Messier 89

Object Name: Messier 89
Alternative Designations: M89, NGC 4552
Object Type: Type E0 Elliptical Galaxy
Constellation: Virgo
Right Ascension: 12 : 35.7 (h:m)
Declination: +12 : 33 (deg:m)
Distance: 60000 (kly)
Visual Brightness: 9.8 (mag)
Apparent Dimension: 4.0 (arc min)


Locating Messier 89: Begin with the base M84/M86 pairing located almost exactly mid-way between Beta Leonis (Denebola) and Epsilon Virginis (Vindemiatrix). The above map shows quite some distance between the galaxies, but by running a “grid” pattern, you can starhop the Virgo galaxy field with ease. Once you have M84/M86 in sight, move one low power eyepiece field east and hop north less than and eyepiece field for M87. Now you understand how Charles Messier ran his sky patterns! Continue north for 1 or two eyepiece fields and then shift east by one. This should bring you to M88. Now shift one more field east and drop south between 1 to 2 fields. In the eyepiece, M89 will appear as a very faint round haze, while it will take on a brighter core region for larger aperture. Because M89 nears magnitude 10, it will require a dark night.

m89malinWhat You Are Looking At: At some 6 million light years away, Messier 89 might not appear like much other than a round, hazy patch in the night sky, but it’s what we can’t see that makes this galaxy so unusual. Through high sensitivity photography done by David Malin, M89 was the first galaxy discovered to have a faint enveloping structure. While the 150,000 light year sized sheath is interesting enough, it’s the fact that M89 also contains a jet of material extruding through it that really raises some eyebrows. Is it coming from a black hole? Or a close encounter? “One of the early successes of the photographic amplification technique was the discovery of the peculiar nature of the Virgo cluster galaxy Messier 89 (NGC 4552). This galaxy looks quite normal on ordinary photographs, but it reveals a faint, very extended feature on deep images such as this.” says Malin. “In the Nature paper where this was announced it was described as a jet, but it is more likely the remains of a dwarf galaxy that M89 has absorbed or disrupted. This paper was also the first to demonstrate the existence of faint ‘shells’ around elliptical galaxies, but generality of this discovery was not recognized until a little later.”

m89_chandraSo what exactly causes the jet of material? Like all the Virgo Cluster members, they’re moving around out there and bumping into one another. “We use a 54.4 ks Chandra observation to study ram-pressure stripping in NGC4552 (M89), an elliptical galaxy in the Virgo Cluster. Chandra images in the 0.5-2 keV band show a sharp leading edge in the surface brightness 3.1 kpc north of the galaxy center, a cool (kT =0.51^{+0.09}_{-0.06} keV) tail with mean density n_e ~5.4 +/- 1.7 x 10^{-3} cm^{-3} extending ~10 kpc to the south of the galaxy, and two 3-4 kpc horns of emission extending southward away from the leading edge. These are all features characteristic of supersonic ram-pressure stripping of galaxy gas, due to NGC4552’s motion through the surrounding Virgo ICM.” says M. Machacek (et al). “Fitting the surface brightness profile and spectra across the leading edge, we find the galaxy gas inside the edge is cooler (kT = 0.43^{+0.03}_{-0.02} keV) and denser (n_e ~ 0.010 cm^{-3}) than the surrounding Virgo ICM (kT = 2.2^{+0.7}_{-0.4} keV and n_e = 3.0 +/- 0.3 x 10^{-4} cm^{-3}). The resulting pressure ratio between the free-streaming ICM and cluster gas at the stagnation point is ~7.6^{+3.4}_{-2.0} for galaxy gas metallicities of 0.5^{+0.5}_{-0.3} Zsolar, which suggests that NGC4552 is moving supersonically through the cluster with a velocity v ~ 1680^{+390}_{-220} km/s (Mach 2.2^{+0.5}_{-0.3}) at an angle xi ~ 35 +/- 7 degrees towards us with respect to the plane of the sky.”

m89_chandra2More? According to Harvard-Smithsonian Center for Astrophysics; “Results from NASA’s Chandra X-ray Observatory, combined with new theoretical calculations, provide one of the best pieces of evidence yet that many supermassive black holes are spinning extremely rapidly. The images above show 4 out of the 9 large galaxies included in the Chandra study, each containing a supermassive black hole in its center. These images show pairs of huge bubbles, or cavities, in the hot gaseous atmospheres of the galaxies, created in each case by jets produced by a central supermassive black hole. Studying these cavities allows the power output of the jets to be calculated. This sets constraints on the spin of the black holes when combined with theoretical models.”

m89_hubbleBut not only does Messier 89 contain a supermassive black hole, but it has a miniature active galactic nucleus, too. “The complex phenomenology shown by the UV-bright, variable spike rst detected with the Hubble Space Telescope (HST) at the center of the otherwise normal galaxy NGC 4552 is further investigated with both HST imaging (FOC) and spectroscopy (FOS). HST/FOC images taken in 1991, 1993, and 1996 in the near UV have been analyzed in a homogeneous fashion, showing that the central spike has brightened by a factor 4:5 between 1991 and 1993, and has decreased its luminosity by a factor 2:0 between 1993 and 1996. FOS spectroscopy extending from the near UV to the red side of the optical spectrum reveals a strong UV continuum over the spectrum of the underlying galaxy, along with several emission lines in both the UV and the optical ranges.” says Michelle Cappellari (et al). “In spite of the low luminosity of the UV continuum of the spike ( 3 105L ), the spike is de nitely placed among AGNs by current diagnostics based on the emission line intensity ratios, being just on the borderline between Seyferts and LINERs. Line pro les are very broad, and both permitted and forbidden lines are best modeled with a combination of broad and narrow components, with FWHM of 3000 km s 1 and 700 km s1 , respectively. This evidence argues for the variable central spike being produced by a modest accretion event onto a central massive black hole (BH), with the accreted material having possibly being stripped from a a star in a close y by with the BH. The 1996 broad H luminosity of this mini-AGN is 5:6 1037 erg s1 , about a factor of two less than that of the nucleus of NGC 4395, heretofore considered to be the faintest known AGN.”

History: M89 was one of 8 members of the Virgo Galaxy cluster discovered by Charles Messier on the night of March 18, 1781. In his notes he writes: “Nebula without star, in Virgo, a little of distance from and on the same parallel as the nebula reported above, No. 87. Its light was extremely faint and pale, and it is not without difficulty that one can distinguish it.”

m89aBy the time Sir William Herschel made it to Messier’s catalog number 89, he’s realized what an awesome field that he’d stumbled on. From his notes Of the remarkable situation of nebulae: “The number of compound nebulae that have been noticed in the foregoing three articles [on multiple nebulae] being so considerable, it will follow, that it they owe their origin to the breaking up of some former extensive nebulosities of the same nature with those which have been shewn to exist at present, we might expect that the number of separate nebulae should far exceed the former, and that moreover these scattered nebulae should be found not only in great abundance, but also in proximity or continuity of each other, according to the different extents and situations of the former diffusions of such nebulous matter. Now this is exactly what by observation, we find to be the state of the heavens. In the following seven assortments we have not less than 424 nebulae.”

Although Herschel never published these notes, we’re mighty glad he took the time to catalog the rest of the Virgo field!

Top M89 image credit, Palomar Observatory courtesy of Caltech, M89 Jet by David Malin, M89 Chandra Images, M89 Hubble Image, and M89 image courtesy of NOAO/AURA/NSF.