Meet the AAS Keynote Speakers: Dr. Paolo Soffitta and Dr. Martin Weisskopf

In this series of posts, we sit down with a few of the keynote speakers of the 245th AAS meeting to learn more about them and their research. You can see a full schedule of their talks here, and read our other interviews here!


X-ray observations trace out some of the hottest objects in the Universe, up to hundreds of millions of degrees Kelvin. It’s a difficult band of light to study as it’s absorbed by the Earth’s atmosphere and can only be measured from space, requiring instruments to be launched into orbit. One of the most famous X-ray observatories is the Chandra mission, which has produced as many papers and citations as the Hubble Space Telescope, and is in funding jeopardy as of 2024. 

The Imaging X-ray Polarimetry Explorer (IXPE) is a joint NASA-Italian Space Agency mission launched in 2021. While an X-ray telescope like Chandra, IXPE focuses on polarimetry, the study of the polarization of light. In astrophysics, there are two types of polarimetry. Imaging polarimetry produces 2D image maps of the polarimetry that shows the spatial distribution of the polarization, like other astrophysical images do with light. Spectropolarimetry breaks down the polarization at a given position by wavelength. It’s analogous to taking a spectra, which measures the amount of light per wavelength at a position, only for the amount of polarization. IXPE does both kinds, and is the first imaging polarimeter in the X-ray band.

By measuring the polarization of X-rays the IXPE mission will learn more about the physical processes going on in the high-energy environments that the light was produced in. There are more than 200 papers from IXPE as of December 2024, and the extended mission is still receiving many new observing proposals. 

IXPE has made a number of observations that go against conventionally held theories, which is certainly giving their theorist colleagues some extra work. For example, astronomers expected the polarization in the Cas A supernova remnant to be produced by magnetic fields perpendicular to the lines observed in radio. IXPE data found that they’re actually coming from radially aligned fields, and that the level of polarization in the X-rays is lower than the radio observations. The IXPE team won the Rossi prize this year, which is awarded annually by the High Energy Astrophysics division of AAS for projects making significant, recent contributions to the field. IXPE won because of the many “lovely surprises” like this that it’s uncovered. These surprises mean that the telescope is making major contributions to our understanding of the Universe, and that the theorists are going to have to come up with some new interpretations to explain these observations.

For Dr. Soffitta and Dr. Weisskopf, IXPE was the “realization of a dream”. They’ve been working and advocating for X-ray polarimetry for decades now. Dr. Weisskopf was the American Principal Investigator (PI) during its development, launch, and first year of operations, and Dr. Soffitta has been the Italian PI since its inception. Both are experimentalists, and while their major contribution has been to the optics (Marshall SFC) and detectors (European), they are also heavily involved in working with the data from IXPE. 

via AAS

Dr. Weisskopf received his Ph.D. in atomic physics from Brandeis University before becoming a postdoc at Columbia. There, he worked on X-ray astronomy in the lab where X-ray polarimetry was developed, and on the first rocket-based polarimetry experiments. He then moved to Marshall Space Flight Center and was the Project Scientist for Chandra for 45 years before transitioning to be the PI for IXPE. 

His advice for up and coming astronomers is to not discount the importance of polarization. “You can’t understand a human by just studying a toe. To understand the universe you have to study the entire electromagnetic spectrum and all its properties.” Polarization measurements are difficult, but provide essential information about X-ray sources. 

Dr. Soffitta received his Laurea and Ph.D. in Astronomy from La Sapienza in Rome, with thesis work in X-ray polarimetry for both degrees. He worked on the Stellar X-ray Polarimeter instrument, the Beppo/Sax project studying GRBs, and the design of the X-ray component SuperAGILE of the gamma-ray AGILE satellite. Throughout his career he worked on new instrumentation for X-ray polarimetry and proposing missions, including IXPE.

via AAS

His advice to the next generation of experimentalists: “If you want to open a new window, do it where the photons are”. You need to set up missions and develop detectors that have sensitivity in the bands where the photons of interest are. If you do this, you might find things that are totally unexpected and cause problems for your local theorists.  

The HEAD Bruno Rossi Prize Lecture: Martin Weisskopf (NASA Marshall Space Flight Center) and Paolo Soffitta (INAF-IAPS) is on Wednesday January 15 at 8:10 AM ET in Potomac Ballroom AB. 


Edited by: Jessie Thwaites

Featured Image Credit: AAS

Author

  • Lindsey Gordon

    Lindsey Gordon is a fourth year Ph.D. candidate at the University of Minnesota. She works on AGN jets, radio relics, MHD simulations, and how to use AI to study all those things better.

    View all posts

Submit a Comment

Your email address will not be published. Required fields are marked *