Messier 60 - Giant Elliptical Galaxy
In the spring constellation "Virgo" you can find the wonderful pair of galaxies Messier 60 / NGC 4647 in the well known Virgo Cluster, which together are
also known as Arp 116. Although the halos of the two galaxies overlap, they do not interact with each other, but just happen to be in the same direction.
Messier 60 was discovered in April 1779 by Johann Gottfried Köhler. The galaxy is located at a distance of 54...57 million light years and has an apparent
magnitude of 8.8mag and a diameter of 7.6'x6.2' arcminutes.
The diameter of the galaxy is 120,000 light-years. Since it is an elliptical "E2" type galaxy, the total mass is an incredible 1 trillion solar masses. The absolute
magnitude is M= -22.3mag, which corresponds to a luminosity of 71 billion suns. In the center is a supermassive black hole (SMBH) with a mass of 3.4 to
4.5 billion solar masses. So far only one supernova has been observed in Messier 60, namely "SN 2004W" with a brightness of 18mag.
Especially interesting is the ultracompact dwarf galaxy "M60 UCD-1", which is located only 22,000 light-years away from Messier 60. In an area 300 light-years
across, it contains 140 million stars, making it the densest galaxy known. The stellar density at the center is more than 100 stars per cubic light-year. It is
assumed that the galaxy lost most of its stars and dark matter in a collision with Messier 60 and now only the dense core area is left. Directly in the center
you find a SMBH with 20 million solar masses. It is likely that the dwarf galaxy will merge completely with Messier 60 in the distant future.
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In my 20" telescope, both galaxies appear quite bright, but Messier 60 is much brighter than the adjacent NGC 4647. The brightness increases
moderately towards the center. Directly in the center a fainter stellar nucleus can be seen at high magnification - the central region of Messier 60.
Further details are not visible.
NGC 4647 looks quite different. The nucleus is of nearly uniform brightness and surrounded by an equally uniform halo. A brighter central area
or other structures are not visible.
Observing M60-UCD1 is anything but an easy task, even with an aperture of 20". Fortunately, the position can be estimated relatively well, as UCD1 is located
exactly on the other side of Messier 60 than a faint star. You only need to draw an imaginary line from this star through the center of Messier 60 to find the ultra-
compact dwarf galaxy at the same distance on the other side. At a magnification of 380x, however, it still took me some time before I was able to see the tiny, only
0.7" large and 17mag faint galaxy a few times with averted vision. The observation was certain, but very difficult and at the limit of what was possible under the
less than optimal conditions of that night. But it was also super exciting. :)
All in all a great galaxy trio, where the differences between elliptical galaxies and spiral galaxies can be clearly observed and you get an ultra-compact dwarf
galaxy for some extra fun. :)
