When astronomer Edwin Hubble discovered nearly 100 years ago that the universe was uniformly expanding in all directions, the finding was a big surprise. Then, in the mid-1990s, another shocker occurred: astronomers found that the expansion rate was accelerating perhaps due to a repulsive property called "dark energy." Now, the latest measurements of our runaway universe suggest that it is expanding faster than astronomers thought. The consequences could be very significant for our understanding of the shadowy contents of our unruly universe. It may mean that dark energy is shoving galaxies away from each other with even greater or growing strength. Or, the early cosmos may contain a new type of subatomic particle referred to as "dark radiation." A third possibility is that "dark matter," an invisible form of matter that makes up the bulk of our universe, possesses some weird, unexpected characteristics. Finally, Einstein's theory of gravity may be incomplete.
Astronomy: Cosmic detectives
Nature 534, 7605 (2016). doi:10.1038/534034a
Author: Bernie Fanaroff
Bernie Fanaroff surveys a study that probes telescopes in history and across the electromagnetic spectrum.
Astronomy: Galaxy from the cosmic dark ages
Nature 534, 7605 (2016). doi:10.1038/534008b
Astronomers have found the faintest example yet of a galaxy from the early Universe.Kuang-Han Huang of the University of California, Davis, and his colleagues spotted the 13-billion-year-old galaxy using the Keck Observatory in Hawaii and the Hubble Space Telescope. A cluster of galaxies in
A resonant chain of four transiting, sub-Neptune planets
Nature 533, 7604 (2016). doi:10.1038/nature17445
Authors: Sean M. Mills, Daniel C. Fabrycky, Cezary Migaszewski, Eric B. Ford, Erik Petigura & Howard Isaacson
Surveys have revealed many multi-planet systems containing super-Earths and Neptunes in orbits of a few days to a few months. There is debate whether in situ assembly or inward migration is the dominant mechanism of the formation of such planetary systems. Simulations suggest that migration creates tightly packed systems with planets whose orbital periods may be expressed as ratios of small integers (resonances), often in a many-planet series (chain). In the hundreds of multi-planet systems of sub-Neptunes, more planet pairs are observed near resonances than would generally be expected, but no individual system has hitherto been identified that must have been formed by migration. Proximity to resonance enables the detection of planets perturbing each other. Here we report transit timing variations of the four planets in the Kepler-223 system, model these variations as resonant-angle librations, and compute the long-term stability of the resonant chain. The architecture of Kepler-223 is too finely tuned to have been formed by scattering, and our numerical simulations demonstrate that its properties are natural outcomes of the migration hypothesis. Similar systems could be destabilized by any of several mechanisms, contributing to the observed orbital-period distribution, where many planets are not in resonances. Planetesimal interactions in particular are thought to be responsible for establishing the current orbits of the four giant planets in the Solar System by disrupting a theoretical initial resonant chain similar to that observed in Kepler-223.
Suppressing star formation in quiescent galaxies with supermassive black hole winds
Nature 533, 7604 (2016). doi:10.1038/nature18006
Authors: Edmond Cheung, Kevin Bundy, Michele Cappellari, Sébastien Peirani, Wiphu Rujopakarn, Kyle Westfall, Renbin Yan, Matthew Bershady, Jenny E. Greene, Timothy M. Heckman, Niv Drory, David R. Law, Karen L. Masters, Daniel Thomas, David A. Wake, Anne-Marie Weijmans, Kate Rubin, Francesco Belfiore, Benedetta Vulcani, Yan-mei Chen, Kai Zhang, Joseph D. Gelfand, Dmitry Bizyaev, A. Roman-Lopes & Donald P. Schneider
Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 1010 times that of the Sun; the number of quiescent galaxies has increased by a factor of about 25 over the past ten billion years (refs 1, 2, 3, 4). Once star formation has been shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat the gas that is subsequently accreted from either stellar mass loss or mergers and that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centres of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized-gas velocity gradients from which we infer the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as ten per cent of the quiescent population with masses around 2 × 1010 times that of the Sun. In a prototypical example, we calculate that the energy input from the galaxy’s low-level active supermassive black hole is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.
Astrophysics: How black holes restrain old galaxies
Nature 533, 7604 (2016). doi:10.1038/533473a
Authors: Marc Sarzi
Supermassive black holes are thought to keep star formation under control by ejecting or stirring gas in galaxies. Observations of an old galaxy reveal a potential mechanism for how this process occurs. See Letter p.504
Physics: Invest in neutrino astronomy
Nature 533, 7604 (2016). doi:10.1038/533462a
Author: Spencer Klein
Spencer Klein calls for bigger telescope arrays to catch particles from the most energetic places in the Universe.