Cosmology

Marta Bryan explores what gas giants reveal about the formation and evolution of planetary systems. Their brightness and mass make them useful observational targets, and their gravitational influence can reshape the orbits and environments of smaller planets. The seminar combines several approaches. High-resolution spectroscopy of directly imaged planets measures rotation and obliquity, providing evidence about angular-momentum evolution. Radial-velocity searches for Jupiter-like companions to known inner planets probe how giant planets affect system architecture and inform the search for habitable worlds. The presentation also introduces observational work on planetary interiors and magnetic fields as further ways to test formation models.

The 249th AAS meeting convenes the astronomy and astrophysics community in Salt Lake City from 10–14 January 2027, with the Historical Astronomy Division. The programme offers research presentations and community exchange across astronomical subfields. Registration is open through the official meeting site.

Join Eduardo Bañados’s group to investigate early quasars and their environments. The postdoc will analyze JWST PRISM-DAWN integral-field spectroscopy, contribute to Euclid’s quasar programme, and help prepare and reduce Large Binocular Telescope observations. The full-time position lasts three years, with a negotiable start; the first half of 2027 is preferred. This vacancy belongs to the September 2026 Max Planck Postdoc Program call, which accepts applications until 13 October 2026 at 12:00 CEST through the official application platform.

Uddipan Banik derives a dynamical account of dark-matter halo density profiles using the Boltzmann–Poisson equations for an expanding Universe populated by subhalos of many masses. A self-similar solution links density slope to halo mass growth; including gravitational scattering and subhalo capture gives gamma = 6/(s + 2). Initial collapse with s = 2 produces a prompt cusp of slope 3/2. Hierarchical growth connects the slope to the primordial power spectrum and recovers the Syer–White relation during matter domination. Stable clustering selects an inner Navarro–Frenk–White cusp of slope one, while stalled accretion approaches the outer slope of three. The framework connects these profiles to successive stages of halo assembly.

Fraser Cain and Pamela L. Gay examine possible futures of the universe across vastly different timescales. Topics include the Milky Way and Andromeda, cosmic isolation as expansion continues, the fading microwave background, the end of star formation and the era of stellar remnants. They discuss uncertain processes such as proton decay, black-hole evaporation through Hawking radiation, entropy and heat death, alongside alternative outcomes if dark energy evolves. These are model-dependent projections. Pamela Gay is a senior scientist at the Planetary Science Institute. Published on 21 September 2026, the episode appears in the feed as The Beginning and End of Everything, Part 2. Its original duration is 37 minutes 7 seconds.

Arefe Abghari tests whether the reported excess in the quasar number-density dipole challenges the Cosmological Principle. If large-scale homogeneity and isotropy hold, the motion responsible for the cosmic microwave background dipole should also predict the dipole in distant-source counts. The analysis examines quasar selection and dipole-estimation systematics. Higher multipoles in the quasar density map, plausibly caused by survey and selection effects, can explain the apparent discrepancy. The talk argues that these effects need careful control before interpreting the measurements as evidence against the standard cosmological model.

Ania Liu examines gravitational-wave lensing as a probe of compact objects, dark matter and cosmic large-scale structure. Propagation over cosmological distances can distort signals, but identifying lensing in observations requires disentangling those distortions from uncertain waveform models and other astrophysical effects. The talk describes this phenomenology and the ambiguities it creates for interpretation, then presents recent methods and results from lensing searches using LIGO–Virgo–KAGRA data.

Pratika Dayal examines galaxy and black-hole formation during the first billion years, when the first galaxies ended the cosmic dark ages and began reionizing intergalactic hydrogen. JWST has revealed unexpectedly abundant, massive black holes, reaching about one hundred million solar masses within the first six hundred million years, challenging formation models. These observations can constrain the progress and spatial structure of reionization in preparation for 21-centimeter measurements. Early galaxies also test alternatives to cold dark matter. The talk considers the gravitational-wave event rates that early black holes could produce for the future LISA mission.

Arka Banerjee introduces k-nearest-neighbor distributions as summaries of cosmological survey data that capture information beyond two-point statistics. They respond to moments of all N-point correlations while retaining a computational cost comparable to two-point measurements. The talk covers auto-correlations and cross-correlations in discrete and continuous datasets, their relationship to other higher-order summaries, and applications that improve detection significance or parameter constraints. It also explores modeling these distributions with methods already successful for two-point functions in real and redshift space.