Object 71: Messier 61
Podcast release date: 18 April 2022
Right ascension: 12:21:54.9
Corresponding Earth location: About 470 km northeast of Howland Island in the Pacific Ocean
I just discussed a Messier object back in episode 67, so I am surprised that the random number generator has given me the coordinates for another Messier object so soon. Messier 61 (or M61) is actually a nice-looking face-on spiral galaxy. The galaxy is located not only in the constellation of Virgo but also within the Virgo Cluster, which is an enormous but amorphous cluster of over 1000 galaxies located at a distance of 53.8 million light years (16.5 Mpc) from Earth [1, 2, 3]. Several other galaxies in the Virgo Cluster are also Messier objects, and I could get sidetracked talking about them, so I'll stay focused on M61.
M61 was simultaneously discovered by the Italian astronomer Barnabus Oriani and the French astronomer Charles Messier in May 1779 . Both astronomers had been looking for a comet called the Comet of 1779, and while Oriani instantly recognized that M61 was not a comet, Messier thought it was. After watching it for several nights, Messier discovered that it wasn't moving like a comet should, which annoyed him, so he placed it in his list of fuzzy things that aren't really comets and aren't really interesting to anyone. Today, that list is known as the Messier Catalogue, and it lists star clusters, nebulae, and galaxies that are much more interesting than any comet that Charles Messier ever discovered.
The galaxy M61 is classified as a barred spiral galaxy, which means that it has a bar-like structure of stars running through its center. In fact, M61 has been a good place for astronomers to look if they want to understand bars in spiral galaxies. Bars form through gravitational instabilities in spiral galaxies' disks. Once they form, they end up exerting strong gravitational forces on the interstellar gas within these galaxies, funneling gas clouds inwards to the center. Pushing a lot of interstellar gas into a small place will cause the gas clouds to collapse and form lots of stars. All of this has been seen happening in M61, and people have been particularly interested in the enhanced star formation in the galaxy's center [5, 6, 7, 8, 9, 10, 11, 12].
What's actually cool about the inner regions of the bar is that the stars and gas have formed a miniature spiral pattern, and if you took a picture of just the center, you would think that it's a completely different spiral galaxy [5, 6, 7, 8, 10, 11]. However, in overexposed photos, these types of inner structures tend to look like bulges when they actually aren't, so they are called pseudobulges.
Having said all of this, neither the extra star formation nor the miniature spiral pattern are what I personally think are the most interesting things about M61. Instead, what I found interesting was that the very nucleus of the galaxy contains a supermassive black hole. The measurements of the mass of this black hole are not that good, but it's estimated to be somewhere around 5 million times the mass of the Sun .
Supermassive black holes are actually quite common at the centers of galaxies, and they form the cores of what are called active galactic nuclei. These black holes are often surrounded by thick disks of interstellar gas falling inwards. While the black holes themselves don't radiate light, the gas in these gas disks ends up being gravitationally compressed and getting really hot, and because of this, the gas radiates huge amounts of energy across the electromagnetic spectrum. Additionally, a lot of that gas gets so hot that, instead of falling into the black hole, the gas expands and blows away, forming jets of gas above the poles of the black hole moving at close to the speed of light. These jets of gas can travel thousands of light years and produce huge amounts of X-ray and radiowave emission. These types of active galactic nuclei are truly exciting objects to look at, and the black hole in M61 is absolutely nothing like this .
Instead, the black hole in M61 is just kind of sitting there and doing nothing except exerting some gravitational forces . A little bit of really thin interstellar gas might be falling into the black hole, but it's not much, and it doesn't produce much radiation while it falls inwards. It's kind of like the supermassive black hole didn't get its morning coffee, so instead of doing something exciting with its day, it's going to stay at home in its onesie and binge-watch Downton Abbey.
The reason why the black hole hasn't gotten its morning coffee (or, in other words, the reason why huge amounts of interstellar gas are not falling into the black hole and producing large amounts of electromagnetic radiation) seems to be because no gas actually gets near the black hole. As I stated earlier, the bar in this galaxy is pushing interstellar gas towards the galaxy's center, but that gas gets used up by star forming regions surrounding the center of the galaxy, and the young stars that form in these regions produce much more electromagnetic radiation that the area immediately around the black hole itself . So, while the black hole is moping about its lack of caffeine, its neighbors are consuming energy drinks with unnatural colors and partying very, very loudly.
M61 is too faint to see with the naked eye, but it should be easy to see with a medium or large amateur telescope. The Virgo Cluster is located in between the constellation Virgo and the constellation Coma Berenices to the north, and M61 lies at the south end of the cluster. In a 20 cm (8 inch) telescope, the galaxy will look like a fuzzy disk with a bright center (which, as you will recall, is a pseudobulge and not a real bulge) [14, 15]. A 30 cm (12 inch) telescope or larger will actually reveal the spiral arms [14, 15]. Be sure to drink something with caffeine so that you don't fall asleep like the black hole at the center of M61.
 Binggeli, B. et al., Studies of the Virgo cluster. II. A catalog of 2096 galaxies in the Virgo cluster area., 1985, Astronomical Journal, 90, 1681
 Mei, Simona et al., The ACS Virgo Cluster Survey. XIII. SBF Distance Catalog and the Three-dimensional Structure of the Virgo Cluster, 2007, Astrophysical Journal, 655, 144
 Kim, Suk et al., The Extended Virgo Cluster Catalog, 2014, Astrophysical Journal Supplement Series, 215, 22
 Frommert, Hartmut and Kronberg, Christine, Messier 61, 2014, Students for the Exploration and Development of Space
 Colina, Luis and Wada, Keiichi, Nuclear Bar, Star Formation, and Gas Fueling in the Active Galaxy NGC 4303, 2000, Astrophysical Journal, 529, 845
 Colina, Luis et al., Detection of a Super-Star Cluster as the Ionizing Source in the Low-Luminosity Active Galactic Nucleus NGC 4303, 2002, Astrophysical Journal, 579, 545
 Schinnerer, Eva et al., Toward the Secondary Bar: Gas Morphology and Dynamics in NGC 4303, 2002, Astrophysical Journal, 575, 826
 Jimenez-Bailon, E. et al., Nuclear Activity and Massive Star Formation in the Low-Luminosity Active Galactic Nucleus NGC 4303: Chandra X-Ray Observations, 2003, Astrophysical Journal, 593, 127
 Koda, Jin and Sofue, Yoshiaki, The Virgo High-Resolution CO Survey: VI. Gas Dynamics and Star Formation along the Bar in NGC 4303, 2006, Publications of the Astronomical Society of Japan, 58, 299
 Riffel, Rogemar A. et al., A SINFONI view of the nuclear activity and circumnuclear star formation in NGC 4303, 2016, Monthly Notices of the Royal Astronomical Society, 461, 4192
 Dametto, Natacha Z. et al., A SINFONI view of the nuclear activity and circumnuclear star formation in NGC 4303 - II. Spatially resolved stellar populations, 2019, Monthly Notices of the Royal Astronomical Society, 482, 4437
 Yajima, Yoshiyuki et al., CO Multi-line Imaging of Nearby Galaxies (COMING). III. Dynamical effect on molecular gas density and star formation in the barred spiral galaxy NGC 4303, 2019, Publications of the Astronomical Society of Japan, 71, S13
 Pastorini, G. et al., Supermassive black holes in the Sbc spiral galaxies NGC 3310, NGC 4303 and NGC 4258, 2007, Astronomy & Astrophysics, 469, 405