Astronomers have recorded for the first time a strange jet resembling a garden sprinkler from a neutron star.

The S-shaped structure of the jet arises due to the changing direction of the jet caused by the wobbling of the hot gas disk around the star – a process known as precession, which has been observed in black holes but never before in neutron stars.

This object is located in the binary system Circinus X-1, more than 30,000 light-years from Earth, and was formed from the core of a massive supergiant star that collapsed around the time of the construction of Stonehenge.

This object is so dense that a teaspoon of its material weighs as much as Mount Everest.

Binary systems consist of two stars gravitationally bound together. In the case of Circinus X-1, one of these stars is a neutron star.

Neutron stars and black holes are cosmic monsters that form when the largest stars in the universe die and collapse under their own gravity. Black holes are much more massive and can only be detected through their gravitational effects, whereas neutron stars can be directly observed despite their density.

They are some of the most extreme objects in the universe with interiors almost entirely made up of neutrons.

The jet coming from the neutron star was observed by a team of astronomers from the University of Oxford, using MeerKAT – a radio telescope in South Africa – to create the most detailed images of Circinus X-1 to date.

First Observation of an S-shaped Jet
These images, presented at the National Astronomy Meeting at the University of Hull, include the first image of an S-shaped jet coming from a confirmed neutron star. This is a breakthrough that could help understand the extreme physics behind this astronomical phenomenon.

Research leader Fraser Cowie stated that there is another system known for S-shaped jets, called SS433, but recent results suggest that this object is likely a black hole.

"This image shows for the first time strong evidence for a precessing jet from a confirmed neutron star," Cowie said.

"This evidence comes from the symmetric S shape of the radio-emitting plasma in the jets and from the fast, wide shock waves, which can only be created by a jet that changes direction."

"This will provide valuable information about the extreme physics behind jet launching, a phenomenon that is still not well understood."

The immense density of the neutron star creates a strong gravitational force that strips gas from the companion star, creating a disk of hot gas around it that spirals down towards its surface.

This process, called accretion, releases enormous amounts of energy per second with more power than a million Suns. Part of this energy drives the jets – narrow beams of material that shoot out from the binary system at speeds close to the speed of light.

Research Findings and Next Steps
Recent upgrades to the MeerKAT telescope have resulted in excellent sensitivity and high-resolution images. Thanks to these improvements, the team observed clear evidence of the S-shaped structure, similar to water spraying from a garden sprinkler, in the jet of Circinus X-1.

Additionally, researchers discovered moving shock waves – recorded for the first time from an X-ray binary system. These are areas where the jet violently collides with surrounding material, causing a shock wave.

The team measured the waves moving at about 10 percent of the speed of light, confirming they are caused by a fast jet rather than something slower like material winds from stars.

"The fact that these shock waves cover a wide angle fits our model," Cowie said. "So, we have two strong pieces of evidence telling us that the neutron star jet is precessing."

Measuring the speed of the shock waves will also help astronomers understand what the jet causing them is made of. Shock waves act as particle accelerators in space, producing high-energy cosmic rays, and the maximum energy of particles that can be accelerated depends on their speed.

"Circinus X-1 is one of the brightest objects in the X-ray sky and has been studied for more than half a century," Cowie said. "Despite this, it remains one of the most enigmatic systems we know."

"The next steps will be to continue monitoring the jets and see if they change over time in the way we expect. This will allow us to more precisely measure their properties and further learn about this enigmatic object."

The research was conducted as part of the X-KAT and ThunderKAT projects on the MeerKAT telescope operated by the South African Radio Astronomy Observatory (SARAO). The observations were made using recently installed S-band receivers provided by the Max-Planck Institute (MPG).

Source: Royal Astronomical Society