Daunting image of a pair of stars and its surrounding nebula
Last Monday, the European Southern Observatory (ESO) released a new Picture of the Week. It is an image of a pair of stars and its surrounding nebula. The two stars constitute the binary system AFGL 4106, which was recently studied in a recent Astronomy and Astrophysics paper, of which René Oudmaijer of the Royal Observatory of Belgium is a co-author.
The binary system AFGL 4106 (black dots at the centre) and its surrounding nebula (in orange). Image taken with ESO’s Very Large Telescope (VLT). Credit: ESO/G. Tomassini et al.
The two stars, shown as a pair of black dots at the centre of the image, are an old stellar couple. As most stars are born in pairs, a big question for astronomers is: how does being in a couple impact a star’s death?
Before dying, stars expel huge amounts of gas and dust, ingredients for a growing nebula. The massive stars shown here are at close yet distinct late stages of their lifecycles, with one having blown off enough mass to produce a dusty surrounding envelope (shown in orange in the picture).
In a recent paper led by Gabriel Tomassini (Université Côte d’Azur, France) and of which René Oudmaijer is co-author, researchers have mapped this debris and precisely characterised the central stars.
Imaging astronomical objects close to stars poses a challenge due to the overpowering effect of a star’s brightness and, in fact, the stars themselves appear in black as their brightness saturated the detector of the instrument used to make this image.
Fortunately, the SPHERE instrument on the VLT is well equipped to deal with large contrasts in light levels, enabling a detailed study of both the high luminosity stars and the faint surrounding nebula for the first time. Moreover, it can correct the blur caused by atmospheric turbulence, delivering very sharp images.
The shape of the nebula reveals the significant impact the companion is having on the gas ejection of the dying star, introducing asymmetries and shifting the clouds of gas and dust away from a perfectly spherical shape. Further observations of star systems like this one allow scientists to better understand how the presence of companions affects the death of stars.
The ESO image release: https://www.eso.org/public/images/potw2608a/
The research paper
Tomassini et al., Characterising the post-red supergiant binary system AFGL 4106 and its complex nebula with SPHERE/VLT, Astronomy and Astrophysics, 706, A5, 13 pp., 2026. https://doi.org/10.1051/0004-6361/202557705