Cosmology: Cool start to hydrogen ionization
Nature 506, 7487 (2014). doi:10.1038/nature13051
Authors: Judd D. Bowman
Simulations of the cosmos cast doubt on assumptions about the temperature of primordial hydrogen gas when it was ionized by the first stars and galaxies, complicating the interpretation of ongoing observations. See Letter p.197
The observable signature of late heating of the Universe during cosmic reionization
Nature 506, 7487 (2014). doi:10.1038/nature12999
Authors: Anastasia Fialkov, Rennan Barkana & Eli Visbal
Models and simulations of the epoch of reionization predict that spectra of the 21-centimetre transition of atomic hydrogen will show a clear fluctuation peak, at a redshift and scale, respectively, that mark the central stage of reionization and the characteristic size of ionized bubbles. This is based on the assumption that the cosmic gas was heated by stellar remnants—particularly X-ray binaries—to temperatures well above the cosmic microwave background at that time (about 30 kelvin). Here we show instead that the hard spectra (that is, spectra with more high-energy photons than low-energy photons) of X-ray binaries make such heating ineffective, resulting in a delayed and spatially uniform heating that modifies the 21-centimetre signature of reionization. Rather than looking for a simple rise and fall of the large-scale fluctuations (peaking at several millikelvin), we must expect a more complex signal also featuring a distinct minimum (at less than a millikelvin) that marks the rise of the cosmic mean gas temperature above the microwave background. Observing this signal, possibly with radio telescopes in operation today, will demonstrate the presence of a cosmic background of hard X-rays at that early time.
Astrophysics: Hydrogen river could fuel stars
Nature 506, 7486 (2014). doi:10.1038/506008c
The discovery of a faint filament of hydrogen gas streaming across space could help to explain how some galaxies maintain their pace of star formation.D. J. Pisano from West Virginia University in Morgantown used the Robert C. Byrd Green Bank Telescope to identify a
Cosmology: Planck team replies to data 'anomalies'
Nature 506, 7486 (2014). doi:10.1038/506034c
Author: Jan Tauber
We would like to clarify some points arising from your News report on the debate over data from the European Space Agency's Planck mission (see Naturehttp://doi.org/q8t; 2013).The cosmological parameters estimated by the Planck Collaboration are statistically compatible with those estimated by
Imagine living on a planet with seasons so unpredictable you would hardly know what to wear: Bermuda shorts or a heavy overcoat! That's the situation on a weird world found by NASA's planet-hunting Kepler space telescope. The planet, designated Kepler-413b, is located 2,300 light-years away in the constellation Cygnus. It circles a close pair of orange and red dwarf stars every 66 days. But what makes this planet very unusual is that it wobbles, or precesses, wildly on its spin axis, much like a child's top. The planet's orbit is tilted with respect to the plane of the binary star's orbit. Over an 11-year period, the planet's orbit too would appear to wobble as it circles around the star pair. All of this complex movement leads to rapid and erratic changes in seasons.