Download Slides from Dr. Frank`s Lecture17

ASTR 1102-002
2008 Fall Semester
Joel E. Tohline, Alumni Professor
Office: 247 Nicholson Hall
[Slides from Lecture17]
Interacting Binary Stars
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 3rd Modified
by Newton:
Pyr2 = aAU3/Msuns
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 19-20
Interacting Binary Stars
Classification based on
Roche Lobe Filling
Figure 19-21
Mass transfer can affect the evolution of
close binary star systems.
K0III
B8V
The Algol Paradox: the less massive star is more evolved!
Semidetached binary where the large red-giant blocks the light
from the more luminous, but smaller main-sequence star.
Mass transfer can affect the evolution of
close binary star systems.
Large
B8V
small star+disk
A7V
is eclipsed by the
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.
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
Peak
Luminosity
around
105 L8
Figure 21-15
Supernovae
Figure 20-22
Figure 20-20a,d
Supernovae
Figure 20-22
Figure 20-20a,d
Supernovae
Peak
Luminosity
4x109 L8
Figure 20-22
Figure 20-20a,d
Supernovae Type Ia
• SN Ia are extremely luminous and can be
seen in very distant galaxies.
• Their peak luminosities are very nearly the
same (Lpeak ~ 4x109 L8 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
Millisecond pulsar
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.
Black Widow Pulsar
Figure 21-11
The fastest pulsars were probably created
by mass transfer in close binary systems.
EXAMPLE: PSR 1957+20, the “Black Widow”
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.
Pulsating X-ray Source
Figure 21-12
Figure 21-13
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 (RSch= 2GM/c2) or
RSch= 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)
9.0
6.0
3.0
1.0
2.0
3.0
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 M8;
• 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.
Figure 22-10
Cygnus X-1
BH X-Ray Binary Cyg X-1
donor
Figure 22-11
Cygnus X-1
Figure 22-12
Beamed Radiation
Figure 22-13a
GRBs
Figure 22-13b
GRBs