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Numerical Studies of Accretion Disks, Jets, and Gamma
Ray Bursts
Christopher C.
Abstract
Relativistic Jets are streams
of plasma moving
throughout the universe at
speeds up to 99% the speed
of light. They produce highenergy X-ray, radio, and
visible radiation that are
observable from great
distances across the
universe. (see fig. 1)
Many of these jets have
been attributed to black
hole accretion disk systems.
In these systems a disk of
material surrounds a black
hole and through magnetic
processes the material
accretes onto the black
hole. Strong outflows are
collimated into the fantastic
jets we observe.
1
Lindner
Jet Creation in Accretion Disk
Systems
1
University of Texas at Austin
Gamma Ray Bursts
Gamma ray bursts are extremely energetic outbursts
observable from across the universe. Long duration
gamma ray bursts have been found to be associated with
the deaths of very large stars. The favored models for
these is the “core collapse supernova,” where the massive
core of the star collapses into a black hole and black hole
accretion powers a luminous jet.
Despite numerous observations, many of the details in the
underlying physics of these objects are poorly understood.
The luminosity of these objects varies greatly at late
times, but we do not understand if this is a result of
activity near the central engine (e.g. the black hole) or
turbulent activity further out as the jet interacts with
stellar, interstellar, or intergalactic material.
Figure 2: Early jet breakout (left) and late jets (right) in a black hole accretion disk simulation.
Contours represent unbound jet material and the disk. Lines show magnetic field lines.
Figure 1: The neutron
star, disk and jet known as
the crab nebula (top) and
the jet originating near the
super massive black hole of
M87 (bottom). From NASA.
Gamma ray bursts (GRB) are
an especially exciting
outflow phenomena that are
capable of outputting as
much energy as our sun will
produce in its lifetime in a few seconds. Many of
these intriguing objects are also believed to be
powered by black hole accretion disks, specifically
originating from the death of very massive stars,
when the center of the star collapses into a black
hole.
Although we have much observational data for these
events our physical understanding of these systems is
lacking and further theoretical study is necessary.
Here we present our studies of jets and GRB using
high resolution hydrodynamic and
magnetohydrodynamic simulations, including
investigations of late time GRB evolution and jet
production, power, and orientation.
About the Author
Chris Lindner is a first year
astronomy graduate student at
the University of Texas at
Austin. Chris graduated Magna
Cum Laude from the College of
Charleston with degrees in
Astronomy and Physics, and
was the first (and currently
only) astronomy graduate in
the state of South Carolina.
A wide variety of fast-moving, high energy streams of plasma have been
observed in almost every wavelength of light. Although it is counterintuitive,
it is believed that many of these features originate near some of the strongest
gravitational sinks in the universe: black holes. The physical processes
surrounding these phenomena are quite intriguing, yet much cannot be
determined from observational study alone.
To answer these questions, we aim to perform high
resolution hydrodynamic simulations of gamma ray burst
progenitors (core collapse supernova). We inject powerful
(> 1051 erg/s) jets into a star, and track the evolution of
the system under gravitational and hydrodynamic forces.
The production of these jets is intricately linked to the rotation of the black
hole and its surrounding accretion disk - the disk of material surrounding the
black hole. Previous work has studied these systems where these two
rotations were aligned. However, these simplified models cannot account for
the precessing jets of objects such as SS433 (see fig. 3), and fail to fully explain
which processes set the orientation or power the jet.
By breaking this degeneracy in a system where the two rotations are not
aligned, we may study these processes in more detail and test a possible
explanation for observed precessing systems. We may also learn more about
the origin of other black hole accretion disk phenomena, such as gamma ray
bursts. Our project studies this work through the use of high resolution,
general relativistic magnetohydrodynamic simulations, run in parallel on
supercomputing resources such as UT Austin’s / TACC’s Ranger. We are the
first group to study these tilted systems in detail (see fig. 2).
Figure 3: A tilted disk (left). Here the black hole
spin axis would be pointed upward. Blue
contours show unbound jet material, and red
contours show the disk. Lines represent
magnetic field lines.
In simulation, the disks in these systems
precess – the entire system rotates around the
spin axis of the black hole (vertical here). These
may explain the spiral patterns of jets like that
observed in SS433 (right), shown in a 4.85 Ghz
intensity map, taken from Blundell and Bowler,
2004.
2 x 1011 cm
2 x 1011 cm
Figure 4: Logarithmic density plots of a slice of a star 5 s (left) and
25 s (right) after large amounts of energy have been injected to
simulate a gamma ray burst. The surface of the star is at 2 x 1011 cm.
Notice that much of the star is already disrupted.
Acknowledgements
This work was performed in collaboration with Chris Fragile of
College of Charleston, and Milos Milosavljevic and Sean Couch
of UT Austin. Simulations were performed using the Cosmos++
and FLASH fluid dynamics codes. The software used in this
work was in part developed by the DOE-supported ASC/Alliance
Center for Astrophysicsal Thermonuclear Flashes at the
University of Chicago, using resources at CofC and TACC.
We gratefully acknowledge the support of Faculty R&D and
SURF and RPG grants from the College of Charleston and a
REAP Grant from the South Carolina Space Grant Consortium.