University	  of	  Tsukuba	  	  | Center	  for	  Computational	  Sciences

Solving	  the	  Mysteries	  of	  the	  Universe	  with	  Computational	  Astrophysics
General-­‐relativistic	  radiation-­‐magnetohydrodynamics simulations	  of	  accretion	  flows	  onto	  black	  holes	  and	  neutron	  stars
Accretion flows/disks onto compact objects, such as black holes (BHs) and neutron stars (NSs), are the most powerfulenergy sources in the Universe. However, neither the energy production mechanism nor the flow structure is known.
Our general-­‐relativistic radiation-­‐magnetohydrodynamics simulations revealed that the luminosity of the BH accretion
disks can exceeds the Eddington luminosity, the upper limit for a spherical system. As a result, the strong radiationpressure force drives outflows above the disks (Fig 1a, Takahashi et al. 2016; 2018).
If the NSs have strong dipole magnetic
fields, the accretion disks aretruncated near the NSs and matter
falls onto the magnetic poles throughan accretion column because thestrong magnetic fields prevent
accretion through a disk (Fig 1b,Takahashi & Ohsuga 2017).

(a)Black	  hole(b)(a)

Accretion	  column(b)Outflow

DiskDiskNeutron	  star
Figure 7. Distributions of neutral hydrogen number density (left-handpanel) and temperature (right-hand panel) for a model galaxy.

Cosmological	  galaxy	  formation	  with	  SPH	  and	  radiative	  transfer	  calculations

SEURAT: line transfe

In the standard picture of structure formation, galaxies form through merging of smaller galaxies and continuous
150 The complicatedaccretion of gas. Once stars form, galaxy evolution proceeds under the influence of stellar feedback.
baryonic physics can be treated with state-­‐of-­‐the-­‐art cosmological simulations.
100100	  kpc	  100	  kpc	  GasHot	  bubble

velocity [km/s]

Zoom-­‐in18	  kpc	  First	  galaxy

500-50-100

Stars-150-20horizontal axis is 0Figure 8. Emergent spectra from -40
a model galaxy. Thethe wavelength and the vertical axis denotes the number count of photonr[kpc]
packets in each wavelength bin. A solid curve represents the result withSEURAT, whereas a dashed80
curve does the result with LICORICE. The spectra
are normalized such that the integration of the spectrum over frequencies(left-handshould be unity. In upper panel, the velocity structure is disregarded, whereas
in the lower panel the velocity
60 structure is included.

velocity [km/s]

We performed cosmological SPH simulations with zoom-­‐in Separately, using the three-­‐dimensional radiation
initial conditions which resolved the spatial scale from the hydrodynamic simulations, we modeled the evolution ofFigure
7. Distributionsof neutralethydrogen
numberdensity influenced by stellar UV radiation. The
large-­‐scale structure to star-­‐forming
regions (Yajimaal. thefirst galaxiespanel) andtemperature(right-handoccurspanel) forsimulations
a model galaxy.revealed that stellar feedback creates hot2017). Our simulations showed
thatstar formation
to escape (Abeintermittently due to supernova feedback. The simulated bubbles and allows Lyman-­‐alpha photons −17
coefficient, CLyα = 3.7 × 10 exp (−hν α /kB T)T−1/2 erg s−1 cm3process
Lyman-­‐
galaxies agreed with the stellar mass of observed Lyman-­‐ et al. 2018). The multiple-­‐scattering(Osterbrock & Ferland402006).
We castof
105 photon
packets.
alpha emitters at redshift 7.
alpha photons resulted in the formation of extendedEmergentspectrum
bright sources, which 4.4.2
nicelyreproduced
recent galaxy
20
We calculate the emergent Lyα spectra for the model galaxy withobservations.
SEURAT and LICORICE. In Fig. 8, the spectra calculated with the two

methods are compared. 0
In the upper panel, we set all velocities to-20

contact	  address:	  pr@ccs.tsukuba.ac.jp

http://www.ccs.tsukuba.ac.jp/-40

Fiprtheindneze
prea
beFica
whwe
coafe
To
Inup
ed
simsoanethlothouangi