Using NASA’s Chandra X-ray Observatory, astronomers were able to confirm that the Kes 75 pulsar is the youngest known and also shed light on the evolution of the substance surrounding it, which was emitted during the supernova explosion that gave rise to it.
A supernova occurs when a massive star depletes its nuclear fuel, destroying the core, and then dies as a result of a powerful explosion. After the outer layers of the star are dropped, only a dense neutron star remains – an exotic object the size of a city, but having a mass greater than that of the Sun. These dead stars rotate very quickly, from once in a few seconds to several hundred revolutions per second, and some of them have a magnetic field that is trillions of times stronger than that of the Earth.
The first such object was discovered in the 1960s, however, despite the fact that today the number of known pulsars exceeds two thousand, many of their secrets have not yet been revealed, including the behavior that differs from star to star and the properties of objects preceding their birth.
The hero of the new study, the pulsar Kes 75, is located at a distance of about 19,000 light years from Earth, and it is very interesting. First, the new data Chandra confirmed that it is the youngest of all known in the Milky Way. Secondly, they showed a rapid expansion of the surrounding shell – the pulsar nebula.
By comparing the data obtained by the X-ray Observatory in 2000, 2006, 2009 and 2016, astronomers have calculated that the outer edge of the nebula is moving away from Kes 75 at an enormous speed of 1 million meters per second. Such a rapid expansion, according to researchers, is due to the low density of the environment. In particular, astronomers suggest that the gaseous bubble of the nebula is accelerated by radioactive nickel, which was formed during the supernova explosion that gave rise to Kes 75. If the data is confirmed, it will give scientists new clues about both the processes occurring in the heart of the exploding star and the creation of new elements of supernovae.
The expansion rate also helped to establish the age of the pulsar, which was about 500 years old (the object’s age is measured from the moment it reaches its light of the Earth). However, unlike other supernova remnants from this epoch, there are no known historical records about it, since the explosion, most likely, was not visible on Earth.
The reason for this, as the observations of Chandra and other telescopes show, are very dense interstellar dust and gas filling our galaxy in the direction of a doomed star. Astronomers could not see the explosion with the tools at their disposal several centuries ago.
In addition to the expansion rate, the Chandra data recorded a ten percent drop in the total brightness of the pulsar wind nebula over the past 16 years, and its brightest region has faded by thirty percent. The authors of the study note that the rapid changes observed in the environment of Kes 75, as well as its unusual structure, indicate the need to create more complex models of the evolution of these dense remnants of massive stars.
The youngest pulsar of the Milky Way – Kes 75
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