University of Naples Federico IIAcademic Year 2011-2012

Introduction to Astrophysics

Lectures read by prof. Massimo Capaccioli

Email: capaccioli@na.infn.itPhone: 081 5575601 (secretary at OAC-VSTceN)

Course Outline

� Introduction to the sky

� Basic properties of stars and electromagnetic radiation.

� Measurements of distances, masses, etc.

� Chemical composition of stars (interpretation of spectra).

� Stellar structure (interiors and atmospheres).

� Energy production and transport.

� Stellar evolution (formation, evolution, and death).

� White dwarfs, neutron stars, black holes.

The Fundamentals of Stellar Astrophysicsby G.W. Collins II

http://bifrost.cwru.edu/personal/collins/astrobook/

Fondamenti di Astrofisica Stellareby Vittorio Castellani

http://www.mporzio.astro.it/~marco/AstrofisicaStellare/

Useful books: web editions

J. Binney & M. Merrifield: Galactic Astronomy, Princeton University Press, 1998, pp. 796

D.A. Ostlie & B.W. Carroll: An Introduction to Modern Stellar Astrophysics, Addison-Wesley, 1996, pp. 752,

A.C. Phillips: Physics of Stars, Wiley & Sons, 1999, pp. 262

P. Lena et al.: Observational astrophysics, Springer-Verlag, 1998, p. 512

J. D. Jackson: Classical Electrodynamics, John Wiley & Sons, 1998, pp. 832

G.B. Rybicki & A.P. Lightman: Radiative Processes in Astrophysics, Wiley Interscience, 1985, pp. 400

W.H. Press et al.: Numerical Recipes in FORTRAN 77: The Art of Scientific Computing, Cambridge University Press; 2 ed., 1992, pp. 992

Other useful books

Some fundamental physical constantsrequired in this course (try to learn them by heart)

• a radiation density constant 7.55 × 10−16 J m−3 K−4

• c velocity of light 3.00 × 108 m s−1

• G gravitational constant 6.67 × 10−11 N m2 kg−2

• h Planck’s constant 6.62 × 10−34 J s

• k Boltzmann’s constant 1.38 × 10−23 J K−1

• me mass of electron 9.11 × 10−31 kg

• mH mass of hydrogen atom 1.67 × 10−27 kg

• NA Avogardo’s number 6.02 × 1023 mol−1

• σ Stefan-Boltzmann’s constant 5.67 × 10−8 W m−2 K−4 (σ = ac/4)

• R gas constant (k/mH) 8.26 × 103 J K−1 kg−1

• e charge of electron 1.60 × 10−19 C

• L�

luminosity of Sun 3.86 × 1026 W

• M�

mass of Sun 1.99 × 1030 kg

• Teff� effective temperature of Sun 5780 K

• R�

radius of Sun 6.96 × 108 m

• parsec (unit of distance) 3.09 × 1016 m

The bases of some of these lectures are at the links:

http://quixote.uwaterloo.ca/~mbalogh/teaching/PHYS375/PHYS375.html

Michael L. Balogh, PHYS 375: Astrophysics 2 - Stellar Evolution, University of Waterloo, Department of Physics and Astronomy

http://star.pst.qub.ac.uk/~sjs/teaching/stellarevol/S. Smartt, Online Lecture notes for module 210PHY412,Part II – Stellar structure and evolution

Most pictures and all movies come from the Web. They are used here for teaching purposes only (no profit).

Acknowledgements

Lecture 1

What is this course about ?

University of Naples Federico II, Academic Year 2011-2012

Istituzioni di Astrofisica, read by prof. Massimo Capaccioli

Learning outcomes

In this very introductory lecture the student will:

• see what astrophysics is (compared to astronomy);

• taste samples of phenomenology and classes of objects in the Solar

System, within the Galaxy, and in galaxies;

• be initiated just to the nomenclature of the standard Big Bang

cosmology;

• see the rate of growth of human civilization (technologywise);

• see some examples of the instruments of modern astrophysics.

All that is in preparation of the true goal of the course: the study of the

structure and of the evolution of stars.

… astrophysics made simple

Yes, …but what is

astrophysics ?

Let’s first ask what Astronomy is

Astronomy is:

► the oldest of all sciences (also encumbered with uneasy legacies),

► observationalrather than experimental, as it is instead physics

(give examples and draw consequences),

► in strict connection with other disciplines such as philosophy, and interlaced with estheticsand religion, but also with superstition.

Originally developed to serve astrology and to help everyday life(e.g. time measure), it is the mother of all sciencesin what the periodicity of planetary motions suggested the possibility to build tools to predict nature.

Give your definition of the word “science” ?

Engraving from "Selenografia sive Lunae Descriptio"

by Johannes Hevelius, 1647

ESO VLT

Astrophysicsis the branch of astronomy dealing with the physicsof celestial

bodies at large, from the Solar System to clusters of galaxies.

The basic assumption of this new science, born at the end of the Nineteenth

century (among theyoungest sciences), is the unity of the physical universe,

a belief grown up slowly since Newton’s theory

of a universal gravity, in antagonism with the distinction

between terrestrial and celestial worlds postulated

by Aristotle and supported by the Church of Rome.

Classical astrophysical topics include the physical properties (luminosity, density,

temperature, and chemical composition) of objects such as galaxies, stars, planets,

and the interstellar medium, as well as their interactions.

When the study regards scales much larger than the size of particular

gravitationally-bound objects in the universe, astrophysics turns into cosmology.

… and Astrophysics ?

Sir Isaac Newton (1643-1727)

A cosmic journey: a quick look to the deep sky

Let’s enjoy some examples taken from the night sky.

These all are things and phenomena calling for a physical explanation and

for the insertion within a coherent and unitary picture.

Moon at Cape Sunyon

Moon, Venus and the starry night:

the Glory of the Solar System, an interdisciplinary environment

Within the Solar System there is room and need for:

astrology, celestial mechanics, planetology, cosmogony, cosmology, astronautics, astrobiology, physical labs, philosophy, religion, power, science fiction …

New Physics ?

Dark Matter effects?

Pioneer anomalyor Pioneer effect: the observed deviation from expectations of the trajectories and velocities of various unmanned spacecrafts visiting the outer Solar System, notably Pioneer 10 and Pioneer 11, which seem to be slowing down a bit more than expected.

Nobel Prize medal

Pioneer anomaly or Pioneer effect: a mistery?

you find …

you win …

How do planets move about the Sun ?

( )3

1

The -body (point mass) problem: ,

chaos theory as gets very laNo solution for 3

Further complications

1,...,

rge

: finite sizes of bodies, forces other than gra

Nj k k j

j jk j

k j

m mm jN N

N N

γ≠ =

−= =

−→≥

∑r r

rr r

ɺɺ

vitational, dissipation, relativistic effects ...

Celestial mechanics(classical or relativistic): field of dynamics as applied to celestial bodies moving under their mutual gravitational influencein systems with few bodies. It usually describes and predicts motions in the Solar System, both of naturalbodies such as planets, satellites, asteroids, & comets, and of artificial bodies such as space probes. It can be also applied to small-number star systems.

The Great Rift on Saturn's moon Tethys

Planets’ satellites: from geology to … life ?

life ?

SETI Project

Search for extrasolar planets

Star field imagesWhat do you notice ?

They have various (apparent) luminosities,

various (apparent) sizes,

various colors,

(apparently) random distribution,

long lives (no change over a long time)

Crux, the Southern Cross

Firstly, stars are very numerous.

Picture with no tracking and with increasing defocussing

Star clustersStar clusters contain 102 –107 stars,which are:

• all at same distance;• dynamically bound;• with the same age and• thesame chemical composition.

The young (1.5×108 y) open cluster M35 (up) and the 10 times older NGC 2158(down),in the Gemini constellation.

M35

NGC 2158

What is a star ?How can we model its

“steady-state” structure ?How does it produce the

needed energy ?

Star clustersGlobular cluster ω Centauri, ∼1.5×104 ly away, 150 ly in size, contains ∼107 stars.

Three-color image taken with the wide-field optical telescope VST located at Cerro Paranal, Chile.

ω Cen

VST

Which is the key parameter setting the destiny of a star ?

The young star cluster M45The Pleiades = M45 contains over 3×103 stars,

is ∼400 ly away, and only 13 ly across.

Charles Messier(1730-1817)

M

(search on Web for stars & galaxies catalogs,

including old Messier’s)How do stars form ?

The young star cluster NGC 2266

This open (or galactic cluster) lies ∼105 ly distant in the constellation Gemini. With an age of ∼109 yr, it is old for a galactic cluster. Its evolved red giant stars are readily apparent in the three-color image (Calar Alto Observatory).

William Herschel(1738-1822)

John Louis Emil Dreyer(1852–1926)

NGC(search on Web for stars & galaxies catalogs, including

NGC’s)

NGC 2266

The old star cluster M3The Globular Cluster M3 contains ∼5×105 stars & spans 150 ly. It is ∼105 ly away.

For the Messier catalog see: http://www.ipac.caltech.edu/2mass/gallery/messiercat.html

M3

How do stars die ?

Star-forming region Messier 17, also known as the Omega Nebula or the Swan Nebula. This vast region of gas, dust and hot young stars lies in the heart of the Milky Way in the constellation of Sagittarius.Pictured by the VST.

Stars ⇔ gas & dust (ISM)

How do stars form ? How do they end ?quod pulvis es et in pulverem reverteris (Gen. 3,19)

Which are the forms assumed by cosmic

matter ?

Star life cycle

time

initi

al m

ass

Color-magnitude diagram

color

lum

inos

ityIn stars there are plain observables such luminosityand color (see next lecture for a correct definition of these quantities) which do correlate.

Can this be a starting point to try to understand these physical systems ?

A priori you do not know, but indeed your models of a star must contemplate the ability to reproduce the color-magnitude diagrams.

Against what doe we test the stellar models ?

Explore the Milky Way looking at http://mipsgal.ipac.caltech.edu/iracmips_map.html

The Milky Wayone hundred billion of stars

MW in IR from COBE

For the discovery of galaxies and the 1920 Great Debate see:

http://antwrp.gsfc.nasa.gov/diamond_jubilee/debate_1920.html

Harlow Shapley (1885-1972)

Sun

27.7 kly

nucleus & bulge

disc

Herber D. Curtis(1872-1942)

We are not at the center of the world!

Review the Copernican Principle!

you are here

200 kly

Galaxies & ClustersOn average, a galaxy is made of 100 millions of stars as the Sun. Why I do not see them individually?

A cluster of galaxies consists of hundreds to thousands of galaxies

(Hercules cluster pictured by VST)

Elliptical galaxies: a morphological family 10 millions to 10,000 billions of stars, gas & Dark Matter

The (peculiar) elliptical galaxy NGC 5128 = Centaurus A

The S0 galaxy NGC 3115

Edwin Powell Hubble (1889 –1953)

Spiral galaxies 1 to 100 billions of stars, gas, dust & Dark Matter

The barred spiral galaxy NGC 1300 in Eridanus

The spiral galaxy M81 in Ursa Major

Gérard Henry de Vaucouleurs(1918 –1995)

Spiral galaxies

A VST view of the spiral galaxy NGC 253 in Sculptor showing dust patches and gaseous nebulae

Active galaxiesobjects with a very compact nucleus (BH) causing a large variety of

phenomena which depend both on intrinsic properties and on the line of view

M87 = NGC 4486 = Virgo A

Active galaxiesObjects with a very compact nucleus (BH) causing a large variety of

phenomena which depend both on intrinsic properties and on the line of view

M87 = NGC 4486 = Virgo A

Radio Galaxy Fornax ARadio-optical composite image of giant E

galaxy NGC 1316, showing the galaxy (center), a smaller companion galaxy

being cannibalized by NGC 1316, andthe resulting “lobes” (orange) of radio

emission caused by jets of particles spewed from the core of the giant galaxy A Seyfert Galaxy

Active galaxies

Hoag’s object

Interacting galaxiesGalaxies interact gravitationally and eventually merge.

The titanic encounters, which take hundreds of millions of yearsto complete, may be reconstructed by N-body simulations.

To see movies search in the Web for «galaxy merging»e.g. http://hubblesite.org/newscenter/archive/releases/2002/11/image/d/e.g. http://www.cita.utoronto.ca/~dubinski/nbody/

The mice NGC 4676 (HST)

Clusters of galaxies

The Coma Cluster: hundreds of galaxies gravitationally bound & Dark Matter

VIMOS Visible Multiobject Spectrograph

Hubble Space Telescope HST

Fritz Zwicky

(1898-1974)

George Abell

(1927-1983)

Clusters heavier than the sum of their galaxiesDark haloes as gravitational lenses

Abell 2218: a galaxy cluster gravitational lens in Draco at 3×109 ly distance

Bernard Pierre Fort (1954-)

Dark Matter

Dark Energy

LHCPeter Higgs(1929-)

Within the cosmic horizon there are about 500 billions of galaxies

M31 in Andromeda

M87 in VirgoGiant

Dwarf

Satellite

How many are the galaxies ?

How do you know ?

going backwards in time they grow

temperature T & densityρρρρ

Dim

ensi

on

Everything started with the Big Bang 13.7 Gyr ago

How do you know ? Which are the proofs of the Big Bang ? How do you gauge the age of the Universe ?

you are here and now

The cosmic horizon

You reach the edge of the now knowable world travelling at the speed of the light for a time equal to the age of the universe (13.7 Gly), accounting for expansion. It makes R = 46.5 Gly.

R

Key steps in the history of the universe

cosmic time

look-back time

• Big Bang January 1

• Origin of Milky Way Galaxy May 1

• Origin of the solar system September 9

• Formation of the Earth September 14

• Origin of life on Earth ~September 25

• Formation of the oldest rocks known on Earth October 2

• Date of oldest fossils (bacteria and blue-green algae) October 9

• Invention of sex (by microorganisms) ~November 1

• Oldest fossil photosynthetic plants November 12

• Eukaryotes (first cells with nuclei) flourish November 15

Cosmic Calendar: from January to Novemberthe scaling of all events to a cosmic age of one year is

a way to feel the paucity of our history

• Origin of ancestors of apes and men ~ 1:30 p.m.

• First humans ~10:30 p.m.

• Widespread use of stone tools 11:00 p.m.

• Domestication of fire by Peking man 11:46 p.m.

• Beginning of most recent glacial period 11:56 p.m.

• Extensive cave painting in Europe 11:59 p.m.

• Invention of agriculture 11:59:20 p.m.

• Neolithic civilization; first cities 11:59:35 p.m.

• First dynasties in Sumer, Ebla and Egypt; development of astronomy 11:59:50 p.m.

• Greek philosophy and science; Roman Empire; birth of Christ 11:59:56 p.m.

Cosmic Calendar: December 31what follows happened in one afternoon!

Possible models of the expanding universe

Technology drives discoveries

VST

Which are the goals of astrophysics ?

• Discover new objects and new phenomena � observations, which may be serendipitous, focused or broad/blind (surveys)

• Understand what is observed (object or phenomenon) and model it as it appears

• Understand how it is born/caused and how it evolves, testing the results observationally (through predictions)

• Trace its future history

• Place it within a consistent scenario which unifies objects/phenomena

• Use all that to understand how the universe evolves

X-ray ultraviolet infrared radio

This course: PHYSICS OF THE STARS

A star may be simply schematized as a roughly spherical ball of (mostly) hydrogen gas, which responds to gravity and to its own pressure only.

However, to understand how this simple system behaves requires the knowledge and use of:

1. Classical & Fluid mechanics

2. Electromagnetism

3. Thermodynamics

4. Special Relativity

5. Chemistry

6. Nuclear Physics

7. Quantum Mechanics

+ Astronomy & Technology

The Sun