slide 1 calculate the net force acting on a particle mass transfer in a binary system
TRANSCRIPT
Slide 1
Calculate the net force acting on a particle
Mass transfer in a binary system
Slide 2
Gravitational potential in the corotating frame
Slide 3
Mass Transfer in Binary StarsIn a binary system, each star controls a finite region of space,
bounded by the Roche Lobes (or Roche surfaces).
Matter can flow over from one star to another through the Inner Lagrange Point L1.
Lagrange points = points of stability, where matter can
remain without being pulled towards one of the stars.
Slide 4
Slide 5
Accretion from stellar windAccretion through Roche lobe outflow
Two mechanisms of mass transfer in a binary system
How the matter from a star can be brought to L1 point?
Slide 6
Accretion from a stellar wind
Slide 7
Star overflows its Roche lobe
Slide 8
Formation of an Accretion DiskThe rotation of the binary systems implies that gas flowing through the L1 point will have relatively high specific angular momentum - too much to directly accrete onto a compact companion star.
Slide 9
Initial ring of gas spreads into the disk due to diffusion.
To be able to accrete on the star, matter should lose angular momentum as a result of viscous friction
Friction leads to heating of the disk and intense radiation!!
Slide 10
Accreting binary systems
• White dwarf binaries
• Neutron star binaries
• Black hole binaries
Slide 11
Nova Explosions: a mechanism
Nova Cygni 1975
Hydrogen accreted through the accretion
disk accumulates on the surface of the WD
Very hot, dense layer of non-fusing hydrogen
on the WD surface
Explosive onset of H fusion
Nova explosion
Slide 12
Accreting neutron stars and black holes
Black holes and neutron stars can be part of a binary system.
=> Strong X-ray source!
Matter gets pulled off from the companion star, forming an accretion
disk.
Infalling matter heats up to billions K. Accretion is a very efficient process of
energy release.
Slide 13
The Universe in X-ray and gamma-ray eyes
Giacconi: Nobel prize 2002
Slide 14
Accretion onto a neutron star
Slide 15
X-ray pulsar: an accreting neutron star
Compare with a radio pulsar
Slide 16
Pulsars are slowing down with time.
Millisecond pulsars: how can an old neutron star rotate at a rate 1000/sec?
Slide 17
Accretion onto black holes
There is no hard surface. Will there be any radiation from the infalling matter??
Slide 18
Cygnus X1 – first black hole
Slide 19
Measurement of binary system parameters gave M ~ 7 Msun
Slide 20
High-Mass X-ray binary: accretion from a windCygnus X1
Slide 21
Low-Mass X-ray binary: accretion through Roche-lobe overflow
Slide 22
;2
3
21 P
aMM
a – in AUP – in yearsM1+M2 – in solar masses
Binary systems
If we can calculate the total mass and measure the mass of a normal star independently, we can find the mass of an unseen companion
Slide 23
Slide 24
Low-mass X-ray binaries are best candidates because the mass of a red dwarf is much less than a black-hole mass
212
3
21 ; MMP
aMM
Slide 25
Black-Hole vs. Neutron-Star Binaries
Black Holes: Accreted matter disappears beyond the event horizon without a trace.
Neutron Stars: Accreted matter produces an X-ray flash as it impacts on the
neutron star surface.
Slide 26
Soft X-ray transients (X-ray Novae)
Slide 27
Black Hole X-Ray Binaries
Strong X-ray sources
Rapidly, erratically variable (with flickering on time scales of less than a second)
Sometimes: Quasi-periodic oscillations (QPOs)
Sometimes: Radio-emitting jets
Accretion disks around black holes
Slide 28
Radio Jet Signatures
The radio jets of the Galactic black-hole candidate GRS 1915+105
V ~ 0.9 c
Slide 29
Gamma-ray bursts
Discovered in 1968 by Vela spy satellitesOccur ~ 3 times a day at random positions in the sky
Slide 30
Slide 31
Variability on a less than 1 ms timescale – must be a very small object R < ct ~ 100 km
Slide 32
Compton gamma-ray observatory discovered two puzzles:
• GRBs are distributed isotropically on the sky
• There is a deficiency of weak bursts – are we looking over the edge of their distribution?
Slide 33
Gamma-ray sky
GRB distribution
Slide 34
Slide 35
Breakthrough: in 1997 when BeppoSAX satellite was able to detect the burst position at 1 arcmin resolution and coordinate with optical telescopes within 1 hour after the burst
An X-ray image of the gamma-ray burst GRB 970228, obtained by the team of Italian and Dutch scientists at 5:00 AM on Friday 28th February, 1997, using the BeppoSAX satellite.
Slide 36
Discovery of the optical and radio counterparts of GRBs
Spectral lines with redshift from 0.8 to almost 4!
• GRBs are at the edge of the observable universe• They must be the most powerful explosions in the universe: ~ 1 solar mass is converted into gamma-rays in a second!
Slide 37
Gamma-ray burst models
Hypernova??
Slide 38 Fig. 10-18, p. 202
Known types of supernovae
Type II: hydrogen lines; collapse of a massive starType I: no hydrogen lines
Slide 39
Hard to imagine a supernova without ejection of a star shell
Slide 40
Colliding neutron stars
Slide 41
Slide 42
Continuing cycle of stellar evolution
Slide 43
Our Earth and our bodies are made of atoms that were synthesized in previous generations of stars