by A neutron star is the remnant of a massive star that once died in a supernova explosion. Neutron stars are generally considered to be some of the most extreme objects in the known universe — and that’s especially true when these incredibly dense remnants are alongside companion stars (not yet “thrown”) close enough to for massive neutron stars. gravity to remove matter from that second star. In other words, the companion star is like the star victim of the neutron star.
These “neutron vampire stars” are special because they come back to life as cosmic Bela Lugosi. This is because the inflowing material of a companion star triggers thermonuclear explosions at the surface of the neutron star. Some of this stolen material is sent towards the poles of the neutron star, from where it explodes at near-light speeds in the form of powerful astrophysical jets. However, what causes these jets to launch – and how they connect to these thermonuclear explosions – remains a mystery.
However, new research has provided a breakthrough in the answer.
Scientists have revealed one way to measure the speeds of these jets and relate the values to the qualities of a neutron star and the binary companion stars it feasts on. This could help to finally resolve this dilemma of jets, and perhaps offer information about other objects that also destroy material from a companion star, such as supermassive black holes.
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“For the first time, we were able to measure the velocities of the steady jets launched from a neutron star,” lead author and National Institute of Astrophysics (INAF) scientist Thomas Russell told Space.com. “These jets, like those associated with accreting black holes, are extremely important in our Universe, because they inject huge amounts of energy into their environment, affecting star formation, the growth of galaxies, and even the how galaxies gather together. But we don’t really understand how these jets are launched.”
Russell explained that previously, scientists thought that the jets could be launched due to the rotation of material removed from a sacrificial star as material spirals in. There was also the theory that the jets are connected to the spin of the rotating object itself. .
This new research could help to find an answer regarding the mechanism that is mainly responsible.
“Our discovery of a link between the thermonuclear explosions and the jets now offers us a readily accessible probe to disentangle the mechanism of jet conduction in neutron stars,” continued Russell. “Because we think that jets are launched in very similar ways for all types of objects, this will help us understand how the jets are launched from all objects, even the supermassive black holes that live in the center of galaxies.”
How do neutron stars blow their top?
To reach their conclusion, Russell and his colleagues examined two systems where the neutron stars were feeding: The X-ray binaries 4U 1728-34 and 4U 1636-536. Both systems are known to erupt periodically with thermonuclear explosions.
Thermonuclear explosions on the surfaces of neutron stars are not a new phenomenon to scientists. These explosions have been analyzed for years, and Russell points out that at least 125 “exploding” neutron stars have been observed by astronomers.
“As the neutron star consumes material from a nearby star, the accreted material on the surface of the neutron star increases,” Russell said “At some point, the pressure becomes too great, and an unstable thermonuclear explosion occurs, runaway that spreads across. the entire surface of the neutron star in a second.”
Bursts associated with 4U 1728-34 and 4U 1636-536 are visible in the X-ray band, meaning the team was able to use the European Space Agency’s International Gamma-ray Astrophysics Laboratory (INTEGRAL) space telescope to betray them.
“We found that these bursts cause some extra material to be pumped into the jets during the tens of seconds that the bursts last,” continued Russell. “Using radio telescopes to monitor the jets with the Australian Telescope Array, we were able to track this extra material as it flowed down the jets, essentially providing us with a cosmic speed camera to measure the speed of the jet.”
What they wanted to see were changes in radio emissions after the X-ray bursts.
In fact, the team detected increases in radio brightness within minutes of every single thermonuclear explosion. As a result of this the researchers came to the conclusion that the evolution of jets is closely related to thermonuclear explosions.
“We were surprised at how clear the response was in the jets. The flares were very bright and clear flowing down the jet which was easily noticeable,” said Russell. “We were expecting some response but we thought it would be much more subtle.”
Neutron star jets sped up
The speed of these jets was the missing piece of the puzzle, the team says, linking the jets’ violent flapping to explosive feeding events.
“Speed is very important to understanding how the jets are launched, and this new discovery opens a very accessible window to answer that question,” said Russell. “We can now apply this experiment to many other exploding neutron stars, and then we can correlate the jet speed with the spin, mass, and possibly even the magnetic field of the neutron star, and it is estimated that they are all key ingredients. launching a jet.”
If the team can see a correlation between one of these properties and the speed of the jet, it will reveal what the main driving mechanism for these jets is — whether it is the spin of the neutron star or the rotation of the infalling material.
This is the first time that the speed of such a jet from a neutron star has been measured, but it is worth noting that it has been measured before for black holes. However, Russell explained that neutron stars have a huge advantage over black holes when used as a probe to investigate the mechanisms of jet propulsion.
“Neutron stars can have precisely measured spins, well-determined masses, and perhaps even known magnetic field strengths, all of which are much harder to measure in black holes,” he said. . “So, it is only with neutron stars that we can, for now, begin to relate the properties of the system to the jets.”
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In all, the team has now seen this result with two feeding neutron star systems, but these are the only two they have looked at so far.
“We are applying our new technique to as many other exploding neutron stars as we can to show how jet speeds vary with different neutron star properties,” he said. “Once we have taken a sufficient sample, we will be able to disentangle the key properties of jet production, showing how the jets are launched.”
The team’s research was published on Wednesday (March 27) in the journal Nature.
