No signature of ejecta interaction with a stellar companion in three type Ia supernovae.

Type Ia supernovae are thought to be the result of a thermonuclear runaway in carbon/oxygen white dwarfs, but it is uncertain whether the explosion is triggered by accretion from a non-degenerate companion star or by a merger with another white dwarf. Observations of a supernova immediately following the explosion provide unique information on the distribution of ejected material and the progenitor system. Models predict that the interaction of supernova ejecta with a companion star or circumstellar debris lead to a sudden brightening lasting from hours to days. Here we present data for three supernovae that are likely to be type Ia observed during the Kepler mission with a time resolution of 30 minutes. We find no signatures of the supernova ejecta interacting with nearby companions. The lack of observable interaction signatures is consistent with the idea that these three supernovae resulted from the merger of binary white dwarfs or other compact stars such as helium stars.

Discrete clouds of neutral gas between the galaxies M31 and M33.

Spiral galaxies must acquire gas to maintain their observed level of star formation beyond the next few billion years. A source of this material may be the gas that resides between galaxies, but our understanding of the state and distribution of this gas is incomplete. Radio observations of the Local Group of galaxies have revealed hydrogen gas extending from the disk of the galaxy M31 at least halfway to M33. This feature has been interpreted to be the neutral component of a condensing intergalactic filament, which would be able to fuel star formation in M31 and M33, but simulations suggest that such a feature could also result from an interaction between both galaxies within the past few billion years (ref. 5). Here we report radio observations showing that about 50 per cent of this gas is composed of clouds, with the rest distributed in an extended, diffuse component. The clouds have velocities comparable to those of M31 and M33, and have properties suggesting that they are unrelated to other Local Group objects. We conclude that the clouds are likely to be transient condensations of gas embedded in an intergalactic filament and are therefore a potential source of fuel for future star formation in M31 and M33.