Spring 2019, Number 14 Department of Physics Newsletter A CENTURY AND A HALF OF OCEAN WARMING AND SEA LEVEL RISE THE EXTREME USING POLYMER WORKING WITH THE UNIVERSE: PHYSICS TO SPACE INDUSTRY: ASTROPHYSICAL IMPROVE CANCER Oxford’s role in the UK’s TRANSIENTS TREATMENT growing space sector www.physics.ox.ac.uk PROUD WINNERS OF: SCIENCE NEWS SCIENCE NEWS www.physics.ox.ac.uk/research www.physics.ox.ac.uk/research Right: Fig. 2. The hunt for the electromagnetic EXPLORING THE HIGH ENERGY afterglow of the LIGO-Virgo neutron star-neutron star TRANSIENT UNIVERSE merger event GW170817. Left Astrophysical transients – very short- motion of the electrons around the ThunderKAT to track the radio panel: combining lived astronomical events observed from magnetic field lines produces the emission from relativistic transients localisations from earth – are both the sites and signatures synchrotron emission we can observe with this telescope over a five-year LIGO and Virgo of the most extreme phenomena in our with radio telescopes. survey. Oxford Astrophysics also leads with those from the Universe: for example, exploding stars, other major programmes on MeerKAT, Fermi and INTEGRAL Radio emission provides some notable compact object mergers, black holes, including deep extragalactic surveys spacecraft allowed neutron stars and ultra-relativistic flows. advantages to observations of transient and timing of pulsars. ThunderKAT’s an optical transient phenomena at other wavelengths. Firstly, They are invaluable probes for subjects targets include accretion events onto Prof Rob Fender to be identified in a year as relativistic ejecta from the in the sky. Combining observations in it is the only reliable tracer of the amount THE FUTURE as diverse as relativistic astrophysics, white dwarfs, neutron stars and black (Astrophysics) a galaxy 40 Mpc event ploughed into the surrounding the radio and X-ray bands can tell us stellar evolution and cosmology. They of kinetic energy released in an explosive holes; the explosions of massive away. The optical medium (see Fig. 2). First year DPhil how changes in the flow of matter in Combining radio and X-ray also have the potential to act as probes event, as it is this kinetic energy which stars; and gravitational wave bursts, emission probed the student Lauren Rhodes, who is jointly the most relativistic regions of the event observations of high energy transients of the intervening interstellar and powers the shock-accelerated electrons which are accompanied by a short radioactive decay funded by Oxford and The Max Planck couple to variations in the degree and tells us about the matter very close to intergalactic medium on all scales, up that we observe. Without a good gamma-ray burst. We already have of rare elements Institute for radio astronomy in Bonn, as form of kinetic feedback from the event. the relativistic event, and the explosive to and including cosmological distances. estimate of the kinetic feedback from some breakthrough results, such as the formed in the merger part of a radio transients collaboration, transport of kinetic energy to large an event, we cannot properly balance discovery of a large-scale relativistic jet event. Right panel: will lead future MeerKAT observations distance away from the transient. Within two weeks Our research group within Oxford the energy budget associated with the from a nearby black hole by third-year of such afterglows. This is a very exciting RELATIVISTIC OSCILLATIONS Between these two frequency regimes Astrophysics focuses on observations phenomenon. Secondly, because radio an X-ray and radio DPhil student Joe Bright. time, as LIGO resumed operation on Analysis of X-ray emission from lie the optical and infrared bands, in of such phenomena in the radio and observations can be performed by counterpart emerged, Dr Adam Ingram 1 April 2019, and the estimated rate of transients and high energy sources is which the majority of transients are X-ray bands, using the world’s largest interferometers many 1,000s of km apart as a powerful (Royal Society URF) neutron star mergers may be as high as led in our group by two fellows: Dr Sara first discovered, and which provide us radio telescopes and cutting-edge (effectively only limited by the diameter MULTI-MESSENGER OBSERVATIONS relativistic outflow several per year. Motta (Glasstone and Hintze Fellow) with information about the radioactive orbiting observatories. In the near of the Earth), extremely high angular OF LIGO BURSTS decelerated in the and Dr Adam Ingram (Royal Society decays and mildly relativistic ‘thermal’ future we will be embracing Oxford’s resolutions can be achieved, allowing interstellar medium The electromagnetic counterparts of and produced University Research Fellow), with DPhil ejecta often associated with such commitment to the Large Synoptic an image detail impossible at other X-RAY EMISSION gravitational wave events is one of synchrotron emission. students Lise du Buisson and Ed Nathan. events. Only by piecing together all Survey Telescope (LSST) project and wavelengths where such techniques the hottest topics in astrophysics right Our group was At almost the other extreme of the Together, Adam and Sara have shown wavelengths (and in some cases also expanding into the area of optical cannot be used. now, following the joint discovery involved in radio electromagnetic spectrum from radio that the most likely interpretation of the gravitational wave signal) can we transients to cover the full range of Our group uses all of the world’s major of gravitational and electromagnetic observations of this emission is the X-ray band. X-rays tend oscillations in the X-ray flux from build a coherent physical picture of what electromagnetic phenomena from these 8 radio telescope arrays, and most notably waves from the same event, for the ‘afterglow’ with to originate in the hot plasma (>10 K) black holes, such as those illustrated is taking place. events. Dr Sara Motta is leading a project on astrophysical first time in history, in August 2017. (Glasstone Fellow) MeerKAT and is ready very close to the central relativistic in Fig. 3, is the precession of a torus transients with the new MeerKAT This event, the merger of two neutron to follow-up new object or explosive event. Rapid X-ray of matter very close to the black hole. In the near future, the LSST will begin radio telescope in South Africa (Fig. 1). stars codenamed GW170817 (the date events when LIGO variability can be used as a probe of the Adam has recently made predictions operations to monitor the southern sky RADIO EMISSION FROM TRANSIENTS On 13 July 2018 this major new radio of the discovery), produced at early resumes operation on regions of largest gravitational curvature for the polarisation signature of such with unprecedented depth and cadence Essentially, all explosive or relativistic telescope was inaugurated and began full times both a gravitational wave and 1 April 2019. in the universe since the Big Bang. a precessing torus, which will be tested to look for optical transients. Oxford phenomena in astrophysics have operations. It is the most powerful radio gamma-ray signal. This was followed by Plasma close to a black hole of mass with the launch of NASA’s Imaging has been a leading partner in LSST associated synchrotron emission, which telescope in the southern hemisphere, strong optical emission from radioactive ten times that of our sun (quite typical, X-ray Polarimetry Explorer in 2021. since its inception, and is looking to is primarily detectable at radio bands. and part of the last stage of precursor decay of rare r-process elements on a we expect there to be millions of such exploit this involvement in a range of Extremely high velocity ejecta (‘jets’) telescopes before construction begins on timescale of days, and then later by a black holes in our Galaxy) will orbit it Sara is also working closely with science areas, not least of which is the from the explosion shock-accelerate the Square Kilometre Array in ~2025. synchrotron-emitting radio and X-ray Joe Bright (DPhil student 200 times per second, and we can probe the ThunderKAT team to provide study of optical transients. The goal electrons to relativistic energies and, at Prof Rob Fender is co-lead, together afterglow, which was visible for nearly working on jets with these physical scales by performing X-ray coverage of all radio transients for our group is that by combining our the same time, amplify and compress with Prof Patrick Woudt (University ThunderKAT) Fourier analysis of photons collected observed with MeerKAT, and vice versa. existing radio expertise, strengthening magnetic fields. The resulting spiralling of Cape Town), of a project called with precise arrival times by orbiting By combining these data we are our X-ray expertise, and now moving spacecrafts. Accretion of matter onto building a uniquely rich data set for into optical transients, we can provide these ‘stellar mass’ black holes is the understanding the connection between the most coherent possible approach origin of the brightest X-ray transients accretion and jets. to the study of astrophysical transients. Fig. 1: The MeerKAT radio telescope, South Africa, the most powerful radio telescope in the southern hemisphere, began full operations in July 2018. Oxford leads several large survey programmes on this Fig. 3: A quasi-periodic oscillation in the X-ray flux of an facility, including the ThunderKAT transients survey. accreting stellar-mass black hole. The inner accretion disk, Lauren Rhodes (DPhil close to the black hole, is undergoing a nodal precession – a student who will follow ‘wobble’ of the inner disk, like a spinning top. This is due to the up new LIGO GW events relativistic frame dragging effect, whereby a spinning massive with MeerKAT) object drags the surrounding space around with it, like a ‘gravitational vortex’. This precession has been measured in the orbit of satellites around Earth, but the effect is tiny – one precession cycle would take around 33 million years! Around a black hole, a precession cycle takes only one second.