Astronomy Picture of the Day 9-27-02

Explanation: Don't be fooled by the familiar symmetry. The graceful spiral structure seen in this computer visualization does not portray winding spiral arms in a distant galaxy of stars. Instead, the graphic shows spiral shock waves in a three dimensional simulation of an accretion disk -- material swirling onto a compact central object that could represent a white dwarf star, neutron star, or black hole. Such accretion disks power bright x-ray sources within our own galaxy. They form in binary star systems which consist of a donor star (not shown above), supplying the accreting material, and a compact object whose strong gravity ultimately draws the material towards its surface. For known x-ray binary systems the size of the accretion disk itself might fall somewhere between the diameter of the Sun (about 1,400,000 kilometers) and the diameter of the Moon's orbit (800,000 kilometers). One interesting result of the virtual reality astrophysics illustrated here is that the simulated disk develops instabilities which tend to smear out the pronounced spiral shocks.

Astronomy Fun Fact:

Over the past 3 decades we have seen an incredible increase in computing power. Astrophysicists and other scientists now have the ability to run staggeringly complex simulations on today's supernumbercruncher computers. As they add data and variables, the need for speed becomes obvious. One supercomputer being built for genetic research ("Blue Gene") is to be rated at 100 teraflops (100 trillion floating point operations per second)!

Looks like IBM's going to do some serious processor stacking in that "Blue Gene" gizmo. They are shooting for a PETAFLOP (one quadrillion floating point ops per second).

PETA shows up everywhere... ;-D

Here's a chart of how supercomputing has grown:

Computing Performance in FLOPS

Performance Tier	FLOPS equivalent	Key Platforms
kiloflops (KFLOPS)	1,000 FLOPS	IBM 701 (1953) IBM 704 (1955) Apple II (1977)
megaflops (MFLOPS)	1,000,000 FLOPS	CDC 6600 (1966) Cray 1 (1976) Intel Pentium (1993)
gigaflops (GFLOPS)	1,000,000,000 FLOPS	Cray 2 (1985) Thinking Machines CM-2 (1987) Microsoft Xbox (2001)
teraflops (TFLOPS)	1,000,000,000,000 FLOPS	Intel ASCI Red (1996) IBM ASCI Blue Pacific (1998) IBM ASCI White (2000) NEC Earth Simulator (2002)
petaflops (PFLOPS)	1,000,000,000,000,000 FLOPS	IBM Blue Gene (2005-2010?)

This points out something concerning Global Warming. Or I think it does. Computer simulatons have gotten horrendously complex as computer power has increased. Now here is a model of an accretion disk. This kind of number crunching is done for any number of science problems, the structure of the Milky Way, of the universe itself. But most of them use an abstract data set and don't try to model our galaxy in fact, actual star by actual star. They will get something at the end of the run that has the same overal characteristics as our galaxy, but it isn't our galaxy in particular.

What about Global Warming? It's the same bujt even more complex. On top of that they are attempting to model a real system, not just a general abstract planet similar to earth. Their model is doomed to be nothing more than an approximation forever. The second order components in fluid dynamics have been known from basic newtonian physics for hundreds of years. These components are what they plug into their climate model. Then complicate matters by having different limits in different regions of the space. Then use up precious CPU time by having smaller and smaller regions, millions of regions, each different in some way. Right there you have diverged from reality because you don't have all the measurements for each cell and have to make assumptions.

Computational complexity might be a hindrance for an accretion disk model, but for a climate model upon which to base public decisions, the situation is beyond hope.

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THEN	NOW