Star's death throes a cosmic mystery.

University of Chicago astrophysicists Donald Lamb and Coleman Miller and Northwestern University physicist Ronald Taam are chasing a cosmic mystery--a bizarre, pulsating object near the center of our galaxy--that may be a never-before-seen signature of the death throes of a star. The object, GRO J1744-28, first was observed in December, 1995, by an Earth-orbiting satellite, the Burst and Transient Source Experiment on board the Compton Gamma Ray Observatory. BATSE detected a source near the center of the Milky Way that was emitting X-ray and gamma-ray radiation--in both regular pulses and erratic bursts--at a rate of up to 18 per hour. Astronomers nicknamed the object a bursting pulsar.

Because of the pulsing behavior, astronomers think the object consists of two stars locked in orbit around each other, called a binary. The regular pulsations are like a lighthouse beacon, as the two stars rotate around each other. One is a small, but very dense, neutron star--the remnant of a star that exploded in a supernova and then collapsed to an incredibly dense, dark core about the size of the city of Chicago. Because of the timing of the pulses, scientists have determined that the two stars orbit each other once every 12 days.

The neutron star is being orbited by a smaller star that is dying, puffing up so that its outer hydrogen shell is being pulled to the neutron star. Because of the neutron star's incredible density and high magnetic field, the...