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Illustration: A view towards the black hole in the X-ray binary Cygnus X-3 and the X-rays we see that are reflected from the inner surface of the powerful outflow surrounding the hole. Credit: Alexander Mushtukov

Published: 27 September 2024

Webinar with Juri Poutanen
(University of Turku, Finland)

recorded on September 26, 2024

Game Changers Online Seminar

Neutron Stars

Game Changers Webinar

Black Holes

How to See the Unseen: Learning about the Geometry of the Emitting Region in Accreting Black Holes and Neutron Stars using X-ray Polarimetry

Webinar with Juri Poutanen (University of Turku, Finland)

recorded on September 26, 2024

Electromagnetic radiation observed from various cosmic sources is intrinsically polarized, with its polarization depending on the geometry and, specifically, the asymmetry of the source. Polarimetry offers an independent method for exploring the physics and astrophysics of cosmic objects, complementing traditional techniques such as imaging, spectroscopy, and timing. It enables us to determine the geometry of otherwise unresolved sources—for instance, identifying the orientation of the symmetry axis of a source or the magnetic field in the sky—providing insights that no other technique can offer.

Recorded Seminar

Abstract

While polarization measurements in radio and optical wavelengths are commonly used in astrophysics, polarized X-rays have been underutilized in the past due to the absence of X-ray polarimeters. The only satellite equipped for X-ray polarimetry before recent times was OSO-8, launched in 1975, which successfully measured significant polarization from only two sources. However, the landscape changed at the end of 2021 with the launch of the Imaging X-ray Polarimetry Explorer (IXPE), the first satellite specifically designed for X-ray polarimetry.

In this talk, the speaker reviews the discoveries made with IXPE, focusing on the progress in understanding the geometry and physics of the emission regions in accreting black holes and neutron stars.

About the Speaker

Juri Poutanen is professor of astronomy at the University of Turku in Finland. He got his MSc in astronomy from the Leningrad State University and PhD in astronomy from the University of Helsinki. He worked previously at Stockholm and Uppsala Universities in Sweden and University of Oulu in Finland before moving to Turku to take up the Directorship of Tuorla Observatory. His main research interests lie in the field of high-energy astrophysics of black holes and neutron stars. His recent research is based on the ground-breaking data obtained with the Imaging X-ray Polarimetry Explorer (IXPE), the first observatory dedicated to X-ray polarimetry that was launched in December 2021. He is leading the efforts to uncover geometry of X-ray emission region in X-ray pulsars and non-magnetic neutron stars as well as involved in discoveries of X-ray polarization from accreting black holes.

History

Starting in the summer of 2020, the International Space Science Institute has organised the weekly on-line seminar series called “Game Changers”. After six series of weekly talks on the themes of “Missions that Changed the Game in Solar System, Astrophysics and Earth Sciences” , “Ideas and Findings about the Solar System, the Universe and our Terrestrial Environment”, “Habitability – From Cosmic to Microbial Scales”, “Viewing Earth from Space – the Changing Environment and Climate of our Planet”, and “Captivating Cosmology: From the Big Bang to Tomorrow” and the topic “Space Environmental Hazards: Mitigation and Prediction”, the webinar series continues on a monthly basis.

A Spiral Amongst Thousands

Credits ESA/Webb, NASA & CSA, A. Martel