Pulsars are remarkable laboratories for the study of gravitation. In both the highly relativistic interior and the vicinity of a pulsar (and its binary companion, in case of double neutron-star systems or potential pulsar-black hole system) space-time may significantly deviate from the predictions of General Relativity (GR) [15]. Pulsar timing therefore provides a unique tool for probing gravity in the strong field regime, enabling high-precision tests of GR or other theories of gravity. Double-neutron-star systems such as the Double Pulsar [16] provide unrivalled probes for testing most aspects of GR. Binary pulsars with a white dwarf companion and hence large mass dipole can set interesting constraints on alternative theories that predict, for instance, the existence of gravitational dipole radiation [17]. Resolving tight binary orbits to investigate effects such as the Shapiro delay requires short-spaced observations with high sensitivity. Meanwhile, identifying the weak signatures of subtle relativistic effects needs long-term monitoring with good cadence. MeerKAT’s excellent sensitivity (surpassing even our high expectations in 2010) and good frequency coverage will make it the premier telescope for studying Southern-sky pulsars. This will not only improve existing GR tests but will allow us to measure new effects to probe new physics. This is best demonstrated with the unique Double Pulsar, where the precision of tests of gravity will go beyond the current best weak-field tests in the solar system. As has been shown (Kehl 2015, Masters thesis, University of Bonn), we expect to measure the moment-of-inertia of the J0737-3039A in the Double Pulsar for the first time, providing a handle on the equation-of-state of super-dense matter. With the sensitivity provided by MeerTime, we will also determine masses for both pulsars and their companions. These can be used to test theories of binary evolution [18] and to investigate the distribution of neutron-star masses. In particular, the discovery of massive neutron stars [19,17] suggests that high-mass population of neutron stars exists, even possibly resulting from birth [20,21]. As mass statistics improve, we will get closer to identifying the maximum mass possible for a neutron star, itself a constraint on the equation of state. MeerTime will furthermore provide astrometry (distances, proper motions and hence velocities) for millisecond and binary pulsars, allowing us to infer their birth velocities and constrain asymmetric supernova kicks, particularly in double-neutron-star systems[22].
References:
[15] T. Damour and G. Esposito-Farèse, Tensor-scalar gravity and binary-pulsar experiments, PhysRevD 54, 1474 (July 1996).
[16] 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’Amico, J. M. Sarkissian, G. B. Hobbs, J. E. Reynolds, P. C. C. Freire and F. Camilo, Tests of General Relativity from Timing the Double Pulsar, Science 314, 97 (October 2006).
[17] J. Antoniadis, P. C. C. Freire, N. Wex, T. M. Tauris, R. S. Lynch, M. H. van Kerkwijk, M. Kramer, C. Bassa, V. S. Dhillon, T. Driebe, J. W. T. Hessels, V. M. Kaspi, V. I. Kondratiev, N. Langer, T. R. Marsh, M. A. McLaughlin, T. T. Pennucci, S. M. Ransom, I. H. Stairs, J. van Leeuwen, J. P. W. Verbiest and D. G. Whelan, A Massive Pulsar in a Compact Relativistic Binary, Science 340, p. 448 (April 2013).
[18] T. M. Tauris and G. J. Savonije, Formation of millisecond pulsars. I. Evolution of low-mass X-ray binaries with Porb> 2 days, A&A 350, 928 (October 1999).
[19] P. B. Demorest, T. Pennucci, S. M. Ransom, M. S. E. Roberts and J. W. T. Hessels, A two-solar-mass neutron star measured using Shapiro delay, Nature 467, 1081 (October 2010).
[20] T. M. Tauris, N. Langer and M. Kramer, Formation of millisecond pulsars with CO white dwarf companions - I. PSR J1614-2230: evidence for a neutron star born massive, MNRAS 416, 2130 (September 2011).
[21] J. Antoniadis, D. L. Kaplan, K. Stovall, P. C. C. Freire, J. S. Deneva, D. Koester, F. Jenet and J. G. Martinez, An Eccentric Binary Millisecond Pulsar with a Helium White Dwarf Companion in the Galactic field, ApJ 830, p. 36 (October 2016).
[22] I. H. Stairs, S. E. Thorsett, R. J. Dewey, M. Kramer and C. A. McPhee, The formation of the double pulsar PSR J0737-3039A/B, MNRAS 373, L50 (November 2006).
References:
[15] T. Damour and G. Esposito-Farèse, Tensor-scalar gravity and binary-pulsar experiments, PhysRevD 54, 1474 (July 1996).
[16] 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’Amico, J. M. Sarkissian, G. B. Hobbs, J. E. Reynolds, P. C. C. Freire and F. Camilo, Tests of General Relativity from Timing the Double Pulsar, Science 314, 97 (October 2006).
[17] J. Antoniadis, P. C. C. Freire, N. Wex, T. M. Tauris, R. S. Lynch, M. H. van Kerkwijk, M. Kramer, C. Bassa, V. S. Dhillon, T. Driebe, J. W. T. Hessels, V. M. Kaspi, V. I. Kondratiev, N. Langer, T. R. Marsh, M. A. McLaughlin, T. T. Pennucci, S. M. Ransom, I. H. Stairs, J. van Leeuwen, J. P. W. Verbiest and D. G. Whelan, A Massive Pulsar in a Compact Relativistic Binary, Science 340, p. 448 (April 2013).
[18] T. M. Tauris and G. J. Savonije, Formation of millisecond pulsars. I. Evolution of low-mass X-ray binaries with Porb> 2 days, A&A 350, 928 (October 1999).
[19] P. B. Demorest, T. Pennucci, S. M. Ransom, M. S. E. Roberts and J. W. T. Hessels, A two-solar-mass neutron star measured using Shapiro delay, Nature 467, 1081 (October 2010).
[20] T. M. Tauris, N. Langer and M. Kramer, Formation of millisecond pulsars with CO white dwarf companions - I. PSR J1614-2230: evidence for a neutron star born massive, MNRAS 416, 2130 (September 2011).
[21] J. Antoniadis, D. L. Kaplan, K. Stovall, P. C. C. Freire, J. S. Deneva, D. Koester, F. Jenet and J. G. Martinez, An Eccentric Binary Millisecond Pulsar with a Helium White Dwarf Companion in the Galactic field, ApJ 830, p. 36 (October 2016).
[22] I. H. Stairs, S. E. Thorsett, R. J. Dewey, M. Kramer and C. A. McPhee, The formation of the double pulsar PSR J0737-3039A/B, MNRAS 373, L50 (November 2006).