On 15 June 2015, a long-time acquaintance of X-ray and gamma ray astronomers made its comeback to the cosmic stage: V404 Cygni, a system comprising a black hole and a star orbiting one another. It is located in our Milky Way galaxy, almost 8,000 light-years away in the constellation Cygnus, the Swan.
Delta (δ) Cephei, prototype of Cepheids, which has given its name to all similar variable stars, was discovered 230 years ago by the English astronomer John Goodricke. The Cepheids role as distance calibrators for more than a century means δ Cephei is one of the most studied stars, but astronomers were shocked to discover that they lacked an essential piece of information…
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