DSO of the Month
Messier 104
AKA: Sombrero Galaxy; NGC 4594
Due south at 22.04 (BST) on 15 May
Position: 12 hr 40.0 min -11 deg 37 min
Image of the Sombrero Galaxy by HAS Member Martin Gill.
At the beginning of the Covid pandemic, Boris Johnson spoke about “flattening the sombrero”, meaning reducing the peak of infections and people needing intensive care so that the NHS was not overwhelmed. However this deemed to be rather politically incorrect (and perhaps even cultural appropriation) and medical experts and politicians thereafter restricted themselves to talking about flattening the peak or flattening the curve, and the squashed sombrero was quietly dropped. However there is a rather flattened sombrero in the night sky at the moment, namely Messier 104 or the Sombrero Galaxy. To be honest it does not look much like a sombrero to me, but it joins the Eskimo Nebula as one of those slightly dodgy astronomical tags given to deep sky objects.
Spring is the period of the galaxies with no less than 11 Messier galaxies in Virgo, 7 in Coma Berenices, and 5 in Leo (to which the third member of the Leo triplet, NGC 3628, should really be added). To this core group, we must add five Messier galaxies in Ursa Major, four in Canes Venatici and M83 in Hydra. This is a grand total of 34 relatively bright galaxies which can be seen in the space of one evening, before we even consider adding other galaxies from the NGC. But this series is dedicated to visual astronomy in Havering using small telescopes or binoculars and frankly they are not easy to see under such light polluted conditions (even before we take our neighbours’ security lights into account). Of all these galaxies, I have seen M81 and M82 with ease even without filters. Using filters I have seen ill-defined red blobs where M51 and M101 are located and beyond that I have not had much success at all. As I explained earlier in the case of M33 (DSO Object for November 2019), the problem with galaxies is that they have the magnitude of a relatively dim star which nonetheless can be easily seen in a telescope, but an angular size approaching that of the full moon. This means that its light is spread over a large area which makes it very difficult to see against a light polluted sky.
However it is hard to ignore a galaxy as beautiful as the Sombrero Galaxy with its dust lane and bright bulge. As its high M number indicates, it was not listed in the official Messier list until 1921 when Camille Flammarion found Messier’s handwritten list of his later objects and expanded the list to include M104 to M109. It was first discovered by Charles Messier’s collaborator Pierre Méchain in 1781 and rediscovered in 1784 by William Herschel, who noted the dark band which is the hallmark of the Sombrero Galaxy. When the New General Catalogue was drawn up, it became NGC 4594. The dark band contains cold molecular gas, which is prime fuel for star formation and it is thus no surprise that infrared studies have shown that it is also the major star forming region of this galaxy. The galaxy is roughly 30 million light years away—the latest estimates based on Hubble observations give a figure of 31.15 million light years. It is a giant elliptical galaxy with a supermassive black hole.
To find the Sombrero Galaxy, locate Porrima (Gamma Virginis) in Virgo and Algorab (Delta Corvi) in Corvus—both excellent double stars as it happens—and M104 is roughly half-way between them, roughly on the same level as Spica (Alpha Virginis) and slightly to the east of the line between Porrima and Algorab. There is a curious arrow-shaped asterism (STF 1664) of four roughly eighth magnitude stars which points westward to the Sombrero Galaxy (although to be precise the arrow is pointing the wrong way!). At magnitude 8, it is comparable to the Cigar Galaxy M82 (8.4). Its size is also comparable to M82 being 9 by 4 arcminutes (M82 is 11 by 4 arcminutes) so it should be as easy to see as M82. The problem is that it is fairly low in the sky although it does reach a fairly decent 26 degrees in altitude when it crosses the meridian. Good luck in trying to see it!
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