New Study Data Improves Merger Models

Scientists are improving their methods of modeling the merger of two neutron stars, an event that is considered one of the most powerful in the known universe.

Neutron stars are spinning extremely fast, being ultradense husks of bigger stars that exploded as supernovae. Neutron stars usually measure around 12 miles across. To get an idea of how dense these stars are, one single teaspoon of their matter weighs as much as  1,125 Golden Gate bridges or 2,735 Empire State buildings.

In 2017, researchers detected gravitational waves and an explosive burst that were caused by the merger of two neutron stars. Earlier this year, scientists observed yet another likely neutron-star-merger event.

These events can be compared to models developed by researchers to help them gain a better understanding of these mergers.

According to a new study published in the Monthly Notices of the Royal Astronomical Society journal, a team of researchers led by scientists at Northwestern University simulated the formation of a disc of matter, an enormous burst of ejected matter, and the startup of energetic jets around the remaining object, which could be a larger neutron star or a black hole, and studied them in the aftermath of this merger.

Three different simulations were used, testing out different geometry for the magnetic fields around the merger.

Rodrigo Fernandez, a co-author of the study, said: “We’re starting from a set of physical principles, carrying out a calculation that nobody has done at this level before, and then asking, “Are we reasonably close to observations or are we missing something important?”

Daniel Kasen, a scientist in the Nuclear Science Division at Berkeley Lab and an associate professor of physics and astronomy at UC Berkeley, said, “Magnetic fields provide a way to tap the energy of a spinning black hole and use it to shoot jets of gas moving at near the speed of light. Such jets can produce bursts of gamma-rays, as well as extended radio and X-ray emission, all of which were seen in the 2017 event.”

The data collected by the team during the simulations suggest that the neutron-star merger observed two years ago most probably did not lead to the creation of a black hole. Also, the simulations confirmed some long-standing models for fluid behavior.