Andy Briggs has spent the past 30 years communicating astronomy, astrophysics and information technology to people. You can hear his weekly astronomy and space news update, on Mondays, on the global internet radio channel AstroRadio (http://www.astroradio.earth), where he also contributes to other programmes. He has been active in many astronomy societies in the UK and is a frequent contributor to Astronomy Ireland magazine. Andy also lectures regularly on astrophysics-related themes such as gravitational waves and black holes. He lives in Catalonia, Spain, with his daughter.
Unlike the open star clusters – containing sibling stars, scattered through the disk of our galaxy and presumably other galaxies – globular clusters are big, symmetrical and old, like an earthly city’s oldest and most staid citizens.
Dark matter doesn’t emit light. It can’t be directly observed with any of the existing tools of astronomers. Yet astrophysicists believe that it and dark energy make up most of the mass of the cosmos. What dark matter is, and what it isn’t. here.