The Prize was shared equally by Victoria M. Kaspi, a Professor of Physics and Director of McGill Space Institute at McGill University in Canada and Greece’s Chryssa Kouveliotou, Professor and Chair in the Department of Physics at George Washington University, USA.
A magnetar is a type of neutron star believed to have an extremely powerful magnetic field. The magnetic-field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays. The theory regarding these objects was proposed in 1992 by Robert Duncan and Christopher Thompson.
Kouveliotou received her bachelor’s degree in physics from the National & Kapodistrian University of Athens, Greece in 1975, and earned her master’s degree in science from the University of Sussex in England in 1977.
She received her doctorate in astrophysics in 1981 from the Technical University of Munich, Germany, under the supervision of Klaus Pinkau. She was a faculty member at the Department of Physics of the National & Kapodistrian University of Athens before pursuing research work in the United States.
In 2012 she was selected as recipient of the Dannie Heineman Prize for Astrophysics, which is given annually to recognize outstanding work in the field.
Kouveliotou was also an astrophysicist at NASA’s Marshall Space Flight Center in Huntsville, Alabama, and has been the principal investigator on numerous research projects in the United States and Europe. She is also the founding member of multiple scientific collaborations worldwide.
Through the development of new and precise observational techniques, the two astronomers who won the Shaw Prize in Astronomy for 2021 confirmed the existence of neutron stars with ultra-strong magnetic fields and characterized 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.
Research by Greek astronomer shows extreme magnetic fields
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 centers.
From observations of a class of X-ray/gamma-ray sources called “soft gamma-ray repeaters” (SGRs) Chryssa Kouveliotou and her colleagues established the existence of magnetars and provided a stunning confirmation of the magnetar model in 1998-1999.
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.
The Shaw Prize 2021 recognizes the seminal contributions of Victoria M. Kaspi and Chryssa Kouveliotou to the understanding of the enigmatic properties of magnetars, pulsars and gamma-ray bursts.