On October 17 the Chandra X-ray Observatory released an updated image of the supernova remnant known as Tycho. Supernova remnants, the aftermath of a stellar explosion, are key to understand how stars end their lives, and how physical elements are synthetized and distributed in the galaxy. The new image, besides being visually striking, contains important clues to understand the explosion physics. Two papers are introduced in the text of the image release. The first paper, Sato et al 2019 (Genus Statistic Applied to the X-ray Remnant of SN 1572: Clues to the Clumpy Ejecta Structure of Type Ia Supernovae), used a new image analysis technique to mathematically characterize the clumpiness of the ejecta. The second paper, Ferrand et al 2019 (From the supernova to the supernova remnant: the three-dimensional imprint of a thermonuclear explosion), presented 3D numerical simulations made from a physically-motivated supernova explosion model. Both works conclude that part of the irregularities visible on the image, at an age of about 450 yr, were actually present from the very beginning. The two teams are now collaborating on the image analysis for the comparison of observations with models. Related work is also on-going with other colleagues at Rikkyo University.

The 3D printed model on the photo was made from G. Ferrand's simulations.
Credit: RIKEN/G. Ferrand, et al & NASA/CXC/SAO/A. Jubett, N. Wolk & K. Arcand

Professor Masaki Tsukamoto of Kyushu University, the winner of 2019 Geometry Prize of the Mathematical Society of Japan, visited iTHEMS for October 21 - 23 and gave a series of talks at Math Seminar. The theme of his talks was `Mean dimension of dynamical systems and information theory'. On October 21, 15:30-16:30, 16:40-17:40, he gave survey talks at Okochi Hall; In the first part he explained the notion of mean dimension in relation with information theory as an obstruction to embedding dynamical system to the shift on the Hilbert cube. In the second part he explained the notion of mean dimension in relation with data compression and showed that the mean dimension is obtained by applying to a (mini-max) variational principle to the dynamical rate distortion. His talks on October 22 and 23, 13:30-14:30 at the room 435-437 were on the key observation concerning the embedding problem and that on that concerning the dynamical rate distortion, respectively. The participants enjoyed his clear explanations on this mean dimension defined by Gromov which can play important role in the future study of infinite dimensional dynamical systems.