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Compact Binaries - 2ASTR2110
Sarazin
Test #2 Monday, November 13, 11 - 11:50 am Ruffner G006 (classroom) Bring pencils, paper, calculator You may not consult the text, your notes,
or any other materials or any person You may bring a 3x5 card with equations ~2/3 Quantitative Problems (like
homework problems) ~1/3 Qualitative Questions
Multiple Choice, Short Answer, Fill In the Blank questions No essay questions
Test #1 (Cont.) Equation/Formula Card: You may bring one 3x5 inch index card with
equations and formulae written on both sides. DO NOT LIST pc, AU, M¤, L¤, R¤
DO NOT INCLUDE ANY QUALITATIVE MATERIAL (text, etc.)
Test #2 (Cont.) Material:
Chapters 5, 7, 13.5-13.7, 14, 15, 17, 18, 23.3 Binary Stars, the Sun, Atomic Physics, Stellar
Spectra and Atmospheres, Stellar Interiors, Nuclear Energy, Stellar Evolution, Stellar Remnants, General Relativity, Black Holes, Stellar Deaths, Neutron Stars and Pulsars
(Quantitative problems only) (Qualitative problems only) Homeworks 6-9
Know pc, AU, M¤, L¤, R¤
Test #2 (Cont.)
No problem set week of November 6 – 13 to allow study for test
Review Session: Discussion session Friday, November 10, 3-4 pm
Compact Binaries - 2ASTR2110
Sarazin
Energy from Accretion • Nuclear energy
• Enuc ≈ 0.008 mc2 • Requires surface for material to accumulate → Enuc = 0 for BHs
• Gravitational energy • Egrav ≈ (1/2) GMm/R = (1/4) (RS/R) mc2 (Virial Theorem) • Egrav > Enuc if R ≲ 30 RS
• Egrav > Enuc for BHs, NSs (and Enuc = 0 for BHs) • Enuc > Egrav for WDs
• BHs, NSs: Egrav ≈ 0.1 - 0.3 mc2 !!
Accretion Disks • Accreted material has angular momentum
• Binary orbit • Other motions
• Moves in, orbits faster, centrifugal force increases, forms disk
Accretion Disks Lgrav = d Egrav / dt = (G M* / 2 R*) Ṁ
Ṁ ≡ d M* / dt accretion rate
Lgrav ≈ 1041 (M*/M�)(Ṁ/ M�/yr)(R*/R�)-1 erg/s
Typically,
Ṁ ~ 0.1 M� / tKelvin ~ 10-1 M� / 107 yr ~ 10-8 M�/yr
Accretion Disks Disk dense, ~ blackbody
Lgrav ≈ A σ T4
A ≈ 2 π R2
T ≈ (L/ 2 π σ R2)1/4
2 sides of disk
Zoology of Binary Stars
Zoology of Binary Stars
Cataclysmic Variables Accreting WD Gravitational Energy: Dwarf novae
Mainly UV
Episodic outburst
Cataclysmic Variables Accreting WD Gravitational Energy: Dwarf novae
Mainly UV
Episodic outburst
SS Aur
Cataclysmic Variables Nuclear Energy: Novae
Build up shell of H on surface of WD Bottom heats, fusion, explosion (degen. press.)
Shell blown into space
Nova Cygni 1992
C/O
H
Novae
Old Nova Persei
Novae
Z Cam
Dwarf nova with old nova shell
Zoology of Binary Stars
Type Ia Supernovae • Not associated with massive, young stars
• Not core collapse supernova • No hydrogen or helium • No stellar remnant (corpse: WD, NS, or BH)
Type Ia Supernovae Spectra:
• No H, He • Dominated by Fe, Co lines
No compact object (NS or BH) ever found in Type Ia remnant (e.g., no pulsar)
Type Ia Supernovae • WD accretes to M > MCh Chandrasekhar limit • Starts to implode, heats up
• Mainly C/O (not Fe), nuclear fuel, burns, explodes • Enuc > Egrav for WDs, WD blows up completely
Accretion by WD, old, low mass, dead star C/O WD → no H, He WD blows up completely → no stellar remnant Enucl ≈ 0.001 x M� c2 ≈ 1051 ergs
Type Ia Supernovae • Burn C → “Fe”
Type Ia Supernovae • Burn C → “Fe”
• Common lighter elements beyond H (He, C, O, …) have Z=N=even
• Fusion will make only Z=N=even directly
• e.g. 12C + 12C → 20Ne + 4He
• 56Fe has Z = 26, N = 30, A = 56 → cannot make directly • Nearest even-even isotope to 56Fe is 56Ni
• Fusion burns C → 56Ni • 56Ni radioactive
56Ni → 56Co → 56Fe 6.4 d 77 d
Type Ia Supernovae
6.4 d 77 d Light curve double
exponential
Type Ia Supernovae • Fusion makes Ni, Co, Fe → lines in spectrum
Each Type Ia makes ~ 0.6 M� of iron • Core collapse SN, iron core → NS or BH
Type Ia SN make most of iron in Universe
Zoology of Binary Stars
Zoology of Binary Stars
X-ray Binary Stars • BH or NS accreting from normal star
• Egrav > Enuc • T ~ 108 K • L ~ 1036 - 1039 ergs/s • Mainly X-ray emission • BH brighter and hotter
Zoology of Binary Stars
X-ray Binary Pulsar • NS accreting from normal star
• Strong magnetic field, gas channelled onto magnetic poles • Makes X-ray pulses
X-ray Burster Layer of accreted H eventually burns
• Burst of X-rays • Egrav > Enucl , material not blown off
NS
H
X-ray Binary Pulsar Spin-Up • Accreted material has high angular momentum
• Spins up neutron star (true of ~all X-ray binary pulsars)
Millisecond Radio Pulsars
Very fast rotation Very weak magnetic field Very Accurate Clocks Many in globular clusters OLD Most are binaries (circles) Not on life track of normal radio pulsars How are they made?
Millisecond Pulsars • Accretion spins up NSs in binaries • Accretion and age weaken magnetic field • After second star dies or accretion stops • Recently, several objects caught in transition
X-ray binary çè millisecond pulsar Millisecond Pulsars (``Recycled Pulsars’’)
• Older pulsars (many in globular clusters) • Most found in binaries • Very rapid rotation (Prot ~ 1 msec = 0.001 sec • Weak magnetic field, dP/dt ~ 10-20 sec/sec • Very good clocks!!
Binary Pulsars - Tests of General Relativity
PSR1913+16 • 1974, Hulse-Taylor discover • Orbital Period 8 hours, very compact • Elliptical orbits, determine masses very accurately, ~1.4 M�
PSR 1913+16 Orbit contracting due to gravitational waves Rate exactly matches General Relativity All other theories fail
PSR 1913+16 - Noble Prize 1993
Neutron Star Masses X-ray Binary Pulsars and Binary Millisecond Pulsars = NSs in binaries, derive masses
Neutron Star Masses
1.97+- 0.04 Msun NRAO/UVa
Neutron Star Masses X-ray Binary Pulsars and Binary Millisecond
Pulsars = NSs in binaries, derive masses
Most young NSs have M ~ 1.4 M�
Formed by collapse of iron core in massive star
Maximum mass > 1.97 M�
Rules out quark matter, other exotic possibilities for NS interiors
Zoology of Binary Stars
Gamma-Ray Bursts First lecture
Accidental Discovery 1960’s
Long Bursts:Collapsar Supernova Due to Jets from a
Black Hole?
Short Bursts: NS-NS or NS-BH Mergers to Form a Black Hole?
LIGO Detects Gravitational Waves NS-NS Mergers on August 17!
LIGO Detection GW source = Short GRB in nearby galaxy
è Confirms NS-NS merger theory for Short GRB
After the burst, kilo-nova = ejection of highly radioactive heavy nuclei made in neutron-rich environment
èConfirms theory for production of heaviest elements via NS-NS mergers
Where gold comes from
LIGO Detects Gravitational Waves NS-NS Mergers on August 17!
Zoology of Binary Stars
X-ray Binary Black Holes • First BH detected Cygnus X-1
• Like NSs, but brighter and hotter, no pulses, no nuclear energy • Highly irregular emission
X-ray Binary Black Holes Often, first detected as high mass stellar corpse
X-ray Binary Black Holes • First BH detected Cygnus X-1
• Like NSs, but brighter and hotter, no pulses, no nuclear energy • Highly irregular emission • Highly Doppler and Gravity (red)shifted X-ray lines
X-ray Line from Black Hole Grav. redshift
Dopp redshift Dopp blueshift
Accretion Disks Highly blueshifted and redshifted (Dopper and
gravity) from accretion disk gas.
X-ray Line from Black Hole Grav. redshift
Dopp redshift Dopp blueshift
X-ray Binary Black Holes • First BH detected Cygnus X-1
• Like NSs, but brighter and hotter, no pulses, no nuclear energy • Highly irregular emission • Highly Doppler and Gravity (red)shifted X-ray lines • Make both light and kinetic energy in jets
Jets from Black Holes
Jets from Black Holes
Jets from Black Holes
Jets from Black Holes
Jets from Cygnus X-1 BH
Paradox of Black Holes • Blackest things in Universe
• no light escapes from event horizon, but . . .
• As material falls in, makes more light than any other objects in Universe
• Brightest lights in Universe
• Best garbage disposals in Universe
• nothing escapes from event horizon, but . . .
• As material falls in, part is shot out in jets at v ~ 0.9999 c • Most powerful cannons in Universe