The Sombrero Galaxy

My personal favourite galaxy, M104, the Sombrero Galaxy. Simply stunning, I’m sure you’ll agree, in this Hubble Telescope image. Discovered in 1781 by Pierre Méchain, the Sombrero is interesting because of that long dust lane you can see running across the middle of it. Almost all galaxies contain dust lanes. They’re collections of cold dust and molecular gas where star formation usually takes place. The Milky Way has a few of these that we know of, including the Gould belt (home of the Orion Nebula and the Taurus-Auriga dark cloud complex), and the Sagittarius B2 Complex. Sag B2, in particular, forms a ring around the centre of the Milky Way, where practically every interstellar molecule ever detected can be observed. But I digress…

The Sombrero Dust lane is interesting because it forms a complete ring around the edge of the whole galaxy. In turn, this whole ring emits 8µm infrared radiation (shown in the smaller image in red). In other words, it’s believed by some that the whole Sombrero galaxy is surrounded by a ring of polycyclic aromatic hydrocarbons. A little like some of the stars I’ve been looking at, only on a much much grander scale. In fact, to look at it, it doesn’t look dissimilar to a vast circumstellar accretion disk. Only this disk is actually made of stars as well as dust. Observations suggest that most of the Sombrero’s molecular gas is indeed inside this dust ring, making it likely the galaxy’s primary star formation region.

The Sombrero also holds a mystery. As well as synchotron emission (radio frequency) from the galactic nucleus and it’s supermassive black hole, the Sombrero emits some curious submillimetre radiation. With a wavelength of around 850µm (deep infrared, approaching microwave frequencies), no one’s quite sure where it’s coming from. The usual suspects would be warm dust or molecular gas, but seemingly it doesn’t originate from either. More exotic possibilities are unusual synchotron emission or hot gas shocks, but it seems these aren’t the source either. How curious…

Some papers:

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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