The discovery of planets orbiting stars other than our own Sun has been one of the most sensational advances in human knowledge. Researchers in the Department of Physics have played an important part in discovering extra-solar planets through the phenomenon of gravitational microlensing.

Microlensing is the time-dependent magnification of a background object, usually a star, by the gravitational field of a foreground object, usually another star, see Figure 1. The presence of a planet in the lens system will be seen as a brief deviation (lasting a few hours for planet masses a few times that of Earth) from the magnification profile expected of a single, planet-less lens object.

Figure 1: A schematic representation of gravitational microlensing. Light from a background star is deflected by the gravity of a foreground planetary system. Observers on Earth look for characteristic perturbations in the lensed light, indicating the presence of any planets in the “lens” system.

Science with microlensing

Microlensing is a fascinating phenomenon that has allowed a number of exciting discoveries, such as:

• The Galaxy might harbour 100 billion Earth-like planets,
• Every star in the Galaxy has at least one planet in orbit around it,
• There exists a large population of planets which do not orbit a star,
• A multiple planetary system with Jupiter and Saturn “lookalikes”.

Extra-solar planet research at The University of Auckland

Researchers at the Department of Physics and the MOA collaboration developed what has now become the favoured method for the whole field of detecting extra-solar planets by gravitational microlensing, see for example papers by Bond, Rattenbury and Yock. Staff and students at Auckland have continued to refine the existing techniques for analysing observed microlensing data, and to develop new, more powerful techniques. A/Professor Phil Yock and Dr Nicholas Rattenbury presently lead the work of discovering extra-solar planets at The University of Auckland.

Microlensing research also offers the opportunity to conduct investigations other than the detection of extra-solar planets. See here for a selection of other research projects related to microlensing.

The MOA collaboration

The Microlensing Observations in Astrophysics collaboration (MOA) is a Japan/New Zealand collaboration which began operations in 1994, looking for evidence of cold baryonic dark matter by looking at the rate of microlensing events towards the centre of our Galaxy.

From the late 1990s, the MOA collaboration turned to the discovery of extra-solar planets, and was rewarded a few years later with the first firm discovery of an extra-solar planet discovered by microlensing. Other planets have been discovered by microlensing, most using data collected and provided by the MOA collaboration.

The MOA collaboration operates the largest telescope dedicated to the task of detecting microlensing events. The MOA-II telescope operates at the Mount John University Observatory, Lake Tekapo, see Figure 2.

Figure 2: The MOA-II telescope at Lake Tekapo, New Zealand.

The study of microlensing events has matured, with the MOA collaboration continuously providing the international community with vital survey data and alerts of exciting microlensing events.

The MOA collaboration maintains a list of microlensing events, including events currently in progress.

Research Opportunities in Microlensing at The University of Auckland

Students wishing to do microlensing research in the Department of Physics at The University of Auckland should contact  Dr Nicholas Rattenbury.