Annotated composite image of W44
This image shows a composite view of supernova remnant W44 (SNR W44), a prime example of the interaction between the remains of a supernova and the dense interstellar material around it. The composite image is based on data from ESA's Herschel and XMM-Newton space observatories, which observed the source at far-infrared and X-ray wavelengths, respectively.
The Herschel view of SNR W44 shows its asymmetric expanding shell, which can be seen as the large violet bubble with filamentary texture occupying the left half of the image. The shell is about 100 light-years across and, just above the centre of the image, it is impacting the arc-shaped bright feature to the right – an HII region known as G34.8-0.7.
The XMM-Newton image illustrates how the shell is filled with hot gas that 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 the XMM-Newton image is the pulsar PSR 1853+01, which most likely derives from the core of SNR W44's progenitor star. The pulsar can be seen as the bright point source towards the top left of the remnant.
With both a glowing, expanding shell and the hot, X-ray emitting gas that fills it, SNR W44 is classified as a mixed-morphology supernova remnant.
Around 10 000 light-years from us, SNR W44 is located in the molecular cloud complex known as W48, a rich star-forming region where a multitude of massive stars are being born. Two HII regions stand out in violet in the image, showing the intense activity of star formation in W48: 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 centre. 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.