BLOGS

Artist's impression of a neutron-star merger (Courtesy: NASA)

Topics: Astronomy, Astrophysics, Chemistry, Materials Science, Neutron Stars

The amounts of heavy elements such as gold created when black holes merge with neutron stars have been calculated and compared with the amounts expected when pairs of neutron stars merge. The calculations were done by Hsin-Yu Chen and Salvatore Vitale at the Massachusetts Institute of Technology and Francois Foucart at the University of New Hampshire using advanced simulations and gravitational-wave observations made by the LIGO–Virgo collaboration. Their results suggest that merging pairs of neutron stars are likely to be responsible for more heavy elements in the universe than mergers of black holes with neutron stars.

Today, astrophysicists have an incomplete understanding of how elements heavier than iron are made. In this nucleosynthesis process, lighter nuclei must be able to capture neutrons from their surroundings. Astrophysicists believe this can happen in two ways, each producing about half of the heavy elements in the universe. These are the slow process (s-process) that occurs in large stars and the rapid process (r-process), which is believed to occur in extreme conditions such as the explosion of a star in a supernova. However, exactly where the r-process can take place is hotly debated.

One event that could support the r-process is the merger of a pair of neutron stars, which can result in a huge explosion called a kilonova. Indeed, such an event was seen by LIGO–Virgo in 2017, and simultaneous observations using light-based telescopes suggest that heavy elements were created in that event.

Merging neutron stars create more gold than collisions involving black holes, Sam Jarman, Physics World

The pulsar J0030 appears to have two to three hotspots on its southern hemisphere only – finding astronomers didn’t expect.
NASA’s Goddard Space Flight Center/CI Lab (animation on the page link below)

Topics: Astronomy, Astrophysics, NASA, Neutron Stars, Pulsars

NASA’s NICER instrument reveals that neutron stars are not as simple as we thought.

Pulsars are the lighthouses of the universe. These tiny, compact objects are neutron stars — the remnants of once-massive stars — that spin rapidly, beaming radiation into space. Now, for the first time, astronomers have mapped the surface of a 16-mile-wide pulsar in exquisite detail. The discovery calls into question astronomers’ textbook depiction of pulsar appearance and opens the door to learning more about these extreme objects.

The Neutron star Interior Composition Explorer, or NICER, searches for X-rays from extreme astronomical objects such as pulsars from its perch on the exterior of the International Space Station. Researchers used NICER to observe the pulsar J0030+0451, or J0030 for short, which is located 1,100 light-years away in the constellation Pisces, in a series of papers published in The Astrophysical Journal Letters. Two teams, one led by researchers at the University of Amsterdam and the other by researchers at the University of Maryland, used X-ray light from J0030 to map the pulsar’s surface and calculate its mass. Both teams arrived at a conclusion that was unexpected.

A New Picture

What the teams found presented a different picture: J0030 has two or three hotspots, all of which are located in the southern hemisphere. The researchers at the University of Amsterdam believe the pulsar has one small, circular spot and one thin, crescent-shaped spot spinning around its lower latitudes. The University of Maryland team discovered that the X-rays could be coming from two oval spots in the star’s southern hemisphere, as well as one cooler spot near the star’s south pole.

Neither result is the simple picture astronomers expected, indicating that the pulsar’s magnetic field, which causes the hotspots, is likely even more complex than originally assumed. While the result certainly leaves astronomers wondering, “It tells us NICER is on the right path to help us answer an enduring question in astrophysics: What form does matter take in the ultra-dense cores of neutron stars?” NICER science lead and study co-author Zaven Arzoumanian said in a press release.

Astronomers Map a Neutron Star’s Surface for the First Time, Ignat, I Love the Universe