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News from the NBIA - Niels Bohr Institute - November 22, 2012
Dr. Martin Pessah
A Universe of Disks, from Planets, to Stars, to Black Holes...
I. Basics of Disk Physics
IV. Numerical Simulations
II. Types of Disks in the Universe
III. Observational Evidence
Plan for the Talk
I. Basics of Disk Physics
What is a Disk?
Astrophysical Disks
Angular Momentum Conservation
Why Do Disks Form?
* To a first approximation the gas is falling into a central potential
* Angular momentum is mostly conserved
* Gas can cool down faster than it can get rid of angular momentum
* Flattened, rotating structure (also known as disk!) forms...
Imagine a cloud of gas collapsing due to its own gravity
R
Astrophysical disks rotate differentially
Particles in a central potential move in stable Keplerian orbits(like planets in solar system!)
Basic Disk Dynamics
Why Do We Study These Disks?
- How stars and planets form?- What powers the brightest X-ray sources in the sky?- Why Active Galactic Nuclei (Quasars) shine?- How does space-time behave close to a black hole?
Release of gravitational energy in accretion disks responsible for some of the most powerful phenomena in nature!
Proto-star X-ray Binary Active Galactic Nucleus
II. Types of Disks in the Universe
Saturn’s Rings
Saturn’s Rings
Protoplanetary Disks
Atlas featuring 30 proplyds, or protoplanetary discs, recently discovered in the Orion Nebula with the Hubble Space Telescope. CREDIT: NASA/ESA and L. Ricci (ESO)
Protoplanetary Disks
Formation of Protostellar Cores
Disk Dispersal and Planet Formation
Accretions Disks in Binary Systems
Remillard & McClintock, 2006
X-ray Binary Disks
Disks in Active Galactic Nuclei
Spiral Galaxies
M51
NGC 4565
Centaurus A
Disk-like Galaxies
Disk-like Galaxies
Typical Masses, Sizes, and Luminosities
1 AU = Sun-Earth distance 1 pc = 206365 AU
III. Observational Evidence
Basics of Light
The Perfect Emitter
Spectral Lines
Line profiles encode a lot of physical information!
Doppler Effect
Evidence for Disks. I.
Time
Evidence for Disks. II.
From ‘Accretion Power in Astrophysics’; Frank, King, & Raine, 1995
Evidence for Disks. III.
From ‘Accretion Power in Astrophysics’; Frank, King, & Raine, 1995
Evidence for Disks. IV.
From ‘Accretion Power in Astrophysics’; Frank, King, & Raine, 1995
Relativistic Iron Lines
Broad iron lines in AGN (Fabian et al.)Sensitive to ‘inner edge’
Sensitive to inclination
Detailed modeling of lineprofile allows us to ‘map’
the space-time aroundblack holes
IV. Numerical Simulations
Why Are Accretion Disk so Hard to Understand?
Magnetic fields do not seem to influence stellar structure significantly
Gravity balanced bypressure gradient along REnergy flows along R too!
R
Magnetic fields are essential for accretion
disks to work
Rφz
MassMomentumEnergy
Non-thermal processesMostly thermal energy
Turbulent Magnetized Accretion Disks
From J. Hawley’s websiteFrom J. Stone’s website
We need to understand the dynamics of magnetic fields in differentially rotating plasmas!!!
Supercomputers
Global 3D MHD Simulations
Beckwith et al. 2011
Global 3D MHD Simulations
Beckwith et al. 2011
Magnetized Accretion onto a Black Hole
Kato et al. 2011
Magnetized Accretion onto a Black Hole
Tchekhovskoy et al. 2011
Global 3D MHD Simulations
Flock et al. 2012
Magnetized Accretion onto a Black Hole
Flock et al. 2012
Planet-Disk Interactions
Thank you for coming to NBIA!
We hope to see you soon again...
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