Black holes, previously believed to have been the only objects in the universe capable of forming powerful jets of materials shooting out into space, now have a little “friendly competition” in the form of an extremely dense double-star system known as PSR J1023+0038.
New observations conducted of this neutron star have revealed that it is also blasting these strong jets, scientists from the International Centre for Radio Astronomy Research (ICRAR) reported in research published this week in the Astrophysical Journal. Originally identified as a neutron star in 2009, it wasn’t until 2013 and 2014 that the researchers realized PSR J1023+0038 was actually producing stronger-than-expected jets, they explained.
Neutron stars, which are formed when a massive star undergoes a supernova, causing its central parts to collapse beneath their own gravity, are essentially stellar corpses, ICRAR astronomer Dr. James Miller-Jones explained in a statement. In PSR J1023+0038’s case, the study authors said that they expected to find it producing a weak jet, since it was only consuming a small amount of material, but observations revealed its jets rivaled those of a black hole in strength.
Exploring the significance of this discovery
So what makes this discovery important? Lead investigator Dr. Adam Deller, an astronomer at the Netherlands Institute for Radio Astronomy (ASTRON), explained to redOrbit via email that the detection of these jets “highlights a gap in our understanding of how accretion works.”
Accretion, he explained, is a fundamental process which plays a key role in turning protostars into main sequence stars which form many of the elements found in the universe, growing into the supermassive black holes found at the centers of nearly all galaxies. Prior to their research, Dr. Deller said, researchers believed that there was a clear-cut distinction between how accretion worked onto black holes and how it worked onto neutron stars and other objects.
“This result implies that black holes are less special than we thought,” he added, “even though unlike everything else in the universe, they have an event horizon.” Neutron stars, in comparison, have a solid surface, Dr. Miller-Jones added. Discovering that these stars can also produce these powerful jets “suggests that an event horizon is not needed to produce jets,” he noted, “which gives us an important clue as to how jets get launched and accelerated in the first place.”
Dr. Miller-Jones pointed out that there are “competing theoretical models for how jets can be produced, and a better understanding of the similarities and differences between the jets in black holes and neutron stars can give us important clues as to the conditions needed to produce jets, hence helping pin down which of those theoretical models is more correct.” He and Dr. Deller also said that they hope the findings will improve the overall understanding of these jets.
Exploring the phenomenon of ‘transitional’ neutron stars
The study authors explained that PSR J1023+0038 is what is known as a “transitional” neutron star, meaning that it shifts between accreting and non-accreting phases – in other words, the star spends several years being powered primarily by the rotation of the neutron star, but changes to an active gathering state on occasion, becoming far brighter in the process.
“PSR J1023+0038 is actually a really interesting system, that only accretes some of the time,” Dr. Dellar explained. “The rest of the time it acts like a normal ‘radio pulsar’, which is a neutron star that acts like a cosmic lighthouse: it has a very strong magnetic field, and it emits very strong radiation from its magnetic poles, but it also rotates, and that rotation causes the beam of radiation to sweep across the sky, so we see regular “pulses” of emission here on Earth.”
When it was originally discovered, he told redOrbit, it was behaving like a radio pulsar, and continued to do so until 2013. At that time, it began to accrete gas that had been falling off of its companion star. The infalling material interfered with the processes which generated the radio pulses, causing them to disappear and prompting Dr. Dellar and his colleagues use telescopes to look at it in the optical and X-ray bands.
“All the hallmarks of accretion were present,” he said. Having found that the neutron star was accreting material, they used the Very Large Array to search for radio emissions coming from the jet of material being blasted out of the system. This emission, Dr. Dellar explained, was not the same as the one they observed when they found that PSR J1023+0038 was a radio pulsar – “it has a different spectrum, and it doesn’t pulse with the rotation of the neutron star.”
This emission is “coming from the electrons racing away from the system at relativistic speeds in the jet,” and once they found it, they used it to estimate how strong the jet is. Much to the team’s surprise, he said, “it came out much stronger than we had expected!” PSR J1023+0038 is just the third “transitional” pulsar to be found, Dr. Dellar added, and to follow up on their study, he and Dr. Miller-Jones hope to find and study more of these types of systems.
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