Australian Sky & Telescope Oct 2016

How do you spot something that’s invisible? Simple, use something else that’s invisible to help you. That’s what astronomers are doing in their quest to understand the nature of dark energy and dark matter — both of them so far invisible to us — by using the invisible force of gravity to map the distorting effects they have on the universe’s ordinary matter in the form of stars and galaxies. It’s a technique called ‘weak lensing’ (see page 14), and it’s being used to answer some of the most fundamental questions about the origin and evolution of the cosmos. Closer to home, within our own Milky Way, are a group of planetary nebulae that are not invisible but quite hard to spot. And it is their challenging observational nature, of…

Anew analysis by the Kepler team has doubled the total number of confirmed exoplanets. Over four years, the Kepler spacecraft stared at a patch of sky straddling the Cygnus-Lyra border and tallied up 4,696 exoplanet candidates. But to confirm that any one planet is real requires difficult, time-consuming, follow-up observations, often impossible for the smaller candidates. Timothy Morton (Princeton University) and colleagues took a different tack. Instead of looking for additional evidence supporting a given candidate’s existence, they searched for signs that it wasn’t there. Their fully automated code first examined the transit light curve itself — a real planet will block the star’s light in a certain way that can sometimes be distinguished from imposters, such as an eclipsing binary star. Then the code factored in how common imposters…

Last year, ASASSN-15lh gained fame as the most luminous supernova ever discovered. Now almost a year Later and against all odds, the supernova has rebrightened. Subo Dong (Peking University, China) and colleagues discovered ASASSN-15lh on June 14, 2015, using the All-Sky Automated Survey for Supernovae (ASASSN). Its peak power was more than twice that of any previously known stellar explosion. Usually, much of a supernova’s initial glow actually comes from the decay of radioactive nickel, created in abundance near the core. What’s weird about ASASSN-15lh and a few others like it is that they’re so bright, they’d need an awful lot of nickel to explain their glow. Then, three months after it began fading, the supernova changed its mind. Over some 40 days, its ultraviolet radiation increased fivefold before plateauing…

China’s amazing Five-hundred-metre Aperture Spherical Telescope (FAST) was completed in July 2016, construction having begun in 2011. The dish is made of 4,450 triangular metal panels, each 11 metres on a side. While the telescope has a diameter of 500 metres, only 300 metres can actually be used at any one time. A system of cables and actuators can deform the parabolic shape of the dish, effectively making it point in different directions (anything up to 40 degrees away from the zenith). A ‘feed cabin,’ where the radio receivers are housed, dangles above the dish. A 19-beam receiver was built by the CSIRO for the project, as part of an Australia-China collaboration.…

ON MAY 12–13, AMATEURS AND professionals interested in supporting NASA’s Juno mission met in Nice, France, for a workshop dedicated to projects and techniques related to observing Jupiter. The spacecraft arrived at the giant planet on July 4. Although Juno will image Jupiter at very high resolution, especially in the polar regions, it lacks the ability to create global portraits. So it falls to Earth-based observers to watch regions out of view from the probe and to acquire the large-scale views that provide context for the spacecraft’s small-scale scrutiny. Highest on the ‘to do’ list for the months ahead is to sustain the ongoing ground-based survey of Jupiter, so lots of discussion focused on the necessary equipment, imaging and processing tools and techniques needed for that task. For example, more…

LIGHT ECHOES MAP PLANET DISK. Astronomers have used light’s finite speed to pinpoint the location of the ‘inner wall’ of the disk of dust and gas that’s feeding a growing baby star. Protostars naturally flicker in brightness, and the photons from these surges reach us two ways: by flying directly at us from the star, or after first bouncing off the disk surrounding it (see above). The latter are called light echoes . The delay between the two flashes reveals how far the gas is from the central object. Observers have long used light echoes to measure the mass of supermassive black holes, but now for the first time Huan Meng (Caltech) and colleagues have used them to study a protostar, YLW 16B. By watching the star’s…