Presentation on theme: "Slide 1 Calculate the net force acting on a particle Mass transfer in a binary system."— Presentation 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 Stars In 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 8 Formation of an Accretion Disk The 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 19 Measurement of binary system parameters gave M ~ 7 M sun
Slide 20 High-Mass X-ray binary: accretion from a wind Cygnus X1
Slide 21 Low-Mass X-ray binary: accretion through Roche-lobe overflow
Slide 22 a – in AU P – in years M 1 +M 2 – 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 24 Low-mass X-ray binaries are best candidates because the mass of a red dwarf is much less than a black-hole mass
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 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 satellites Occur ~ 3 times a day at random positions in the sky
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 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.image
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!