At one-third the speed of light, the jets from a neutron star are much slower than those from a black hole, but they may open the door to answering some important questions.
Astronomers say they have found a way to measure the rays produced by accreting neutron stars IFLScience. We hope that, after conducting a large sample of these measurements, the question that has been troubling astronomers since the discovery of jet engines will be answered.
What accelerates these rays so amazingly?
One theory is the magnetic fields around the star. Another said: It is the star itself.
Many black holes, especially supermassive black holes at the core of galaxies, accelerate the flow of matter to incredible speeds. But some lesser-known neutron stars do the same thing.
White dwarfs also occasionally emit matter, Dr. Tom Russell of the Institute for Astrophysics and Cosmic Physics told IFLScience.
How are rays generated?
Matter rays are the product of the accretion of neutron stars. These stars gradually attract more material to them, for example from a companion star being torn apart by their powerful gravity. Only a small fraction of neutron stars do this, but that's still tens of thousands in the Milky Way alone.
The material in the accretion disk slowly spirals inward until it falls onto the neutron star. “It's a very stable and ongoing process,” Russell told IFLScience. However, once they reach the star, they accumulate until they reach a critical density and undergo a thermonuclear explosion, accompanied by gamma rays and X-rays.
How often this happens depends on the accretion rate and possibly other factors associated with the star. For 4U 1728-34, these explosions occur every few hours.
This is how I was finally able to measure it
Russell is part of a team that has discovered that an array of telescopes operating at different wavelengths can use these bursts to measure the jets' speed.
Professor James Miller-Jones from the International Center said: “The explosion tells us when the jets of emitted matter were released, and we simply time them as they travel downwards – just like a 100m runner moving between the starting blocks and the finish line.” For radio astronomy research.
In space and time
To calculate speed, you need to know the distance and time. Russell explained that the frequency of the beam varies depending on the distance from the star. “We can use theory and previous studies of black holes and neutron stars to determine the distance associated with a particular frequency,” he said.
Together, the team reached 38% of the speed of light (114,000 kilometers per second) for 4U 1728-34. This is small compared to black holes, whose radius is thought to exceed 99% of the speed of light. Given the lower escape velocity of neutron stars, the difference is not surprising.
The most important result comes when the work is extended to many neutron stars
“If the star itself is responsible, we should see a direct relationship between the speed of the jet and the spin of the neutron star,” Russell said. The spin of neutron stars is much easier to measure than the spin of black holes, making comparisons easier. If the connection is not found, magnetic fields are likely to blame.
“The great thing about this work is that it is highly replicable,” Russell said. “We need two telescopes to look at a neutron star at the same time, but we don't rely on a set of theories to get the result.”
In this case, those two telescopes were the Integrated Gamma-ray Space Telescope and the Australian Telescope's Compact Array, an array of six dishes that can work together. Each requires several hours to achieve results, but this may decrease with experience.
Streams of matter emitted by supermassive black holes can shape galaxy evolution, so understanding them is even more important
“Despite having fundamentally different physical properties, i.e. the event horizon compared to the stellar surface, very little difference has been identified between the emitted rays, other than the fact that the rays tend to appear brighter in black hole systems with similar X-ray luminosities,” the authors note. . These results suggest that the lessons learned here can be applied more broadly.
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