Astronomers using NASA’s Chandra X-ray Observatory have confirmed that a supernova remnant called Kes 75 contains the youngest known pulsar in our Milky Way Galaxy.
In this composite image of Kes 75, high-energy X-rays observed by Chandra are colored blue and highlight the pulsar wind nebula surrounding the pulsar, while lower-energy X-rays appear purple and show the debris from the explosion. Image credit: X-rays – NASA / CXC / NCSU / S. Reynolds; optical – PanSTARRS.
After some massive stars run out of nuclear fuel, then collapse and explode as supernovas, they leave behind dense stellar nuggets called ‘neutron stars.’
Rapidly rotating and highly magnetized neutron stars produce a lighthouse-like beam of radiation that astronomers detect as pulses as the pulsar’s rotation sweeps the beam across the sky.
The rapid rotation and strong magnetic field of the Kes 75 pulsar, which is located about 19,000 light-years from Earth, have generated a wind of energetic matter and antimatter particles that flow away from the pulsar at near the speed of light.
This pulsar wind has created a large, magnetized bubble of high-energy particles called a pulsar wind nebula, seen as the blue region surrounding the pulsar.
The Chandra data taken in 2000, 2006, 2009, and 2016 show changes in Kes 75’s pulsar wind nebula with time.
Between 2000 and 2016, the Chandra observations reveal that the outer edge of the pulsar wind nebula is expanding at a remarkable 2 million mph (894 km per second).
This high speed may be due to the pulsar wind nebula expanding into a relatively low-density environment.
“It is expanding into a gaseous bubble blown by radioactive nickel formed in the explosion and ejected as the star exploded,” said Dr. Stephen Reynolds and his colleagues from North Carolina State University.
“This nickel also powered the supernova light, as it decayed into diffuse iron gas that filled the bubble.”
If so, this gives the astronomers an insight into the very heart of the exploding star and the elements it created.
The expansion rate also tells the scientists that Kes 75 exploded about 500 years ago as seen from Earth.
Unlike other supernova remnants from this era such as Tycho and Kepler, there is no known evidence from historical records that the explosion that created Kes 75 was observed.
The findings were published in the Astrophysical Journal (arXiv.org preprint).
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Stephen P. Reynolds et al. 2018. Expansion and Brightness Changes in the Pulsar-wind Nebula in the Composite Supernova Remnant Kes 75. ApJ 856, 133; doi: 10.3847/1538-4357/aab3d3
