Science

Astronomers in New Zealand plan to use the SKA to significantly advance our understanding the fundamental laws of Nature, the evolution of our Universe, and the origins of Life.  We intend to collaborate with international teams on a wide variety of fundamental questions and challenges in astrophysics, including:

  • What is the origin of the gamma ray excess from the Galactic Centre? Gamma-ray measurements from the Fermi large area telescope have found that there is an excess of gamma rays from the Galactic Centre direction. The two main competing hypotheses for this excess are self-annihilating dark matter and an unresolved population of millisecond pulsars. Due to the large distances and the difficulties imposed by scattering and the dispersive effects of ionised interstellar gas, the frequency range (Band 5) and unparalleled sensitivity of the SKA are required to test the millisecond pulsar hypothesis. The particle nature of dark matter is a very pressing problem and so by either confirming or refuting the millisecond pulsar explanation for the Galactic Centre excess, the SKA will be providing a crucial service in our understanding of cosmology and particle physics.
  • How are jets formed in the vicinity of a supermassive black hole?  By undertaking the most sensitive imaging surveys of extragalactic radio sources, SKA-VLBI will provide a wealth of new information on the nature of physical phenomena in the vicinity of active galactic nuclei (AGN). Understanding the extreme physics in the vicinity of the supermassive black hole that is the central engine of AGN requires the significant improvement in resolution and sensitivity that will be provided by SKA-VLBI.
  • Using SKA-VLBI for astrometry of galactic and extragalactic molecular maser sources, including direct measurement of the distance and proper motions of individual young and evolved stars, calibrating their astrophysical properties, refining parameters of Galactic rotation and the local standard of rest, refining the distance to the Galactic centre, and establishing accurate configurations of the spiral arms.  Such astrometric measurements impact on a broad variety of fundamental science, such as experiments that place stringent limits on temporal variation of Newton’s gravitational constant.
  • Using molecular maser spectral lines in SKA-VLBI mode to trace star forming regions and the circumstellar envelopes of evolved stars. This will produce a detailed 6-dimensional (3D locations in space + 3D velocities) map of our Galaxy and its spiral arms, thereby enabling study of its physics, dynamics, formation and evolution.  This VLBI research is currently underway, but adding hundreds (SKA1) and thousands (SKA2) of dishes to existing international VLBI arrays will provide sensitivity to areas of the Galaxy that are currently out of reach.
  • Matching SKA-VLBI radio astrometry with the optical astrometry of Gaia space telescope. Gaia will measure distances to 1 billion stars, but Gaia’s ability to penetrate the dust is limited. SKA-VLBI will provide distances to the dust enshrouded regions and individual evolved stars.
  • Using SKA-VLBI for ultra-precise astrometry at the μas level up to a distance of tens of kpc. Achieving this for a large fraction of the radio pulsar population detected by the SKA Galactic Pulsar Census will enable mapping the ionized interstellar gas (HII) in the Galaxy and increase the sensitivity of pulsar timing experiments to low-frequency gravitational waves.
  • Using galaxy clusters as cosmological probes. The unprecedented sensitivity and angular resolution of the high-frequency SKA will allow the detection of high-redshift clusters and in-depth reconstruction of their pressure profiles. In conjunction with future surveys in the X-ray and optical/near-infrared wave bands (e.g. with the Athena and LSST telescopes), this will allow accurate determination of masses for large samples of clusters, greatly enhancing their use as cosmological probes. At the same time, the low-frequency SKA will be ideal for observing synchrotron emission produced by relativistic electrons, providing a means for understanding the merging processes that occur between clusters of galaxies.
  • What experimental test will General Relativity ultimately fail, providing important clues and motivation for a quantum theory of gravitation?  The ultimate laboratory for high precision tests of gravity would be provided by the discovery of a pulsar in orbit around a black hole, and the SKA will be used to perform the deepest, most sensitive survey of our Galaxy for such a system.
  • How do galaxies and their dark matter halos merge to form larger galaxies? Following a merger, the newly formed pair of supermassive black holes at the galactic centre are expected to orbit each other until the energy lost to gravitational wave emission leads to the final coalescence of the pair.  In this scenario, the Universe should be ringing with a background of low-frequency gravitational waves. Although invisible to Earth-based detectors like LIGO, these waves are detectable by the SKA, which will be capable of performing measurements of the highest precision of an array of pulsars distributed across our Galaxy and combining these signals to synthesize the most sensitive detector of nanoHertz gravitational waves.
  • Where are the missing baryons?  Around 30% of the baryons predicted to exist by Big Bang Nucleosynthesis have not yet been detected.  However, the mysterious impulsive radio signals known as Fast Radio Bursts (FRBs) encode information about the column density of free electrons along the line of sight to the origin of the burst.  The SKA will detect large numbers of FRBs and accurately locate the host galaxies in which these signals originate. Combined with the measured redshifts of the hosts, the SKA will weigh the otherwise invisible ionised baryon content of the Universe.
  • What is the nature and origin of the large-scale Galactic magnetic field?  By measuring the dispersion, scattering, and Faraday rotation along the sight lines to thousands of pulsars, including those newly discovered by the SKA, the SKA will enable the most detailed tomography of the large-scale structure of ionised gas and magnetic fields in both the Galactic disk and the Galactic halo.