An anonymous reader quotes a report from Space.com: NASA's Chandra X-ray Observatory has found a brand new type of an otherwise familiar object -- compact binary systems that steal gas from other stars, but which do so while emitting very low-energy X-rays but copious amounts of ultraviolet. Chandra spotted 84 suspicious object emitting very low-energy X-rays in six galaxies -- four evolved ellipticals and two spirals, namely our near-neighbor the Andromeda Galaxy (M31) and the Pinwheel Galaxy (M101). "We've never encountered a group of objects that act like this," said Mustafa Muhibullah of the University of Alabama in a statement. Compact objects, in the form of black holes, neutron stars and white dwarfs, are the remains of stars that have died. Their small size and powerful gravity means that they're adept at getting close to orbiting companion stars and ripping the stars' outer layers of gas away. The gas swirls around the compact object, falling onto its surface, and this accretionary process usually produces torrents of high-energy X-rays because the stolen gas becomes superheated by the compact object's gravitational vice-like grip. Because of their weak X-rays, Muhibullah's team refer to them as 'hypersoft X-ray sources'. Since low-energy X-rays and ultraviolet light are next to each other on the electromagnetic spectrum, Muhibullah and his team suspect that the low-energy X-rays are spillover from objects emitting prodigious amounts of ultraviolet. Moreover, they think that these objects are lower-level compact binaries. They're hard to find though, because the interstellar medium of hydrogen and helium gas between the stars absorbs ultraviolet light. This could be why we have yet to find any hypersoft X-ray sources in our own galaxy, because we have to look through the interstellar medium through the plane of the Milky Way. Consequently, there could be a large population of hypersoft X-ray sources that remain undiscovered and they could have an important effect on the universe around them. The findings have been published in the journal Nature Astronomy.

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A new study suggests Mercury may have shrunk about 30% more than scientists previously thought, losing as much as 14 miles in diameter as its interior cooled and contracted over billions of years. "That's significant for a planet barely 3,000 miles (4,900 kilometers) across," reports the Associated Press. From the report: Mercury's rough surface, continually reshaped by debris hurled from impact craters, may have hidden the true extent of the loss, according to the researchers whose findings appear in the journal Geophysical Research Letters. The news comes one week after a pair of European and Japanese spacecraft shed its cruising platform and advanced toward Mercury. Known as BepiColombo, the linked craft are expected to enter orbit around Mercury in November before splitting up for a fuller survey. BepiColombo's laser instrument should confirm how much Mercury is withering as a result of internal cooling, said Gaku Nishiyama, the study's lead author who is taking part in the space mission. The shrinkage could be even more than his team is estimating based on measurements from NASA's Messenger spacecraft in the 2010s. Only one other spacecraft has ever visited Mercury, NASA's Mariner 10 in the 1970s.

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alternative_right shares a report from ScienceDaily: A new analysis of more than 1,700 supernovae is questioning whether the universe is really accelerating at all. After accounting for the ages of the stars that produce these explosions, researchers found signs that cosmic expansion may actually be slowing. They also argue that the apparent acceleration changes with direction, which would be difficult to explain with dark energy. Other cosmologists dispute the conclusion, setting up a major test for upcoming observatories. The analysis has been published in Monthly Notices of the Royal Astronomical Society. The conclusion is disputed, though. The report mentions a separate paper co-authored by Professor Maria Vincenzi, also at the University of Oxford, that "concludes that observations continue to support an accelerating universe."

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