Category: Astronomy

Object Name: Messier 104
Alternative Designations: M104, NGC 4594, The Sombrero Galaxy
Object Type: Type Sa Spiral Galaxy
Constellation: Virgo
Right Ascension: 12 : 40.0 (h:m)
Declination: -11 : 37 (deg:m)
Distance: 50000 (kly)
Visual Brightness: 8.0 (mag)
Apparent Dimension: 9×4 (arc min)

Locating Messier 104: M104 is easily found exactly 11 degrees – about a fistwidth – due west of Alpha Virginis (Spica). With excellent conditions from a dark sky site, it can be spotted in binoculars as a small, eye-shaped patch of nebulosity. With telescopes as small as 3″ in aperture, it takes on a galactic signature and reveals its dark dustlane beginning at about 4.5″ in aperture. The more light gathering ability, the more the beautiful Sombrero Galaxy reveals! As always, galaxies prefer dark sky sites and good seeing conditions.

What You Are Looking At: The Sombrero, also known as M104, is one of the largest galaxies in the nearby Virgo cluster, about 28 million light years from Earth. This Great Observatories view of the famous Sombrero galaxy was made using NASA’s Chandra X-ray Observatory, Hubble Space Telescope and Spitzer Space Telescope. The main figure shows the combined image from the three telescopes, while the three inset images show the separate observatory views. The Chandra X-ray image (in blue) shows hot gas in the galaxy and point sources that are a mixture of objects within the Sombrero as well as quasars in the background. The Chandra observations show that diffuse X-ray emission extends over 60,000 light years from the center of the Sombrero. (The galaxy itself spans 50,000 light years across.) Scientists think this extended X-ray glow may be the result of a wind from the galaxy, primarily being driven by supernovas that have exploded within its bulge and disk. The Hubble optical image (green) shows a bulge of starlight partially blocked by a rim of dust, as this spiral galaxy is being observed edge on. That same rim of dust appears bright in Spitzer’s infrared image, which also reveals that Sombrero’s central bulge of stars.

Like “Diamonds on the Hat”, globular clusters are all parcel and part of M104’s makeup. “Images from the Hubble Space Telescope Advanced Camera for surveys are used to carry out a new photometric study of the globular clusters (GCs) in M104, the Sombrero galaxy. The primary focus of our study is the characteristic distribution function of linear sizes [size distribution function (SDF)] of the GCs. We measure the effective radii for 652 clusters with point spread function-convolved King and Wilson dynamical model fits. The SDF is remarkably similar to those measured for other large galaxies of all types, adding strong support to the view that it is a ‘universal’ feature of GC systems. We use the Sombrero and Milky Way data and the formation models of Baumgardt & Kroupa (2007) to develop a more general interpretation of the SDF for GCs. We propose that the shape of the SDF that we see today for GCs is strongly influenced by the early rapid mass loss during their star-forming stage, coupled with stochastic differences from cluster to cluster in the star formation efficiency (SFE) and their initial sizes. We find that the observed SDF shape can be accurately predicted by a simple model in which the protocluster clouds had characteristic sizes of 0.9 ± 0.1 pc and SFEs of 0.3 ± 0.07 .” says Wlliam E. Harris (et al).

“The colours and luminosities of the M104 clusters show the clearly defined classic bimodal form. The blue sequence exhibits a mass/metallicity relation, following a scaling of heavy-element abundance with luminosity of Z?L0.3 very similar to what has been found in most giant elliptical galaxies. A quantitative self-enrichment model provides a good first-order match to the data for the same initial SFE and protocluster size that were required to explain the SDF. We also discuss various forms of the GC Fundamental Plane of structural parameters and show that useful tests of it can be extended to galaxies beyond the Local Group. The M104 clusters strongly resemble those of the Milky Way and other nearby systems in terms of such test quantities as integrated surface density and binding energy.”

But, just like our own galaxy, globular clusters aren’t all that’s hiding inside that awesome halo. “We used the CTIO 4m telescope to make a complete and kinematically unbiased survey of M104 (NGC 4594; the Sombrero galaxy) for planetary nebulae (i.e., stars) out to 16 kpc. We present the positions and monochromatic [O III] lambda 5007 magnitudes of 294 planetaries, and use the observed planetary nebula luminosity function (PNLF) to measure a distance of 8.9+/-0.6Mpc to the galaxy. The luminosity-specific PN number lambda 2.5 in the halo of M104 is approximately 21.7×10^-9^L_{sun}_, which for its color (B-V)=0.95, is comparable to the values in other galaxies.” says H.C. Ford (et al).

“We use the PNLF distance to M104 to compare its luminosity to the luminosities of the brightest galaxies in the Virgo Cluster, finding that if M104 were in the Virgo Cluster, it would be the third brightest galaxy. We combined the PNLF distance and the observed velocity corrected for Virgo infall to calculate a Hubble constant H_0_=91+/-8km/s/Mpc. We also used the PNLF distances to the NGC 1023 group, the Leo group, the Virgo Cluster, and the Fornax Cluster to derive Hubble constants corrected for Virgo infall. The values of H_0_ for M104, the NGC 1023 group, the Virgo Cluster, and the Fornax Cluster are in excellent agreement, suggesting that the PNLF distances and Schechter’s linear infall model provide a self-consistent representation of the Hubble expansion and Virgo infall within most regions of the local supercluster.”

History: Messier 104 was not included in Messier’s originally published catalog. However, Charles Messier added it by hand to his personal copy on May 11, 1781, and described it as a “very faint nebula.” It was Camille Flammarion who found that its position coincided with Herschel’s H I.43, which is the Sombrero Galaxy (NGC 4594), and added it to the official Messier list in 1921. This object is also mentioned by Pierre Mechain as his discovery: “On May 11, 1781, I discovered a nebula above the Raven [Corvus] which did not appear to me to contain any single star. It is of a faint light and difficult to find if the micrometer wires are illuminated. I have compared it [its position] on this day and the following with Spica in the Virgin and from this derived its right ascension 187d 9′ 42″ and its southern declination 10d 24′ 49″ [the same position as in Messier’s handwritten note]. It does not appear in the Connoissance des Temps.”

William Herschel found this object independently on May 9, 1784, but it would be his son John who would first notice there was something a bit different about it: “There is a faint diffused oval light all about it, and I am almost positive that there is a dark interval or stratum separating the nucleus and general mass of the nebula from the light above (s of) it. Surely no illusion. There is a faint diffused oval light all about it, and I am almost positive that there is a dark interval or stratum separating the nucleus and general mass of the nebula from the light above (south of) it.”

Enjoy your observations of this great galaxy!

Top M104 image credit, Palomar Observatory courtesy of Caltech, M104 Composite – Spitzer, Chandra and Hubble, M104 Hubble Remix, M104 Hubble Details, M104 Spitzer Image and M104 image courtesy of Todd Boroson/NOAO/AURA/NSF.

Object Name: Messier 103
Alternative Designations: M103, NGC 581
Object Type: Type D Open Cluster
Constellation: Cassiopeia
Right Ascension: 01 : 33.2 (h:m)
Declination: +60 : 42 (deg:m)
Distance: 8.5 (kly)
Visual Brightness: 7.4 (mag)
Apparent Dimension: 6.0 (arc min)

Locating Messier 103: Locating M103 is fairly easy even under moderately light polluted conditions. Simply identify Delta Cassiopeiae (Ruchbah), a bright, blue-white star that marks one of the lower positions of Cassiopeia’s class “W” asterism. Simply center it in the finderscope and look about 1/2 a degree north and 1 degree east in the direction of Epsilon. In binoculars and a finderscope it will appear as a diamond shape patch of nebulosity which tries to resolve and will reveal its individual stars to even a small telescope. Loosely constructed, M103 makes a wonderful target for urban skies and less than perfect sky conditions.

What You Are Looking At: Located some 8,500 light years away and spanning over an area about 15 light years wide, this 25 million year old star cluster can sometimes be a little hard to pick out of the surrounding star field because of its wide open profile. Notable non-member binary Struve 131 dominates the scene, and only through radial velocity studies has genuine cluster members been identified. “The cluster has been assigned a class III2p by Ruprecht {1966). Oja (1966) determined the membership of the stars for the cluster on the basis of a proper motion study and reported 73 stars to be its possible members. Out of these, UBV photoelectric magnitudes and colors are presently known for only twenty stars.” says Ram Saga arid U.C. Joshi.

But look for M103’s prominent red giant! Is there a special reason? Yes. “A statistical research on evolved stars beyond hydrogen exhaustion is performed by comparing the H-R diagrams of about 60 open clusters with a set of isochronous curves without mass loss derived from Iben’s evolutionary tracks and time scales for Population I stars.” says G. Barbaro (et al). “Although evidence concerning mass loss from stars of different types and especially red giants and supergiants is gradually increasing, still not much is known about the real causes and the quantitative aspects of this phenomena, so that up to know little can be foretold concerning its bearing on stellar evolution.”

History: This sparkling open cluster was discovered by Pierre Mechain in either March or April of 1781and added by Charles Messier to his catalog before he had a chance to observe it. From Mechain’s notes: “Cluster of stars between Epsilon and Delta of the leg of Cassiopeia.”

Sir William Herschel would capture it again on August 8, 1783 when he describes: “14 or 16 pL. [pretty large (bright)] stars with a great many eS. [extremely small (faint)] ones. Two of the large [bright] ones are double, one of the 1st the other of the 2nd class. (*) The compound eye glass shews a few more that may be taken into the cluster so as to make them about 20. I exclude a good many straggling ones, otherwise there would be no knowing where to stop.”

But observing M103, didn’t stop and it would be Admiral Smyth who would be the first to see red. “”A neat double star in a cluster, on Cassiopeia’s knee, about a degree to nf of Delta. A 7 [th mag], straw coloured; B 9, dusky blue. This is a fan-shaped group, diverging from a sharp star in the nf quadrant. The cluster is brilliant from the splash of a score of its largest members, the four principle ones of which are from the 7th to the 9th magnitude; and under the largest, in the sf, is a red star of the 8th magnitude, which must be that mentioned by JH [John Herschel], No. 126 of his Catalogue of 1833. My attention was first drawn to this object, by seeing it among Srtuve’s acervi (double stars); but soon found that it was also the 103 which Messier describes so vaguely, as being between Delta and Epsilon Cassiopeiae, whereas it is pretty close to Delta, on the Lady’s knee.”

Look for the colors and enjoy your observations!

Top M103 image credit, Palomar Observatory courtesy of Caltech, M103 – Roberto Mura – Wikipedia Image, M103 2MASS image and M103 image courtesy of NOAO/AURA/NSF.

Object Name: Messier 102
Alternative Designations: M102, NGC 5866, The Spindle Galaxy
Object Type: Lenticular Galaxy
Constellation: Draco
Right Ascension: 15 : 06.5 (h:m)
Declination: +55 : 46 (deg:m)
Distance: 45000 (kly)
Visual Brightness: 9.9 (mag)
Apparent Dimension: 5.2×2.3 (arc min)

Locating Messier 102: Locating Messier 102 isn’t particularly easy and will require a good start chart and some work. It’s rough location is about 10 degrees east/northeast of Eta Ursa Major – or about 10 degrees south of Gamma Ursa Minor. It will require at least a 4″ telescope at a relatively dark sky to be seen brightly, and will begin to show both structure and its dark dustlane at apertures approaching 6-8″. For smaller scopes, it will appear as a thin streak of nebulosity. If you are at a very dark sky site, you can use Iota Draconis and shift about 3 deg southwest in the direction of Eta Ursae Majoris or use Theta Bootis where M102 is just to the south.

What You Are Looking At: Located some 45 million light-years and part of a galaxy grouping, M102 is a wonderful lenticular galaxy seen almost edge-on. And seeing is believing! From this beautiful Hubble image and the words of Bill Keel: “The dust lane is slightly warped compared to the disk of starlight. This warp indicates that NGC 5866 may have undergone a gravitational tidal disturbance in the distant past, by a close encounter with another galaxy. This is plausible because it is the largest member of a small cluster known as the NGC 5866 group of galaxies. The starlight disk in NGC 5866 extends well beyond the dust disk. This means that dust and gas still in the galaxy and potentially available to form stars does not stretch nearly as far out in the disk as it did when most of these stars in the disk were formed.”

“The Hubble image shows that NGC 5866 shares another property with the more gas-rich spiral galaxies. Numerous filaments that reach out perpendicular to the disk punctuate the edges of the dust lane. These are short-lived on an astronomical scale, since clouds of dust and gas will lose energy to collisions among themselves and collapse to a thin, flat disk. For spiral galaxies, the incidence of these fingers of dust correlates well with indicators of how many stars have been formed recently, as the input of energy from young massive stars moves gas and dust around to create these structures. The thinness of dust lanes in S0s has been discussed in ground-based galaxy atlases, but it took the resolution of Hubble to show that they can have their own smaller fingers and chimneys of dust.”

But what happens when the stars are done forming? Take a look in infrared… “S0 galaxies are often thought to be passively evolved from spirals after star formation is quenched. To explore what is actually occurring in such galaxies, we present a multi-wavelength case study of NGC 5866—a nearby edge-on S0 galaxy in a relatively isolated environment. This study shows strong evidence for dynamic activities in the interstellar medium, which are most likely driven by supernova explosions in the galactic disk and bulge.” says Jiang-Tao Li (et al).

“Understanding these activities can have strong implications for studying the evolution of such galaxies. We utilize Chandra, Hubble Space Telescope, and Spitzer data as well as ground-based observations to characterize the content, structure, and physical state of the medium and its interplay with the stellar component in NGC 5866. A cold gas disk is detected with an exponential scale height of ~102 pc. Numerous distinct off-disk dusty spurs are also clearly present: prominent ones can extend as far as ~3 × 102 pc from the galactic plane and are probably produced by individual SNe, whereas faint filaments can have ~kpc scale and are likely produced by SNe collectively in the disk/bulge.”

But what’s hot can also be very cool… and it the Spindle Galaxy’s case it the amount of interstellar medium. Says G.K. Kacprzak (New Mexico State University) and G.A. Welch (Saint Mary’s University): “The nearly edge-on S0 galaxy NGC 5866 is notable for its massive molecular interstellar medium, prominent central dust lane, and large IRAS 100 micron flux. The galaxy is relatively isolated, and neither the kinematics nor morphology of the gas suggests that a merger has taken place. Instead, NGC 5866 may be entering an era of star formation fueled with gas donated by its aging stellar population. Are we seeing a counter example of the popular view that galaxies evolve through mergers? We explore that possibility using multi-transition CO observations and SCUBA (Submillimetre Common-User Bolometer Array) imagery of NGC 5866. We analyze the dust and gas components of the interstellar medium using techniques such as the large velocity gradient (LVG) models and a three-dimensional Monte Carlo radiation transfer code. A comparison of SCUBA and appropriately convolved H alpha images reveals both to have similar structure and morphology. This complements the fact that the SCUBA fluxes were under predicted by the Monte Carlo code which does not take star formation into account. Both of those facts indicate that NGC 5866 is indeed under going star formation.”

History: NGC 5866 was probably first turned up by Pierre Mechain during March 1781 – or was observed by Charles Messier himself around that time. Despite Mechain’s disclaimer 2 years later, chances are good that NGC 5866 is object #102 rather than a reclassification of Messier 101. (Considering the personal problems Messier was having during that period, it’s small wonder that an error could have been made.) While Messier orginally added it to his published catalog without verifying its position, he did return later to verify this beautiful galaxy was almost exactly 5 degrees preceding (west) of the actual position previously published. In his 1781 personal notes, Messier writes: “Nebula between the stars Omicron [actually Theta] Bootis and Iota Draconis: it is very faint; near it is a star of the sixth magnitude. (Handwritten position added by Messier in his personal copy: 14h 40m, +56.).”

Even Pierre Mechain was vexed by the error and his letter to Bernoulli on May 6, 1783, he writes: “I will add only that No. 101 & 102 on the p. 267 of the Connoissance des tems [for] 1784 are nothing but the same nebula, which has been taken for two, by an error in the [sky] charts.” Later, Bode would find in his notes: “On page 267 of the “Connoissance des Temps for 1784″ M. Messier lists under No. 102 a nebula which I have discovered between Omicron [actually Theta] Bootis and Iota Draconis; this is a mistake. This nebula is the same as the preceding No. 101. Mr. Messier, caused by an error in the sky charts, has confused this one in the list of my nebulous stars communicated to him.” Although the positioning error occurred, the description was correct for NGC 5866.

It’s Messier designation will probably forever by the subject of debate, but even other notable astronomers called in errors on this one as well. Both Herschels observed it and even Admiral Smyth – who probably following an error by John Herschel in his 1833 catalog, confuses its number with H I.219 (which is NGC 3665, a galaxy in Ursa Major), and thus erroneously gives that object’s discovery date, March 1789: “A small but brightish nebula, on the belly of Draco, with four small stars spreading across the field, north of it. There may be a doubt as to whether this is the nebula discovered by Mechain in 1789, since Messier merely describes it as “very faint,” and situated between Omicron Bootis and Iota Draconis. But there must be some mistake here; the one being on the herdman’s leg, and the other in the coil of the Dragon far above the head of Bootes, having 22 deg of declination and 44′ [44 min] of time [in RA] between them, a space full of all descriptions of celestial objects. But as the Theta in the raised right hand of Bootes, if badly made, might be mistaken for an omicron, this is probably the object seen by Mechain, and JH’s 1910 [NGC 5879]; it being the brightest nebula of five in that vicinity [actually, the brightest is NGC 5866]. A line from Kappa in Draco’s tail, led to the south-east of Thuban, and prolonged as far again, strikes upon its site.”

Don’t you mistake the beautiful Spindle Galaxy for anything but a great observation!

Top M102 image credit, Palomar Observatory courtesy of Caltech, M102 Hubble Images, 2MASS M102 image, M102 data images by AANDA and M102 image courtesy of NOAO/AURA/NSF.