Abstract

The inaugural decade of gravitational-wave observations seeded by LIGO's discoveries have shown the breakthrough impact this new cosmic messenger has on fundamental physics, astronomy, and cosmology. With new LIGO detector in India and ESA-NASA mission LISA, the next decade promises several firsts in the field of multi-messenger astrophysics. In this talk, we will discuss LILA (Laser Interferometer Lunar Antenna) - a new initiative between experimental gravitational physics, planetary geoscience and lunar exploration community to develop a gravitational-wave detector on the surface of the Moon. The Moon's unique environment and location opens a new window in the sub-hertz gravitational-wave spectrum that is inaccessible by any current or upcoming detector on earth or in space. Access to sub-hertz band will fundamentally change the landscape of multi-messenger astrophysics by providing early-warning alerts of up to months for binary neutron stars. We will highlight LILA's astrophysics deliverables and synergy with LISA/LIGO, which includes independent measurements of the cosmic acceleration to high redshifts, tests of General Relativity at cosmological scales, and new probes for physics beyond the Standard Model. We will discuss LILA's timeline in the context of NASA Artemis, the commercial lunar exploration programs in the US, and lunar missions from Asia and Europe. In doing so, we invite the broader community to engage in our efforts for building an inclusive astrophysics collaboration for US's return to the Moon.

Abstract

Since more than 10 years, an unexpected gamma-ray component over astrophysical backgrounds has been detected at GeV energies towards the Galactic center in the data of the Fermi-Large Area Telescope. Initially, this excess was considered to be hinting at GeV thermal relics annihilating in the Galactic dark matter halo. However, recent works have demonstrated that the excess is better explained by a population of millisecond pulsar-like sources in the Galactic bulge. While the excess photon flux is peaked at about few GeV, a significant high energy tail extending up to tens of GeV has been detected. Such high-energy photons are naturally explained by the inverse Compton emission of energetic electrons and positrons emitted by a stellar population in the Galactic bulge.

After a short review of the topic, I will discuss a novel study of the Galactic center excess at energies above 10 GeV based on an innovative method, which combines adaptive template fitting and pixel-count statistics in order to assess the role of sub-threshold point sources while minimizing the mis-modeling of Galactic diffuse emission backgrounds.

Abstract

Large-scale mass outflows from Active Galactic Nuclei (AGN) naturally connect a galaxy to its central black hole and enable an AGN feedback mechanism. However, quantifying the feedback efficiency is challenging because it involves considering multidimensional fluid dynamics, radiative processes, magnetic processes, and other factors. In this talk, I will summarize the main results from our ongoing work on developing a comprehensive physical model of AGN outflows. Observations indicate that these outflows are not smooth, including the fastest ones, like the ultrafast outflows. Therefore, I will focus on discussing the physical processes that could create multiphase structures within such outflows. We will also present synthetic ultraviolet and X-ray absorption spectra, which probe different outflow phases and can be used to test our model against observations.

Abstract

Modern synoptic time domain surveys are revolutionizing our understanding of compact objects in binary systems, and transforming the field of gravitational wave multi-messenger astrophysics. In this talk, I will highlight some recent advances in our understanding of white dwarfs, neutron stars, and black holes in binary (and triple) systems. These results encompass phenomena which span orbital periods of 7 minutes to >70000 years, and have major implications in our understanding of compact object physics, as well as binary stellar evolution. I will conclude with a discussion of upcoming facilities including the Vera Rubin Observatory and LISA, and technological advances such as CMOS based imagers that will propel this field into its golden era.

Abstract

Perhaps the biggest question Stephen Hawking tried to answer in his extraordinary career was how the universe could have created conditions so perfectly hospitable to life. Pondering this mystery led him to study the big bang origin, but his early work ran into a crisis when the math predicted many big bangs producing many universes, most far too bizarre to harbor life. Holed up in theoretical physics departments across the globe, Hawking and I worked shoulder to shoulder for twenty years, to develop a novel quantum framework for early universe cosmology that could account for the emergence of life. At the heart of our cosmogony lies a physical theory hat predicts that time and indeed physics itself fade away back into the big bang. In this colloquium I recount our quest to get a grips on the origin of time, and the bold new take on some of the universe's fundamentals we are being led to.

Abstract

Fast particles, with energies far above thermal, are ubiquitous in astrophysics, playing important roles in star formation, galactic structure, active galaxies, and elsewhere. It is now generally accepted that fast electrons and ions are produced through the diffusive shock acceleration process, with the strong shock waves from supernova remnants (SNRs) a prime candidate for acceleration sites. In particular, electrons make themselves apparent through synchrotron radiation at photon energies from radio through hard X-rays, and through inverse-Compton scattering in gamma rays. Synchrotron radiation dominates the X-ray spectrum of a handful of Galactic SNRs, and contributes substantially to that of several more. These objects allow detailed study of the electron populations and the local environments of their acceleration. I shall summarize the properties of this population of X-ray synchrotron SNRs (XSSNRS), and describe in detail results on several objects. Ongoing monitoring of the youngest Galactic SNR G1.9+0.3 with the sub-arcsecond spatial resolution of the Chandra X-ray Observatory has allowed the characterization of velocities and brightness changes, both increases and decreases, on length scales of a small fraction of the remnant radius. These results and others pose significant problems for theoretical modeling of electron acceleration.

Abstract

Two lessons learned from Planck was the importance of global analysis of instrumental, astrophysical and cosmological parameters as well as the usefulness of joint analysis of multiple datasets. These lessons has been further developed into a coherent pipeline for global analysis of multiple datasets by BeyondPlanck and Cosmoglobe, which has been successfully applied to joint end-to-end analysis of raw data from WMAP and Planck LFI. The recent Cosmoglobe Data Release 2 generalizes this to the infrared spectrum, performing a reanalysis of the COBE-DIRBE raw data, supported by Planck HFI, WISE, Gaia and COBE-FIRAS. Expanding the upper frequency range of the Cosmoglobe Sky Model from 1 to 240 THz requires a drastically altered thermal dust model, as well as adding models for starlight, CII line emission and dynamical Zodical light emission. This global analysis leads to the strongest constraints on the cosmic infrared background (CIB) spectrum from DIRBE published to date. We will give an introduction to global analysis before presenting our latest results.

Abstract

The standard model of cosmology has successfully explained astrophysical observations as diverse as anisotropies in the cosmic microwave background, baryon acoustic oscillations, and the flatness of galaxy rotation curves. A key phenomenon within this framework is weak gravitational lensing, which describes the small distortions of more distant galaxies due to the gravitational influence of intervening matter. Gravitational lensing is thus a direct probe of all matter, dark and baryonic, offering insights into the universe's total mass density and the clustering amplitude of cosmic structure. In this seminar, I will describe three very different campaigns to measure weak gravitational lensing signal from the ground (LoVoCCS), in the stratosphere (SuperBIT), and from space (COSMOS-Web). The discussion will focus on the unique features of each of these observational programs and what they could ultimately contribute to our evolving understanding of dark matter's role in structure formation.