5 November 2016 | Cosmic Fireworks


Credit & copyright: Marco Lorenzi | Click image to enlarge | Click here for full size (12MB)


Floating in the depths of infinite space, this cosmic scene depicts the remains of a star that exploded as a supernova! Catalogued as Puppis A, this supernova remnant is a tangled tapestry of colourful gaseous filaments with red hydrogen (Ha), blue oxygen (OIII) and vibrant pink and purple shades where both Ha and OIII intersect.

Located in the southern constellation Puppis, its name signifies the fact it is the strongest radio source in this constellation. It belongs to the relatively rare class of oxygen-rich supernova remnants, other examples include Cassiopeia A and MSH 11-54 (more commonly referred to as G292.0+1.8 by professional astronomers). Puppis A is of great interest to professional astronomers and has been observed across a wide range of the electromagnetic spectrum from x-rays with ROSAT, Chandra and XMM-Newton, infrared with Spitzer, gamma rays with Fermi and radio with the VLA.

Spanning 2 degrees, this deep widefield image shows the full extent of the 50 arcminute filamentary shell. As it expands outwards, it interacts with the surrounding interstellar medium and is therefore a useful astrophysical laboratory to study cloud-shock interactions. Various studies over a period of many decades conclusively pinpoint the origin of Puppis A to be a core collapse supernova.

Detailed observations have detected multiple metal rich ejecta in Puppis A containing a wide variety of elements such as oxygen, neon and magnesium. Many oxygen rich filaments and knots have eventually been discovered over time. The majority of the oxygen knots are confined to the central region and can be seen more clearly in images taken with larger telescopes.

The appearance of Puppis A is vastly different in x-ray images and appears bright but is faint in the gamma-ray domain. In fact, it is the brightest supernova remnant in x-rays! It is also a special case as it is located in a region containing many molecular clouds and shows signs of encountering a higher ambient density. Measurements of the proper motions of some of its knots indicate it is a middle aged supernova remnant with an age of approximately 3700 years. At an estimated distance of 6500 light years, the full size of Puppis A is about 100 light years.

A unique aspect of Puppis A is it is one of the very rare examples of a supernova remnant where the ejecta material of the original supernova explosion has been observed! This ejecta consists of many oxygen-rich knots. Most supernova remnants consist of material that has been swept up and ionized by the supernova shockwave colliding with the surrounding ISM. These oxygen-rich knots possess radial velocities of 1500 km per second and are also unaffected by the surrounding interstellar medium. However the infrared emission of Puppis A is the result of interstellar dust being heated by collisions with hot shocked gas.

A mystery associated with Puppis A is the presence of a neutron star near the centre that is bright in x-rays but emits no radio waves. This specific category is known as a central compact object and only about a dozen are known. Some other supernova remnants that are known to host a central compact object (CCO) include Cassiopeia A and RCW 103. Most supernova remnants include a type of neutron star called a pulsar, which rotate rapidly and emit radio waves. According to recent proper motion measurements of the CCO in Puppis A, the estimated age of the supernova remnant is 4450 years, making it higher than the commonly accepted age of 3700 years, which is based on the proper motion of the optical filaments.

The region surrounding Puppis A is complex with multiple objects sharing the same line of sight. Overlapping with the faint filaments of Puppis A are the brighter and larger filaments of the closer Vela Supernova Remnant visible towards the bottom left corner of the image. Near the top centre is the faint refection nebula vdBH15 and the smaller but brighter reflection nebula vdBH11 can be seen near the top right corner.

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