SLIDE 1
Introductory Lecture on Astrophysics (for astroparticle physicists)
Pasquale D. Serpico
International School on AstroParticle Physics - Zaragoza 13/07/2010
SLIDE 2
- Astrophysics is a huge field: In no way I can provide anything close
to a general overview, both for the lack of time and competence.
- I’ll try to give you an overall introduction to concepts, mechanisms &
a way of reasoning that those of you unfamiliar with astrophysics should learn in order not to get lost in the astro jargon & zoology.
- I’ll try to keep in mind that most of you have likely a particle physics
background, and may lack even an introduction to key concepts in astrophysics (e.g. virial theorem, shock waves, etc.) Sorry for the experts among you!
- Physical basis and impact of these “tools” for astroparticle
“applications” are my main guidelines: based on my experience!
Disclaimer Disclaimer
SLIDE 3 References References
“ “Theoretical Astrophysics Theoretical Astrophysics” ”, , by by T.
Padmanabhan
( (Vol
. I: Astrophysical Processes Astrophysical Processes; ; Vol
. II.: Stars Stars & Stellar & Stellar Systems Systems) )
General Astrophysical Concepts General Astrophysical Concepts Introduction to Introduction to High High Energy Astrophysics Energy Astrophysics Astroparticle Bounds from Astroparticle Bounds from Stellar Stellar Systems Systems “ “Stars as Laboratories for Fundamental Physics Stars as Laboratories for Fundamental Physics” ”, , by by G.
Raffelt “ “High High Energy Astrophysics Energy Astrophysics” ”, , by by M.
Longair
( (Vol
. I: Particles Particles, , Photons Photons and and their their detection; detection; Vol
. II.: Stars Stars, The , The Galaxy Galaxy and the ISM) and the ISM)
More More advanced advanced ( (still accessible still accessible!) !) “ “Stellar Stellar Structure Structure and and Evolution Evolution” ”, , by by R.
Kippenhahn and A. and A. Weigert Weigert “ “Galactic Astronomy Galactic Astronomy” ”, , by by J.
Binney and M. and M. Merrifield Merrifield “ “Galactic Dynamics Galactic Dynamics” ”, , by by J.
Binney and S. and S. Tremaine Tremaine “ “Cosmic Ray Astrophysics Cosmic Ray Astrophysics” ”, , by by R.
Schlickeiser “ “Foundations Foundations of
- f High-Energy Astrophysics
High-Energy Astrophysics” ”, , by by M.
Vietri
SLIDE 4 Outline Outline o
f the lectures lectures
Introduction Introduction ( (history history, , definition definition and basic and basic concepts concepts) ) Galaxies Galaxies and and Stars Stars: basic : basic notions notions on
structure & & evolution evolution Quick detour to Quick detour to “ “applications applications” ” to astroparticle to astroparticle
Lecture Lecture I: I: Intro Intro & Stellar & Stellar phenomena phenomena Lecture Lecture II: II: “ “Non-thermal Non-thermal” ” phenomena phenomena
Energy losses Energy losses of
- f charged particles as diagnostic tool
charged particles as diagnostic tool Notions Notions on the
acceleration of
particles Some Some notions notions on
galactic and and extragalactic sites extragalactic sites of
acceleration acceleration
SLIDE 5 Astronomy: the oldest natural science,
dealing with positional determination of celestial bodies, description of their motion
History History & some & some “ “definition definition” ”
On the subject of stars[…]
all investigations which are not ultimately reducible to simple visual
- bservations are necessarily denied to us.
We shall never be able to determine their chemical composition or even their density […] I regard any notion concerning the true mean temperature of the various stars as forever denied to us.
Auguste Comte, 1835 - Cours de la Philosophie Positive Astrophysics: deals with physical
properties & processes of celestial objects
Venus Tablet of King Ammizaduga ~XVII century BC Babylon (nowadays Irak)
The The latter is very young latter is very young, in XIX , in XIX century still doubted it could be possible century still doubted it could be possible! !
SLIDE 6 The situation changed as a consequence of Lab discoveries: In 1860, German physicist Gustav Kirchoff and chemist Robert Bunsen published their findings:
Physical diagnostics Physical diagnostics at at distance distance! !
1.
- 1. A hot solid object produces light with a continuous spectrum.
A hot solid object produces light with a continuous spectrum. 2.
- 2. A hot tenuous gas produces spectral lines with gas-specific wavelengths
A hot tenuous gas produces spectral lines with gas-specific wavelengths 3.
- 3. A hot solid object surrounded by a cooler tenuous gas produces an almost
A hot solid object surrounded by a cooler tenuous gas produces an almost continuous spectrum with gaps at discrete line positions of continuous spectrum with gaps at discrete line positions of Point 2. Point 2.
- A “new particle” was soon identified thereafter “from the sky”:
Helium Helium in the solar spectrum (1868 - Janssen & Lockyer)
- First observed on Earth in 1882 (by Neapolitan physicist Luigi
Palmieri, analyzing lava of Mount Vesuvius) The study of physical properties of celestial objects was now possible via the analysis of their light!
founder founder & first & first editor of editor of “ “Nature Nature” ”
587.49 nm
Birth of Birth of “ “Astroparticle Astroparticle” ”
SLIDE 7 In the XX In the XX century century, , also also the first the first assumption dropped assumption dropped! !
all investigations […] not […] reducible to simple visual observations are necessarily denied to us.
Karl Karl Jansky Jansky, early , early ‘ ‘30: Discovery of Radio Signal of the Milky Way 30: Discovery of Radio Signal of the Milky Way Astrophysics finally possible even with Astrophysics finally possible even with “ “invisible messengers invisible messengers” ”! ! In the present day, it is routinely accepted that astrophysics In the present day, it is routinely accepted that astrophysics can be performed without light altogether ( can be performed without light altogether (CRs CRs, neutrinos, , neutrinos, GWs GWs… …) )
Reber Radio Telescope Wheaton, IL (1937) (near Fermilab site) Janky and his antenna - Bell Telephone Laboratories Holmdel, NJ
SLIDE 8
(Astro) (Astro)physics with invisible messengers physics with invisible messengers (I, HE) (I, HE)
Aerobee Aerobee Rocket Rocket Kamiokande Kamiokande Homestake Homestake Mine Mine ν ν astrophysics astrophysics X-ray astrophysics X-ray astrophysics
Nobel Nobel Prize Prize 2002 2002
SLIDE 9
(Astro) (Astro)physics with invisible messengers physics with invisible messengers (II, LE) (II, LE)
SLIDE 10 How extreme How extreme? ?
Astroparticle Astroparticle: using physics to : using physics to understand astrophysics, which in turn understand astrophysics, which in turn we want to understand to learn about we want to understand to learn about (new?) physics in environments which (new?) physics in environments which are too extreme (density, temperature, are too extreme (density, temperature, distance and time-scales distance and time-scales… …) to ) to reproduce them in the Lab. reproduce them in the Lab. “ “unusual scales unusual scales” ” by many by many
- rders of magnitude!
- rders of magnitude!
Not crazy to think that some Not crazy to think that some physical laws may lose their physical laws may lose their domain of applicability domain of applicability… …
SLIDE 11 The Space The Space Age was crucial Age was crucial! !
Atmosphere is opaque Atmosphere is opaque to to most most ‘ ‘invisible invisible’ ’ light light (Actually, we (Actually, we’ ’ve rather ve rather adapted ourselves to adapted ourselves to detect detect… … what available!) what available!) To explore other bands, To explore other bands,
- ne needs to go in space
- ne needs to go in space
- r to use
- r to use
indirect techniques indirect techniques
SLIDE 12 Luminosity Luminosity scale: scale: magnitude magnitude
First First law law of
astronomy: : Astronomers Astronomers are are traditionalist traditionalist ( (by particle physics standards by particle physics standards) )
The Greek astronomer Hipparchus (II century BC) classified stellar objects based on how bright they appeared: the brightest were “magnitude 1”…down to "magnitude 6", the faintest visible objects (lower magnitude means brighter!) The response of the human eye (and most senses) is actually logarithmic. The above historical classification justified to define a difference of 5 magnitudes as a factor of 100 difference in flux.
Traditionally, Traditionally, m=0 m=0 for Vega ( for Vega (α α Lyr Lyr) ) m=-26 m=-26.74 for the Sun .74 for the Sun m=-12 m=-12.74 for the Moon (mean) .74 for the Moon (mean) m=-4 m=-4.67 for Venus at maximum .67 for Venus at maximum m=1 m=1.21 .21 for Saturn at minimum for Saturn at minimum m=3 m=3.03 SN1987A .03 SN1987A m=5 m=5.95 .95 for Uranus at minimum for Uranus at minimum m=13 m=13.65 for Pluto at maximum .65 for Pluto at maximum m=31 m=31.5 faintest object in visible light at HST .5 faintest object in visible light at HST
SLIDE 13 Distance scales: AU (Sun-Earth distance): 1.5 x 1011 m [solar system unit] pc (~nearest star): 3.1 x 1016 m [stellar systems unit] kpc 3.1 x 1019 m [~distances within galaxies] Mpc (~distance to M31) 3.1 x 1022 m [~clusters of Galaxies] Gpc 3.1 x 1025 m [large fraction of the visible universe]
Distance scales Distance scales & & absolute magnitude absolute magnitude
Absolute magnitude = apparent magnitude
- f an object when seen from d=10 pc
(the Sun has M=4.83) If the distance of an object is known, its apparent magnitude translates into an absolute measurement. Vice versa, having an estimate for the absolute brightness, the apparent one (accounting for attenatuations) allows to estimate d
Cosmic distance ladder Cosmic distance ladder
SLIDE 14
Roughly speaking astrophysics deals with self-gravitating systems (not going with the Cosmological Hubble flow) & the radiation/particles they emit/absorb There are two “main blocks” you should be aware of: Stars & Galaxies.
Division cosmology/astrophysics Division cosmology/astrophysics
Sources of energy: Sources of energy: Fusion (Stars) Fission/Decay (e.g. like young SNRs) Accretion (e.g. AGNs) Rotational Energy (e.g. Pulsars) Magnetic (e.g. solar flares) … Alternative Alternative ways to classify astrophysical objects ways to classify astrophysical objects Different ways of Different ways of “ “balancing gravity balancing gravity” ”: : Rotational support (Planets around the Sun) Velocity Dispersion (As “pressure in an ideal gas”) Fermi degeneracy (purely quantum effect)
SLIDE 15
Galaxies Galaxies… … and the and the Milky Milky Way Way
SLIDE 16 3 constituents constituents, with rough mass ratio 1/10/100 : Gas / Stars / Dark Matter Gas (ISM): collisional (processes exist exchanging E, ang. Momentum…) Stars: 107-1014, collisionless but feedback on ISM (winds, SN expl., etc.) Dark Matter: collisionless "gas”(of WIMPs?) supported by v-dispersion
Galaxies Galaxies
~75% H, ~25% He ~1-2% Z>2
}
Several components components, with varying prominence depending on galaxy type Nucleus: dense; star formation; supermassive black hole; non-th. activity Bulge: spheroidal; relatively old; large v-dispersion & little rotation Disk: gas & stars; younger; spiral arms & star formation; low σv , but rotates Halo: low density; GCs present; old; DM dominates (far from center…)
SLIDE 17 Traditional Classification Traditional Classification ( (Hubble Hubble’ ’s tuning fork s tuning fork) )
currently believed that the early Universe was dominated by spiral currently believed that the early Universe was dominated by spiral and irregular and irregular galaxies, while galaxies, while ellipticals ellipticals would form as a result of mergers of the above types. would form as a result of mergers of the above types.
significant significant population population
Stars Stars Predominantly Predominantly Old Stars Old Stars
SLIDE 18
radius of disk = 50000 l.y. (15 radius of disk = 50000 l.y. (15 kpc kpc) ) number of stars > 200 billion number of stars > 200 billion thickness of disk = 1000 l.y. (300 pc) thickness of disk = 1000 l.y. (300 pc) The Sun is in disk, 30000 l.y. from center (~8 The Sun is in disk, 30000 l.y. from center (~8 kpc kpc) )
Typical Parameters for our Galaxy Typical Parameters for our Galaxy
SLIDE 19
It is the low-density “ “stuff stuff” ” between the stars between the stars (~ 1 atom cm (~ 1 atom cm-3
).
- It is composed of 90% gas and 10% dust.
It is composed of 90% gas and 10% dust.
- gas: individual atoms and molecules
gas: individual atoms and molecules
- dust: large grains made of heavier elements
dust: large grains made of heavier elements
- The ISM effectively absorbs or scatters visible light!
The ISM effectively absorbs or scatters visible light!
- it masks most of the Milky Way Galaxy from us
it masks most of the Milky Way Galaxy from us
- Radio & infrared light does pass through the ISM.
Radio & infrared light does pass through the ISM.
- we can study and map the Milk Way Galaxy by making observations
we can study and map the Milk Way Galaxy by making observations at these wavelengths (e.g. 21 cm line) at these wavelengths (e.g. 21 cm line)
The The InterStellar InterStellar Medium (ISM) Medium (ISM)
- There is also an ISR field, made of light (UV, visible, Infrared) with
There is also an ISR field, made of light (UV, visible, Infrared) with typical overall energy density of ~O(1) eV/cm typical overall energy density of ~O(1) eV/cm3
3
- Furthermore, the medium is magnetized, with a field of strength of
Furthermore, the medium is magnetized, with a field of strength of a few a few µ µ-Gauss. Magnetization in (molecular) clouds can be much higher
- Gauss. Magnetization in (molecular) clouds can be much higher
- K. M. Ferriere, “The Interstellar Environment of our Galaxy,”
- Rev. Mod. Phys.73, 1031 (2001) [arXiv:astro-ph/0106359].
SLIDE 20
The The Multiwavelength Milky Multiwavelength Milky Way Way
SLIDE 21
- Stars in the disk all orbit the
Galactic center:
- in the same direction
- in the same plane, like planets do
- they “wobble” up and down due to
gravitational pull from the disk (hence “disk thickness”)
- Stars in the bulge & halo all orbit
the Galactic center:
- in different directions
- at various inclinations to the disk
- they have higher velocities
- Kepler’s 3rd Law P2 = 4π2/GM a3
can be used to estimate M~1012 M
Orbits Orbits in the in the Galaxy Galaxy
SLIDE 22
Stars Stars
SLIDE 23
Size of stars dictated by fundamental properties! Size of stars dictated by fundamental properties! Scale at which a self-gravitating object can ignite at its core nuclear Scale at which a self-gravitating object can ignite at its core nuclear reactions releasing enough energy to sustain its weight reactions releasing enough energy to sustain its weight
Stars Stars: estimate of : estimate of scales scales
Gravitational energy of a sphere of mass M & radius R Thermal+degeneracy pressure balancing gravity means Require that the maximal thermal energy is high enough that nuclear reaction can take place (“nuclear wavefunctions overlap”) , within a nuclear fudge factor η~0.1-10 Show that the condition above requires N to be at least as large as ~1/10 of the particles present in our Sun: “Stellar mass scale recovered”! Exercise: From the formulae above deduce that for fixed N there’s a critical density for which T is maximal.
SLIDE 24 Stars Stars: estimate of : estimate of scales scales - Some
relevant formulae
Estimated minimal number of protons Estimated minimal mass Estimated minimal radius For the Sun, one has
SLIDE 25
Stars Stars: : what what can can we observe we observe? ?
Nearby star distances are calibrated via parallax Relative masses (and in some cases absolute ones) can be inferred by measuring orbital parameters in binary systems. In turn, AU calibrated via radar measurements within the solar system.
SLIDE 26 Stars Stars: : what what can can we observe we observe? ? Introducing Introducing HR HR diagram diagram
- Usually we can determine “the colour” (relative intensity of flux at different wavelengths
via different filters) & the apparent luminosity Lapp (“overall # of photons”)
- Assuming blackbody spectrum (~OK for the Sun), one can infer Teff from the spectra.
If distance (and intervening attenuation!) is known, the absolute Labs can be derived →
- ne can map observations into a Labs- Teff plot.
Hertzsprung-Russell Diagram
SLIDE 27 Simplified Equations Simplified Equations of Stellar
Structure
Can we ‘explain’ the HR diagram? Modeling needed! The simplest ones assume spherical symmetry, static structure, no rotation, no B-fields…
Hydrostatic Equilibrium-Newton’s law Energy Conservation Energy Transport Equation of State
SLIDE 28 Virial Theorem Virial Theorem and and Hydrostatic Equilibrium Hydrostatic Equilibrium
Hydrostatic Equilibrium Integrate both sides x 4πr3 Partial Integration of LHS with P=0 at surface r=R Classical monatomic gas, P= 2U/3 (U internal energy density) Average energy of single “particles”
Most important tool to understand self-gravitating systems Most important tool to understand self-gravitating systems
SLIDE 29 Application to Application to the the Sun Sun( (like like) ) object
Approximate the Sun as a homogeneous sphere, with Gravitational potential energy of a p near the center For a classical gas & virial theorem it follows Central temperature from standard solar model
SLIDE 30 Feedback Feedback… … and and size size of
massive stars
Is Is the the burning process stable burning process stable? ?
As a consequence of a small Contraction → Heating → Increased nuclear burning → Increased pressure → Expansion (negative feedback: stable!) The thermonuclear fusion process is self-regulating and proceeds at almost fixed temperature (dictated by nuclear wavefunction overlap condition) Hence, the gravitational potential GM/R ~ const ⇒ R∝M. More massive stars are also bigger. H-burning H-burning Just another example of the power of the virial theorem
SLIDE 31 Luminosity-Mass Luminosity-Mass relation relation
From Stefan-Boltzmann law From Virial theorem Estimating the radius as One infers a law close to what observed More specifically,
SLIDE 32
Massive stars Massive stars are are significantly short-lived significantly short-lived
So, stars ~10 times more massive than the Sun live only ~10 million years! Can we use the previous considerations to estimate the lifetime of stars ? Yes!
Assume that the lifetime is given by the time needed to burn ~10% of their mass at the inferred luminosity. E.g. for the Sun: From the L-M relation, one has
SLIDE 33 Thermonuclear Reactions Thermonuclear Reactions and and Gamow Gamow Peak Peak
How to trigger nuclear reactions if the available E~keV<< MeV,(~ nuclear binding energy scale)? Quantum mechanics to the rescue: tunnelling effect!
PRL 82 (1999) 5205-5208
cross-sections in the fb →pb range (“LHC-like” but low E!) Need low background →underground facilities! Reactions dominated by σ @ so-called Gamow peak. This explains the typical parametrization in nuclear astrophysics
SLIDE 34 Different Nuclear Burnings Different Nuclear Burnings
Which nuclear reactions Which nuclear reactions are are effective effective? ?
Effectively converts 4p+2e 4p+2e-
→ 4
4He
He + 2 + 2ν νe
e
proceeds @ T~1 keV
Hydrogen Burning Hydrogen Burning Helium Burning Helium Burning
converts 3 3 4
4He
He → → 4
4He +
He +8
8Be*
Be*→ → 12
12C
C
12 12C+
C+ 4
4He
He → → 16
16O
O
16 16O+
O+ 4
4He
He → → 20
20N
N proceeds @ T~10 keV
Carbon Burning Carbon Burning
Many reactions, as12
12C+
C+12
12C
C → → 23
23Na +p
Na +p requires T~100 keV
Advanced burning Advanced burning
O/Ne…Sil burning. Very inefficiency & fast
SLIDE 35 Hydrogen Hydrogen 3 3 H H → → He He − − 2.1 2.1 5.9 5.9 1.2 1.2
×
×10 107
7
Duration Duration [years] [years] L Lν
ν/L
/Lγ
γ
ρ ρc
c
[g/cm [g/cm3
3]
] T Tc
c
[keV] [keV] Dominant Dominant Process Process Burning Phase Burning Phase L Lγ
γ [10
[104
4
L Lsun
sun]
] Helium Helium 14 14 He He → → C, O C, O 1.7 1.7
×
×10 10−
−5 5
6.0 6.0 1.3 1.3× ×10 103
3
1.3 1.3
×
×10 106
6
Carbon Carbon C C → → Ne, Mg Ne, Mg 53 53 1.7 1.7× ×10 105
5
8.6 8.6 1.0 1.0 6.3 6.3
×
×10 103
3
Neon Neon Ne Ne → → O, Mg O, Mg 110 110 1.6 1.6× ×10 107
7
9.6 9.6 1.8 1.8
×
×10 103
3
7.0 7.0 Oxygen Oxygen O O → → Si Si 160 160 9.7 9.7× ×10 107
7
9.6 9.6 2.1 2.1
×
×10 104
4
1.7 1.7 Silicon Silicon Si Si → → Fe, Ni Fe, Ni 270 270 2.3 2.3× ×10 108
8
9.6 9.6 9.2 9.2
×
×10 105
5
6 days 6 days
Nuclear Burnings Nuclear Burnings of a M=15
Msun
sun
star star
Slide by G. Raffelt
SLIDE 36 SNO SuperK (real time) Homestake Gallex GNO
Sage
Borexino (real time)
Do Do we have we have a a “ “proof proof” ” that nuclear burning takes place that nuclear burning takes place? ?
For the Sun, Yes! We measure the neutrino flux from reactions in its core!
See lectures by Aldo Ianni & Andrea Giuliani
SLIDE 37 99,77%
p + p → d+ e+ + νe
Eν ≤ 0,42 MeV 0,23%
p + e - + p → d + νe
Eν = 1,44 MeV
3He + 3He → α + 2p 3He + p→ α+e++νe
Eν ≤ 18 MeV
~2×10-5 % 84.7% 13,8% 0.02% 13.78%
3He + 4He → 7Be + γ 7Be+e- → 7Li + γ + νe
Eν ≤ 0,86 MeV
7Be + p → 8B + γ
d + p → 3He +γ
7Li + p → α + α
pp pp I I pp pp III III pp pp II II hep hep
8B → 8Be*+ e+ +νe
2α Eν ≤ 14,06 MeV
pp chain pp chain: : main energy source main energy source in the in the Sun Sun
SLIDE 38 An An alternative alternative path path: CNO : CNO cycle cycle
Carbon nuclei can enter in a “cycle” whose net result is to convert protons into helium (Carbon not burned, simply used as cathalyst) Due to higher charge of C, it requires higher T than those at the center of the Sun to be Dominant. For our star, it is sub-leading, and yet to be measured (it’s a possible target of Borexino)
SLIDE 39 The The Death Death of
Stars
SLIDE 40 Evolution Evolution “ “tracks tracks” ” on the
- n the Hertzsprung-Russell diagram
Hertzsprung-Russell diagram
SLIDE 41 The The spectacular spectacular birth of birth of White Dwarfs White Dwarfs
Stars with Stars with M M ≲
≲ 8
8 M Msun
sun
are are not able to burn beyond carbon not able to burn beyond carbon in in their their core.
- core. They actually expel most
They actually expel most
their outer material in the material in the form form of
winds, , later to be illuminated as later to be illuminated as “ “planetary nebulae planetary nebulae” ” But what happens But what happens in the in the He-C-O He-C-O core core when when the the thermonuclear energy source stops thermonuclear energy source stops? ? A A very very dense dense atomic atomic medium medium remains remains, , relatively cool relatively cool, , which supports which supports the the object
via degeneracy pressure degeneracy pressure
SLIDE 42
Detour Detour: : Lame-Emden Equation Lame-Emden Equation
Hydrostatic Equilibrium Plus the (barotropic) EOS Integrated from ξ=0 to the point ξ* at which θ vanishes (the physical ‘surface’) Can be ‘rescaled’ and rewritten via new variables
ξ
SLIDE 43 White Dwarfs White Dwarfs
For growing masses For growing masses, the , the radius becomes smaller radius becomes smaller… … at some at some point point the the electrons become relativistic electrons become relativistic and and there is there is a a limiting limiting mass mass above which above which no no stable configuration exist stable configuration exist: : Chandrasekar
Chandrasekar Mass Mass limit limit
(The exact proportionality constant depends on composition of the Degenerate gas.)
What remains What remains of the
cores of
“light light” ” stars stars is nothing but packed atomic species with is nothing but packed atomic species with degenerate electron degenerate electron sea sea: : these these are are called called White Dwarfs White Dwarfs, , with sizes with sizes of the
the the Earth Earth and and densities densities of
106
6 g/cm
g/cm3
3
SLIDE 44 Possible SN 1054 Petrograph by the Anasazi people (Chaco Canyon, New Mexico)
Loosely speaking, a Supernova event is the spectacular, final (not repeated!) act in the life of a star. It’s triggered when the evolution of the system leads to an instability, yielding to a destructive explosion of the star.
Supernovae Supernovae
SLIDE 45 Core Collapse (Type II, Core Collapse (Type II, Ib/c Ib/c) ) Thermonuclear (Type Thermonuclear (Type Ia Ia) )
Collapse sets in when Chandrasekhar limit is reached Collapse sets in when Chandrasekhar limit is reached Nuclear burning of C&O ignites
Nuclear burning of C&O ignites → → Nuclear deflagration Nuclear deflagration ( (“ “Fusion bomb Fusion bomb” ” triggered by collapse) triggered by collapse)
Collapse to nuclear density
Collapse to nuclear density Bounce & shock Bounce & shock Implosion Implosion → → Explosion Explosion Gain of nuclear binding energy Gain of nuclear binding energy ~ 1 ~ 1 MeV MeV per nucleon per nucleon Gain of gravitational binding energy Gain of gravitational binding energy ~100 ~100 MeV MeV per nucleon 99% into per nucleon 99% into ν ν’ ’s s Powered by gravity Powered by gravity Powered by nuclear binding energy Powered by nuclear binding energy Comparable Comparable “ “visible visible” ” energy release of ~ 3 energy release of ~ 3 × ×10 1051
51 erg
erg Carbon-oxygen white dwarf (remnant of low-mass star) accretes matter from companion Degenerate core of evolved massive star accretes matter by nuclear burning at its surface
Two Two ( (main main) ) kinds kinds of
beasts
SLIDE 46 The core of a massive star cannot sustain equilibrium by The core of a massive star cannot sustain equilibrium by thermonuclear fusion indefinitely. thermonuclear fusion indefinitely. → → 8-10 8-10 M Msun
sun
conditions unsuitable to fuse beyond conditions unsuitable to fuse beyond O-Ne-Mg O-Ne-Mg. . → → For M>10 For M>10 M Msun
sun, fusion becomes
, fusion becomes endoenergetic endoenergetic beyond Ni-Fe beyond Ni-Fe The degenerate core collapses until nuclear densities are The degenerate core collapses until nuclear densities are reached: a shock wave (SW) propagates outwards. reached: a shock wave (SW) propagates outwards. The SW energy is mostly dissipated by dissociating the outer The SW energy is mostly dissipated by dissociating the outer layer of metals: usually no explosion happens layer of metals: usually no explosion happens
What happens next? What happens next?
Stellar Stellar Collapse Collapse & SN & SN explosion explosion
SLIDE 47
Slide by C.D. Slide by C.D. Ott Ott
SLIDE 48 The core of a massive star cannot sustain equilibrium by The core of a massive star cannot sustain equilibrium by thermonuclear fusion indefinitely. thermonuclear fusion indefinitely. → → 8-10 8-10 M Msun
sun
conditions unsuitable to fuse beyond conditions unsuitable to fuse beyond O-Ne-Mg O-Ne-Mg. . → → For M>10 For M>10 M Msun
sun, fusion becomes
, fusion becomes endoenergetic endoenergetic beyond Ni-Fe beyond Ni-Fe The degenerate core collapses until nuclear densities are The degenerate core collapses until nuclear densities are reached: a shock wave (SW) propagates outwards. reached: a shock wave (SW) propagates outwards. The SW energy is mostly dissipated by dissociating the outer The SW energy is mostly dissipated by dissociating the outer layer of metals: usually no explosion happens layer of metals: usually no explosion happens
What happens next? What happens next?
Stellar Stellar Collapse Collapse & SN & SN explosion explosion
Neutrinos to the rescue! Neutrinos to the rescue!
The core (now a The core (now a “ “T~O(10) MeV T~O(10) MeV” ” p-n star) p-n star) dissipates its binding energy into dissipates its binding energy into ν ν’ ’s s ν ν heating increases pressure behind shock front, heating increases pressure behind shock front, rescuing stalled shock. It eventually ejects star rescuing stalled shock. It eventually ejects star’ ’s s
- uter mantle (explosion). While it lasts,
- uter mantle (explosion). While it lasts,
ν ν luminosity outshines whole universe luminosity outshines whole universe
SLIDE 49 Sanduleak -69 202 Supernova 1987A 23/02/1987
Gravitational binding energy Eb ≈ 3×1053 erg ≈ 17% MSUN c2
Showing up as Showing up as 99% Neutrinos 99% Neutrinos 1% Kinetic energy of explosion 1% Kinetic energy of explosion (~1% of this into cosmic rays) (~1% of this into cosmic rays) 0.01% 0.01% γ γ, outshine host galaxy , outshine host galaxy
Neutrino luminosity Lν ≈ 3 × 1053 erg / 3 sec ≈ 3 × 1019 LSUN
While it lasts, outshines the entire visible universe Unfortunately, only ~2-3 events/century in our Galaxy
“ “Figures Figures of
merit” ”
SLIDE 50
Neutron Stars Neutron Stars
In a SN progenitor core, one can reach much higher densities than in the core of smaller stars. At sufficiently high densities, the reactions In this case, the degenerate core relic left behind is a Neutron
Neutron Star Star (made of n, with some p and e).
Composition and structure ruled by β-equilibrium and (poorly known) EOS of dense matter. are above threshold (reverse reactions inhibited for the lack of available states for electrons) (He,C,O)
Among the most extreme Among the most extreme “ “Labs Labs” ” in the sky! in the sky!
SLIDE 51
Pulsars Pulsars
Since angular momentum and magnetic flux are ~ conserved, the size contraction of the NS compared to that of the progenitor implies So, we expect NS to be Strongly Magnetized and rapidly spinning with non-aligned rotation and magnetic axes, remnants of core-collapse SNe Pacini, Gold 1967-68. Actually, NS are usually identified as “pulsars” via their regular radio-pulse emission, but also seen in other bands (recently, hard γ-ray band!)
SLIDE 52 Energy source Energy source
A time-varying magnetic dipole moment emits radiation at the rate What supplies the e.m. energy? The rotational kinetic energy In first approximation, can be tought as rotating magnetic dipole Hence One can thus introduce a characteristic timescale In terms of which the spindown luminosity writes
SLIDE 53
1 2 Log[Period (s)]
- 20
- 19
- 18
- 17
- 16
- 15
- 14
- 13
- 12
- 11
- 10
- 9
Log [Period derivative (s s
Radio pulsar AXP SGR
10
3
yr 10
5 yr
1
7
y r 10
9
yr B = 10
1 2
G 1
1 1
G 109 G 1014 G 1015 G 1
1 3
G 1010 G
ATNF catalog
Fermi Fermi
Pulsar Pulsar diagnostics diagnostics
By combining observed time info
- n the pulsating signals with other
information (e.g. Mass, age…)
properties of the objects, perform population studies, etc. In turn, these can be used to study the structure of NS, their high energy emission mechanisms, constrain physics in extreme environment (or even new physics)
SLIDE 54 Black Black Holes Holes
Stars supported by degeneracy pressure cannot have arbitrarily Stars supported by degeneracy pressure cannot have arbitrarily high high mass: the mass: the greater greater M, the M, the smaller smaller R R… … until until a a limiting limiting mass mass is reached is reached, , above which above which no no stable configuration exist stable configuration exist ( (Chandrasekar
Chandrasekar Mass limit) Mass limit)
If If the compact star the compact star exceeds this value exceeds this value (e.g. (e.g. by accretion by accretion), ), nothing nothing can stop the can stop the collapse collapse: a black : a black hole forms hole forms ( (singularity singularity in space-time) in space-time) which which in the in the simplest simplest case of case of non-rotating non-rotating & & neutral configuration is characterized only by its neutral configuration is characterized only by its mass M. mass M. The single The single most important quantity to most important quantity to deal deal with with such objects is its such objects is its “ “Schwarzschild radius Schwarzschild radius” ” The The “ “Schwarzschild radius Schwarzschild radius” ” can can be defined for any object be defined for any object, , but only but only if its size is smaller than R if its size is smaller than Rs
s we
we are are actually dealing with actually dealing with a BH a BH The The importance importance of
- f General Relativity corrections to newtonian formulae
General Relativity corrections to newtonian formulae can can be typically estimated as be typically estimated as ratio of the ratio of the distance to distance to the BH the BH to its to its R Rs
s
SLIDE 55 Event Horizon Event Horizon
Indeed Indeed, a , a precursor precursor of the idea of a
“BH BH” ” was already was already formulated formulated in 1783 in 1783 by reverend John Michell by reverend John Michell (and 1796 (and 1796 by Laplace by Laplace) ) as as a body so compact a body so compact that that the the escape escape velocity from it exceeds velocity from it exceeds the the velocity velocity of light
Practically Practically, , for for a remote a remote observer
the BH is is “ “hidden hidden” ” by by a a spherical surface spherical surface of
radius R Rs
s within which
within which no no signal signal can can escape to escape to infinity infinity ( (does not mean that its existence does not mean that its existence cannot be inferred cannot be inferred via via gravitational effects gravitational effects!) !)
- Phil. Trans. Royal Soc. London.
- Phil. Trans. Royal Soc. London.
74, 35 (1783) 74, 35 (1783)
SLIDE 56
- Ex. 1:
- Ex. 1: NS have strong
NS have strong fields, sensitive to GR fields, sensitive to GR
- effects. In a close binary
- effects. In a close binary
system, the loss of energy system, the loss of energy due to GW emission is due to GW emission is
- sensible. Measuring the
- sensible. Measuring the
- rbital parameters, one can
- rbital parameters, one can
test the theory of gravity test the theory of gravity
Opportunities for tests Opportunities for tests of new
physics
- Ex. 3:
- Ex. 3: Weakly interacting particles, if light enough, can be emitted and escape (
Weakly interacting particles, if light enough, can be emitted and escape (“ “cooling cooling argument argument” ”) or, if heavy but captured ( ) or, if heavy but captured (WIMPs WIMPs), alter energy transport within stars ), alter energy transport within stars
If ν ν’ ’s s had had minuscule el.charges, minuscule el.charges, their path from SN1987A would their path from SN1987A would have been have been bent bent by galactic B-field, inducing a time delay larger than the observed duration of signal. by galactic B-field, inducing a time delay larger than the observed duration of signal.
SLIDE 57 E-loss argument to constrain E-loss argument to constrain new new physics physics
Let us assume that a star undergoes modified (typically enhanced) E-losses (cooling). Examples are exotic properties of ν’s or existence of other light weakly interacting particles such as axions. Frieman, Dimopoulos, Turner 1987 Often, for sufficiently small losses the stellar structure is only modified a little, with the main effect being a reduced lifetime due to the increased consumption of nuclear fuel. For a first estimate, Lx can be evaluated using unperturbed stellar models. If As a consequence, one expects a feedback of Contraction-Heating-Increased burning Let’s parametrize and typically ok when a single process dominates
SLIDE 58 Globular clusters as labs Globular clusters as labs
The turnoff turnoff (TO) (TO) is given by is given by the the “ “most massive stars still alive most massive stars still alive” ”, , hence measures hence measures the the age age. . From comparing From comparing the the “ “theoretical theoretical” ” age with age with the the observed
limit e.g. on e.g. on δ δx
x can
can be put be put. .
- Relatively unperturbed clusters of
~106 objects in the halo of the MW.
- Due to the very small vesc for the
gas, star formation was soon “halted” by the wind of the first SN to explode
- Its stars formed almost at the same
time, hence its HR works as isochrone: all stars have roughly the same age.
