The Shaw Prize in Astronomy 2021 is shared equally by Victoria M. Kaspi, Professor of Physics and Director of McGill Space Institute, McGill University, Canada and Chryssa Kouveliotou, Professor and Chair, Department of Physics at George Washington University, USA for their contributions to our understanding of magnetars, a class of highly magnetised neutron stars that are linked to a wide range of spectacular, transient astrophysical phenomena. This prestigious award is one way in which the Shaw Prize Foundation seeks to promote astronomy, a mission shared by the IOASA and one which the two organisations have ongoing collaborations to pursue.

Through the development of new and precise observational techniques, Victoria M. Kaspi and Chryssa Kouvelioto confirmed the existence of neutron stars with ultra-strong magnetic fields and characterised their physical properties. Their work has established magnetars as a new and important class of astrophysical objects.

Neutron stars are the ultra-compact remnants of stellar explosions. Most are rapidly rotating with periods of milli-seconds to seconds and emit powerful beams of electromagnetic radiation (observed as pulsars). As such they are accurate ‘cosmic clocks’ that enable tests of fundamental physics in the presence of a gravitational field many billion times stronger than Earth’s. Reflecting their importance, the Nobel Prize in Physics has been awarded twice for work on pulsars (in 1974 and 1993).

Pulsars also have strong magnetic fields, since the magnetic field lines in the progenitor star are ‘frozen in’ in the stellar remnant as it collapses to become a neutron star. These magnetic fields funnel jets of particles along the magnetic poles, but classical radio pulsars are powered mainly by rotational energy and slowly spin down over their lifetimes.

The research carried out by Kaspi and Kouveliotou was motivated by the theoretical prediction that neutron stars with extreme magnetic fields up to a thousand times stronger than those in regular pulsars could form if dynamo action were efficient during the first few seconds after gravitational collapse in the core of the supernova. Such objects (termed magnetars) would be powered by their large reservoirs of magnetic energy, rather than by rotation, and were predicted to produce highly-energetic bursts of gamma-rays through the generation of highly energetic ionised particle pairs at their centres.

From observations of a class of X-ray/gamma-ray sources called “soft gamma-ray repeaters” (SGRs) Chryssa Kouveliotou and her colleagues in 1998–99 established the existence of magnetars and provided a stunning confirmation of the magnetar model. By developing new techniques for pulse timing at X-ray wavelengths and applying these to data from the Rossi X-ray timing satellite (RXTE), Kouveliotou in 1998 was able to detect X-ray pulses with a period of 7.5 seconds within the persistent X-ray emission of SGR 1806-20. She then measured a spin-down rate for the pulsar, and derived both the pulsar age and the dipolar magnetic field strength — which lay within the range of values predicted for magnetars, close to 1014 gauss (1010 T). The spin-down measurements were extremely challenging because of the faintness of the pulsed signal and the need to correct the rotation phase across multiple epochs.

Victoria Kaspi showed that a second class of rare X-ray emitting pulsars, the anomalous X-ray pulsars (AXPs), were also magnetars. Kaspi took the techniques used by radio astronomers to maintain phase coherence in pulsar timing and adapted them to work in the much more challenging X-ray domain. This allowed her to make extremely accurate timing measurements of X-ray pulsars with full phase coherence across intervals of months to years, and hence to measure spin-down rates far smaller than those seen in SGR 1806-20. Kaspi has also made fundamental contributions to the characterisation of magnetars as a population, through the elucidation of their physical properties and their relationship to the classical radio pulsars. Her work has cemented the recognition of magnetars as a distinct source class. Today, magnetars are routinely invoked to explain the physics underlying a diverse range of astrophysical transients including gamma-ray bursts, superluminous supernovae and nascent neutron stars.

Magnetars probe extreme physical conditions inaccessible on Earth, such as strong gravity, ultra-nuclear densities and the strongest magnetic fields in the Universe. In this high energy environment particle-antiparticle pairs are created from the vacuum, and unique tests of general relativity and quantum electrodynamics become possible. In 2020–2021, the first associations of a Galactic magnetar with millisecond duration outbursts of radio emission, so called Fast Radio Bursts (FRBs), were established. These results may suggest that “flaring” magnetars are the central engines of at least some of the spectacular extragalactic FRBs. Future studies will undoubtedly shed further light on these exciting discoveries.

The Shaw Prize 2021 recognises the seminal contributions of Victoria M. Kaspi and Chryssa Kouveliotou to the understanding of the enigmatic properties of magnetars, pulsars and gamma-ray bursts.

The Gruber Cosmology Prize, which is co-sponsored by the IOASA, recognises scientists whose contributions have driven fundamental advances in our understanding of the Universe. The 2021 prize has been awarded to Marc Kamionkowski, Uroš Seljak and Matias Zaldarriaga for the development of techniques for studying the Cosmic Microwave Background that have provided deep insights into the primordial Universe, as early as a fraction of a second after the Big Bang.

The Gruber Foundation today announced the recipients of this year’s Cosmology Prize. The prize is awarded annually to leading scientists and cosmologists who have made groundbreaking discoveries that change or challenge our understanding of the Universe.

This year’s prize goes to Marc Kamionkowski, Johns Hopkins University, Uroš Seljak, University of California at Berkeley and Lawrence Berkeley National Laboratory, and Matias Zaldarriaga, Institute for Advanced Study, for their contributions to the study of the Cosmic Microwave Background (CMB) and the early Universe. The CMB is the ubiquitous radiation left over from when atoms first formed, releasing radiation that remains as the Universe’s “background noise”. The three recipients of the prize developed techniques to use observations of the CMB to derive information about the early Universe.

They will equally share the US$500 000 award, and each will receive a gold medal at a ceremony that will take place in August, at the 24th International Conference on Particle Physics and Cosmology (COSMO’21) conference series at the University of Illinois and online.

The CMB provides an image of the Universe when it was just 379 000 years old, but it represents an observational limit — direct measurements of the Universe before this time are not possible. However, Kamionkowski and, independently but simultaneously, Seljak and Zaldarriaga developed a mathematical technique to use the CMB radiation to infer what’s on the other side of this limit, all the way back to the first fraction of a second of the Universe’s existence. That method uses the property of polarisation — the degree to which an oscillating wave, bouncing up and down relative to the direction of travel, diverges from a strictly perpendicular orientation.

In 1997, their work was published in two papers side by side in Physical Review Letters. (Kamionkowski shared authorship with Albert Stebbins, Fermilab, and Arthur Kosowsky, University of Pittsburgh.) The impact of the papers was seismic and enduring. In the words of one nominator to this year’s Gruber Prize, “The significance of this work for cosmology cannot be overstated.”

By observing polarisation in the CMB, cosmologists can match theoretical predictions of early‐Universe properties using data that would otherwise be inaccessible. Among the observatories that have been used to make those polarisation measurements are the WMAP and Planck satellites (whose principal investigators and teams received the Gruber Cosmology Prize in 2012 and 2018, respectively). Those measurements have allowed cosmologists to determine that the Universe is 13.8 billion years old and comprises roughly 5 percent ordinary matter, 26 percent dark matter, and 69 percent dark energy.

Polarisation continues to be an essential tool for filling in our picture of the Universe; it is now inspiring a new generation of research programmes that will detect — or not — the final piece in that reigning cosmological model: inflation, a theoretical moment at the very beginning of the Universe’s existence when space would have undergone an expansion of almost unfathomable proportions. (The theorists who independently created that idea, Alan Guth and Andrei Linde, received the 2004 Gruber Cosmology Prize.) The two 1997 papers by Kamionkowski, Seljak and Zaldarriaga identified a signature in the CMB polarisation that would render a verdict on the existence of primordial gravitational waves — a key prediction of inflationary theory.

Although the 1997 papers are two of the seminal works by Kamionkowski, Seljak, and Zaldarriaga, the 2021 Gruber Prize also recognises their career‐long contributions to cosmology.

Even before writing their 1997 paper, Seljak and Zaldarriaga had already created a code that made the study of certain aspects of the CMB thousands of times faster, named CMBfast. Because they made the code available for free it dominated CMB research for years to come. Today it endures as the foundation for every code analysing CMB polarisation. Over the decades, singly and together, they have continued to perform influential mathematical analyses and to create new theoretical interpretations in such areas as inflation, gravitational waves, and the use of general relativistic effects (weak lensing) on light from distant sources to infer the characteristics of the dark matter in individual galaxy halos as well as in the large‐scale structure of galactic formation.

Kamionkowski is also well known for his work on cosmological‐parameter determination and parity‐breaking effects in the CMB, and he has over the years made important subsequent contributions to the study of CMB polarisation. He has also done significant work in many other areas of cosmology, including dark matter, inflation, the acceleration of the expansion of the Universe, cosmic phase transitions, and gravitational waves.

In addition to the cash award, each recipient will receive a gold laureate pin and a citation that reads:

The Gruber Foundation is pleased to present the 2021 Cosmology Prize to Marc Kamionkowski, Uroš Seljak, and Matias Zaldarriaga for their work on the Cosmic Microwave Background, the most direct tracer of the primordial universe and of its physics. Their theoretical predictions and analysis tools for the cosmic background, its intensity, and even more its polarization, have been essential to the development of this field of research over the last twenty-five years, already testing predictions of the inflation model for the early expansion of our universe. Furthermore, their work has been key to initiating new observation projects extending over the next fifteen years, in the quest for detecting the imprint of primordial gravitational waves on the microwave background.