white dwarfs, black holes, dark matter · the discovery of white dwarfs: siriusb 1844 friedrich...
TRANSCRIPT
Frank Verbunt
White dwarfs, black holesand dark matter
Quantum mechanics and
General Relativity
Wageningen 26 March 2015
Outlinediscovery white dwarfs
quantum-mechanics:pressure
gravity and pressure:maximum mass
discovery neutron stars
general relativity theory
general relativity tests
black holes
the Universe
dark matter & energy
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 1 / 37
The discovery of white dwarfs: Sirius B 1844
Friedrich WilhelmBessel 1844
The motion ofSirius
Sirius A and B
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 2 / 37
Why are white dwarfs different?
From light to densitythe amount of light emittedby a star increases with thearea of its surface and withits surface temperature
Sirius B has (almost) thesame temperature asSirius A
but emits only 0.0001 asmuch lighthence: its
I surface area is 0.0001,I radius 0.01,I density 106
times that of Sirius A
More accuratelySirius A: a normal star
massa 2 × that of Sun
radius 1,7 × that of Sun
density 0,4 × that of Sun
(density Sun: 1.4 × water)
Sirius B: white dwarf
mass 1,0 × that of Sun
radius is 0,0084 × that ofSun
density 1.7 × 106 that of Sun
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 3 / 37
The simile of the Swiss village
Mayor Heisenberg
hotel rooms have
minimum size
Policeman Pauli
maximum 2 persons in
each room
Average priceLow-season: freechoice of rooms.High-season: manyrooms full; averageprice high
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 4 / 37
Quantum-mechanics: ‘rooms for velocity’
Chandrasekhar
application to whitedwarfs
Heisenberg uncertainty relation, Pauliexclusion principle
p is momentum = mass × velocityh is side of cube ( Planck constant)
electron: 0,00072 m/s proton: 0,000 000 4 m/s
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 5 / 37
Velocity and pressure; stellar structure
Pressurea particle collides: force:mass × velocity =momentum
many particles: pressureideal gas: higher pressurewhen
I temperature higher: highervelocities
I density higher: moreparticles
at very high densitypresseure depends only ondensity
‘degenerate pressure’
Equilibrium in stargravity pulls star in
pressure-difference pushesout
star settles at equilibrium
ordinary star: pressure ofideal gas
without source of energy starcools and constracts
white dwarf: degeneratepressure
size unaffected by cooling
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 6 / 37
Maximum mass of white dwarf
White dwarfs of increasing massa low-mass white dwarf is fullynon-relativistically degenerate(v � c)a heavier white dwarf
I is smallerI has a relativistically
degenerate center (v ' c)
the heavier the white dwarf, the(fractionally) larger therelativistic center
until at Mch the whole dwarf isrelativistically degenerate
Maximum mass of white dwarfwhen a white dwarf massexceeds Mch
I central pressure increasesI gravity increases faster
no equilibrium betweenpressure difference andgravity possible
gravity wins: the white dwarfcollapses
hence Mch is maximum mass
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 7 / 37
From neutron to the prediction of neutron stars
1932 Chadwick discoversneutron
1934 Baade & Zwicky predictneutron star
radius compared to that ofwhite dwarf scales as massof electron to that of neutron:Rns
Rwd=
me
mn× 25/3 '
1580
14 mile diameter
too small to detect . . .
formation = supernova
LA Times 19 jan 1934⇒
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 8 / 37
Crab pulsar in visible light: 30 rotations/s
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 9 / 37
Philosopher George Berkeley criticises Newton
Berkeley 1685-1753in an empty universe rotationand distance are not defined:hence they do not exist. ‘noabsolute space’
example: bucket of waterI in space with stars: water
rises along edge inrotating bucket
I in empty space: waterdoes not rise
I (Newton: water rises inboth cases: ‘absolutespace’)
picture of merry-go-round:‘Mach principle’ inspirationfor Einstein
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 10 / 37
SRT: Special Relativity - Theory: velocity of light
low velocitiesvelocity ball w.r.t. cyclist:20 + 30 = 50 km/h
high velocitiesvelocity light w.r.t. cyclist:200 000 + 300 000 , 500 000 km/sbut 300 000 km/s! how can this be?velocity = distance / time:something wrong with distanceand/or time
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 11 / 37
General Relativity - Theory: heavy and inert mass
a heavy mass is strongly attracted by gravity, e.g. from Earth; a lowmass less so
it takes more effort to bring a heavy mass into motion than a lightmass: the inert mass of a heavy object is bigger
as a result a low-mass object falls equally fast as a heavy one: heavymass = inert mass. Accidentally? Newton: yes. Einstein: no!
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 12 / 37
GRT-: simple axioms, complicated mathematics
AxiomsSRT: velocity of light thesame for all observers atconstant velocities
ART: velocity of light thesame for all observers ataccelerating velocities
acceleration = gravity
Einstein 1915re-writes physics
horrendously complicatedmathematics
needs help from Hilbert. . .
General relativityComplicated mathematicalequation can only be solved intwo very simple cases
1. spherical mass inotherwise empty universe(classical tests of GRT)
Schwarzschild solved thiscase analytically!Consequence: black hole
2. homogeneous andisotropic universe
Nowadays: fastest computerssolve other problems numerically(e.g. two masses)
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 13 / 37
GRT: the field equations of Einstein 1915
distribution of mass = curvature of space-time
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 14 / 37
GRT-: differences with Newton’s gravity
Distances in GRTin empty space thecircumference of a circle isO = 2πr
near a massa the circumferenceof a circle is O < 2πr
to draw this we must draw ahollow
Consequences: 1long axis of ellipse advances(Einstein 1915: Mercury)
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 15 / 37
GRT: the classical tests
Consequences: 2light follows curved orbit nearmass (Eddington 1919: solareclipse)
this made Einstein famous
Consequences: 3distances in direction ofmass are longer (Shapiro1964: Venus 0.0002 s)
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 16 / 37
GRT: binary neutron stars and stronger tests
neutron-star binary: orbital period 8 hr
rotation long axis ellipse: as much in one day as Mercury in a century!
orbit shrinks due to emission of gravitational radiation
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 17 / 37
GRT: binary neutron stars and stronger tests
2 effects determine masses of neutron stars; 3rd effect tests GRT
PSR1913+16 PSR J0737−3039
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 18 / 37
GRT: binary neutron stars and stronger tests
The accurracy of the pulsar as a clock allows unprecented accurracy indetermining the orbit (period, eccentricity, masses of the neutron stars).
PSR1913+16 PSR J0737−3039,valid on 6 July 1984 30 May 2004pulse-period P 0.059030002593481(7)s 0.022699378599624(1)sderivative P 8.62713(8) × 10−18ss−1 1.75993(5) × 10−18ss−1
2nd derivative | P | < 2 × 10−29s s−1
orbital period Pb 0.322997448930(4)d 0.10225156248(5)dderivative Pb −2.4184(9) × 10−12 −1.252(17) × 10−12
eccentricity e 0.6171338(4) 0.0877775(9)periastron-motion ω 4.226595(5)◦yr−1 16.89947(68)◦/yrmass pulsar M1 1.4414(2)M� 1.3381(7)M�mass companion M2 1.3867(2)M� 1.2489(7)M�
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 19 / 37
GRT: strong effects and the black hole
deeper depression for larger mass
when the ratio radous / mass becomes too small, the bottom dropsout: the distance to the edge (the ‘horizon’) is infinite
we call this a black hole
to understand this we consider first the Newtonian dark star
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 20 / 37
Gravitation according to Newton: the dark stsr
Michel 1784, Laplace 1795the escape velocity vescdepends on ratiomass/radius
vesc =
√2GM
R
vesc for Sun: 440 km/s
when we compress the Sunto radius 3 km vesc is equal tothe velocity of light
Propertiesa particle of light that moves upis decelerated and falls back:light cannot reach us
the star for us is dark:astre occlu
a dark star is stable
one can travel there . . . andreturn in a finite time
clocks near the surface tick atthe same rate as clocks far away
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 21 / 37
Gravity according to Einstein: the black hole
the radius Rs of the horizonequals the radius of the darkstar
classical testslight is bent already outside thehorizon
nothing can pass the horizonfrom inside, not even light
a dark star inescapablycollapses
one can travel there . . . but thencannot return
the traveller sees his clock ticknormally but for a farawayobserver the clocks slow downnear the horizon and thetraveller hovers just outside it
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 22 / 37
Gravity according to Einstein: the black hole
classical testslight is bent already outside thehorizon
nothing can pass the horizonfrom inside, not even light
a dark star inescapablycollapses
one can travel there . . . but thencannot return
the traveller sees his clock ticknormally but for a farawayobserver the clocks slow downnear the horizon and thetraveller hovers just outside it
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 22 / 37
GRT: the universe
The Universe‘Copernican principle’: the Sunhas no special position in theUniverse‘extended Copernican principle’:there are no special positions inthe Universe
homogeneous: mass-densitythe same everywhere
isotropic: the same in alldirections
complicated equationsbecomes very simple
2nd-order differentialequation: 2 constants
Einstein 1915Solution for homogeneousUniverse
expands or shrinks
but stars do not move fromus
the Universe is static
mathematical trick:‘cosmological constant’
1921: Friedman: static, butnot stable
Einstein ignores this
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 23 / 37
Nebulae beyond the stars: M81 en M82
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 24 / 37
Spiral galaxies
Voorbeeld van diverse bulgedisk verhoudingenin edge-on stelsels
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 25 / 37
Vesto Slipher discovers that galaxies move away from us
first measurement 1912: Andromeda nebula moves towards us:vr = −300 km/s. Most other galaxies move away: V.M. Slipher , 1917,Proceedings of the American Philosophical Society, vol. 56, p.403-409
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 26 / 37
The expanding Universe
Einstein & Lemaître ±1933 Lemaître1925 Einstein static but notstable
I the Universe expandsI according to GRTI and measured by SlipherI velocity proportional to
distance
Einstein not impressed. . .
discovery later claimed byHubble
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 27 / 37
The expanding Universe: the Big Bang
Lemaîtrethe Universe expands
was smaller in the past
its temperature was higher
its density was higher
The Universe started as anexploding primordial atom
George Gamow 1904-1968the inital Universe was hotand dense
therefore: nuclear fusion; allelements made in first 3minutes
Alpher, Bethe, Gamow 1948
as the Universe expands itbecomes transparent
radiation and matter coolindependently
radiation now 5 á 50 K
(in fact: 3 K)
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 28 / 37
Cluster Abell 1185
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 29 / 37
Dark matter in clusters of galaxies
Zwicky 1933/37: Coma clustervelocities v ' 700 km/s
size R = 0.8 Mpc
mass in galaxies too small toconfine cluster: most massinvisible
Coma cluster of galaxies
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 30 / 37
Dark matter in clusters of galaxies
Confirmation 1curved stripes in galaxyclusters
gravity lense: mass in clusterdeforms and amplifies imageof faraway galaxy
from this derive mass incluster
agrees with kinematic mass
Confirmation 2hot X-ray emitting gas
confinement requires largemass
agrees with kinematic mass
Cluster of galaxies
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 31 / 37
3 K background radiation
Discovery
from all directions
3 K + dipole=direction ownmotion
COBE / WMAP
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 32 / 37
3 K background radiation: fluctuations: 9 yr WMAP
variation across sky ∼< 1 : 105: how does one side know about the other?
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 33 / 37
3 K background radiation: fluctuations: 4 yr Planck
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 34 / 37
Dark matter and dark energy
Dark matter fractionsolar system: negligible
10 pc (globular cluster):negligible
103 pc (solar environment):30 %
104 pc (galaxy): 64-84 %
107 pc (cluster of galaxies):70 %
Dark matter naturenot baryonic
primordial black holes (?)
new type of particles (?)
Het standaard-model
voor elk deeltje eensupersymmetrisch deeltje
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 35 / 37
Dark energy
Discovery of dark energywhite dwarf collapse startsfusion
leading to explosion =supernova Ia
all equally bright
brightness known: distanceknown
faraway supernovae indicatepush: dark energy
also indicated by details ofcosmic background radiation
supernova 1994D
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 36 / 37
Ordinary matter, dark matter and dark energy
WMAP and Planckat largest scales: 109 pc
dark energy 72.1±2.5%
dark matter 23.3±2.3%
baryons 4.6±0.2%
Frank Verbunt ( Dept. Astronomy Nijmegen) White dwarfs, black holes, dark matter March 26, 2015 37 / 37