AST 248, Lecture 6 - Stony Brook University · James Lattimer AST 248, Lecture 6 The peak \Late...

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AST 248, Lecture 6 James Lattimer Department of Physics & Astronomy 449 ESS Bldg. Stony Brook University February 14, 2020 The Search for Intelligent Life in the Universe [email protected] James Lattimer AST 248, Lecture 6

Transcript of AST 248, Lecture 6 - Stony Brook University · James Lattimer AST 248, Lecture 6 The peak \Late...

AST 248, Lecture 6

James Lattimer

Department of Physics & Astronomy449 ESS Bldg.

Stony Brook University

February 14, 2020

The Search for Intelligent Life in the [email protected]

James Lattimer AST 248, Lecture 6

Distance Between Stars

1000 lyr?

6

The galaxy’s volume isπR2d .

d = 1000 lyrR = 50, 000 lyrV = 8 · 1012 lyr3

Number of stars isN = 4 · 1011.

Volume per star isV /N = 20 lyr3.

Distance between stars D:4πD3/3 = V /ND = 1.7 lyr.

Near Sun, D = 1 pc be-cause core density is large.

James Lattimer AST 248, Lecture 6

Star Formation

• Dense cores of molecularclouds collapse into hotplasma which eventuallytriggers nuclear reactions.

• Conversion of gravitationalenergy both heats thematerial and releases infraredradiation. csep10.phys.utk.edu/astr161/lect/solarsys/nebular.html

• Dense clumps form in protostellar disc that eventuallythemselves collapse into planets.

• Conservation of angular momentum requires spin rate toincrease during collapse and disc formation.

• Emissions of protostar hidden by cooler infalling matter;eventually breaks out at poles (least resistance), producingjets.

James Lattimer AST 248, Lecture 6

• Sufficiently rapidlyrotating collapsesform double ormultiple stars.

• Young star’semissions sweep outgas and dust fromplanetary system.

C. R. O’Dell and S. K. Wong (Rice U.), WFPC2, HST, NASA

B. Reipurth (Univ. of Col.), NASA

James Lattimer AST 248, Lecture 6

Star Formation in the Hertzsprung-Russel Diagram

James Lattimer AST 248, Lecture 6

Star Forming Regions

H.Yang(U

IUC)&

J.Hester

(ASU),

NASA

C.R. O’Dell (Rice U.), NASA

NGC 604

M42

M8

James Lattimer AST 248, Lecture 6

Solar System Formation – History• Georges Buffon suggested (1745) that the planets formed

when a massive object (a comet, he thought) collided with theSun and splashed out debris that coalesced into planets.

• Immanuel Kant proposed (1755) that the solar system formedfrom the gravitational collapse of an interstellar gas cloud.

• Pierre-Simon Laplace (1790) independently proposed Kant’sidea and suggested planets formed in successive rings of gas.

• Kant and Laplace idea is called the nebular hypothesis.• Laplace’s ring idea was eventually replaced by condensation of

solids into planetismals and gravitational accretion of solidsand gases into planets.

• Modified nebular hypothesis agrees well with observations ofcompositions of different objects in the solar system.

• Chance close encounters are too rare.• New observations of extra-solar planets are forcing

modifications to explain surprising planetary orbits.James Lattimer AST 248, Lecture 6

Solar System Formation – Major Stages• Contraction: of a diffuse interstellar gas cloud due to gravity.

• Conservation of angular momentum: leads to increase inrotation rate and flattening. Thermodynamic laws result inheating as the central density rises.

• Condensation: Heavier elements condense into solid dust grains– metals and rocks (inner), ices like H2O and CO2 (outer).

• Accretion: Dust grains collide and stick.

• Continued accretion leads to formation of rocks; gravity helpsform planetismals and planets. Gases retained on outer planets.

• Clearing: Solar heating repels gaseous matter that is not boundto planets. Most dust is incorporated into planets.

• Comets can be ejected far beyond planets by gravitationalencounters with planets, which also causes planetary migrations.Asteroids are either material which never formed a planet(Jupiter’s influence?), or debris from collisions of planetismals.

James Lattimer AST 248, Lecture 6

Addiso

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James Lattimer AST 248, Lecture 6

Addison-W

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James Lattimer AST 248, Lecture 6

Nick

D.Kim

,nearin

gzero

.net

Addison-Wesley

Cartoons in Science

James Lattimer AST 248, Lecture 6

Planetismals Form

www.astro.virginia.edu/class/skrutskie/astr121/notes/sscond.html

HH-30

James Lattimer AST 248, Lecture 6

Solar System Formation – Timeline

James Lattimer AST 248, Lecture 6

NASA/JPL-Caltech/R. Hurt

James Lattimer AST 248, Lecture 6

Wikipedia

James Lattimer AST 248, Lecture 6

Kuiper Belt

Wikipedia

Green = Kuiper belt objectOrange = Scattered disc object or CentaurMagenta = Trojan of JupiterYellow = Trojan of Neptune

Eris

James Lattimer AST 248, Lecture 6

Oort Cloud

herschel.jpl.nasa.gov/solarSystem.shtml

James Lattimer AST 248, Lecture 6

Formation of the Earth

• Earth formed 4.5 Gyrs ago.

• From a small accumulationof gas and dust, it grew byaccretion and bombardmentof rocky material.

• Impacts and radioactiveenergy release kept the earlyEarth very hot and molten.

• A large impact about 4.4 Gyrago resulted in the formationof the Moon.

The moon is the largest natural satellite of the Earth; theother moons being Cruithne , asteroid 2003 YN107, 1998 UP1and 2000 PH5.

James Lattimer AST 248, Lecture 6

• The peak “Late HeavyBombardment” was fromabout 4.0-3.8 Gyrs ago.

• The Earth’s high temperaturepromoted differentiation,forming the core and mantleas heavier elements (Fe, Ni,Co, Mn and S) sank andlighter elements (Si, Mg andO) floated.

www.physci.wsc.ma.edu/young/hgeol/geoinfo/timeline/formation/formation.html

6400 kmconvective

Lithosphere

• The molten character of the Earth destroyed most traces, butsome 4.4 Gyr-old zircons have survived.

• The Earth’s crust solidified and oceans formed about 4 Gyrago.

• Life seems to have formed on the Earth about the same time.

James Lattimer AST 248, Lecture 6