The Secret Life of Nebula

Robert Williams, President of Huddersfield Astronomy Society, is exploiring nebula in this mini series. In part 1 he takes a closer look at Messier 42, the Great Nebula of Orion.

The Orion Nebula, also known to Amateur Astronomers as Messier 42, is one of the best-known fuzzy blobs in the night sky. Its location, close to the celestial equator, means that it can be viewed, at some time of the years, from almost every inhabited location on Earth. Because of this, it is right of passage for any budding stargazer, to view, and then image this amazing structure, which is located in our, relatively close, starry neighbourhood.

Messier 42 – Imaged from Norfolk in 2021, during a photographic Aurora. Credit: Robert Williams

Messier 42 has been known about for longer than the telescope has been used and has been recorded by many civilisations in numerous ways. Most viewers of this misty patch in the sky, widely known as the middle of the Sword of Orion, see the 4 or 5 stars depending upon their location. From a very dark site, such as Kielder Forest and other registered Dark Sky Discovery Sites, it is possible to see that the 4 or more stars that make up the centre of the Nebula, more usually known as the Trapezium Cluster, are surrounded by a cloud of glowing gas (Messier 42) which itself is embedded within a much larger structure. This larger structure is the front-side edge of a huge dusty cloud - an enormous, but very cold bubble of dust and gas, known as the Orion Molecular Cloud.

The Orion Molecular Cloud stretches right across the entire constellation of Orion and is split up into individual structures, each of which were responsible for the construction of the Orion nebula alongside the  Flame Nebula and9 Horsehead Nebula near the star Zeta Orionis [Alnitak, LHS Star of Orion's Belt] and Messier 78 NE of Alnitak), as well as many of the less well known structures residing in Orion and neighbouring constellations.

 IC405 - The Flaming Star Nebula - imaged from Norfolk in 2023. Credit: Robert Williams

What is less-well known is that the Orion nebula is missing at least 2 stars.

In the constellation of Auriga, resides another Nebula – the Flaming Star Nebula. As its name suggests this nebula is being created by a star in the 'fast lane' - AE Aurigae. Scientists have discovered that around 5 million years ago, AE Aurigae was originally born within and, at the same time as the stars, of the Trapezium Cluster.

Star-chart showing the juxtaposition of Messier 42, IC 405 and Mu Columbae in the sky. Star-chart created in Carte du Ciel [SkyCharts]

Additionally, another star, Mu Columbae, in the constellation of Columbae the Dove (which is in the far south of the sky and not visible from Kielder), was also ejected from the Trapezium at around the same time.  Furthermore, another star in the constellation of Leo may also have been ejected, but the evidence for this is less certain. Both AE Aurigae and Mu Columbae have similar stellar properties (Mass, type, temperature, age) to the stars of the trapezium Cluster.