This composite image shows a beautiful X-ray and optical view of Cassiopeia A (Cas A), a supernova remnant located in our Galaxy about 11,000 light years away. These are the remains of a massive star that exploded about 330 years ago, as measured in Earth's time frame. X-rays from Chandra are shown in red, green and blue along with optical data from Hubble in gold.
At the center of the image is a neutron star, an ultra-dense star created by the supernova. Ten years of observations with Chandra have revealed a 4% decline in the temperature of this neutron star, an unexpectedly rapid cooling. Two new papers by independent research teams show that this cooling is likely caused by a neutron superfluid forming in its central regions, the first direct evidence for this bizarre state of matter in the core of a neutron star.
The inset shows an artist's impression of the neutron star at the center of Cas A. The different colored layers in the cutout region show the crust (orange), the core (red), where densities are much higher, and the part of the core where the neutrons are thought to be in a superfluid state (inner red ball). The blue rays emanating from the center of the star represent the copious numbers of neutrinos -- nearly massless, weakly interacting particles -- that are created as the core temperature falls below a critical level and a neutron superfluid is formed, a process that began about 100 years ago as observed from Earth. These neutrinos escape from the star, taking energy with them and causing the star to cool much more rapidly.
This new research has allowed the teams to place the first observational constraints on a range of properties of superfluid material in neutron stars. The critical temperature was constrained to between one half a billion to just under a billion degrees Celsius. A wide region of the neutron star is expected to be forming a neutron superfluid as observed now, and to fully explain the rapid cooling, the protons in the neutron star must have formed a superfluid even earlier after the explosion. Because they are charged particles, the protons also form a superconductor.
Using a model that has been constrained by the Chandra observations, the future behavior of the neutron star has been predicted. The rapid cooling is expected to continue for a few decades and then it should slow down.
The image features an X-ray and optical composite image of the supernova remnant Cassiopeia A, which is a remnant of a supernova explosion in the constellation Cassiopeia. The image shows a bright blue and orange glowing object in the center, surrounded by various colors and stars. The colors represent different wavelengths of X-ray light from Chandra emitted by the supernova remnant in addition to an optical image that shows stars in the field of view. The key structures of the supernova remnant include bright blue central and outer regions, which are likely caused by high-energy particles accelerated by the explosion, and an orange halo in between. The structure of the supernova remnant resembles a sunflower, with its bright blue center and colorful petals spreading outwards. This comparison to a sunflower highlights the beauty and complexity of the supernova remnant, as well as its symmetrical structure. Overall, the X-ray and optical composite image of supernova remnant Cassiopeia A provides a fascinating glimpse into the aftermath of a catastrophic cosmic event, showcasing the vibrant colors and intricate structure of this celestial object.
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