Astrophysics: Portrait of a doomed star
Nature 512, 7512 (2014). doi:10.1038/512034a
Authors: Stephen Justham
Some stars explode in thermonuclear supernovae, but understanding of why this occurs comes mainly from indirect clues. Now, the progenitor of a member of a strange class of such explosions may have been detected directly. See Letterp.54
A luminous, blue progenitor system for the type Iax supernova 2012Z
Nature 512, 7512 (2014). doi:10.1038/nature13615
Authors: Curtis McCully, Saurabh W. Jha, Ryan J. Foley, Lars Bildsten, Wen-fai Fong, Robert P. Kirshner, G. H. Marion, Adam G. Riess & Maximilian D. Stritzinger
Type Iax supernovae are stellar explosions that are spectroscopically similar to some type Ia supernovae at the time of maximum light emission, except with lower ejecta velocities. They are also distinguished by lower luminosities. At late times, their spectroscopic properties diverge from those of other supernovae, but their composition (dominated by iron-group and intermediate-mass elements) suggests a physical connection to normal type Ia supernovae. Supernovae of type Iax are not rare; they occur at a rate between 5 and 30 per cent of the normal type Ia rate. The leading models for type Iax supernovae are thermonuclear explosions of accreting carbon–oxygen white dwarfs that do not completely unbind the star, implying that they are ‘less successful’ versions of normal type Ia supernovae, where complete stellar disruption is observed. Here we report the detection of the luminous, blue progenitor system of the type Iax SN 2012Z in deep pre-explosion imaging. The progenitor system's luminosity, colours, environment and similarity to the progenitor of the Galactic helium nova V445 Puppis suggest that SN 2012Z was the explosion of a white dwarf accreting material from a helium-star companion. Observations over the next few years, after SN 2012Z has faded, will either confirm this hypothesis or perhaps show that this supernova was actually the explosive death of a massive star.
Binary star to spill celestial secrets
Nature 512, 7512 (2014). http://www.nature.com/doifinder/10.1038/512013a
Author: Alexandra Witze
Close approach and violent interaction of stars in η Carinae system will provide rare insight into stellar enigma.
Astronomers using NASA's Hubble Space Telescope have unexpectedly discovered the most distant cosmic magnifying glass yet, produced by a monster elliptical galaxy. The galaxy, seen here as it looked 9.6 billion years ago, is so massive that its gravity bends, magnifies, and distorts light from objects behind it, a phenomenon called gravitational lensing. In the Hubble image, the galaxy is the red object in the enlarged view at left.
The tidal–rotational shape of the Moon and evidence for polar wander
Nature 512, 7513 (2014). doi:10.1038/nature13639
Authors: Ian Garrick-Bethell, Viranga Perera, Francis Nimmo & Maria T. Zuber
The origin of the Moon’s large-scale topography is important for understanding lunar geology, lunar orbital evolution and the Moon’s orientation in the sky. Previous hypotheses for its origin have included late accretion events, large impacts, tidal effects and convection processes. However, testing these hypotheses and quantifying the Moon’s topography is complicated by the large basins that have formed since the crust crystallized. Here we estimate the large-scale lunar topography and gravity spherical harmonics outside these basins and show that the bulk of the spherical harmonic degree-2 topography is consistent with a crust-building process controlled by early tidal heating throughout the Moon. The remainder of the degree-2 topography is consistent with a frozen tidal–rotational bulge that formed later, at a semi-major axis of about 32 Earth radii. The probability of the degree-2 shape having both tidal-heating and frozen shape characteristics by chance is less than 1%. We also infer that internal density contrasts eventually reoriented the Moon’s polar axis by 36 ± 4°, to the configuration we observe today. Together, these results link the geology of the near and far sides, and resolve long-standing questions about the Moon’s large-scale shape, gravity and history of polar wander.