My research focuses on how the present-day Universe came to be the way we see it today. That is a Big Question. To tackle it, one must combine observations of the Universe at very large distances, where, thanks to the finite speed of light, we also look back in time. Billions of years back in time, in fact. At least as important, one must look at the Universe much closer to home, where we may discern processes in enough detail that we may hope to understand the physics involved. Only thus can we hope to correctly interpret observations in the distant, past, Universe.
All trouble started with a big bang. As we rarely bother with other universes, we call it The Big Bang. The Universe started tiny, incredibly hot and dense, but rapidly cooled as it expanded and soon cooled to the point that electrons and nuclei could join into atoms. Only a few hundred million years later, the first small galaxies lit up, immersed in a Universe, ever expanding, of tenuous neutral gas and the afterglow of the Big Bang.
Galaxies appear to be universal building blocks in which visible, normal matter aggregates. Normal matter may represent a mere trace of the total matter-energy content of the Universe, but since it is what I'm made from, I tend to be quite fond of it. The first, small, galaxies probably formed around seeds of dark matter, invisible and interacting with normal matter only through its gravitational pull. The normal matter that first aggregated around those seeds formed massive black holes. Many galaxies found themselves engaged in a gravitational tug of war with their nearest neighbors. Bigger galaxies cannibalized their smaller peers and grew yet bigger through collisions and mergers. Their central black holes merged into even more massive black holes, that continue growing also by feeding on infalling material. All big galaxies today are thought to contain such massive black holes in their center. The surviving galaxies formed bound groups and later clusters of galaxies, vast structures that contain enough mass to resist dissolution due to the general expansion of the Universe.
Stars formed in galaxies whereever normal matter condensed into cooling gas clouds. The first generation of stars in no way resembled stars like our Sun. They consisted of only primordial hydrogen and helium. Each generation of stars synthesized heavier elements in the nuclear furnace of their cores or of their explosive deaths. The resulting debris, now contaminated with traces of the chemical elements that make up planets and humans, was incorporated into subsequent generations of stars. The protostellar gaseous nebula from which our Sun and our Solar System condensed, contained the products from at least several such generations.
But stars don't form in mathematically aesthetic isolation. In fact, star formation is a very complex and messy process. The radiation and winds, and the mechanical energy released in the violent deaths of massive, short-lived stars, affect their galactic and even extragalactic environment. Dust particles form from the chemical contaminants in the gaseous debris and may absorb and re-radiate some of the radiation. Feasting black holes (quasars or QSOs) blast energetic beams of radiation through their surroundings and out far beyond the limits of their host galaxy. Over time, radiation emerging from galaxies and energetic enough to knock the sole electron out of a hydrogen atom, or packing enough punch even to strip both electrons off helium started to reionize the ever more tenuous gas between galaxies. (Reionize, since the Universe was also ionized during the brief time before there were any atoms). By the time the Universe celebrated its first billionth birthday, all hydrogen gas between galaxies had been ionized, and, as quasars powered up, helium soon followed suit.
The star formation process in its varied aspects appears to be a driving
force in shaping the galaxies we see today. No computer program has yet
been fully successful in creating a virtual star from realistic initial
conditions. I therefore have followed an observational approach to
understanding several of the key variables and intend to continue pursuing
this approach with ground, sub-orbital, and space based future instruments
to provide key observational input to theoretical models and confrontation
of their predictions. Although, perhaps, seemingly unrelated, all
topics on which I have published (see my bibliography) bear in some way or other on the star formation process
and the complex path from the Big Bang to People.
Last updated: Feb 8, 2010