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Testing the ΛCDM model requires cosmological probes spanning the wide redshift interval between Type Ia Supernovae (SNe Ia, z ≲ 2.9) and the Cosmic Microwave Background (CMB, z ≈ 1100). Gamma-Ray Bursts (GRBs), observed up to redshift z=9.2, offer the opportunity to explore part of this regime. Here, we investigate how many GRBs are needed to become a useful cosmological probe capable of independently testing deviations from ΛCDM suggested by the recent DESI BAO observations. We develop forecasts based on the two-dimensional X-ray and optical Dainotti relations, between the luminosity at the end of the plateau phase and its rest-frame duration. Using simulated GRB samples constructed from the observed population, we evaluate the constraining power of GRBs on cosmological parameters within the wCDM and w0waCDM models, both independently and in combination with CMB observations. Our results show that GRB samples containing several tens to hundreds of well-characterized plateaus can already approach the precision currently achieved by CMB measurements on the Dark Energy (DE) Equation of State (EoS) parameter w. Particularly, a sample of ∼ 66 optical GRBs can reach a precision σw ≈ 0.47, comparable to that obtained from Planck within the wCDM framework. Such sample sizes are already attainable through machine-learning techniques that double the number of GRBs using inferred redshifts. These forecasts indicate that future GRB observations, when combined with next-generation transient missions and improved statistical techniques, will provide an independent high-redshift probe of cosmic expansion and will play an important role in testing the robustness of potential Dynamical DE signals suggested by other cosmological datasets.
While most near-Earth asteroids (NEAs) are thought to originate from the main belt, recent discoveries have suggested the existence of a lunar-derived NEA population, such as the asteroids Kamo‘alewa and 2024 PT5. These objects may hold key clues to the dynamical evolution of NEAs and the recent impact history of the Earth–Moon system. However, the population, distribution, and dynamical characteristics of these lunar-origin asteroids (LOAs) remain poorly constrained. By combining the lunar ejecta production with N -body orbital simulations of the ejecta, we investigate their orbital evolution in the past millions of years and the current LOA population, revealing their significant potential for detection by future surveys. Specifically for the Vera C. Rubin Observatory’s upcoming Legacy Survey of Space and Time, we predict an average detection rate of about six LOAs (with D > 5 m) per year. Additionally, we find that the LOAs tend to approach from sunward and antisunward directions, with encounter velocities significantly lower than those of typical NEAs. These findings offer valuable insights in guiding targeted ground-based surveys and planetary defense efforts for LOAs in the future.
Dense neutrino systems, which display collectivity mediated by the weak interaction, have deep parallels with mean-field kinetic systems governed by other fundamental forces. We identify analogues in fast flavor conversion (FFC) of some time-honored nonlinear phenomena in plasmas and self-gravitating systems. We focus in particular on nonlinear Landau damping and collisionless equilibria, which are likely important pieces of the unsolved puzzle of neutrino oscillations in core-collapse supernovae and neutron star mergers. Our analysis additionally reveals the previously unexplored phenomenon of flavor-wave synchronization.
The formation of the first stars and galaxies marked the onset of chemical enrichment, yet direct observations of such primordial systems remain elusive. Here we present James Webb Space Telescope spectroscopic observations of LAP1-B, an ultra-faint galaxy at redshift zspec = 6.625 ± 0.001, corresponding to a cosmic age of 800 million years after the Big Bang. This galaxy is strongly magnified by gravitational lensing. LAP1-B exhibits a gas-phase oxygen abundance of (4.2 ± 1.8) × 10-3 times the solar value, making it the most chemically primitive star-forming galaxy discovered to date. The galaxy displays an exceptionally hard ionizing radiation field, which is inconsistent with chemically enriched stellar populations or accreting black holes but matches theoretical predictions for an exceptionally metal-deficient stellar population1. It also shows an elevated carbon-to-oxygen abundance ratio for its metallicity in the interstellar medium, consistent with nucleosynthetic yields from a stellar population formed in the absence of initial metals2-4. The lack of detectable stellar continuum constrains the stellar mass to below 3,300 M⊙, and the dynamical mass, derived from emission-line kinematics, exceeds the combined stellar and gas mass, which indicates a dominant dark matter halo. Our findings establish LAP1-B as a 'fossil in the making', a direct high-redshift progenitor of the ancient ultra-faint dwarf galaxies observed in the local Universe and offers a rare window into the earliest stages of galaxy formation.
The Galaxy's most common known planetary systems have several Earth-to-Neptune-size planets in compact orbits1. At small orbital separations, larger planets are less common than their smaller counterparts by an order of magnitude. The young star V1298 Tau hosts one such compact planetary system, albeit with four planets that are uncommonly large (5 to 10 Earth radii)2,3. The planets form a chain of near-resonances that result in transit-timing variations of several hours. Here we present a multi-year campaign to characterize this system with transit-timing variations, a method insensitive to the intense magnetic activity of the star. Through targeted observations, we first resolved the previously unknown orbital period of the outermost planet. The full 9-year baseline from these and archival data then enabled robust determination of the masses and orbital parameters for all four planets. We find the planets have low, sub-Neptune masses and nearly circular orbits, implying a dynamically tranquil history. Their low masses and large radii indicate that the inner planets underwent a period of rapid cooling immediately after dispersal of the protoplanetary disk. Still, they are much less dense than mature planets of comparable size. We predict the planets will contract to 1.5-4.0 Earth radii and join the population of super-Earths and sub-Neptunes that nature produces in abundance.
