Many observed phenomena in the universe are not unchanging or static. Variable stars, supernovae, comets, gamma-ray bursts, pulsars: all these objects show some characteristic variability. A great deal of our understanding of the universe comes from measuring these variations over time, including how extra-solar planets form and how the universe is structured and is evolving. Researchers in the Department of Physics interested in Time Domain Astrophysics are working on the following topics.

Extra-Solar Planets

We have known for the last 20 years that there are other planets orbiting stars other than our own Sun. Alien worlds exist — if not necessarily the aliens themselves. The types of planets discovered to date show a wonderful variety, from massive gas giant planets orbiting very close to their host star, to cooler rocky planets. A recent discovery is of a population of free-floating “nomad” planets, which roam the Galaxy without a host star. How planets form — and form in such diversity — is an open question. For an answer we will need a more thorough sampling of the planets in our Galaxy.

Microlensing is the time-dependent magnification of a background object, usually a star, by the gravitational field of a foreground object, usually another star. 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.

Microlensing is complementary to the techniques used by – for example – the Kepler space telescope. There is a lot of work to do in modelling the events that are recorded by the networks of telescopes involved in microlensing, and in order to keep on top of it all we need to have clever algorithms to do as much of the modelling work as possible, without – or with minimal – human interaction. Getting a computer to take the place of a human’s decision capabilities is a challenge.

Read more about extra-solar planetary microlensing research in the Department of Physics.

Galaxy Structure and Dynamics

We still lack a full understanding of the structure and dynamics of our own Galaxy, particularly in its inner regions. We have obtained a lot of data from the various microlensing surveys, which observe towards the centre of the Galaxy. As new data sets are becoming available, previous models need to be updated. Dynamical information can also be folded into the models. There is scope for extending this modelling work to using non-parametric models – as opposed to the parametric models presently in use – and letting the data drive the best-fit model morphology of the Galaxy.

Massive Microlensing Dataset Mining

The Japan/New Zealand Microlensing Observations in Astrophysics (MOA) collaboration has amassed a huge dataset of stellar light curves. Researchers at Auckland are interested in using the multi-variate data mining software WEKA (developed at the University of Waikato, New Zealand) to search this dataset for new discoveries. Experience with this sort of analysis will become valuable when instruments such as the Large Synoptic Survey Telescope comes online early in the next decade.

Other analysis techniques – not associated with any particular known phenomena – could be used in this work, including, for example, wavelets or other signal processing techniques.

Detecting Optical Counterparts to Gravitational Wave Transients

From 2015, the gravitational wave observatories of the LIGO consortium will start to seek evidence for gravitational waves. It is postulated that the gravitational waves which LIGO might see arise from the collision of two neutron stars, or a neutron star and a black hole. It is possible that these collisions are accompanied by electromagnetic emission – including at optical wavelengths. Dr Rattenbury is considering whether the BOOTES network of rapid response telescopes can contribute to this optical follow-up work. One of the BOOTES telescopes – the Yock-Allen telescope – resides in New Zealand. If the BOOTES network does sign up to become one of collaborations to perform follow-up observations to GW transients, there will be opportunities to develop software to detect rapidly any optical transients associated with GW transients.

Pulsar Microlensing

Pulsars are rapidly spinning dense stellar remnants, detectable by their intense radio emissions. Whether these objects could act as a source in a gravitational microlensing event, what the resulting signal would look like, what we could learn from such a system, and how we could design code to detect any microlensing signal in the set of recorded pulsar data are open questions.