Transcript Great Migrations & other natural history tales

Huge accretion disks (AGNs)
Accretion disk +
Black Hole in the
core of elliptical
galaxy NGC 4261
(Hubble Space Telescope)
A disk of cold gas and dust
fuels a black hole (BH).
300 light-years across, the
disk is tipped by 60 deg, to
provide a clear view of the
bright inner disk. The dark,
dusty disk represents a cold outer region which extends inwards to an
ultra-hot accretion disk with a few AU from the BH. This disk feeds matter into
the BH, where gravity compresses and heats the material. Hot gas rushes
from the vicinity of the BH creating the radio jets. The jets are aligned
perpendicular to the disk. This provides strong circumstantial evidence for the
existence of BH "central engine" in NGC 4261.
ARTIST’S VIEW...
BH radius (Schwarzschild radius)
R = 2GM/c^2 =
3 km (M/M_sun)
e.g., 10 M_sun ==> 30 km (binaries)
3e6 M_sun ==> 3/50 AU (galaxies)
1e8 M_sun ==> 2 AU
(AGNs)
1e9 M_sun ==> 20 AU (quasars)
Large disk luminosities
L ~ 1e46 erg/s for quasars =
= 1e34 erg/s (Sun) * 1e12
Grav.energy release in disk:
L_dsk = 50% * GM/R * dM/dt
R ~ 2GM/c^2
L ~ 25% * d(M c^2)/dt
Small (circumstellar) disks
Spectroscopic tomography
of Cataclismic Variables
cf. Keith Horne et al.
Accretion disks are often found in close, interacting pairs of stars,
such as the cataclysmic variables (CVs). One star, originally more
massive, evolves to a compact companion: a white dwarf or perhaps
a neutron star (pulsar) or a black hole.
The other, originally less massive, star bloats toward the end of its
main-sequence life and fills the critical surface called ROCHE LOBE,
after which it sends a stream of gas onto a compact companion,
creating an accrition disk
Superhumps are distortions (local maxima) of the light curve
of the s-called dwarf novae systems, belonging to cataclysmic
variables class. The light curve is due to the varying viewing
angle of the accretion disk and companion. Superhumps are
due to resonances and waves in the disk.
PPM simulation (Piecewise Parabolic Method) VH-1 code
Owen, Blondin et al.
z
Smaller disks
Gas density

Oph
Giant Molecular Cloud, 160 pc away
contains numerous dark clouds

Dark clouds
L57
Barnard 68
From: Diogenes Laertius,  (3rd cn. A.D.), IX.31
The first description of an accretion disk?
“The worlds come into being as follows: many bodies of all
sorts and shapes move from the infinite into a great void; they
come together there and produce a single whirl, in which,
colliding with one another and revolving in all manner of ways,
they begin to separate like to like.”
Leucippus, ca. 460 B.C.?
Kant-Laplace nebula ~ primitive solar nebula ~ accretion disk
~ protoplanetary disk ~ T Tauri disk
R. Descartes (1595-1650) - vortices of matter
-> planets
I. Kant (1755) - nebular hypothesis
(recently revived by: Cameron et al, Boss)
P.S. de Laplace (1796) - version with rings
ALL STARS form
in/via such disks!
Planets are just a
by-product.
These protostellar
disks are usually
seen with mass of
gas and dust ~ 0.01
to 0.1 solar masses.
They are ~solarcomposition.
Grain agglomeration
is ongoing.
Matthew Bate
(2003),
Bate and Benz (2003)
SPH, 1.5M particles
simulation of gravitational
collapse of a turbulent
gas cloud
(Jeans unstable)
the cloud forms a stellar
cluster including freefloating brown dwarfs
and protoplanetary disks.
Flaring shape
jets
Outflows disappear
before the disks do
Observed dM/dt ~ 1e-6 M_sun/yr for ~0.1 Myr time
==> total amount accreted ~0.1 M_sun
Observed dM/dt ~ 1e-7 M_sun/yr for ~Myr time
==> total amount accreted ~0.1 M_sun
etc.
The smallest disks
Planetary rings are also accretion disks, sort of. They are special:
their thickness is extremely small: z/r = 10 m/ 66000 km ~ 1e-6,
which makes them rather slowly accreting disks.
The sub-compact intro to planetary
systems and their evolution
-450: Extrasolar systems predicted (Leukippos, Demokritos). Formation in
disks
-325 Disproved by Aristoteles
1983: First dusty disks in exoplanetary systems discovered by IRAS
1992: First exoplanets found around a millisecond pulsar (Wolszczan & Dale)
1995: Radial Velocity Planets were found around normal, nearby stars,
via the Doppler spectroscopy of the host starlight,
starting with Mayor & Queloz, continuing wth Marcy & Butler, et al.
Orbital radii + masses of the extrasolar planets (picture from
2003)
Radial migration
Hot jupiters
These planets were found
via Doppler spectroscopy
of the host’s starlight.
Precision of measurement:
~3 m/s
Marcy and Butler (2003)
Like us?
NOT REALLY
WHY?
Accretion disk theory