The Royal Astronomical Society published this original article on July 16, 2024. Edits by EarthSky.
On July 16, 2024, the Royal Astronomical Society released the first image of a strange ‘garden sprinkler-like’ jet coming from a neutron star. The structure has an S shape, created as the jet changes direction due to the wobbling of the disk of hot gas around the star. The wobbling is due to a process called precession. Astronomers had observed precession with jets around black holes before but never with neutron stars.
This particular object sits in the binary system Circinus X-1, which is more than 30,000 light-years from Earth. It formed from the core of a massive supergiant star that collapsed around the same time Stonehenge was built. It is so dense that a teaspoon of its material weighs as much as Mount Everest.
Binary systems have two stars that are bound together by gravity. In the case of Circinus X-1, one of these is a neutron star.
Both neutron stars and black holes are cosmological monsters. They form when the biggest stars in the universe die and collapse under their own gravity.
However, black holes are considerably more massive. And scientists can only detect them through their gravitational effects. Meanwhile, scientists can observe neutron stars directly, despite their denseness. Neutron stars are some of the most extreme objects in the universe and have interiors almost entirely made of neutrons.
A team of astronomers at the University of Oxford used MeerKAT – a radio telescope in South Africa – to spot the jet emanating from the neutron star. The radio telescope created the most detailed high-resolution images of Circinus X-1.
The pictures – presented at this week’s National Astronomy Meeting at the University of Hull – include the first-ever image of an S-shaped jet coming from a confirmed neutron star. It’s a breakthrough that could help unravel the extreme physics behind the astronomical phenomenon.
Lead researcher Fraser Cowie of the University of Oxford said there was another system known for its S-shaped jets, called SS433, but recent results suggest that object is likely a black hole. Cowie said:
This image is the first time we have seen strong evidence for a precessing jet from a confirmed neutron star. This evidence comes from both the symmetric S shape of the radio-emitting plasma in the jets and from the fast, wide shockwave, which can only be produced by a jet changing direction. This will give valuable information about the extreme physics behind the launching of the jet, a phenomenon which is still not well understood.
The neutron star’s huge density creates a strong force of gravity that strips gas from the companion star. That hot gas forms a disk that spirals down toward the neutron star’s surface.
This process, known as accretion, releases huge amounts of energy per second with more power than a million suns. Some of this energy powers jets – or narrow beams of outflowing material – from the binary system, traveling close to the speed of light.
Recent upgrades to the MeerKAT telescope have resulted in excellent sensitivity and higher-resolution images. With these the team saw clear evidence of an S-shaped structure, similar in shape to water spraying from a garden sprinkler, in Circinus X-1’s jet.
Not only that, but researchers also discovered moving termination shocks. These were the first recorded from an X-ray binary. These are regions where the jet violently rams into the surrounding material, causing a shockwave.
Cowie’s team measured the waves moving at roughly 10% the speed of light. This confirmed the fast-moving jet caused them and not something slower, such as a wind of material from the stars. Cowie said:
The fact that these shockwaves span a wide angle agrees with our model. So we have two strong pieces of evidence telling us the neutron star jet is precessing.
Measuring the velocity of the shockwaves will also help astronomers understand what the jets causing them consist of.
The shockwaves effectively act as particle accelerators in space – producing high-energy cosmic rays – and the maximum energy of particles that can be accelerated depends on their velocity. Cowie said:
Circinus X-1 is one of the brightest objects in the X-ray sky and has been studied for over half a century. But despite this, it remains one of the most enigmatic systems we know of. Several aspects of its behavior are not well explained. So it’s very rewarding to help shed new light on this system, building on 50 years of work from others.
The next steps will be to continue to monitor 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 continue to learn more about this puzzling object.
Bottom line: Astronomers using the MeerKAT radio telescope in South Africa have observed a neutron-star jet with an S shape for the first time. The star’s wobble creates the jet’s S shape.
Via Royal Astronomical Society
The post Neutron-star jet sprays like a garden sprinkler first appeared on EarthSky.
