Astronomers have found a likely supermassive neutron star hiding beside a red giant, and its weight may help fill a gap in their map of dead stars. The unseen object sits near the mass gap between the heaviest neutron stars and the lightest black holes.
The system, named J0008+0128, pairs a visible red giant with a companion astronomers have never seen directly. They traced it through the gravitational pull it exerts on the red giant. The team puts the companion’s mass at 1.8 to 2.8 times the mass of the sun, with a best estimate of 2.2.
That range matters because no neutron star heavier than 2.5 solar masses has been found, while black holes typically start at five solar masses. The gap between them has left astronomers unsure where neutron stars end and black holes begin. The upper end of this object’s estimated mass reaches into that gap.
The researchers, led by Xinlin Zhao, drew on data from China’s LAMOST telescope and the Apache Point Observatory Galactic Evolution Experiment. They ran around 300,000 simulations to test how such a wide binary could have formed, and found the pair completes an orbit in about 3.3 years.
The team describes the companion as most likely a neutron star, but the label is an interpretation, not a settled fact. Further observations will be needed to pin down its true nature. The closest known comparison is Gaia NS1, a neutron star candidate of about 1.9 solar masses in a roughly two-year orbit.
The findings were published in Science Advances on November 11.
Source: Phys.org
