The image above shows the supernova remnant W44 (SNR W44) as viewed by ESA's XMM-Newton space observatory at X-ray wavelengths. The image illustrates the hot gas that fills the supernova remnant's expanding shell and gives off large amounts of X-rays. These appear in the image as the dark blue and light blue clouds that fill the bubble, and correspond to lower-energy (1.2-2 keV) and higher-energy (2-8 keV) X-rays. Also visible in this X-ray view of SNR W44 is the pulsar PSR 1853+01, which most likely derives from the core of the supernova's progenitor star.
Most supernova remnants either possess a glowing shell created by the ejecta as they sweep up interstellar material, or the remnant has a more diffuse, nebula-like structure that is usually powered by the wind of a pulsar – a spinning neutron star which originates from the core of the exploded star. SNR W44 is one of the few supernova remnants that overlaps between these two classes. It's classified as a mixed-morphology supernova remnant. The expanding shell can be seen as the large violet bubble with filamentary texture occupying the left half of the image.
As the shell blasts outwards, shock waves heat up the surrounding material, raising the temperature of dust particles present there to about 100 K. This causes them to radiate at the shortest of the wavelengths probed by Herschel. With a temperature of several million K, the hot gas inside the bubble gives off large amounts of X-rays. These appear in the image as the dark blue and light blue clouds that fill the bubble, and correspond to lower-energy (1.2-2 keV) and higher-energy (2-8 keV) X-rays detected by XMM-Newton.
As in other mixed-morphology supernova remnants, the presence of hot gas inside a shell that is expanding and cooling down is quite puzzling. One of the possible explanations is linked to the interaction between the remnant and its clumpy environment of gas and dust clouds. Dense and cool cloudlets from the surroundings could be swept over by the expanding shell and evaporate once inside it, due to the higher temperature, contributing to replenishing the remnant's interior with gas. Also visible in SNR W44 is the pulsar PSR 1853+01, which most likely derives from the core of the supernova's progenitor star.
The pulsar, which shines brightly both in X-rays and radio waves, can be seen in the XMM-Newton image as the bright point source towards the top left of the remnant. The age of the remnant was estimated by measuring how much the pulsar's spin slows down over time and is believed to be a relatively young 20 000 years. The pulsar drives a wind of highly energetic particles but this represents only a minor contribution to the remnant's X-ray emission. Two HII regions stand out in violet in the image, showing the intense activity of star formation in W48. These are G035.1387-00.7622 in the upper part of the image to the right, and G35.0-0.5 just to the right of the image center.
The bright flecks scattered across the image are denser clumps in the turbulent cloud medium and are the seeds of future massive stars. In the lower left corner of the image, the diffuse glow corresponds to emission from warm dust in the Galactic Plane, the disc-like structure that contains most of the stars and star-forming clouds in our Galaxy, the Milky Way.
Supernova remnant W44 shown below was created by combining data from ESA's Herschel and XMM-Newton space observatories. W44 is the vast purple sphere that dominates the left hand side of this image, and measures about 100 light-years across. Image credits: Herschel: Quang Nguyen Luong & F. Motte, HOBYS Key Program consortium, Herschel SPIRE/PACS/ESA consortia. XMM-Newton: ESA/XMM-Newton.
The Daily Galaxy via European Space Agency
Image credit: ESA/XMM-Newton