Warren Physics Department NC State University. State event leader

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1 2013 North Carolina Science Olympiad Coaches Institute Astronomy (C) Don Warren Physics Department NC State University State event leader

2 Event Rules Description:Students will demonstrate an understanding of the basic concepts of mathematics and physics relating to stellar evolution and variable stars. Team size:up to 2 Event parameters:each teamis allowed two laptops, two 3-ring binders (any size), or one of each. Each membermay bring a programmable calculator. No internet access! Scoring:Each question is worth a set amount of points. Highest score wins. Ties broken by score on selected questions. Check NCSO website regularly for changes/updates!

3 My Philosophy The purpose of science is not acquisition of facts. Science is about understanding the Universe with the simplest theories possible.

4 My Philosophy My tests require more than just rote memorization! Understand the concepts, and know how to read graphs and charts. Q1:What is the most common element in the Universe? A. Helium B. Hydrogen C. Carbon D. Iron vs. Q2: Stars near which letter have the smallest radius?

5 My Philosophy Finally, Can t do astronomy without physics and mathematics, so students should expectto have to do math at some point!

6 Brief Outline I. How stars work II. Stellar evolution III. Filling out the stellar zoo IV. Astronomical concepts V. List of objects

7 I. How stars work A star (like the Sun) is a mass of incandescent gas (really, a miasma of incandescent plasma) They re HUGE Earth

8 I. How stars work Two competing forces perpetually in near perfect balance Gravity pulls star inward (Thermal) Pressure from burning fuel through nuclear fusion

9 All stars begin as cloud of gas (nebula), which collapses to form a protostar Protostars contract under gravity until fusion begins II. Stellar evolution Single most important attribute for a star: its massat birth

10 Stellar life cycle splits into three paths based on mass at birth Low mass stars (d0.5 M Sun ) Medium mass stars (0.5 M Sun 8 M Sun ) Massive stars ( t8 M Sun ) II. Stellar evolution Many, many morelow mass stars than high mass stars!

11 II. Stellar evolution Low Mass Stars (d0.5 M Sun ) Fuse hydrogen to helium at core (Slowly!) Convert all fuel, and eventually dim as fuel runs out (Not very interesting, eh?) No dead low-mass stars exist: Universe not old enough

12 II. Stellar evolution Medium Mass Stars (0.5 M Sun 8 M Sun ) Fuse hydrogen to helium at core Convert core to helium, and contract due to gravity Have inert core of helium inside shell of burning hydrogen

13 II. Stellar evolution Medium Mass Stars (0.5 M Sun 8 M Sun ) Star becomes a red giant increased energy production pushes outer layers away from star; outer layers cool down

14 Medium Mass Stars (0.5 M Sun 8 M Sun ) Core of star continues to contract, reaching helium burning temperatures Burning rate increases, until pressure is blowing away outer layers of star (i.e. pressure wins battle vs. gravity) II. Stellar evolution

15 Medium Mass Stars (0.5 M Sun 8 M Sun ) Outer layers become planetary nebula. II. Stellar evolution What about the core?

16 Medium Mass Stars (0.5 M Sun 8 M Sun ) Carbon core (C + O, but sometimes O + Ne) becomes white dwarf About size of Earth, about mass of Sun: incredibly dense! (Very!) Slowly radiates heat, cooling into black dwarf (Again, none exist yet) II. Stellar evolution

17 Massive Stars (t8 M Sun ) II. Stellar evolution Fuse hydrogen to helium at core Convert core to helium, and contract due to gravity Have inert core of helium inside shell of burning hydrogen

18 Massive Stars (t8 M Sun ) II. Stellar evolution Star becomes a red supergiant increased energy production pushes outer layers away from star; outer layers cool down

19 Massive Stars (t8 M Sun ) II. Stellar evolution Core of star continues to contract, reaching helium burning temperatures Sound familiar? These stars too massive to blow off outer layers. Instead

20 Massive Stars (t8 M Sun ) Core fusion continues until iron Can t fuse iron and gain energy, so no more thermal pressure only gravity Entire star collapses under own weight II. Stellar evolution

21 Massive Stars (t8 M Sun ) Rebounds off of core, becomes (core-collapse) supernova Explosion (roughly) 10,000,000,000 times brighter than Sun briefly outshines entire host galaxy II. Stellar evolution

22 Massive Stars (t8 M Sun ) Outer layers expand as a supernova remnant Detectable tens, hundreds, to thousands of years later. II. Stellar evolution What about the core?

23 Massive Stars (t8 M Sun ) Core becomes either neutron star or black hole. Neutron star: 2 M Sun in 10 km radius Very dense, very strong magnetic field, very fast rotation Supported by strong nuclear force II. Stellar evolution

24 Massive Stars (t8 M Sun ) Black hole: so dense nothing opposes collapse Nothing even light can escape after getting too close ( event horizon ) II. Stellar evolution Can t be directly observed must be inferred from presence of accretion disk and/or jet

25 II. Stellar evolution Summary: Low-mass stars: slowly burn all fuel Medium mass stars: burn H, become red giant, separate into planetary nebula & white dwarf Massive stars: burn H all the way to Fe, explode in supernova, leave behind remnant and either neutron star or black hole

26 III. Filling out the stellar zoo T Taurivariables Protostars surrounded by gas cloud in which they formed Dusty blobs may become planets Mira variables Red giants just beginning to transform into planetary nebulae (Sun will be one in 5 billion years)

27 III. Filling out the stellar zoo RR Lyraevariables Regular (periodic) variable star Low mass stars ( 0.8 M Sun ) nearing end of life (like Mira vars) Much brighter than Sun ( 40x) All stars in this class roughly the same brightness Used as distance indicator

28 III. Filling out the stellar zoo (Classical) Cepheid variables Regular (periodic) variable star Massive stars (4-20 M Sun ) near death Muchbrighter than Sun (up to 1,000,000 times brighter) Strong relation between period of pulsation and peak brightness M V = 2.43log P Used as distance indicator

29 III. Filling out the stellar zoo S Doradusvariables Irregular variables Also called Luminous Blue Variables Massive stars (up to 150 M Sun ), with brightness > 1 million times the Sun So massive it s permanently unstable Very short lifetimes, very violent ends LBV Sun

30 III. Filling out the stellar zoo Magnetars Neutron stars with very intense magnetic fields (up to times stronger than Earth s) Pulsars Rapidly spinning neutron stars Emit light from magnetic pole As beam sweeps across Earth, we see regular pulses of light

31 III. Filling out the stellar zoo (Classical) Novae White dwarf with companion star Companion donates matter, which forms layer on surface of WD Eventually, layer dense enough to start nuclear burning, briefly shining like Sun does Burning finishes, star dims, but is slightly heavier Cycle repeats until

32 III. Filling out the stellar zoo Type IaSupernova White dwarf becomes too heavy to support its own weight Explodes in runaway thermonuclear event Briefly outshines entire host galaxy (i.e times brighter than Sun) Uniform peak magnitude Used as distance indicator

33 III. Filling out the stellar zoo Type II Supernova Explosion after massive star burns all the way to iron in core Leaves behind remnant, and neutron star or black hole X-ray binary system Compact object (NS or BH) with a companion, visible in X-rays Could be two NSs, or NS+BH

34 IV. Astronomical concepts Stellar temperature At birth, heavy stars hotter Surface temps from 3000 K to over 50,000 K Easy to accurately measure because light curve only depends on temperature Temperature determines color of star

35 Spectral class Temp also determines spectral class of star Easy way to group similar stars IV. Astronomical concepts

36 IV. Astronomical concepts Luminosity Stars release a lotof energy Solar luminosity: 3.9 x Joules/sec (93,000,000,000 Megatons of TNT each second) Other stars measured in units of L Sun, not Joules/sec IMPORTANT: Luminosity related to temperature and radius of star 2 4 L 1 R 1 T 1 = L2 R2 T2 Cooler star can be brighter if radius large enough!

37 IV. Astronomical concepts Hertzsprung-Russell diagrams Way to show information about groups of stars Each star plotted by temp and luminosity Many, many possible questions using HR diagrams. KNOW HOW TO READ & USE THEM

38 IV. Astronomical concepts The distance problem Everything in astronomy depends on distance from Earth: Size & age of Universe History & fate of Universe, Sun, stars, Milky Way, etc. Size of Milky Way galaxy Nearby cosmic neighborhood Etc., etc., etc. Problem: Neareststars are light-years away. Nobody makes rulers long enough How to determine distance, then?

39 IV. Astronomical concepts Parallax Use motion of object against distant background to get distance New unit of measurement: 1 parsec= distance at which parallax is one arcsecond (1 arcsecond: size of ping pong ball from 5 miles away) Distance-parallax relation: D pc = 1 p arcsec

40 IV. Astronomical concepts Magnitude Another way to measure brightness 2 kinds: apparent magnitude and absolute magnitude Apparent magnitude: how bright star appears from Earth (depends on distance and type of star) Lower number means brighter star (i.e. magnitude 1 brighter than magnitude 6) Absolute magnitude: how bright star would be at 10 parsecs from Earth

41 IV. Astronomical concepts Distance modulus Relates apparent (m) and absolute (M) magnitudes to get distance (d) to star

42 IV. Astronomical concepts Light spectrum Know where radio, infrared (IR), visible/optical, ultraviolet (UV), and X-ray fall on the spectrum

43 Mira Star at right of UV image V. List of objects Namesake of Mira variable class of stars Moving through space, trailing outer layers (so no Moving through space, trailing outer layers (so no planetary nebula)

44 W49B Supernova remnant Pictured in radio, IR & X-ray Barrel shape suggests SN was gamma-ray burst 1000 years old lyfrom Earth V. List of objects

45 Tycho ssnr Type Ia supernova remnant (seen here in IR and X-ray) SN seen in 1572 (so 440 years old), observed by Tycho Brahe 9000 lyfrom Earth Expanding at t5000 km/s V. List of objects

46 Vela SNR Type II supernova remnant (seen here in optical) Old SNR ( 12,000 yrs) Close to Earth (800 ly) V. List of objects Left behind pulsar, which was first confirmation of supernova/pulsar relationship Huge in night sky (16 times wider than full Moon)

47 G Type Ia supernova remnant (shown in X-ray) Youngest remnant in Milky Way (just 140 years old) 25,000 ly away, toward galactic center V. List of objects

48 Eta Carinae Luminous blue variable (a.k.a. S Doradus variable) Surrounded by nebula ejected in 1841 outburst Binary system, with primary 100 M Sun and 5x10 6 L Sun Shown in visible light V. List of objects Strong contender for next galactic supernova

49 SS Cygni Dwarf nova (recurring bursts due to accretion disc, not burning on WD) Outbursts every 7-8 weeks Goes from 12 th to 8 th mag 370 lyaway V. List of objects Closebinary system (stars orbit every 6.5 hrs, d100,000 miles separation)

50 V. List of objects T Tauri Not a star yet: powered by gravitational contraction, not fusion Protostar surrounded by dusty disk Shown in optical Strong wind coming off star, heavy accretion of disk matter onto star (hasn t reached birth mass yet) Trinary+ system, & T Taurimay have been ejected

51 GRS X-ray binary with star & black hole Observed in X-ray as well as radio (pictured at right) Famous for faster-than-light expansion of jets About 40,000 ly distant V. List of objects

52 V. List of objects 47 Tucanae Globular cluster Millions of stars, of multiple populations Many pulsars, but no (observed) planets 17,000 ly distant Size of full moon, but very difficult to see from northern hemisphere impossible from Europe

53 The Trapezium Open cluster in Orion nebula (false color visible image here) 5 primary stars, all of which are O-B stars, > 15 M Sun V. List of objects Only 1600 ly distant, but partially obscured by nebula Very compact telescope needed to resolve individual stars in cluster

54 V. List of objects T Pyxidis Recurrent (but irregular) classical nova with WD & companion WD estimated to be near max. allowed mass, so may become Type Ia supernova soon Normally 15.5 mag, bursts to 7 (2500 times brighter)

55 Abell30 Planetary nebula (shown in visible light) Very rare two-stage expulsion of nebula material 5500 lydistant Spherical shell marks interaction between two stages of nebula emission V. List of objects

56 RX J WD-WD X-ray binary system Orbital period 320 sec, with 50,000 mile separation Radiating energy in form of gravitational waves, moving inwards at 60 cm/day Only 1600 ly distant V. List of objects

57 V. List of objects V1647 Orionis Very new protostarof T Tauritype Rapidly accreting matter from surroundings, so very variable brightness Characterized by large outburst in 2004 that lasted for 18 months

58 M31 V1 Cepheid variable star in nearby Andromeda galaxy (a.k.a. M31) Identified by Edwin Hubble V. List of objects Used to prove that Andromeda did notlie within Milky Way, i.e. was an entirely different galaxy

59 NGC 1846 Globular cluster in Large Magellanic cloud, satellite galaxy of Milky Way As with 47 Tucanae, more than one population of stars visible V. List of objects Suggests that many globular clusters have rich history of interaction with galaxies & molecular clouds

60 NGC 3132 Planetary nebula lit by new white dwarf at center Central WD over 100,000 K but only size of Earth About 2000 lyaway V. List of objects 0.4 lyacross, expanding at 14 km/s, so about years old