Very cold detectors reveal very hot universe and kick off a new era in X-ray astronomy

X-rays are radiated by matter hotter than one million Kelvin, and high-resolution X-ray spectroscopy can tell us about the composition of the matter and how fast and in what direction it is moving. Quantum calorimeters are opening this new window on the universe. First promised four decades ago, the quantum-calorimeter era of X-ray astronomy has finally dawned.