General Meeting Report August

Eternity under the Microscope

The speaker for the evening was Dr Jarrod Hurley, Monash University Centre for Stellar and Planetary Astrophysics, and his subject “Promiscuous Stars and the Fate of Planets in Star Clusters”.

Walk outside on any clear night and look up into the sky and you cannot help but feel that you are face to face with eternity. The infinite shiny blackness of its iris looking back down on you, taking in the ever-changing landscape as the Earth slowly winds out its spiral path through the cosmic geometry. Silent, indifferent and unapproachable the stars are watching every move you make and a shiver creeps over your shoulder as you become aware of your insignificance in this eternal environment. So you go back inside the house to your computer program, go back to something you understand and that makes sense to you, and let the model spin an answer to it all. Already the father of gravity, Newton himself, realised the futility of trying to mathematically solve the gravitational interactions of multiple rotating bodies in the sky. The search fo an answer led Henry Poincaré towards an understanding of the order underlying Chaos. He won the Swedish King Oscar’s price for his work on the problem, even though he did not find a universal solution to the challenge:
"Given a system of arbitrarily many mass points that attract each other according to Newton's Laws, try to find, under the assumption that no two points ever collide, a representation of the coordinates of each point as a series in a variable that is some known function of time and for all whose values the series converges uniformly.”
Not till the advent of high speed computers became it possible to take the investigation further by running simulation of N-body problems with massive computer programs; and even now it remains the domain of Giga and Terra flop machines to run a reasonable size program model in a reasonable time.
Dr Jarrod Hurley, Lecturer in Astrophysics at Monash University, gained his PhD at the Institute of Astronomy at Cambridge University in 2000. He then worked at the American Museum of National History in New York for 3 years. Jarrod completed a year of a Hubble fellowship before moving to CSPA Monash to work on populations synthesis of stellar systems. His contributions and involvement in astrophysics publications include: ‘White dwarf sequences in dense star clusters’; ‘Core radius evolution of star clusters’; ‘The Promiscuous Nature of Stars in Clusters’; ‘Evolution of binary stars and the effect of tides on binary populations’; ‘Free-floating Planets in Stellar Clusters: Not So Surprising’.
The holy grail for stellar dynamicists, often called the "gravitational million-body problem", is a complete and realistic model of a globular cluster performed on a star-by-star basis. Is a Virtual Globular Clusters a reality? Recent software and hardware developments have brought such a model within reach. Models using the GRAPE-6 special-purpose hardware focus on the role of white dwarfs as cluster dark matter and chronometers.
With these facilities it now becomes practical to simulate and display the evolution of star clusters on the computer screen, to experiment with different parameters and try to match shape and composition of clusters to information gained from telescope measurements. Immediately noticeable in a fast-forward mode is an unexpected ongoing exchange of stars between many-body systems, where in chaotic encounters the smaller objects are ejected at high speed from a system only to be gravitationally captured in another system or in a merger with a larger body. Jarrod’s animated display was fascinating to watch, and the reference to”Promiscuity” in the title of tonight’s talk became obvious. Not at all like the eternal, unchanging cosmic harmony one associates with classical astronomy. Almost as if you could grab eternity, place it under a microscope and watch the random movements of its atomic particles. William Blake had the gift...

To see the world in a grain of sand,
and to see heaven in a wild flower,
hold infinity in the palm of your hands,
and eternity in an hour.

Tom Richards, in his vote of appreciation pointed out, how the model reminded him of goings-on in the business world, where the interactions and mergers of corporate identities seem to follow a similar Darwinian trend of survival of the fittest. Is there a social parallel to be drawn to the N-body system and celestial promiscuity?