ASTR Fall Semester Joel E. Tohline, Alumni Professor Office: 247 Nicholson Hall [Slides from Lecture17]

Interacting Binary Stars

Definition: A binary is said to be interacting if mass is transferred or exchanged between the components. Note: The mass exchange dramatically alters the observational properties of the binary and the evolution of the components.

Mass transfer can affect the evolution of close binary star systems. Kepler’s 3 rd Modified by Newton: P yr 2 = a AU 3 /M suns

Interacting Binary Stars Why some binaries interact and others don’t? The following processes are inevitable in a binary: 1)The binary separation decreases because of gravitational radiation and other angular momentum losses. 2)The component stars will evolve and change size (for example becoming a red giant) Conclusion: Long period (wide) binaries may never become interacting while short period (close) binaries are much more likely to interact at some stage.

Figure Interacting Binary Stars Classification based on Roche Lobe Filling

Figure 19-21

Mass transfer can affect the evolution of close binary star systems. Semidetached binary where the large red-giant blocks the light from the more luminous, but smaller main-sequence star. B8V The Algol Paradox: the less massive star is more evolved! K0III

Mass transfer can affect the evolution of close binary star systems. Semidetached binary where mass transfer has produced an accretion disk. The light curve is shallow when the cooler star and disk are eclipsed by the larger star. B8V A7V is eclipsed by the Largesmall star+disk

Mass transfer can affect the evolution of close binary star systems. Overcontact binary in which both stars overfill their Roche lobes. The short period indicates that the two stars are quite close.

Accretion onto White Dwarfs Nova Type Ia Supernova

Cataclysmic Variables DONOR ACCRETOR

Chandrasekhar Mass

Novae Figure 21-14

Accretion onto a White Dwarf Figure  Peak Luminosity around 10 5 L 

Figure 20-20a,d Figure Supernovae

Figure 20-20a,d Figure Supernovae

Figure 20-20a,d Figure Supernovae  Peak Luminosity 4x10 9 L 

Supernovae Type Ia SN Ia are extremely luminous and can be seen in very distant galaxies. Their peak luminosities are very nearly the same (L peak ~ 4x10 9 L  or M= -19). They are excellent Standard Candles. They are used to measure distances to galaxies far away.

Sloan Digital Sky Survey Already rising…At the peak

Sloan Digital Sky Survey

Accretion onto Neutron Stars Millisecond pulsar (§21-7) Black Widow pulsar Pulsating X-ray sources (§21-8) X-ray bursters (§21-9)

Different types of close binaries depending on the nature of the compact object Donor is a “normal star” either Main-Sequence or Giant. If the accretor is a WD: cataclysmic variables including novae NS: X-ray binaries including X-ray pulsars BH: Soft X-ray transients, miniquasars

Low-Mass X-ray Binary donor Accretion disk Accretion disk corona Neutron star

Old pulsars stop pulsing when they slow down, but some are “reborn” in binary stars While they are accreting, they emit X-ray pulses and are known as “X-ray pulsars”

Old pulsars stop pulsing when they slow down, but some are “reborn” in binary stars When the NS is spinning fast enough, it is “reborn” as a millisecond pulsar, accretion stops and the companion is blasted by the pulsar radiation. The side facing the pulsar is hot and evaporating. Millisecond pulsar

Black Widow Pulsar Figure 21-11

The fastest pulsars were probably created by mass transfer in close binary systems. Astronomers have cataloged at least 50 super fast pulsars, called millisecond pulsars, that have been “sped up” by mass from a companion star that hits the neutron star and speeds it up. EXAMPLE: PSR , the “Black Widow”

Pulsating X-ray Source Figure Figure 21-12

X-ray Bursters Figure 21-16

ON A WHITE DWARF: NOVA

ON A NEUTRON STAR: X-RAY BURST

Accretion onto Black Holes Primary method of identifying stellar-mass black holes (§22-3) Gamma-ray bursts (GRBs) (§22-4)

A non-rotating black hole has only a “center” and a “surface” The black hole is surrounded by an event horizon which is the sphere for which light cannot escape The radius of the event horizon is the Schwarzschild radius (R Sch = 2GM/c 2 ) or R Sch = 3 km (M/M  ) The center of the black hole is a point of infinite density and zero volume, called the central singularity.

Maximum Neutron Star Mass R (km) M/M 

Black Hole Binaries If the spectroscopy is of sufficient quality to enable a determination of the mass of the accretor and this mass exceeds 3 M  ; If the X-ray binary has never shown X-ray; bursts Then we consider such a binary as a “confirmed” Black Hole Binary We know at least 20 Black Hole Binaries.

Cygnus X-1 Figure 22-10

BH X-Ray Binary Cyg X-1 donor

Cygnus X-1 Figure 22-11

Beamed Radiation Figure 22-12

GRBs Figure 22-13a

GRBs Figure 22-13b