Robert Ferdman joined UEA as a Lecturer in Physics in 2016. He obtained his doctorate from the University of British Columbia in Vancouver, Canada. He subsequently became a postdoctoral researcher with the Observatoire de Paris as part of the radio astronomy group, stationed in Orléans, France. He then took up Research Associate positions in the UK at the University of Manchester, then at McGill University in Montreal, back in his home country of Canada, before returning to the UK, to take up a Lectureship here at UEA.
Dr. Ferdman’s research work focuses on observational astrophysics, particularly on the study of pulsars and analyzing pulsar data to perform a wide variety of astrophysics. Pulsars are the neutron star (NS) remnants of supernova explosions. They produce radio emission beams from their magnetic poles, which are detected once per rotation, every time the beam sweeps past our line of sight. They often display outstanding rotational stability, approaching that of atomic clocks over timescales of several years. Dr. Ferdman takes advantage of the astounding timing precision of pulsars to perform the most demanding tests of Einstein's theory of general relativity, constrain the evolutionary histories of compact stellar binaries that are formed from high-mass stars, and is member of large international collaborations that regularly observe an array of pulsars as a Galactic-scale gravitational-wave detector, and search for even more pulsars with which this exciting science can be performed.
L. G. Spitler, P. Scholz, J. W. T. Hessels, S. Bogdanov, A. Brazier, F. Camilo, S. Chatterjee, J. M. Cordes, F. Crawford, J. Deneva, R. D. Ferdman, P. C. C. Freire, V. M. Kaspi, P. Lazarus, R. Lynch, E. C. Madsen, M. A. McLaughlin, C. Patel, S. M. Ransom, A. Seymour, I. H. Stairs, B. W. Stappers, J. van Leeuwen, W. W. Zhu (2016).
A Repeating Fast Radio Burst.
Nature, 531: 202-205.
Z. Arzoumanian, A. Brazier, S. Burke-Spolaor, S. Chamberlin, S. Chatterjee, B. Christy, J. M. Cordes, N. Cornish, K. Crowter, P. B. Demorest, T. Dolch, J. A. Ellis, R. D. Ferdman, E. Fonseca, N. Garver-Daniels, M. E. Gonzalez, F. A. Jenet, G. Jones, M. Jones, V. M. Kaspi, M. Koop, T. J. W. Lazio, M. T. Lam, L. Levin, A. N. Lommen, D. R. Lorimer, J. Luo, R. S. Lynch, D. Madison, M. A. McLaughlin, S. T. McWilliams, D. J. Nice, N. Palliyaguru, T. T. Pennucci, S. M. Ransom, X. Siemens, I. H. Stairs, D. R. Stinebring, K. Stovall, J. K. Swiggum, M. Vallisneri, R. van Haasteren, Y. Wang, W. W. Zhu (2016).
The NANOGrav nine-year data set: limits on the isotropic stochastic gravitational wave background.
The Astrophysical Journal, 821, 13.
R. D. Ferdman, I. H. Stairs, M. Kramer, G. H. Janssen, C. G. Bassa, B. W. Stappers, P. B. Demorest, I. Cognard, G. Desvignes, G. Theureau, M. Burgay, A. G. Lyne, R. N. Manchester, A. Possenti (2014).
PSR J1756–2251: A pulsar with a light neutron star companion.
Monthly Notices of the Royal Astronomical Society, 443, 2183.
R. D. Ferdman, R. F. Archibald, V. M. Kaspi (2015).
Long-term timing and emission behavior of the young Crab-like pulsar PSR B0540–69.
The Astrophysical Journal, 812, 95.
R. D. Ferdman, I. H. Stairs, M. Kramer, R. P. Breton, M. A. McLaughlin, P. C. C. Freire, A. Possenti, B. W. Stappers, V. M. Kaspi, R. N. Manchester, A. G. Lyne (2013).
The double pulsar: evidence for neutron star formation without an iron core-collapse supernova.
The Astrophysical Journal, 767, 85.
M. Kramer, I. H. Stairs, R. N. Manchester, M. A. McLaughlin, A. G. Lyne, R. D. Ferdman, M. Burgay, D. R. Lorimer, A. Possenti, N. D. D'Amico, J. M. Sarkissian, G. B. Hobbs, J. E. Reynolds, P. C. C. Freire and F. Camilo (2006).
New tests of general relativity from timing the double pulsar.
The NANOGrav 11-year Data Set: High-precision Timing of 45 Millisecond Pulsars,
in Astrophysical Journal Supplement Series
article no. 37Full Text UEA Repository
The NANOGrav Nine-year Data Set: Measurement and Analysis of Variations in Dispersion Measures,
in The Astrophysical Journal Letters
article no. 125Full Text UEA Repository
Key Research Interests
As mentioned in the overview section, Dr. Ferdman’s principal area of research is in the observation-based studies of pulsars, the neutron star (NS) remnants left behind after massive stellar collapse, from which a radio “pulse” is observed once per NS rotation. Precision timing of these emitted pulses—and especially of millisecond pulsars (MSPs), the spun-up result of matter and angular momentum transfer from a binary companion donor—enables Dr. Ferdman and his colleagues to address many questions in fundamental physics and astrophysics. Several of these are discussed below.
Tests of general relativity
General relativity (GR) is currently the best description we have for gravitation; indeed, it has successfully passed every rigorous test it has so far been given. However, given its incompatibility with quantum mechanics, we know that it does not represent the complete picture, and it is thus extremely important to continue to put GR through various trials. Binary pulsar systems are renowned probes of fundamental physics, and are particularly well known for testing relativistic theory. Dr. Ferdman was centrally involved in the confirmation of Einstein's theory in the strong field at the 0.05% level through timing of the double pulsar system PSR J0737–3039A/B, so named because it is the only known double neutron star (DNS) system in which both NSs have been seen as radio-emitting pulsars. He and his collaborators continue to push the limits of GR testing with this system: for instance, this system will soon surpass the the original GR-testing system, the Hulse-Taylor pulsar PSR B1913+16—the outstanding discovery and study of which earned a Nobel Prize—in the precision with which they measure its orbital decay, and the corresponding radiative test of the GR prediction. In addition, it is expected that measurements of second-order post-Newtonian corrections to the orbital periastron advance will be possible for the double pulsar, which would allow them, for the first time, to constrain the moment of inertia in a NS.
Direct detection of gravitational waves
The recent monumental achievement by the LIGO collaboration in detecting GW emission from a coalescing black-hole binary pair has officially launched the era of GW astrophysics, demonstrating an entirely novel way to view the Universe. The most exciting of my current research activities is the major effort to use pulsar observations to directly detect and study GWs from complementary classes of sources to ground-based observatories, including supermassive black hole binary.
These will be found through the correlation of precisely measured pulse times-of-arrival from a large ensemble of pulsars—a so-called “Pulsar Timing Array” (PTA). This effectively uses the distances between Earth and several pulsars as arms of a giant gravitational-wave detector. It aims to measure the common effect of a stochastic GW background on the pulse arrival times of an ensemble of millisecond pulsars, thought to be due to coalescing supermassive black holes at the centres of distant merging galaxies. The PTA is sensitive to the nanohertz frequency region of the GW spectrum, and is thus complementary to the larger frequency ranges probed by ground-based detectors such as Advanced LIGO and VIRGO, which will be sensitive to sources such as merging NS pairs.
This is an international undertaking, with contributions from countless scientists and institutions around the world. Dr. Ferdman is a senior member of the European Pulsar Timing Array (EPTA) collaboration, which uses the five largest radio telescope in Europe, including the 76-metre Lovell telescope at the Jodrell Bank Observatory, to regularly observe over 40 pulsars as part of a PTA. Together with international collaborators, it is expected that a detection of these GWs will be made within 5–10 years.
Binary formation and evolution
The population of pulsars in binary systems is hugely varied; Dr. Ferdman’s research investigates the many channels by which these binaries have evolved. Understanding the properties of compact binary systems, how they formed, and their mass-transfer histories, can expand our knowledge about stellar populations and compact stellar mergers. This can in turn inform expected source count rates for the ground-based GW experiments discussed above, such as Advanced LIGO, whose frequency window includes GWs emitted from coalescing NSs. Population estimates are also used as input to pulsar surveys (see next section), where the efficiency of a given search plan depends greatly on expected discovery rates.
Examples of his work on this topic concerns the double pulsar system PSR J0737–3039A/B, which has proven useful for more more than the GR tests discussed above, and another DNS system, PSR J1756–2251. His analysis of several years of pulse profile data strongly implies a near-alignment of the first-formed pulsar's rotation axis and orbital angular momentum vector. This provides strong evidence that the supernova (SN) progenitor to the second-formed pulsar was likely symmetric, possibly involving an electron-capture scenario onto an O-Ne-Mg core. These studies provide some of the strongest evidence to date of NS formation without the need to invoke standard asymmetric, violent iron-core collapse. The question of how commonly DNS systems are formed in this manner is one that he plan to help answer.
Another example of Dr. Ferdman’s contribution to the understanding of the pulsar binary population is with the intermediate-mass binary pulsar (IMBP) system PSR J1802–2124. He has detected Shapiro delay of the pulsar emission, which occurs when the NS is behind its companion star during its orbit, relative to the observer’s line of sight. During this time, the emitted signal crosses the gravitational potential of its companion on its way to Earth, delaying its arrival time. This has allowed for one of the most precise mass measurements in a NS-WD binary, confirming that the system is composed of a low-mass NS and a carbon-oxygen WD. This has provided convincing evidence that the NS must have avoided hypercritical accretion—and thus black hole formation—during an inspiral and common-envelope phase. Dr. Ferdman is continuing to monitor this system, primarily with help from the Lovell Telescope at the Jodrell Bank Observatory, which will better characterise the IMBP population as a whole, allowing comparison to other pulsar binary types.
Surveys and searches for pulsars
There exist relatively few known binary pulsars compared to the overall NS population, and even fewer with measurable masses. To continue to perform all the above exciting research, it is therefore vital that many more suitable pulsar systems are found. Dr. Ferdman is a member of the PALFA consortium, which is conducting a survey program with the 305-metre Arecibo radio telescope in Puerto Rico. PALFA aims to search and discover hundreds of pulsars in a blind systematic search in and around the Galactic plane, and thus far, it has discovered over 160 pulsars, including more than 20 MSPs, and several binary systems. The PALFA project is expected to continue for at least another 2-3 years, and the resulting search data set that will have been amassed will likely be pored over for years to come, continuing to find new systems for study.