Starship Asterisk*

Image Credit: ESO/Dusán Tubín et al.

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Do you ever get the feeling that you're being watched? This friendly-looking object is the result of two galaxies merging into one another, complete with a pair of eyes hiding two growing supermassive black holes and a swirling grin. Such mergers are rare in our galactic neighbourhood; Mrk 739 is close enough (astronomically speaking) to study the event in detail, and thus gain a better understanding of the dramatic processes that take place during these cosmic mergers.

By using the MUSE instrument on ESO’s Very Large Telescope, the team of astronomers, led by master’s student Dusán Tubín at the Pontificia Universidad Católica de Chile, were able to study the effects of both the merger and the radiation emitted by the growing gigantic black holes. Their study answers questions about the motion of the galaxies, the age of their stars, and the elements they are made up of. They have found that one of these galaxies is much older than its companion, and that their merging process is at an early stage.

MUSE is a 3D spectrograph that takes images — known as “datacubes” — of the object being observed over thousands of wavelengths. With MUSE, astronomers are therefore able to map in great detail the properties of the objects they study, because each individual pixel contains an impressive amount of information. Obtaining these exciting insights into galaxy merging and evolution with MUSE is enough to make anyone smile.

• Astrophysical Journal 911(2):100 (2021 Apr 23) DOI: 10.3847/1538-4357/abedba
• arXiv.org > astro-ph > arXiv:2103.12180 > 22 Apr 2021

Image Credit: ESA/Hubble & NASA, K. Noll

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The interaction of two doomed stars has created this spectacular ring adorned with bright clumps of gas — a diamond necklace of cosmic proportions. Fittingly known as the Necklace Nebula, this planetary nebula is located 15 000 light-years away from Earth in the small, dim constellation of Sagitta (The Arrow).

The Necklace Nebula — which also goes by the less glamorous name of PN G054.2-03.4 — was produced by a pair of tightly orbiting Sun-like stars. Roughly 10 000 years ago, one of the aging stars expanded and engulfed its smaller companion, creating something astronomers call a “common envelope”. The smaller star continued to orbit inside its larger companion, increasing the bloated giant’s rotation rate until large parts of it spun outwards into space. This escaping ring of debris formed the Necklace Nebula, with particularly dense clumps of gas forming the bright “diamonds” around the ring.

The pair of stars which created the Necklace Nebula remain so close together — separated by only a few million kilometres — that they appear as a single bright dot in the centre of this image. Despite their close encounter the stars are still furiously whirling around each other, completing an orbit in just over a day.

The Necklace Nebula was featured in a previously released Hubble image, but now this new image has been created by applying advanced processing techniques, making for a new and improved view of this intriguing object. The composite image includes several exposures from Hubble’s Wide Field Camera 3.