Surprise find: Astrophotographers discover giant nebula near Andromeda galaxy

(Hier finden Sie die deutsche Version des Beitrags)

A group of amateur astronomers has surprisingly discovered a previously overlooked giant structure in the region of the Andromeda Galaxy. It could be the largest such structure in the still comparatively nearby neighborhood, the University of Innsbruck now explains. It is a giant nebula that can only be seen when observations are filtered for emissions of doubly ionized oxygen. Because of the enormous extent of the structure, it has apparently simply not been visible in the usual observations with long focal lengths so far. What exactly it is is unclear, but one explanation is particularly spectacular.

Spectacular theory

As the research team involved in the discovery now explains, the Andromeda Galaxy (Messier 31 = M31) has been one of the most photographed astronomical objects since it was first imaged in 1888. Without technical aids, the neighboring galaxy is the most distant object visible to the naked eye. Until a few years ago, however, broadband filters had been used almost exclusively for the photographs in order to capture light in the entire spectrum. Ambitious astrophotographers, however, are now increasingly using narrowband filters that can highlight individual emissions and thus make certain structures visible.

The three astrophotographers Yann Sainty, Marcel Drechsler and Xavier Strottner found such an image with a so-called OIII filter last August. This filter allows almost exclusively the wavelength of doubly ionized oxygen to pass and thus makes planetary nebulae and the remnants of supernovae visible (oxygen is only formed in the interior of stars by nuclear fusion). The images taken in this way also show exactly these in the Andromeda Galaxy, but in close proximity the newly discovered arc-shaped stripes. To make them visible, a total exposure time of over 111 hours and lengthy post-processing were necessary. In the process, the amateurs and established researchers collaborated.

The existence of the object was confirmed beyond doubt by several images taken from different locations, the research team writes. The nature of the object is still being puzzled over. The most spectacular but speculative theory is that the emissions are caused by the collision of the extremely thin gas envelopes around the Andromeda Galaxy and the Milky Way. The two are moving toward each other and will collide in several billion years. If the theory is correct, we would see the beginnings of this collision here.

It is still possible, but unlikely, that it is the remnant of a supernova far outside the galaxy. Also one discussed whether it could be a result of interactions between star and tidal streams. However, observational data would also speak against it. The finding is presented in a scientific article in the journal Research Notes of the AAS, which has not been externally reviewed.

(mho)