A stellar ejecta fragment identified among the supernova remnant SN 1006

Four X-ray observations of the supernova remnants SN 1006
An article published in the journal “Astronomy & Astrophysics” reports a study of the supernova remnant cataloged as SN 1006 which led to the identification of an ejecta fragment of the progenitor star. A team of researchers led by Roberta Giuffrida of the University of Palermo and the Italian National Institute of Astrophysics used observations conducted with various telescopes exploiting X-ray emissions and compared them with theoretical models. The conclusion is that this iron-rich fragment is moving at a very high speed within the debris cloud generated by the supernova. This discovery is useful in the study of supernovae like this one, generated by explosions of white dwarfs.

The top image (Courtesy R. Giuffrida et al., A&A, 2024. All rights reserved) shows four X-ray observations of the supernova remnants SN 1006. Each observation shows the indications of the telescope used and the year in which it occurred. The white line in the top left panel indicates the direction of the supernova remnant, also shown in the top right panel to highlight its movement.

The supernova SN 1006 was cataloged like this because it was observed on Earth in the year 1006. It was so bright that it was visible to the naked eye even during the day for at least three years and there are many historical records with detailed descriptions. Centuries later, those descriptions helped locate its remnant to study it.

This supernova is of the type Ia and this means that it was generated by the explosion of a white dwarf, an already dead star because it’s the remnant of a small-medium mass star. A white dwarf can explode when it captures a lot of gas by stripping it from a nearby star until it triggers an explosive reaction or following the merger of two white dwarfs.

Astronomers are interested in type Ia supernovae among other things because they generate a brightness peak that is very similar in all explosions of this type. The consequence is that they are used as a reference to make cosmological measurements such as the distance to the galaxy that hosts one and to calculate the velocity of the universe’s expansion.

For all these reasons, the supernova remnant SN 1006 was studied with several instruments in various electromagnetic bands. Last year, an article published in “The Astrophysical Journal” reported the first results of observations of polarized X-ray light coming from this remnant.

There are various mechanisms that can generate energetic emissions such as X-rays in supernova remnants, which is why this new study used observations of SN 1006 in that band obtained with NASA’s NuSTAR and Chandra space telescopes and ESA’s XMM-Newton. Infrared observations conducted with NASA’s Spitzer Space Telescope were added because the supernova remnant’s region object of this study is bright in that band as well.

The researchers compared the information obtained thanks to the various observations of SN 1006 over the years with theoretical models connected to the different mechanisms that can generate X-ray emissions within those supernova remnants.

The analysis of the emissions allowed to find chemical traces that indicate that the fragment is rich in iron and also contains silicon and neon. The strong ionization of these elements generates energetic emissions. This means that the mechanism that was found to be compatible is the one with an ejecta fragment of the progenitor star with a mass that is about one-thousandth of the Sun’s traveling at thousands of kilometers per hour within the cloud of materials. The velocity carried that fragment more than six light-years away, beyond the shock wave’s debris shell.

The supernova remnant SN 1006 is just over 7,000 light-years from Earth and therefore in the cosmic neighborhood. This represents an advantage in observing the processes taking place even a millennium after the light from the explosion reached Earth. This study offers new information that is useful in studying other supernova remnants caused by exploding white dwarfs.

The supernova remnants SN 1006 as seen by the Chandra X-ray Observatory (Image Smithsonian Institution)
The supernova remnants SN 1006 as seen by the Chandra X-ray Observatory (Image Smithsonian Institution)

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