simulating the fermi bubble - arizona/nasa space grant … · 2015. 5. 19. · dr. carl gardner...

OutlineBackground and Motivation

Our ModelOur Numerical Scheme

ResultsFuture Work

Acknowledgements & References

Simulating the Fermi Bubble

Charles ShugertAdvisor

Dr. Carl Gardner

April 3, 2015

Charles Shugert Advisor Dr. Carl Gardner Simulating the Fermi Bubble



ResultsFuture Work


Outline

I Background and Motivation

I Our Model

I Our Numerical Scheme

I Results

I Future Work




ResultsFuture Work


PicturesAstrophysical JetsGoals

Detection of the Fermi Bubbles

I On June 11, 2008, NASA launched the Fermi Gamma-RayTelescope

I On November 2010, two gamma-ray / x-ray bubbles weredetected in the center of the Milky Way

I These bubbles extend symmetrically ≈ 10 kpc above andbelow the Galactic center, with a width ≈ 8.4 kpc

I These bubbles emit gamma-rays at energies between 1 . Eγ .100 GeV, with x-rays emitted at the edge of the bubbles.

I These bubbles have approximately uniform surface brightness.




ResultsFuture Work






ResultsFuture Work



Astrophysical Jets

I Phenomena in which matter is ejected along the axis ofrotation of a an accretion

I Gigantic astrophysical jets are launched from accretion disksaround the central black holes in active galactic nuclei

I The mechanism that drive these jets remains contraversial




ResultsFuture Work



I Illustration of radio galaxy inearly Universe

I Material emmited via twosymmetric jets, with twolobes at the ends of the jets

I Detected 25 February, 2013;Satellite: Herschel

I Copyright: ESA/C.Carreau/ATG medialab




ResultsFuture Work



Our Goals

I We believe that the Fermi Bubbles are the result of anastrophysical jet pulse that occured millions of years ago

I We hope to uncoverI How old the Fermi Bubbles areI Gain a better understanding of the mechanisim that powers

the Fermi Bubbles




ResultsFuture Work


Approximation

I The outflow velocity of the Fermi Bubbles O(104 kms )I This ammounts to about a 1.01 γ valueI Special Relativistic Effects can be ignored

I Therefore we can use non-relativistic models to simulate theFermi-Bubbles

I We Model the Fermi-Bubbles through the Euler Gas-DynamicEquations




ResultsFuture Work


Euler Gas-Dynamic Equations

∂ρ

∂t+∇ · (ρu) = 0

ρ∂u

∂t+ ρu · ∇u +∇P = 0

∂E

∂t+∇ · (u(E + P)) = −n2Λ(T )

Energy density & pressure (polytropic gas with γ = 5/3)

E =3

2nkBT +

1

2ρu2

P = nkBT




ResultsFuture Work





ResultsFuture Work


Our Numerical Method: the 3rd Order WENO Scheme

I High-Order Finite Difference Upwind Method for nonlinearhyperbolic differential equations

I Solves for solutions to nonlinear hyperbolic conservation lawscontaining sharp discontinuities such as shock waves andcontacts

I We use a 13 X 13 kpc2 grid to model the bubble, with a totalrun time of 6.3 million years




ResultsFuture Work


Fermi Bubble Parameters

Units Bubble Ambient Computational Units

ρ Hcm3

ρ=0.06 ρ=60 ρ̄=10−2

P kgkms2

P=1.38·10−4 P=1.38·10−4 P̄=1.67·10−8u kms u=3·10

4 u=0.0 ū=103

Table : Fermi Bubble Parameters




ResultsFuture Work





ResultsFuture Work


Further Projects to be investigated

I Further improve the initial conditions of the simulation

I Simulate a 3-D model of the Fermi Bubble

I Create a movie of the Fermi Bubble




ResultsFuture Work



Acknowledgements

I Dr. Carl Gardner

I NASA Space Grant

I Friends and Family




ResultsFuture Work


References1. Fox, A., et al., Probing the Fermi Bubbles in Ultraviolet

Absorption: A Spectroscopic Signature of the Milky Way’sBiconical Nuclear Outflow (2015)

2. Guo, F. & Mathews, W. G., The Fermi Bubbles. I. PossibleEvidence for Recent AGN Jet Activity in the Galaxy (2012)

3. Guo, F. & Mathews, W. G., The Fermi Bubbles. II. ThePotential Roles of Viscosity and Cosmic Ray Diffusion in JetModels (2012)

4. Gardner, C. et al., Numerical Simulations of High MachNumber Astrophysical Jets with Radiative Cooling


OutlineBackground and MotivationPicturesAstrophysical JetsGoals

Our ModelOur Numerical SchemeResultsFuture WorkAcknowledgements & References

simulating the fermi bubble - arizona/nasa space grant … · 2015. 5. 19. · dr. carl gardner...

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