Game Changers Seminar

Solar energetic eruptive processes, such as flares and coronal mass ejections, are relatively well-studied during the past decades of direct observations. Although their maximum strength/energy is not constrained by direct data because of a too-short period of observations, we know that extreme events do occur rarely on the Sun over the last millennia, thanks to cosmogenic-proxy data, and also on sun-like stars, thanks to high-precision stellar photometry. Not only we can estimate their occurrence probability but even reconstruct energy spectra and assess the dramatic terrestrial and societal impacts. However, the nature of such events remains unclear – are they ‘normal’ but just extremely strong solar flares (Black Swans) or do they represent an unknown type of solar events (Dragon Kings)? A summary of the existing pieces of knowledge will be presented along with a try to make a distinction between the Black-swan and Dragon-king scenarios of the extreme events.

Ilya Usoskin graduated from Leningrad Polytechnics in 1988, then worked as a researcher at Ioffe Physical-Technical Institute in St. Petersburg until 1997, a postdoc at INFN Milano from 1997-1999, and head of Oulu Cosmic ray station since 2000. He has Cand.Sci. degree in Astrophysics (1995) and PhD in Space Physics (2000). Full professor of Space Physics since 2012. He has several awards, most honourable are: 1^st-class Knight of the Order of Lion of Finland (2013), Julis Bartels medal of EGU (2018), full membership in the Finnish Academy of Sciences and Letters (2019), ISEE Science Award (Nagoya, 2020). He is an expert in Solar, Heliospheric, Cosmic-ray, Solar-terrestrial and Atmospheric physics, a founder of the Space-Climate research discipline, and an actively servant to the community: Vice-President of IAU, member of the C4 commission of IUPAP, editor for several journals, etc.

Webinar was recorded on November 24, 2022

In this last year, the Pantheon+ and SH0ES teams released likely our last measurements of the expansion history of the universe.  On one hand, constraints from Pantheon+ show a universe consistent with the Lambda-CDM model, where dark energy can be described by a cosmological constant.  On the other hand, constraints combining Pantheon+SHOES data find a high value of the Hubble constant, now 5sigma away from the value inferred using Lambda-CDM from measurements of the Cosmic Microwave Background.  How can both these statements be true? In this talk, the speaker goes over these separate but overlapping measurements, and discussess how we can have tensions with some parts of the cosmological model but not others. The speaker discusses possible explanations to the Hubble tension, and goes over how other tensions have arisen in cosmology. Finally, the speaker talks about how new telescopes, like the James Webb Space Telescope, can help resolve these controversies.

Dan Scolnic received his B.S from MIT in 2007, his PhD from Johns Hopkins in 2013, and then received a Hubble fellowship and KICP fellowship to do his postdoc at UChicago. Dan then became a professor at Duke University where he has gotten the chance to start Duke’s cosmology program. In the last few years, he has won a Packard Fellowship, Sloan Fellowship, and Department of Energy Early Career Award.

Webinar was recorded on November 10, 2022

Studies have shown that stars contain very little baryonic matter and that the majority of the baryons in the universe likely exist in gaseous form. Cool baryons are more easily observed, but what have been seen cannot account for the expected number of baryons produced in the early universe. The lack of understanding of the origin and distribution of “missing baryons” is impeding the progress in completing the picture of baryon cycling in galaxy ecosystems. The bulk of the “missing baryons” may be exist in the form of hot, extended halos around galaxies and/or filamentary structures in the cosmic web; recent observations seem to support such scenarios. However, due to the lack of a sensitive probe, the physical and chemical properties of such hot baryons are poorly measured with existing facilities, but carry critical information on the feedback processes that are deemed critical to galaxy evolution. Theory is far ahead of observation in this area; data are severely lacking. The speaker describes the missing baryon puzzle and provide a personal perspective on how to solve it.

Wei Cui is Professor at the Department of Astronomy at the Tsinghua University (China) and an American Physical Society Fellow. He obtained his PhD in physics from the University of Wisconsin-Madison in 1994, and then joined MIT as a Research Scientist, working on the construction and operation of the All-Sky Monitor (ASM) on the RXTE satellite and carrying out research on compact objects based on RXTE observations. In 2000, he joined the faculty of the Department of Physics at Purdue University, and became a full Professor in 2009. He participated in the construction and operation of VERITAS, a state-of-the-art TeV gamma-ray observatory, and re-focused his research on cosmic particle accelerators. In 2016, he accepted a joint appointment from Tsinghua University as Professor of Physics, and then joined the university fully as Professor in the newly-formed Department of Astronomy. He is the PI of the proposed Hot Universe Baryon Surveyor (HUBS) mission, which aims at filling a void in probing cosmic baryons.

Webinar was recorded on November 3, 2022

Dark matter is believed to comprise five-sixths of the matter in the universe, and is one of the strongest pieces of evidence for new fundamental physics. But dark matter does not interact directly with light, making it very difficult to detect except by its gravity. It’s described how various properties of dark matter could lead to observable signals, and how we can attempt to identify those signals from telescope observations. The speaker gives examples of cases where possible signals have been seen, but their origin is not yet fully understood. Furthermore, the speaker discusses how solving the puzzle of those observations will advance our understanding of our Galaxy and cosmos, either by revealing properties of dark matter or providing new insights into astrophysics.

Tracy Slatyer is a theoretical physicist who works on particle physics, cosmology and astrophysics. Her research is motivated by questions of fundamental particle physics — in particular, the nature of dark matter — but she seeks answers by studying possible signatures of new physics in astrophysical and cosmological data. She co-discovered the giant gamma-ray structures known as the “Fermi Bubbles” erupting from the center of the Milky Way. She was born in the Solomon Islands and grew up in Australia and Fiji, completing her undergraduate degree in Australia before moving to the USA in 2006. She did her PhD in physics at Harvard with Prof. Douglas Finkbeiner (2006-2010), worked at the Institute for Advanced Study in Princeton (2010-2013), and joined the MIT faculty in 2013. She has won a number of awards, including a New Horizons in Physics Prize (2021) and a Presidential Early Career Award for Scientists and Engineers (2019).

Webinar was recorded on October 27, 2022

A distinct prediction of our cosmological model is that tiny fluctuations seeded in the primordial Universe have grown under gravity to form the astrophysical objects we observe today. As a consequence of this formation process, on large scales, the matter in our Universe forms the cosmic web: an intricate network-like structure of filaments, sheets, nodes and large almost empty voids. This structure is at the interface between the ‘linear’ regime of cosmic structure formation and the deeply ‘nonlinear’ regime of galaxy formation. It thus fundamentally connects cosmology (and thereby fundamental physics) with the galaxy formation process. In this talk, we discuss how the cosmic web thereby plays a key role in our understanding of how galaxy formation connects to cosmic structure formation, how this connection can influence our interpretation of cosmological observables in the precision era, and how it can serve as a cosmological probe of the mildly non-linear scales. 

Oliver Hahn is a Professor for Data Science in Astrophysics and Cosmology at the University of Vienna (Austria) since 2020. He obtained his PhD in physics from ETH Zurich, Switzerland. He then worked as a postdoctoral researcher at the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) at Stanford University (USA) from 2009-2012, before returning to ETH Zurich as an Ambizione postdoctoral fellow. In 2015, he joined the Université de la Côte d’Azur and the Observatoire de la Côte d’Azur (France) as a professor of Physics. Also in 2015 he received an ERC Starting Grant. His research interests center around the modelling of cosmic structures on supercomputers and range from the modelling of dark matter, galaxy clusters, to precision simulations of the large-scale structure, and include questions of numerical methods, data analysis, and high-performance computing.   

Webinar was recorded on October 20, 2022

A few hundred million years after the Big Bang, the first galaxies formed in the Universe. The detection of such galaxies is very challenging, not only because they are very distant, but also because at that time the Universe was opaque to ultraviolet radiation. Only after the Universe became transparent, in the so-called ‘epoch of reionization’, galaxies became more easily observable and since then galaxy evolution can be studied in full detail. In this talk the speaker will review the current, still rudimentary knowledge of the early stages of galaxy formation and growth, which is based on theoretical predictions and limited observations of distant galaxies. She will discuss how the recently launched James Webb Space Telescope is expected to revolutionise this field of Astronomy by being able to peer into the epoch of reionization and reveal the very first steps of galaxy evolution.

Karina Caputi is Professor of Observational Cosmology and High-Redshift Galaxies at the Kapteyn Astronomical Institute, University of Groningen (The Netherlands). She studied Physics at the Instituto Balseiro, in Bariloche, Argentina, and then did a PhD in Astronomy at the University of Edinburgh (UK). After graduating, she worked as Postdoctoral Researcher at the Institut d’Astrophysique Spatiale in Orsay (France) and at the ET Zurich. She was later on a Leverhulme Trust Early Career Fellow at the University of Edinburgh. In 2012, she joined the University of Groningen where she has worked ever since. Karina Caputi is member of the JWST/MIRI European Science Consortium and is also involved in the scientific preparation for the Euclid space telescope. Her work has been recognised by some prestigious grants and awards. Most notably, she received an ERC Consolidator Grant in 2015 and more recently (in 2022) a Vici Grant from the Dutch Research Council.

Webinar was recorded on October 13, 2022

The use of the Cosmic Microwave Background radiation (CMB) to study the physics of the Universe is one of the greatest success stories of modern cosmology. Over the last two decades, the astonishing agreement between the theory and increasingly-precise observations of CMB temperature and polarization has led to the establishment of a concordance cosmological model. However, despite having constrained the parameters of this model to sub-percent precision, many fundamental questions about the Universe are still unanswered: we still need to find out how the Universe began, what is the nature of dark matter and dark energy, what are the properties of neutrino particles and what happened at cosmic dawn. To answer these questions new, more powerful CMB data are being collected, analysed and planned for. In this talk the speaker gives a snapshot of where we are in CMB cosmology, how we got here and where we are heading next.

Erminia Calabrese is a Professor of Astrophysics at the School of Physics and Astronomy of Cardiff University. She obtained her PhD in Rome at Sapienza University and then moved to the UK in 2011. She spent 4 years in Oxford as postdoctoral research associate and Beecroft Fellow, moved to Princeton University during 2015/2016 as Lyman Spitzer Fellow, and then back to Oxford to start an Ernest Rutherford Fellowship. In May 2017 she moved to Cardiff University to join the Astronomy Instrumentation and Astronomy & Astrophysics groups where she leads a cosmology team supported by a European Research Council Starting Grant. Erminia Calabrese works at the intersection of cosmological theory and data analysis of the Cosmic Microwave Background signals, and combines the CMB with galaxy surveys to obtain state-of-the-art constraints on cosmological scenarios, including limits on neutrino physics, dark energy and inflation. She also works on the design and definition of the next generation of experiments. She is a member of the Atacama Cosmology Telescope collaboration and she chairs the Simons Observatory Theory and Analysis Committee; she also act as UK coordinator and European Deputy Spokesperson of the future LiteBIRD satellite.

Webinar was recorded on October 6, 2022

Inflation, a period of accelerated expansion in the early universe, was likely responsible for setting up initial conditions for the formation of galaxies, and ultimately us. However, inflation also leaves the universe cold and empty. How did inflation end, and how did the universe get populated with particles resulting in the hot big bang? The period between the end of inflation and the era where light nuclei first formed presents an significant gap in our cosmic history. In this talk, the speaker discusses the exciting events taking place during this period, and how we can potentially improve upon our knowledge of this era in the coming years.

Mustafa Amin is an Associate professor of Physics and Astronomy at Rice University in Houston, Texas (USA). Before joining Rice in 2015, Mustafa Amin held a Senior Kavli Fellowship at the University of Cambridge and a Pappalardo Fellowship at MIT. He obtained his PhD from Stanford University, and undergraduate degree from the University of Texas at Arlington. The questions that drive Amin’s current research include: How did inflation end and the hot big bang begin? What is the mass and intrinsic spin of dark matter particles? His expertise lies in nonlinear dynamics of cosmological fields, with his most impactful works being on the formation and implications of solitons at the end of inflation, and in contemporary dark matter. He has around 50, peer-reviewed, published articles and his work is currently supported by NASA and US Dept. of Energy.

Webinar was recorded on September 29, 2022

Since neutrinos are known to be very light and elusive, they are often thought to play a very small part in the history of the universe. This is all but true. A numerous population of neutrinos, known as the Cosmic Neutrino Background, was produced in the early universe and has been staying around since then. Neutrinos have actually been the second most numerous particle in the universe for billions of years, and they were the second contributor to the total energy budget of the universe over most of the initial 50 000 years. These neutrinos are very difficult to measure directly, but we have several indirect (although very clear) indications of their presence. The next generation of cosmological observations will probe this component in more detail, in order to test neutrino properties and weigh their masses.

Julien Lesgourgues is a professor at RWTH Aachen University, Germany, since 2015. He graduated in France at Ecole Polytechnique and received his PhD from the University of Tours. He has occupied various postdoc and junior staff positions at SISSA (Trieste), LAPTh (Annecy), CERN (Geneva) and EPFL (Lausanne). Julien Lesgourgues is a theoretical cosmologist, specialised in the comparison of cosmological models with observations. He is a leading developer of numerical codes simulating the evolution of the whole universe on the largest scales, from the beginning of inflation until today. As a member of the Planck satellite collaboration, he shared the Gruber Cosmology Prize 2018. He is currently a member of the Euclid satellite collaboration. Julien Lesgourgues co-authored more than two hundred publications and a couple of textbooks including one on Neutrino Cosmology (CUP 2013).

Webinar was recorded on September 22, 2022

In the beginning was the Big Bang: an unimaginably hot fire almost fourteen billion years ago in which the first elements were forged. The physical theory of the hot nascent universe—the Big Bang—was one of the most consequential developments in twentieth-century science. And yet it leaves many questions unanswered: Why is the universe so big? Why is it so old? What is the origin of structure in the cosmos? In An Infinity of Worlds, physicist Will Kinney explains a more recent theory that may hold the answers to these questions and even explain the ultimate origins of the universe: cosmic inflation, before the primordial fire of the Big Bang.

Will Kinney is a professor in the Department of Physics at the University at Buffalo, SUNY, where he has been on faculty since 2003. Dr. Kinney received his Bachelor of Arts from Princeton University, and PhD from the University of Colorado, Boulder. He has worked as a research associate at Fermi National Accelerator Laboratory, the University of Florida, and Columbia University, and held visiting positions at Yale University, Perimeter Institute for Theoretical Physics, Harish Chandra Research Institute, Allahabad, the University of Chicago, the University of Valencia, and Stockholm University. Dr. Kinney’s research focuses on the physics of the very early universe, including inflationary cosmology, the Cosmic Microwave Background, Dark Matter, and Dark Energy. He has authored more than seventy published research articles, and received the SUNY Chancellor’s award for excellence in teaching in 2014.

Webinar was recorded on September 15, 2022