quantum density fluctuations present
shortly after the big bang,” says Madau.
“The ordinary matter that forms stars
and planets has fallen into the gravita-
tional wells created by large clumps of
dark matter, giving rise to galaxies in
the centers of dark matter halos.”
Even smaller, on stellar scales, as-
tronomers have employed HPCs to
render a clearer picture of why a class
of compact, dense objects called neu-
tron stars often move through space
at very high velocities, in some cases
1,000 kilometers or more per second.
(Most stars have typical space veloci-
ties of a few tens of kilometers per
second.) A clue may be found in how
neutron stars are created. These ob-
jects, in which protons and electrons
have been gravitationally compressed
into neutrons, form from the collaps-
ing cores of massive stars just before
they explode as supernovae. Most as-
tronomers have long been convinced
the explosion itself somehow gives the
neutron star its high-velocity “kick.”
To explore this possibility, Adam Bur-
rows, an astrophysicist at Princeton
University, created a three-dimension-
al animation of conditions through-
out the star during the explosion. He
found that the star does not explode
symmetrically, but that the explosion
rips through the star asymmetrically.
The hydrodynamic recoil from such
an explosion is more than sufficient to
hurl the neutron star off into space.

“This is a straightforward conse-
quence of momentum conservation
when things aren’t spherical,” says
Burrows. “A lot of exotic mechanisms
have been proposed, but this simplest
of origins seems quite natural.”
The simulation was run on the Cray
XT5 Kraken supercomputer, which is
the 21st most-powerful computer in the
world, and is housed at Oak Ridge Na-
tional Laboratory.

news

Blue Waters project is now online at the National Center for Supercomputer Applications in Urbana-Champaign, IL. Titan should become operational at the Oak Ridge National Laboratory later this year, and Stampede at The University of Texas at Austin is expected to be up and running in January 2013. These and other HPCs promise to reveal new and transformative insights into the world and the universe from the smallest scales to the largest. Their simulations will probe levels of complexity we can only imagine, taking us where no one has gone—or could possibly go—before.

 

Further Reading

Guedes, J., Callegari, S., Madau, P., and Mayer, L. Forming realistic late-type spirals in a ΛCDM universe: The Eris simulation, The Astrophysical Journal 742, 2, Dec. 2011. Nordhaus, J., Brandt, T. D., Burrows, A., Almgren, A. The hydrodynamic origin of neutron kick stars, http://arxiv.org/abs/1112.3342. Prada, F., Klypin, A., Cuesta, A., Betancort-Rijo, J., and Primack, J. halo concentrations in the standard ΛCDM cosmology, http://arxiv.org/pdf/1104.5130.pdf.

Rantsiou, E., Burrows, A., Nordhaus, J., and Almgren, A. Induced rotation in 3D simulations of Ccre collapse supernovae: Implications for pulsar spins, The Astrophysical Journal 732, 1, May 2011. University of California High-Performance AstroComputing Center Bolshoi videos, http://hipacc.ucsc.edu/ Bolshoi/ Movies.html.

Jeff Kanipe is an astronomy writer based in boulder, Co.

© 2012 aCm 0001-0782/12/08 $15.00

Milestones
Computer Science Awards

acM, the european association for theoretical computer Science (eatcS), and the austrian government recently honored five leading computer scientists.

EDSGER W. DiJkStRA PRizE
acM and eatcS selected Maurice
Herlihy, J. Eliot B. Moss, Nir
Shavit, and Dan Touitou to
receive the 2012 edsger w.
dijkstra Prize in distributed
computing. herlihy, a professor
of computer science at Brown
university, and Moss, a professor
of computer science at the
university of Massachusetts,
were honored for their 1993
“transactional Memory” paper.
Shavit, a professor of computer
science at tel aviv university, and
touitou, chief technology officer
at toga networks, were honored
for their 1995 paper, “Software
transactional Memory.” the
edsger w. dijkstra Prize is
awarded to “outstanding
papers on the principles of
distributed computing, whose
significance and impact on the
theory or practice of distributed
computing have been evident for
at least 10 years.”

WittGEnStEin AWARD

the austrian Science fund on
behalf of the austrian Ministry
for Science presented the
wittgenstein award, austria’s
leading science prize, to
thomas henzinger, president
of the Institute of Science and
technology. the wittgenstein
award honors and supports
“scientists working in austria who
have accomplished outstanding
scientific achievements.”
—Jack Rosenberger