Physics Today Daily Edition
Ars Technica: Last week, it was announced that several new dwarf galaxies surrounding the Milky Way had been found. Now, a team led by Alex Geringer-Sameth of Carnegie Mellon University has found that the closest of those galaxies, Reticulum 2, emits gamma rays. The finding is notable because dwarf galaxies generally lack the usual objects, such as black holes and pulsars, that produce gamma rays. And no previous dwarf galaxy has ever been found emitting gamma rays. The signal from Reticulum 2 could be detectable simply because it is the closest dwarf galaxy yet found. Because dwarf galaxies have a high concentration of dark matter, they are believed to be good candidates for study to try to find out what kind of particles dark matter is made of. Geringer-Sameth's team believes that the gamma-ray signal could be evidence of self-interacting dark-matter particles, such as WIMPs, colliding with each other. However, there are still too many characteristics of Reticulum 2 that need to be clarified before that theory can be confirmed.
Nature: Several bright spots have been observed on the asteroid Ceres by NASA's Dawn spacecraft. The asteroid is known to have a significant amount of ice, but the way sunlight is being reflected indicates that the ice does not simply lie exposed on the asteroid's surface. New images from Dawn have revealed that some of the bright spots located in craters are still visible even when the crater walls should block them from the Sun. That observation suggests that, if the reflections are due to ice, the ice must have been pushed up to significant heights. One explanation could be volcano-like eruptions of the ice caused by fluctuating internal pressures within the asteroid. Similar eruptions could also be caused by sunlight warming the asteroid's surface as Ceres rotates from night to day, which could allow icy plumes to form that refreeze and then melt back down to the surface.
New York Times: Despite its reputation as a cool, cloudy country, the UK led Europe in the number of new solar installations in 2014. The combination of government subsidies and low prices because of high production rates from factories in China has driven the spread of solar in many European nations. And direct costs have now reached levels where solar can compete with natural gas without the need for subsidies. Thanks to those trends, European solar companies are building solar plants in developing nations such as Chile and India. In northern Chile, high altitude and low latitude allow solar to produce electricity at 80% the cost of coal, and 60% the cost of natural gas. Subsidies have even had some negative influences in the UK and Germany, where they've pushed up the cost of electricity overall. For large solar installations, the UK has begun auctioning guaranteed rates, which it believes will reduce the overall cost of electricity while still spurring solar growth.
BBC: When the European Space Agency's Rosetta was approaching comet 67P/Churyumov-Gerasimenko, its pictures of the cometary surface revealed 17 objects that appeared to have trails extending northward away from them. Such trails are common on Earth, where they are formed by wind depositing dust behind boulders or other objects. However, because the comet lacks an atmosphere, there isn't any wind. On Monday at the 46th Lunar and Planetary Science Conference, Stefano Mottola, the project leader of the Rosetta Lander Imaging System, announced that the team believes the trails were caused by splash saltation. The trails would have formed when objects impacted the surface and dislodged particles, which then fell back in the patterns seen.
Nature: One of the common methods of 3D printing shines UV light into the bottom of a container of liquid resin, which causes the resin at the very bottom of the basin to solidify. The solid part must then be pulled up to allow new liquid resin to flow in underneath, and the process is repeated. Because of the need to pause after the creation of each layer, the process can take hours to days, depending on the size of the object being printed. Now, Joseph DeSimone of the University of North Carolina at Chapel Hill and his colleagues have developed a new printer that can produce objects in just minutes. They made a reservoir for the liquid resin that has a bottom permeable to oxygen. The oxygen keeps the resin at the bottom from solidifying, resulting in a micron-thick layer of resin that remains liquid beneath the printed object. That allows the object to be printed continuously, with no delays as it is pulled upward. The technique also allows for 3D printing using rubbery materials that did not work in previous machines.