The double-degenerate, super-Chandrasekhar nucleus of the planetary nebula Henize 2-428
Nature 519, 7541 (2015). doi:10.1038/nature14124
Authors: M. Santander-García, P. Rodríguez-Gil, R. L. M. Corradi, D. Jones, B. Miszalski, H. M. J. Boffin, M. M. Rubio-Díez & M. M. Kotze
The planetary nebula stage is the ultimate fate of stars with masses one to eight times that of the Sun (). The origin of their complex morphologies is poorly understood, although several mechanisms involving binary interaction have been proposed. In close binary systems, the orbital separation is short enough for the primary star to overfill its Roche lobe as the star expands during the asymptotic giant branch phase. The excess gas eventually forms a common envelope surrounding both stars. Drag forces then result in the envelope being ejected into a bipolar planetary nebula whose equator is coincident with the orbital plane of the system. Systems in which both stars have ejected their envelopes and are evolving towards the white dwarf stage are said to be double degenerate. Here we report that Henize 2-428 has a double-degenerate core with a combined mass of ∼1.76, which is above the Chandrasekhar limit (the maximum mass of a stable white dwarf) of 1.4. This, together with its short orbital period (4.2 hours), suggests that the system should merge in 700 million years, triggering a type Ia supernova event. This supports the hypothesis of the double-degenerate, super-Chandrasekhar evolutionary pathway for the formation of type Ia supernovae.
A tale of two dwarf planets
Nature 518, 7540 (2015). http://www.nature.com/doifinder/10.1038/518468a
Author: Alex Witze
Graphical guide to the NASA missions that will provide the first close looks at Ceres and Pluto.
Planetary science: The Pluto siblings
Nature 518, 7540 (2015). http://www.nature.com/doifinder/10.1038/518470a
Author: Alexandra Witze
Leslie and Eliot Young have spent their lives studying Pluto. Now they are gearing up for the biggest event of their careers.
Cosmology: A giant in the young Universe
Nature 518, 7540 (2015). doi:10.1038/518490b
Authors: Bram Venemans
Astronomers have discovered an extremely massive black hole from a time when the Universe was less than 900 million years old. The result provides insight into the growth of black holes and galaxies in the young Universe. See Letter p.512
An ultraluminous quasar with a twelve-billion-solar-mass black hole at redshift 6.30
Nature 518, 7540 (2015). doi:10.1038/nature14241
Authors: Xue-Bing Wu, Feige Wang, Xiaohui Fan, Weimin Yi, Wenwen Zuo, Fuyan Bian, Linhua Jiang, Ian D. McGreer, Ran Wang, Jinyi Yang, Qian Yang, David Thompson & Yuri Beletsky
So far, roughly 40 quasars with redshifts greater than z = 6 have been discovered. Each quasar contains a black hole with a mass of about one billion solar masses (109). The existence of such black holes when the Universe was less than one billion years old presents substantial challenges to theories of the formation and growth of black holes and the coevolution of black holes and galaxies. Here we report the discovery of an ultraluminous quasar, SDSS J010013.02+280225.8, at redshift z = 6.30. It has an optical and near-infrared luminosity a few times greater than those of previously known z > 6 quasars. On the basis of the deep absorption trough on the blue side of the Lyman-α emission line in the spectrum, we estimate the proper size of the ionized proximity zone associated with the quasar to be about 26 million light years, larger than found with other z > 6.1 quasars with lower luminosities. We estimate (on the basis of a near-infrared spectrum) that the black hole has a mass of ∼1.2 × 1010, which is consistent with the 1.3 × 1010 derived by assuming an Eddington-limited accretion rate.