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Infrared image of a neutron star (source on the right box) with extended infrared emission obtained from observations with the Hubble Space Telescope. The blue circle indicates the position of the X-ray pulsar (obtained with the Chandra X-ray space telescope), the cross indicates the position of the pulsar in UV optics (measured with the Hubble Space Telescope). Credit: Bettina Posselt, Penn State
An unusual infrared emission detected by the Hubble Space Telescope from a nearby neutron star could indicate that the pulsar has features never seen before. The observation, conducted by a team of researchers from Penn State University, Sabanci University in Turkey and the University of Arizona, could help astronomers better understand the evolution of neutron stars – the incredibly dense remains of massive stars after a supernova. An article describing the research and two possible explanations for the unusual discovery appears on September 17, 2018 in the Astrophysical Journal.
"This neutron star belongs to a group of seven nearby X-ray pulsars – nicknamed" the seven gorgeous "- which are warmer than they should in view of their age and the available energy reservoir provided by the loss of rotational energy, "said Bettina. Posselt, associate professor of astronomy and astrophysics at Penn State and lead author of the paper. "We observed an extended infrared emission zone around this neutron star – called RX J0806.4-4123 – whose total size translates to about 200 astronomical units (or 2.5 times the orbit) of Pluto around the Sun) at the supposed distance from the pulsar. "
It is the first neutron star in which an extensive emission has been observed only in the infrared. The researchers suggest two possibilities that could explain the extended infrared emission seen by the Hubble Space Telescope. The first is that there is a disc of matter – perhaps mainly dust – surrounding the pulsar.
"One theory is that there could be a so-called" fallback disc "of the material that fused around the neutron star after the supernova," said Posselt. Such a disc would be composed of material from the massive precursor star.Its subsequent interaction with the neutron star could have warmed the pulsar and slowed its rotation.If confirmed as a supernova retreat record, this result could change our general understanding of the neutron star evolution. "
Neutron star with a circum-pulsar disk. If viewed at the appropriate angle, the emission scattered by the inner part of the disc could produce the prolonged infrared emission observed by astronomers around the neutron star RX J0806.4 -4123. Credit: Nahks Tr. Ehnl, Penn State
The second possible explanation for the extended infrared emission of this neutron star is a "pulsar wind nebula".
"A pulsating wind nebula would require the neutron star to have a pulsar wind," said Posselt. "A pulsar wind can be produced when the particles are accelerated in the electric field produced by the rapid rotation of a high magnetic field neutron star, when the neutron star passes through the interstellar medium at a speed greater than that of the sound. , a star the shock can form where the interstellar medium and the pulsar wind interact: the shocked particles would then emit a synchrotron emission, causing the prolonged infrared emission that we see.As a rule, the pulsar wind nebulae are observed in X-rays and the only infrared pulsar nebula would be very unusual and exciting. "
Neutron star with a pulsating wind nebula produced by the interaction of the pulsar wind and the interstellar medium coming in the opposite direction. A pulsar nebula could explain the prolonged infrared emission observed by astronomers around the RX neutrino star J0806.4-4123. Such a solely infrared pulsar wind nebula is unusual because it involves a rather low energy of accelerated particles. Credit: Nahks Tr. Ehnl, Penn State
Although neutron stars are generally studied in radio emissions and high-energy emissions, such as X-rays, this study demonstrates that interesting new information about neutron stars can be obtained by studying them in the infrared. With NASA 's new James Webb Space Telescope, which will be launched in 2021, astronomers will be able to further explore this newly opened discovery space in the infrared to better understand the evolution of the star at neutrons.
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More information:
B. Posselt et al, Discovery of infrared emissions extended around the neutron star RXJ0806.4-4123, The astrophysical journal (2018). DOI: 10.3847 / 1538-4357 / aad6df
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