Other research

[ Other Publications ]

Galaxy Evolution

How galaxies evolve over cosmic time is one of the most important and long-standing topics in astrophysics. Our Milky Way is continuing to grow, with stars being stripped from companion galaxies and new stars are being formed in gaseous clouds such as the Orion Nebula. However, most of the stars in the nearby Universe were formed roughly ten billion years ago, when the Universe was very young. As a result, how galaxies grow over cosmic time remains a matter of ongoing and vigourous debate. Dr Brown's research focuses on how galaxies grow over cosmic time. To measure this, he and his collaborators have obtained vast surveys of the distant Universe, using satellites and large telescopes. As the speed of light is finite, these surveys are able to look into the distant past and observe how galaxy populations once were. By comparing the number, mass and spatial distribution of galaxy populations as a function of distance (and time), he and his students are building up a picture of how galaxies evolve over the eons.

	NOAO Deep Wide-Field Survey (NDWFS) in the constellation of Bootes

Particle Cosmology

Recent observations suggest that 95% of the Universe's energy lies in a dark sector: forms of yet undiscovered matter and energy, with unknown composition and origin, called dark matter and dark energy. Elementary particle theorists try to understand how these new phenomena fit into the known framework of physical laws. Theoretical research indicates that near future astrophysical observations and particle collider experiments together may shed light not only on the dark side of the Universe, but discover precursors to new fundamental laws of Nature.

Photo from NASA of the Bullet Cluster Image credit: Wikipedia

Formation of The Solar System

Dr Andrew Prentice is continuing to develop his Modern Laplacian theory(MLT) for the formation of our Solar system. According to this mathematical model, the planets condensed from a concentric family of gas rings which the Sun had cast off over 4 billion years ago, when it was initially a huge spinning cloud of gas and dust, having size larger than the orbit of Neptune. Prentice has long claimed that within the primitive solar cloud, there existed very powerful convective currents which moved with speeds that were many times the speed of sound. These supersonic currents create a turbulent stress which provides the mechanism for shedding individual gas rings. The planets later formed from the gas rings by separate processes of chemical condensation of myriads of solid grains and the subsequent accumulation of those grains into larger bodies, called planetesimals, along the mean orbit of each gas ring.

The MLT is a fully quantitative model. It has also been extended to include the formation of the regular satellite systems of the giant planets Jupiter and Saturn, as well as the satellite systems of Uranus and Neptune. Not everyone, however, is happy with the concept of supersonic turbulence. To counter this opposition, Dr Prentice has used the theory over the past 30 years to make well-defined predictions about the properties of the planets and satellites. These predictions have been timed to coincide with the various flypasts and missions of NASA's fleet of interplanetary spacecrafts. Many of his predictions have been confirmed by the spacecraft observations, despite such an outcome being considered to be statistically unlikely. The 2 most recent confirmations of the MLT relate to measurements made by the Cassini-Huygens mission to Saturn and Titan and the MESSENGER mission to Mercury.

In the case of Titan, which Prentice claims to be a captured moon of Saturn, it was predicted that Cassini would discover gravitational anomalies in the mantle of this planet-sized moon. These anomalies mark the burial sites of 2 former native, low-density moons of Saturn that were destroyed by impact when Titan was captured from solar orbit. The Cassini radio science experiment has confirmed the existence of a negative gravitational anomaly directly below the bright region Xanadu of Titan, just as predicted by Prentice in 2006. And in late 2008, after completing 2 successive flypasts of Mercury, the MESSENGER gamma-ray spectrometer team reported the non-detection of 40K on the surface of the planet. This outcome had again been explicitly predicted by Prentice (here).

This diagram shows the details of the chemical condensation sequence that is expected for the inner planets of our Solar system, based on the MLT.