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Owing to difficulties in directly detecting them, the number of extremely obscured black holes in the universe is unknown. Measurements of the cosmic X-ray background shed light on this mystery.
The destruction of particles is normally associated with high-energy physics and particle detectors. But in solid-state physics the destruction of particles, or rather quasiparticles, is taking place routinely in standard laboratories.
That the magnetic orientation of ferromagnets can be changed using magnetic fields has been known for centuries. But the exploration of magnetization control without any additional magnetic field has only just begun.
Advances in theoretical computation raise again the possibility that 'maximal supergravity' might be free of the ultraviolet divergences that have plagued quantum gravity theories — with puzzling implications for string theory.
Coexisting superconductivity and ferromagnetism due to itinerant electrons is unusual, but even among them URhGe stands out. Its surprising behaviour could help reveal the underlying physics of ferromagnetic superconductors.