Do we really need a ring?

Understanding the structure of our Milky Way is as difficult as trying to see the forest from the trees. Among the many uncertainties, we don’t know whether the molecular ring is really due to a ring structure or it is simply produced by the spiral arms.

If Santa goes Down Under

The moon is usually pictured in illustrations of Christmastime which show evening or night scenes. But, as Peter Barthel reveals in his study, illustrations of the partially lit moon are often astronomically incorrect, unless the scenes take place Down Under.

Two monster black holes in nearby galaxies

Title: Two ten-billion-solar-mass black holes at the centres of giant elliptical galaxies Authors: Nicholas J. McConnell, Chung-Pei Ma, Karl Gebhardt, Shelley A. Wright, Jeremy D. Murphy, Tod R. Lauer, James R. Graham, Douglas O. Richstone First Author’s Institution: Department of Astronomy, University of California, Berkeley This Nature letter reports on a recent discovery that has also met with great interest in the popular press: astronomers have measured the biggest black holes ever! These two ten-billion-solar mass giants are significantly more massive than any other known black hole and more massive than predicted with the widely-used correlations relating the black hole mass to other properties of the host galaxy.First, a bit of context. Black holes are extremely compact concentrations of matter producing such strong gravitational pull that nothing, not even light, can escape. General relativity predicts such gravitational singularities of zero volume and thus infinite density. Studying stellar evolution, we learn that the explosions of heavy stars as supernovae can leave behind remnants of stellar mass-black holes. But super-sized black holes of million solar masses (called supermassive black holes) presumably originate from mergers of other black holes, or by accreting large amounts of stars and gas in an active galactic nuclei (AGN) phase.Nowadays astronomers believe that every galaxy harbours a supermassive black hole at its center, including our own Milky Way where a central mass concentration of four million solar masses has been deduced from 16-years monitoring of stellar proper motions (see also today’s astrobite on the amazing discovery of a huge gas cloud being swallowed by this black hole). As pointed out by Susanna’s astrobite, it is not possible...