Stars, planets and origins
The detection of extrasolar planets over the past decade ranks among the most exciting and remarkable advances in the history of astronomy. More than four hundred such bodies have been found so far, spanning masses from super-Jovians to super-Earths, and arrayed in a diversity of architectures ranging from gas giants in orbits smaller than Mercury’s (‘hot Jupiters’) to multiple planets in orbits analogous to those in the Solar System. As the planetary menagerie swells, the focus has shifted to the fundamental underlying questions: How do these planets form, what range of environments might they be found in, how do their properties depend on those of the host star, and what is their potential for habitability?
The resolution of these issues is in turn intimately related to one of the most enduring and central problems in astrophysics: What is the physics underlying star formation? As presciently proposed by Kant and Laplace two and a half centuries ago, planets are born out of the star-girdling disks of gas and dust that are a natural outcome of stellar birth; the genesis and characteristics of planets, therefore, can only be fully understood in the context of the processes governing the star formation.
Finally, the origin and properties of both stars and planets are closely linked to those of brown dwarfs (BDs). By definition, these are substellar objects: with masses < 75MJUP, BDs cannot sustain stable H-fusion. Instead, like planets, they simply cool down and grow fainter with time (after an initial period of Deuterium fusion); unlike planets, however, most BDs do not orbit stars, but are free-floating bodies. Their importance to stars and planets is threefold. First, the genesis of BDs is deeply puzzling, and key to unraveling the physics of low-mass star formation in general. Second, the ultra-low, planetary temperatures attained by these objects, combined with the ease with which free-floating BDs can be studied directly (in contrast to planets, which circle overwhelmingly brighter stars), makes BDs invaluable guides to planetary atmospheres. Third, accretion disks are ubiquitous around young BDs, raising the novel possibility of forming planets around these ultra-low-mass objects, just as in stars.
Our research at Imperial focuses on this nexus of low-mass stars, BDs and planets, with the ultimate goal of painting a unified picture of the intertwined origins and properties of these three classes of objects.