Astronomers Discover Rare ‘Cannibal’ Star System: A Pulsar’s Unusual Feast
In a groundbreaking discovery, astronomers have identified a rare double-star system where a neutron star, known as a pulsar, appears to have once orbited *inside* its companion star. This peculiar arrangement, detailed in a recent study published in Science, offers unprecedented insights into the evolution of binary star systems and the violent processes that shape them.
The focus of the research is PSR J1928+1815, a pulsar located approximately 455 light-years from Earth. Pulsars are the incredibly dense remnants of massive stars that have exploded in supernovae. They spin rapidly, emitting beams of radio waves from their magnetic poles, which appear to pulse as they sweep across our line of sight. This particular pulsar, born from a hot blue star more than eight times the mass of our sun, caught the attention of scientists due to its unusual behavior.
Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) in China, the world's largest single-dish telescope, astronomers discovered that PSR J1928+1815 has a companion: a helium star with a mass roughly 1 to 1.6 times that of the sun. What makes this system truly remarkable is the incredibly close proximity of the two stars. They are only about 700,000 miles (1.12 million kilometers) apart, completing an orbit around each other in a mere 3.6 hours.
Jin-Lan Han, chair of the radio astronomy division of the National Astronomical Observatories of the Chinese Academy of Sciences in Beijing, highlighted the significance of this discovery. PSR J1928+1815 is a millisecond pulsar, spinning nearly 100 times a second. These dizzying speeds are typically achieved as the pulsar “cannibalizes” its companion, drawing in material that causes it to spin faster and faster.
This observation supports the theory that such systems go through a “common envelope” phase, where the pulsar orbits *within* the outer layers of its companion. According to computer models, the two stars initially had a much greater separation, roughly twice the distance between Earth and the sun. The pulsar then began to siphon off the outer layers of its companion, forming a common envelope. After approximately 1,000 years, the pulsar spiraled closer to the helium star's core, eventually ejecting the remaining envelope and resulting in the tightly bound binary system we observe today.
The researchers estimate that only a handful – between 16 and 84 – of similar systems exist within the Milky Way. This discovery not only confirms long-held theories about binary star evolution but also offers a glimpse into the dynamic and often violent processes that shape the cosmos. Additionally, some reports describe this pulsar as a “spider pulsar” because it consumes so much of the material that has been around its partner, which causes it to scatter away through the emission of strong radio waves.
This newly discovered system provides direct evidence for the common envelope phase. Astronomers observed that the radio signals it emitted disappeared for about one-sixth of the orbital period, “suggesting that the pulsar orbited behind another star, itself hidden by galactic dust”.
What other secrets are hidden within these exotic binary systems? How will this discovery impact our understanding of stellar evolution and the formation of gravitational waves? Share your thoughts and theories in the comments below!
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