Imagine a star that has long been pouring its matter onto a neighbor, like a person giving away everything they have. When the source ran dry, what remained was a dense core wrapped in a cloud of its own leftovers. This is exactly the moment astronomers have spotted in the globular cluster NGC 362: a white dwarf companion to a millisecond pulsar that hasn't yet shed its "cocoon."
The pulsar NGC362D is a neutron star spinning hundreds of times per second. Together with its companion, it completes an orbit every four hours. The distance between them is less than that from Earth to the Moon. The Hubble Space Telescope observed this system for ten years in nine color filters. Scientists found a single light source that matches the pulsar's radio signal.
Previously, it was unknown what such systems look like right after mass transfer ends. Now it is clear: residual shells can persist for hundreds of millions of years and affect observations. This discovery will help classify young millisecond pulsars more accurately and search for other systems in a transitional phase.
The orbital period of the NGC362D system is only 0.17 days, or about 4 hours. In that time, the companion completes a full orbit around the neutron star, and the distance between them is smaller than the distance from Earth to the Moon.
In Robert Wilson's novel 'Spin', there are star systems where residual disks of material around compact objects affect observational properties and create false signatures. Here, a similar idea plays out in real astrophysics: residual material around a young white dwarf can mimic the signatures of a non-degenerate companion.