The combination of a white dwarf mass close to the Chandrasekhar limit (1.4 solar masses) and a fast hydrogen accretion rate (10 -7 solar masses per year) from a companion star leads to frequent thermonuclear runaways in the accumulated envelope of gas on the white dwarf. These are known as nova eruptions and have recurrence times of years to decades. In this work we report that the recurrent nova with the shortest recurrence timescale known (approximately once a year), M31N 2008-12a in the Andromeda galaxy, is surrounded by a giant shell with a projected size of about 134 by 90 pc that is

Numerous exoplanets have been detected around Sun-like stars. These stars end their lives as white dwarfs, which should inherit any surviving planetary systems. In fact, many white dwarf stars show signs of having accreted smaller bodies, implying that they may host planetary systems. A small number of these systems contain gaseous debris discs, visible through emission lines. Here, we report a stable 123.4-minute periodic variation in the strength and shape of the Ca II emission line profiles originating from the debris disc around the white dwarf SDSS J122859.93+104032.9. We used numerical

The supermassive black holes in the centres of galaxies have a basic influence on their evolution. This happens during a phase in which the black hole is consuming the material of the galaxy in which it resides at a very high rate, growing in mass as it does so. During this phase we say that the galaxy has an active nucleus (AGN, for active galactic nucleus). The effect that this activity has on the host galaxy is known as AGN feedback, and one of its forms are galactic winds: gas from the centre of the galaxy being driven out by the energy released by the active nucleus. These winds can

The so-called "fundamental metallicity relation" (FMR) has been known for almost 10 years, and it states that galaxies of the same stellar mass but larger star formation rate have more chemically primitive gas. It is thought to be fundamental because it naturally arises from the stochastic feeding of star-formation from external metal-poor gas accretion, a process extremely elusive to observe but essential according the cosmological simulations of galaxy formation. Galaxies transform gas into stars at a rate that quickly exhaust their gas reservoir. Therefore, a continuous supply of external

The claimed detection of a diffuse galaxy lacking dark matter represents a possible challenge to our understanding of the properties of these galaxies and galaxy formation in general. The galaxy, already identified in photographic plates taken in the summer of 1976 at the UK 48-in Schmidt telescope, presents normal distance-independent properties (e.g. colour, velocity dispersion of its globular clusters). However, distance-dependent quantities are at odds with those of other similar galaxies, namely the luminosity function and sizes of its globular clusters, mass-to-light ratio, and dark