Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the supergiant elliptical galaxy known as Messier 87 (aka. Virgo A)!
During the 18th century, famed French astronomer Charles Messier noticed the presence of several “nebulous objects” while surveying the night sky. Originally mistaking these objects for comets, he began to catalog them so that others would not make the same mistake. Today, the resulting list (known as the Messier Catalog) includes over 100 objects and is one of the most influential catalogs of Deep Space Objects.
One of these objects is the supergiant galaxy Messier 87, also known as the Virgo A (or the Smoking Gun) galaxies. Located at a distance of about 53.5 million light years from Earth, this galaxy is home to several trillion stars, 15,000 globular clusters, and a supermassive black hole. It is one of the brightest galaxies in the northern part of the Virgo Cluster, second only to Messier 49, and the dominant member of that group.
Stretching itself across space for a distance of 120,000 light years, Messier 87 holds not only a lot more stars and mass than our own Milky Way galaxy, but it also tips the scales at extreme luminosity, with an absolute magnitude of about -22. One of the reasons is perhaps because M87 contains the most known globular clusters of any galaxy.
While our Milky Way has an impressive number of about 150 to 200 globulars, M87 possesses a remarkable system of several thousands! As Judith G. Cohen (et al) of the Palomar Observatory indicated in a 1997 study:
“A subset of 150 globular clusters (GCs) in M87 has been selected for abundance and age determinations from the 1997 sample of Cohen & Ryzhov. This has been done solely on the basis of the signal-to-noise ratios of the spectra. Indices that measure the strength of the strongest spectral features were determined for the M87 GCs and from new data for twelve galactic GCs. Combining the new and existing data for the galactic GCs and comparing the (U-R) colors and the line indices gave qualitative indications for the ages and abundances of the M87 GC system. Quantitative results, which confirm and extend the qualitative ones, were obtained by applying the Worthey models for the integrated light of stellar systems of a single age, calibrated by observations of galactic globular clusters, to deduce abundances and ages for the objects in our sample.”
Then along came W. Baade and R. Minkowski in 1954 who made another discovery about this Messier object – it was an impressive radio source… so impressive that it buried its neighbors and came to be known as Virgo A. Some three years later a weaker radio halo was found by J.E. Baldwin and F.G. Smith of Cambridge. But that’s not all. M87 was also identified as a strong source of X-rays, and sits near the center of a hot, X-ray emitting cloud extending far over the Virgo cluster. As M. Beilicke (et al) said in a 2003 study:
“The giant radio galaxy M87, well studied from radio to X-ray energies, is located in the Virgo cluster of galaxies at a distance of 16 Mpc (redshift z=0.00436). M87 has been observed with the HEGRA stereoscopic system of five Cherenkov telescopes in the years 1998 and 1999 for more than 80 h. An excess of TeV ?-rays on the 4? level has been found in the data corresponding to an integral flux (E>730 GeV) of 3.3% of the Crab nebula flux. The HEGRA detection – if confirmed – would make M87 the first TeV ?-ray emitting AGN observed with the imaging atmospheric Cherenkov technique not belonging to the BL Lac class.”
But let’s not stop there, because M87 is also extremely famous for the jet of material extending from a super-massive black hole at its core. While the jet has been known about for years, recently it has shown some activity. Said Juan P. Madrid of the Space Telescope Science Institute in a 2009 study:
“A knot along the M87 jet located 085 from the nucleus of the galaxy, has experienced dramatic and unexpected flaring activity since early 2000. We present analysis of Hubble Space Telescope near-ultraviolet (NUV) imaging of the M87 jet from 1999 May to 2006 December that reveals that the NUV intensity of HST-1 has increased 90 times over its quiescent level and outshines the core of the galaxy. The NUV light curve that we derive is synchronous with the light curves derived in other wavebands. The correlation of X-ray and NUV light curves during the HST-1 flare confirms the synchrotron origin of the X-ray emission in the M87 jet. The outburst observed in HST-1 is at odds with the common definition of active galactic nucleus variability usually linked to blazars and originating in close proximity to the central black hole. In fact, the M87 jet is not aligned with our line of sight and HST-1 is located at one million Schwarzchild radii from the supermassive black hole in the core of the galaxy.”
History of Observations:
M87 was discovered by Charles Messier on the night of March 18, 1781. It must have been a great night for Chuck, because he also cataloged 8 other nebulous objects 7 of them in the same region and all member galaxies of the Virgo Cluster. In his notes, he wrote:
“Nebula without star, in Virgo, below and very near a star of eighth magnitude, the star having the same Right Ascension as the nebula, and its Declination was 13d 42′ 21″ north. This nebula appears at the same luminosity as the two nebulae Nos. 84 and 86.”
William Herschel would also observe M87, cataloging fainter galaxies along the way. While he was a little less than enthusiastic on its appearance, he did note it was “large, brighter, much brighter to the middle, but diminishing very gradually in brightness.” Later historic astronomers would also follow with almost identical descriptions until Curtis had a look through the giant eye of the Lick Observatory Crossley Reflector connected to a photographic plate:
“Exceedingly bright; the sharp nucleus shows well in 5m exposure. The brighter central portion is about 0.5′ in diameter, and the total diameter is about 2′; nearly round. No spiral structure is discernible. A curious straight ray lies in a gap in the nebulosity in p.a. 20deg, apparently connected with the nucleus by a thin line of matter. The ray is brightest at its inner end, which is 11″ from the nucleus. 20 s.n.”
Locating Messier 87:
Begin with the M84/M86 pairing located by aiming almost exactly centered between Beta Leonis (Denebola) and Epsilon Virginis (Vindemiatrix). While the above map shows quite some distance between them, M87 is actually a lot closer to physically find. Simply put our starhop pair in the eyepiece and slowly move east/southeast about an average low power eyepiece field.
If you are using a large aperture telescope, you’ll see many small faint galaxies go by, but the next you’ll encounter in that direction is bright and large enough to easily identify M87. You can’t miss its bright, egg-shape. For smaller telescopes? Relax. Most of the Virgo Galaxy field isn’t visible in your aperture, so follow the same directions until you reach your target!
We might not have photographic plate eyes, but we can definitely enjoy this great galaxy!
Object Name: Messier 87
Alternative Designations: M87, NGC 4486, Virgo A
Object Type: Type E1 Elliptical Galaxy
Right Ascension: 12 : 30.8 (h:m)
Declination: +12 : 24 (deg:m)
Distance: 60000 (kly)
Visual Brightness: 8.6 (mag)
Apparent Dimension: 7.0 (arc min)
We have written many interesting articles about Messier Objects and globular clusters here at Universe Today. Here’s Tammy Plotner’s Introduction to the Messier Objects, M1 – The Crab Nebula, Observing Spotlight – Whatever Happened to Messier 71?, and David Dickison’s articles on the 2013 and 2014 Messier Marathons.