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Supernovae are classified spectroscopically as Type I if they have no hydrogen lines in their optical spectra and Type II if they have hydrogen lines in their optical spectra. Type [...], Spectroscopic and photometric evidence indicates that Type Ia supernovae (SNe Ia) are the thermonuclear explosions of accreting white dwarfs. However, the progenitor binary systems and hydrodynamical models for SNe Ia are still controversial. The relatively uniform light curves and spectral evolution of SNe Ia have led to their use as a standard candle for determining cosmological parameters, such as the Hubble constant, the density parameter, and the cosmological constant. Recent progress includes the calibration of the absolute maximum brightness of SNe Ia with the Hubble Space Telescope, the reduction of the dispersion in the Hubble diagram through the use of the relation between the light curve shape and the maximum brightness of SNe Ia, and the discovery of many SNe Ia with high red shifts.

Supernovae are cataclysmic stellar explosions that are accompanied by bright visual displays. The designation type II is used for supernovae that have hydrogen lines in their optical spectra, and type [...], The optical and ultraviolet emission from the type II supernova SN 1987A is currently powered by the radioactive decay of titanium-44. In contrast, the emission from SN 1993J is dominated by radiation from the interaction of the supernova shock wave with a dense, stellar wind released before the explosion. The dense wind around SN 1987A was displaced by the fast wind from the compact progenitor star, and the interaction of the supernova with dense gas is now being detected at x-ray and radio wavelengths. The expected neutron stars or black holes at the centers of these supernovae are not yet significant power sources.

Some observations suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae (1-4), as do several models (5-7). Establishing a causal connection between these mass-loss [...]

The recent discovery (1) by very long baseline interferometry (VLBI) of a shell-like radio structure in SN 1993J in the galaxy M81 offers the opportunity to monitor a supernova expansion [...], A sequence of images from very long baseline interferometry shows that the young radio supernova SN 1993J is expanding with circular symmetry. However, the circularly symmetric images show emission asymmetries. A scenario in which freely expanding supernova ejecta shock mostly isotropic circumstellar material is strongly favored. The sequence of images constitutes the first 'movie' of a radio supernova.

It is assumed (1,3) that the radioactive decay of [sup.44]Ti powers the infrared, optical and ultraviolet emission of supernova remnants after the complete decay of [sup.56]Co and [sup.57]Co (the isotopes [...]

The progenitor of any type Ia supernova has never been identified. Various candidate classes have been proposed (see Table 1 and Supplementary Information section 1), although arguments and counterarguments have [...], A type Ia supernova is thought to begin with the explosion of a white dwarf star (1). The explosion could be triggered by the merger of two white dwarfs (2,3) (a 'double-degenerate' origin), or by mass transfer from a companion star (4,5) (the 'single-degenerate' path). The identity of the progenitor is still controversial; for example, a recent argument against the single-degenerate origin (6) has been widely rejected (7-11). One way to distinguish between the double- and single-degenerate progenitors is to look at the centre of a known type Ia supernova remnant to see whether any former companion star is present (12,13). A likely ex-companion star for the progenitor of the supernova observed by Tycho Brahe has been identified (14), but that claim is still controversial (15-18). Here we report that the central region of the supernova remnant SNR 0509-67.5 (the site of a type Ia supernova 400 ± 50 years ago, based on its light echo (19,20)) in the Large Magellanic Cloud contains no ex-companion star to a visual magnitude limit of 26.9 (an absolute magnitude of [M.sub.V] = +8.4) within a region of radius 1.43 arcseconds. (This corresponds to the 3σ-maximum distance to which a companion could have been 'kicked' by the explosion.) This lack of any ex-companion star to deep limits rules out all published single-degenerate models for this supernova. The only remaining possibility is that the progenitor of this particular type Ia supernova was a double-degenerate system.

In a double-degenerate model, the orbit of the two white dwarfs shrinks owing to the release of gravitational radiation (2,4). Ultimately, the lighter object (the secondary) is disrupted and accretion [...], Type Ia supernovae are thought to result from a thermonuclear explosion of an accreting white dwarf in a binary system (1,2), but little is known of the precise nature of the companion star and the physical properties of the progenitor system. There are two classes of models (1,3): double-degenerate (involving two white dwarfs in a close binary system (2,4)) and single-degenerate models (5,6). In the latter, the primary white dwarf accretes material from a secondary companion until conditions are such that carbon ignites, at a mass of 1.38 times the mass of the Sun. The type Ia supernova SN 2011fe was recently detected in a nearby galaxy (7). Here we report an analysis of archival images of the location of SN 2011fe. The luminosity of the progenitor system (especially the companion star) is 10-100 times fainter than previous limits on other type Ia supernova progenitor systems (8-10), allowing us to rule out luminous red giants and almost all helium stars as the mass-donating companion to the exploding white dwarf.

We discovered SN 2005cz on 2005 July 17.5 UT in the elliptical galaxy NGC 4589. The spectrum of SN 2005cz taken on July 28 is consistent with post-maximum spectra of [...], The unusual helium-rich (type Ib) supernova SN 2005E is distinguished from all supernovae hitherto observed by its faint and rapidly fading light curve, prominent calcium lines in late-phase spectra and lack of any mark of recent star formation near the supernova location. These properties are claimed (1) to be explained by a helium detonation in a thin surface layer of an accreting white dwarf. Here we report that the observed properties of SN 2005cz, which appeared in an elliptical galaxy, resemble those of SN 2005E. Weargue that these properties are best explained by a core-collapse supernova at the low-mass end (8-12 solar masses) of the range of massive stars that explode (2). Such a low-mass progenitor lost its hydrogen-rich envelope through binary interaction, had very thin oxygen-rich and silicon-rich layers above the collapsing core, and accordingly ejected a very small amount of radioactive [sup.56]Ni and oxygen. Although the host galaxy NGC 4589 is an elliptical, some studies have revealed evidence of recent star-formation activity (3), consistent with the core-collapse model.

The value of the Hubble constant was determined to be in the region of 55 km/sec-Mps by three new methods, primarily the Tully-Fisher method, based on supernovae observation. The constant indicates the speed of remote galaxies.

Using images from the Hubble Space Telescope and the Gemini Telescope, we confirmed the disappearance of the progenitors of two type II supernovae (SNe) and evaluated the presence of other stars associated with them. We found that the progenitor of SN 2003gd, an M-supergiant star, is no longer observed at the SN location and determined its intrinsic brightness using image subtraction techniques. The progenitor of SN 1993J, a K-supergiant star, is also no longer present, but its B-supergiant binary companion is still observed. The disappearance of the progenitors confirms that these two supernovae were produced by red supergiants.

Type Ia supernovae are thermonuclear explosions of white dwarf stars in close binary systems (1). They play an important role as cosmological distance indicators and have led to the discovery [...]

Astronomers Hiraoaki Narumi and Kiyotaka Kanai of Japan spotted the new nova outburst of RS Ophiuchi on 12 February 2005. This recent outburst is helping astronomers in better understanding the physics of nova outbursts. By analyzing the emission from the cooling, post-outburst white dwarf, astronomers hope to determine how much accreted matter remains.