Just how do gas giant planets form? A team of researchers at ETH Zürich, working with both the University of Zürich and the University of Bern, has developed the most fine-grained and instructive computer simulations yet to help us understand the process. Using the Piz Daint supercomputer at the Swiss National Supercomputing Centre (CSCS) in Lugano, ETH Zürich postdoc Judit Szulágyi and Lucio Mayer (University of Zürich) can now show clear and observable differences between the two formation processes under study by theorists. The core accretion model begins with a massive solid core that is large enough to pull in gas from the protoplanetary disk and maintain it. The gravitational instability theory, on the other hand, presumes a massive enough disk around the young host star that spiral arms form in the disk in which gravitational collapse can occur around material that has begun to clump there. The simulations demonstrate that with either formation mechanism, a circumplanetary...

Those of us fascinated by dim red stars find these to be exhilarating days indeed. The buzz over Proxima b continues, as well it should, given the fact that this provocative planet orbits the nearest star. We also have detections like the three small planets around TRAPPIST-1, another red dwarf that is just under 40 light years out in the constellation Aquarius. These are small stars indeed, just 8 percent the mass of the Sun in the case of the latter, while Proxima Centauri is about 10 times less massive (and 500 times less luminous) than the Sun. But just what might we find on planets like these? A new paper from Yann Alibert and Willy Benz (University of Bern) drills down into their composition. The researchers' goal is to study planet formation, with a focus on planets orbiting within 0.1 AU, a range that includes the habitable zone for such stars. While a forthcoming paper will look at the formation process of these planets in greater detail, the present work studies planetary...

First light for the European Extremely Large Telescope (E-ELT) is scheduled for 2024, a useful fact given that a few years later, we may be able to use the instrument in a gravitational lensing opportunity involving Alpha Centauri. Specifically, Centauri A is expected to align with the star 2MASS 14392160-6049528, thought to be a red giant or supergiant and far more distant than Alpha Centauri. This will create an event that not just the E-ELT but other instruments, like the GRAVITY instrument on the Very Large Telescope Interferometer (VLTI), will be able to study -- GRAVITY is capable of extremely high accuracy astrometry. A team of French astronomers led by Pierre Kervella (CNRS/Universidad de Chile) is behind this new study, which involved fine-tuning our knowledge of the trajectories of Centauri A and B. Remember that we see gravitational lensing when a massive object like a star distorts the spacetime around it, so that light from the more distant object must follow a curved...

Determining the age of a star is not easy, but one way of proceeding with at least some degree of confidence is to identify the star as a member of a stellar association. Here we’re talking about a loose cluster of stars of a common origin. Over time, the stars have begun to separate, but they still move together through space. It was the Armenian astronomer Viktor Ambartsumian, the founder of the Byurakan Observatory, who discovered the nature of these associations and demonstrated that they were composed of relatively young groups of stars. Stellar associations, or young moving groups (YMGs), provide an outstanding place to study the evolution of protoplanetary disks around young stars, for all associated stars have a similar age. Indeed, their galactic motion can be traced back to their place of origin. Another benefit: Exoplanets in such infant systems are often still hot, well within the capabilities of our near-infrared direct imaging techniques. Many direct imaging and disk...

Spotting planets a long way from their stars is no easy proposition when you’re using radial velocity methods. The idea is to track the minute movement of the star as it is affected by an orbiting planet, which shows up as a Doppler shift in the data. What we’re actually seeing is the star and planet orbiting the center of gravity, an indirect method of detection that observes not the planet itself but the effects of the planet as it produces this variation in radial velocity. The first exoplanets were detected this way, and the method has continued to produce new discoveries. But as a planet’s distance from its star increases, radial velocity becomes tricky to use. Now observation times become extended as the planet completes its longer orbit. We face the same issue with the transit method, which charts the drop in brightness as a planet moves across the face of its star as seen from Earth. Here, too, planets in distant orbits around their star are hard to detect because of the...

We’ve seen circumstellar disks around numerous stars, significant because it is from such disks that planets are formed, and we would like to know a good deal more about how this process works. Now we have word of planet-forming disks around several low-mass objects that fit into the brown dwarf range, and one small star about a tenth the mass of the Sun. With the brown dwarfs, we’re working with objects small enough to be at the boundary between planet and star. The work is led by Anne Boucher (Université de Montréal), whose team drew photometric data from the Two-Micron All-Sky Survey (2MASS) and the Wide-field Infrared Survey Explorer (WISE) mission, allowing the detection of the objects at infrared wavelengths. Boucher notes the strong attraction such objects hold for astronomers: “Finding disks in low-mass systems is really interesting to us, because objects that exist at the lower limit of what defines a star and that still have disks that indicate planet formation can tell us...