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(THE CONVERSATION) On May 1, NASA’s Rossi X-ray Timing Explorer spacecraft reentered and burned up in Earth’s atmosphere. Although not as well-known to the public as Hubble and Chandra, RXTE ranks among NASA’s most successful astrophysics missions. For the past 16 years RXTE continuously “listened” to the streams of X-ray radiation coming from black holes, neutron stars and pulsars.

Pulsars probe the physics of matter under the most extreme conditions, answering questions not acces...