Astronomers report the discovery of eight extremely rare “millisecond” pulsars hidden inside globular clusters around the Milky Way.
Pulsed stars are dense neutron stars, at least 1.4 times heavier than the Sun, which typically form after a supernova when a large star collapses, causing matter to compress in the nucleus. . Since most of the original star’s angular momentum remains, while the radius is only a fraction, the pulsar has extremely high rotational speeds.
“Most pulsars rotate once on their axis for a few hundred milliseconds or more, which means they rotate a few revolutions per second. They were then called millisecond pulsars, ”explains lead author Alessandro Ridolfi, postdoctoral researcher at the Italian Observatory in Cagliari.
Millisecond pulses are rare in the universe because they can only reach such rotational speeds in binary. In this system, the two celestial bodies must orbit towards each other. For a pulsar, its “companion” is usually a star like our Sun, but sometimes it can be a white dwarf, a black hole, or another neutron star.
“To reach rotational speeds of hundreds of revolutions per second, the pulsar must steal matter from its companion for a long time, up to billions of years,” Ridolfi added. “These types of stars are likened to ultra-precise clocks in the universe. They rotate much more stable than conventional pulsars, and therefore suitable for experiments requiring high precision.”
Spherical clusters – a collection of stars linked together by gravity and their own orbits outside the edge of a galaxy – are ideal objects for finding millisecond pulses in the universe. They contain countless stars and are under the influence of strong gravity, so they are more likely to form binary systems. More than half of the milliseconds currently known are found in these clusters.
In the new study, Ridolfi and his colleagues used the MeerKAT telescope – an array of 64 individual antennas operated by the South African Radio Observatory (SARAO) – to focus the study on the cluster of blood cells surrounding the Milky Way galaxy. . As a result, they found not one but up to eight new millisecond pulses, making it one of the largest millisecond pulse studies to date.
Among these eight new stellar celestial bodies, the team particularly noticed one with an unusual orbit, dubbed PSR J1823-3021G. It is a millisecond pulsar star with a “very elliptical” orbit. It is likely that its original neutron star had a lighter companion in orbit, but was later replaced by a more massive current star as a result of a collision event. PSR J1823-3021G is also the largest millisecond pulsed star when it is more than twice as heavy as our Sun, which is very rare.
“Among the new findings, we are optimistic that we will find a binary system made up of two stars around a few milliseconds, or one star orbiting a stellar-mass black hole,” Ridolfi said. “However, this will require more advanced telescopic systems than MeerKAT in the future.”
