The environmental impact of black holes is perhaps a distant and esoteric concept, unless you’re waiting for part 2 of the latest Doctor Who story, but US astronomers have used the latest observations of nine black holes with NASA’s Chandra X-ray Observatory to estimate directly the efficiency of black holes. Their calculations show that black holes are perhaps the most fuel efficient engines in the universe, with a remarkably high fraction of the energy they consume being converted into work. Read on in the latest issue of our physical sciences webzine – Spotlight.