Month: September 2022

OUR CORNER OF THE ‘VERSE. “There has been huge progress in understanding the properties and history of the MW in recent years thanks to the Gaia satellite. Gaia is an ongoing ESA space astrometry mission (2013-2022+?), measuring the positions, parallaxes and proper motions (change in apparent position) of > 1 billion stars in the MW (∼ 1% of the total number of stars). (MW = Milky Way). https://lnkd.in/e6ifiQMn View in LinkedIn

DOMINANT ERRORS. “It should also be noted that there isn’t a rigid divide between theory/simulations and observations; modelling is required to interpret observations and the statistical errors are often now so small that systematic errors are significant, or even dominant.” https://lnkd.in/e6ifiQMn View in LinkedIn

COSMIC GEOMETRY. “It’s hard to measure the inner slope of the MW’s density profile, as baryons dominate at small radii. The large measured microlensing optical depth towards the Galactic centre implies large stellar densities in the inner MW, which appears to be in tension with the high DM densities at small radii of ‘cuspy’ density profiles.” (MW = Milky Way; DM = dark matter). https://lnkd.in/e6ifiQMn View in LinkedIn

HALO SAUSAGE “A significant fraction of the halo near the Sun is in the Gaia-Enceladus/sausage, which is the aftermath of a major merger with a M ∼ 108 M⊙ dwarf galaxy (8−10) Gyr ago. The name arises from the fact the stellar component has radially biased orbits, and hence the distribution of vr is sausage like.” (M⊙ = solar mass units). https://lnkd.in/e6ifiQMn View in LinkedIn

INHOMOGENEITY. “Particle interactions can lead to primordial and/or evolutionary deviations from vanilla CDM. Primordial effects modify the evolution of density perturbations, and hence, for instance, the initial halo mass function.” (CDM = Cold Dark MatterCold dark matter). https://lnkd.in/e6ifiQMn View in LinkedIn

ELOQUENT BUT FORGOTTEN. “Giambattista Vico (1668-1744) was Professor of Latin Eloquence at the University of Naples. His works, first written in Latin, and then later in Italian, were not understood in his lifetime and have not been widely known or understood since. Vico has remained an obscure and eccentric thinker.” https://lnkd.in/eEHaWAZf View in LinkedIn

A half-shuttered churchnon the edge of Quart (Girona) whose bell still works and where elder people still gather on Sunday mornings. View in LinkedIn

SUPPRESSION OF STRUCTURES. “Warm dark matter (WDM) is semi-relativistic at creation. A concrete candidate is the sterile neutrino. Thermal WDM free streaming erases perturbations and suppresses the power spectrum on (small) mass scales, and consequently structure formation is suppressed below this mass.” (WDM = Warm dark matter). https://lnkd.in/e6ifiQMn View in LinkedIn

PROBING WARM DARK MATTER. “The linear power spectrum, and hence the mass of WDM particles, can be probed via the Lyman-alpha forest. The Lyman-alpha forest is the absorption lines in spectra of galaxies and quasars from the Lyman-alpha electron transition in intergalactic neutral hydrogen ‘clouds’.” (WDM = Warm dark matter). https://lnkd.in/e6ifiQMn View in LinkedIn

PRESENT BY DISTURBANCE. “A DM sub-halo passing by a stellar stream gives the stars in the stream a kick and perturbs their orbits, leading to a gap in the stream which is observable for sub-halo masses.” (DM = dark matter). https://lnkd.in/e6ifiQMn View in LinkedIn