Multi-band, Multi-messenger Astrophysics with LIGO, LISA and GOTO

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This fellowship investigates different areas of gravitational-wave astronomy, from gravitational-wave detection to observing an optical counterpart and interpreting the resulting astrophysical implications. This will be done using three facilities, LIGO (Laser Interferometer Gravitational-wave Observatory), LISA (Laser Interferometer Space Antenna) and GOTO (Gravitational-wave Optical Transient Observatory). LIGO and LISA are both gravitational-wave detectors. LIGO consists of two detectors in the USA. They are sensitive to gravitational waves from 10 Hz to the kHz region. LISA is a future space-based detector, due for launch in the 2030s. LISA is sensitive to gravitational waves from 0.1 to 100 mHz. GOTO on the other hand is an Earth-based optical telescope.Gravitational waves are emitted whenever an asymmetric object accelerates, with the strongest sources of detectable gravitational waves being from the collision of neutron stars and black holes. Both are created at the end of a massive star's life. Gravitational-wave astronomy truly began in 2015 when LIGO observed the gravitational-wave signature of two stellar-mass black holes colliding for the first time. Since then a total of eleven gravitational-wave signals have been observed, ten from the merger of two black holes, and one from the coalescence of two neutron stars. This latter signal was particularly exciting, as prior to this observation it was just speculation that colliding neutron stars would produce an electromagnetic signal. Indeed, in 2017 this binary neutron star merger was not only observed in the gravitational-wave window, but also across the electromagnetic spectrum. Over the coming years the LIGO detectors will become more sensitive, seeing deeper into the Universe and detecting many more gravitational waves.In this fellowship, we will investigate how the changing nature of LIGO sensitivity affects our ability to accurately measure the properties of gravitational-wave signals. We will also develop techniques to overcome periods of poor LIGO sensitivity. We want to ensure that key parameters of the gravitational-wave signal, such as the sky location, masses and spins of the source, are unbiased. This is critical to allow us to point electromagnetic telescopes to the correct sky location, understand the way in which the original binary system formed and measure the equation of state of neutron stars accurately.For LISA, it is imperative that we explore how to maximise the astrophysical potential of the future mission. In this fellowship, we will investigate how the expected changing nature of the LISA sensitivity will limit our ability to separate overlapping gravitational-wave signals. We will investigate techniques to overcome times of poor sensitivity in mock LISA data to separate out gravitational-wave signals and extract their astrophysical properties. This work will increase our chances of identifying unexpected astrophysical signals, as well as those we expect on all scales, from the smallest stellar-mass black holes to the colliding supermassive black holes at the heart of galaxies.Another aspect of this research is to follow-up gravitational wave events with the GOTO telescope. So far, only one gravitational-wave signal has an identified electromagnetic counterpart. With GOTO, we will build a catalogue of the different types of optical signals we expect from different gravitational-wave sources. This will allow us to gain an understanding of how the different optical signatures inform us of the underlying astrophysics. For example, we will begin to understand what type of object is created in the collision of two neutron stars. This information is not easy to deduce from the gravitational-wave signal alone. We will also investigate whether a binary black hole merger will produce an optical counterpart. The presence or absence of an optical signature will begin to indicate how these merging black holes initially formed.