A new study of the youngest pulsar discovered in the Milky Way

An article published in the journal “The Astrophysical Journal” describes the study of a pulsar cataloged as PSR J1846-0258 found among the remnants of a supernova called Kes 75. A team of researchers used information collected with NASA’s Chandra X-ray observatory between 2000 and 2016 to study the pulsar’s characteristics. They confirmed that it’s the youngest discovered in the Milky Way and could help to better understand that kind of objects, also because they discovered a pulsar wind nebula, a cloud of gas around it created thanks to a very elevated rotation and magnetic field.

Approximately 19,000 light years from Earth, the progenitor star of the pulsar PSR J1846-0258 exploded into a supernova visible from Earth about 5 centuries ago. However, no traces of observations of the event were found of the event much later cataloged as Kes 75 in historical archives, a mystery solved thanks to the observations of various telescopes including the Chandra observatory: they indicate the presence of high density interstellar gas and dust in that direction that made the supernova too dim to be seen from the Earth with the instruments of the era.

Only in 2000 it was discovered that among the supernova remnants Kes 75 there was a neutron star, which in the following years was the focus of a number of studies. Cataloged as a pulsar for its rapid rotation and emission of electromagnetic pulses, over the years it also released some powerful X-ray bursts, a behavior more typical of a magnetar, another category of neutron stars. This is an interesting case since generally these objects show a specific behavior but in some cases they have a sort of double personality.

The Chandra observatory was also used to study the pulsar PSR J1846-0258 and now the University of North Carolina astronomers assembled the data collected in 2000, 2006, 2009 and 2016 to examine the changes in brightness that occurred in the pulsar wind nebula. There was a 10% decrease, especially in the northern area, with a 30% decrease in a bright knot. According to the authors, more sophisticated models for the evolution of the pulsar wind nebula will be needed to adequately reconstruct the ongoing processes.

One of those processes is its expansion, visible by comparing the observations from 2000 with those from 2016. The outer edge of the pulsar wind nebula is expanding very quickly as its speed is estimated at around 1,000 km/s (more than 2 million mph). One possible explanation is that the pulsar wind nebula is expanding in an environment where the density is relatively low, within a gas bubble blown by the radioactive nickel that formed during the supernova, from which it was ejected.

The composite image (X-ray: NASA/CXC/NCSU/S. Reynolds; Optical: PanSTARRS) shows in blue the high-energy X-rays detected by Chandra which emphasize the pulsar wind nebula around the pulsar while it shows the rays X at lower energies in purple showing supernova debris. The stars in the background come from an visible light image of the map created by the Sloan Digital Sky Survey.

The study of the decay of radioactive nickel in iron gas that filled the bubble around the pulsar could help to understand which elements were present in the progenitor star. A part of them spread into the interstellar space after the explosion and in the distant future could contribute to forming new solar systems. Various processes occurred or are taking place with consequences on the surrounding space, so many reasons to study supernovae and neutron stars.

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