Sombrero Galaxy

The Sombrero Galaxy (also known as Messier Object 104, M104 or NGC 4594) is a lenticular galaxy[4] in the constellation Virgo found 9.55 Mpc (31,100,000 ly)[2] from Earth. The galaxy has a diameter of approximately 15kpc (50,000 light-years),[5] 30% the size of the Milky Way. It has a bright nucleus, an unusually large central bulge, and a prominent dust lane in its inclined disk. The dark dust lane and the bulge give this galaxy the appearance of a sombrero hat. Astronomers initially thought that the halo was small and light, indicative of a spiral galaxy, but the Spitzer Space Telescope found that the dust ring around the Sombrero Galaxy is larger and more massive than previously thought, indicative of a giant elliptical galaxy.[6] The galaxy has an apparent magnitude of +8.0,[5] making it easily visible with amateur telescopes, and it is considered by some authors to be the galaxy with the highest absolute magnitude within a radius of 10 megaparsecs of the Milky Way.[3] Its large bulge, its central supermassive black hole, and its dust lane all attract the attention of professional astronomers.

Sombrero Galaxy
M104 ngc4594 sombrero galaxy hi-res
Messier 104
Observation data (J2000 epoch)
ConstellationVirgo
Right ascension 12h 39m 59.4s[1]
Declination−11° 37′ 23″[1]
Redshift0.003416±0.000017[1]
Helio radial velocity1024±5 km/s[1]
Galactocentric velocity904±7 km/s[1]
Distance9.55 ± 0.31 Mpc
(31.1 ± 1.0 Mly)[2]
Absolute magnitude (B)−21.8[3]
Characteristics
TypeSA(s)a;[1]
Size15 kpc (49,000 ly)
Apparent size (V)9′ × 4′
Notable featuresThe overwhelming bright center, contrasting the intruigingly detailed dust band
Other designations
M104, NGC 4594, UGC 293, PGC 42407

Observation history

Discovery

The Sombrero Galaxy[5] was discovered on May 11, 1781 by Pierre Méchain, who described the object in a May 1783 letter to J. Bernoulli that was later published in the Berliner Astronomisches Jahrbuch.[7][8] Charles Messier made a hand-written note about this and five other objects (now collectively recognized as M104 – M109) to his personal list of objects now known as the Messier Catalogue, but it was not "officially" included until 1921.[8] William Herschel independently discovered the object in 1784 and additionally noted the presence of a "dark stratum" in the galaxy's disc, what is now called a dust lane.[7][8] Later astronomers were able to connect Méchain's and Herschel's observations.[8]

Designation as a Messier object

In 1921, Camille Flammarion found Messier's personal list of the Messier objects including the hand-written notes about the Sombrero Galaxy. This was identified with object 4594 in the New General Catalogue, and Flammarion declared that it should be included in the Messier Catalogue. Since this time, the Sombrero Galaxy has been known as M104.[8]

Dust ring

Sombrero Galaxy in infrared (Ssc2005-11a3)
M104 in infrared

As noted above, this galaxy's most striking feature is the dust lane that crosses in front of the bulge of the galaxy. This dust lane is actually a symmetrical ring that encloses the bulge of the galaxy.[9] Most of the cold atomic hydrogen gas[10] and the dust[9] lie within this ring. The ring might also contain most of the Sombrero Galaxy's cold molecular gas,[9] although this is an inference based on observations with low resolution and weak detections.[11][12] Additional observations are needed to confirm that the Sombrero galaxy's molecular gas is constrained to the ring. Based on infrared spectroscopy, the dust ring is the primary site of star formation within this galaxy.[9]

Nucleus

The nucleus of the Sombrero galaxy is classified as a low ionization nuclear emission region (LINER).[13] These are nuclear regions where ionized gas is present, but the ions are only weakly ionized (i.e. the atoms are missing relatively few electrons). The source of energy for ionizing the gas in LINERs has been debated extensively. Some LINER nuclei may be powered by hot, young stars found in star formation regions, whereas other LINER nuclei may be powered by active galactic nuclei (highly energetic regions that contain supermassive black holes). Infrared spectroscopy observations have demonstrated that the nucleus of the Sombrero Galaxy is probably devoid of any significant star formation activity. However, a supermassive black hole has been identified in the nucleus (as discussed in the subsection below), so this active galactic nucleus is probably the energy source that weakly ionizes the gas in the Sombrero Galaxy.[9]

Central supermassive black hole

In the 1990s, a research group led by John Kormendy demonstrated that a supermassive black hole is present within the Sombrero Galaxy.[14] Using spectroscopy data from both the CFHT and the Hubble Space Telescope, the group showed that the speed of revolution of the stars within the center of the galaxy could not be maintained unless a mass 1 billion times the mass of the Sun, or 109 M, is present in the center.[14] This is among the most massive black holes measured in any nearby galaxies.

Synchrotron radiation

At radio and X-ray wavelengths, the nucleus is a strong source of synchrotron radiation.[15][16][17][18][19][20][21] Synchrotron radiation is produced when high velocity electrons oscillate as they pass through regions with strong magnetic fields. This emission is quite common for active galactic nuclei. Although radio synchrotron radiation may vary over time for some active galactic nuclei, the luminosity of the radio emission from the Sombrero Galaxy varies only 10–20%.[15]

Unidentified terahertz radiation

In 2006, two groups published measurements of the terahertz radiation from the nucleus of the Sombrero Galaxy at a wavelength of 850 μm.[9][21] This terahertz radiation was found not to originate from the thermal emission from dust (which is commonly seen at infrared and submillimeter wavelengths), synchrotron radiation (which is commonly seen at radio wavelengths), bremsstrahlung emission from hot gas (which is uncommonly seen at millimeter wavelengths), or molecular gas (which commonly produces submillimeter spectral lines).[9] The source of the terahertz radiation remains unidentified.

Globular clusters

The Sombrero Galaxy has a relatively large number of globular clusters. Observational studies of globular clusters in the Sombrero Galaxy have produced estimates of the population in the range of 1,200 to 2,000.[22][23][24] The ratio of the number of globular clusters to the total luminosity of the galaxy is high compared to the Milky Way and similar galaxies with small bulges, but the ratio is comparable to other galaxies with large bulges. These results have been repeatedly used to demonstrate that the number of globular clusters in galaxies is thought to be related to the size of the galaxies' bulges. The surface density of the globular clusters generally follows the light profile of the bulge except for near the center of the galaxy.[22][24][25]

Distance and brightness

At least two methods have been used to measure the distance to the Sombrero Galaxy.

The first method relies on comparing the measured fluxes from planetary nebulae in the Sombrero Galaxy to the known Luminosity of planetary nebulae in the Milky Way. This method gave the distance to the Sombrero Galaxy as 29 ± 2 Mly (8,890 ± 610 kpc).[26]

The other method used is the surface brightness fluctuations method. This method uses the grainy appearance of the galaxy's bulge to estimate the distance to it. Nearby galaxy bulges will appear very grainy, while more distant bulges will appear smooth. Early measurements using this technique gave distances of 30.6 ± 1.3 Mly (9,380 ± 400 kpc).[27] Later, after some refinement of the technique, a distance of 32 ± 3 Mly (9,810 ± 920 kpc) was measured.[28] This was even further refined in 2003 to be 29.6 ± 2.5 Mly (9,080 ± 770 kpc).[29]

The average distance measured through these two techniques is 29.3 ± 1.6 Mly (8,980 ± 490 kpc).[note 1]

The absolute magnitude (in the blue) of the Sombrero Galaxy is estimated to be −21.9 at 30.6 Mly (9,400 kpc) (−21.8 at the average distance of above), that as stated above makes it the brightest galaxy within a radius of 32.6 Mly (10,000 kpc) around the Milky Way.[3]

A report from 2016 used the Hubble Space Telescope to measure the distance to M104 based on the tip of the red-giant branch method yielding 9.55 ± 0.13 ± 0.31 Mpc.[2]

Nearby galaxies and galaxy group information

The Sombrero Galaxy lies within a complex, filament-like cloud of galaxies that extends to the south of the Virgo Cluster.[30] However, it is unclear whether the Sombrero Galaxy is part of a formal galaxy group. Hierarchical methods for identifying groups, which determine group membership by considering whether individual galaxies belong to a larger aggregate of galaxies, typically produce results showing that the Sombrero Galaxy is part of a group that includes NGC 4487, NGC 4504, NGC 4802, UGCA 289, and possibly a few other galaxies.[30][31][32] However, results that rely on the percolation method (i.e. the "friends-of-friends" method), which links individual galaxies together to determine group membership, indicate that either the Sombrero Galaxy is not in a group[33] or that it may only be part of a galaxy pair with UGCA 287.[32]

Besides that, M104 is also accompanied by an ultracompact dwarf galaxy, that was discovered in 2009. This object has an absolute magnitude of −12.3, a radius where half of its light is emitted of just 47.9 ly (3,030,000 AU), and a mass of 3.3*107 M[34]

Amateur astronomy

Sombrero Galaxy (also known as Messier Object 104, M104 or NGC 4594) (cropped)
Amateur photograph of M104

The Sombrero Galaxy is located 11.5° west of Spica[8] and 5.5° northeast of Eta Corvi.[35] Although the galaxy is visible with 7x35 binoculars or a 4-inch (100 mm) amateur telescope,[35] an 8-inch (200 mm) telescope is needed to distinguish the bulge from the disk,[8] and a 10-or-12-inch (250 or 300 mm) telescope is needed to see the dark dust lane.[8]

References in popular culture

On Jack Arnold's sci-fi 1957 feature film The Incredible Shrinking Man during Grant Williams' final voice-over, the Sombrero Galaxy is among several images that depict his thoughts on the life ahead of him, and the similarities between the infinitely large and the infinitely small.

There is also a black-and-white photograph of it in the ending credits of each and every episode of the original version of "The Outer Limits (1963 TV series)."

In the Silver Age, the hero Vartox is from a planet in the "Sombrero Hat" Galaxy.

See also

Notes

  1. ^ average(29.6 ± 2.5, 29 ± 2) = ((29.6 + 29) / 2) ± ((2.52 + 22)0.5 / 2) = 29.3 ± 1.6

References

  1. ^ a b c d e f "NASA/IPAC Extragalactic Database". Results for M104. Retrieved 2008-07-09.
  2. ^ a b c McQuinn, Kristen B. W.; Skillman, Evan D.; Dolphin, Andrew E.; Berg, Danielle; Kennicutt, Robert (2016). "The Distance to M104". The Astronomical Journal. 152 (5): 144. arXiv:1610.03857. Bibcode:2016AJ....152..144M. doi:10.3847/0004-6256/152/5/144.
  3. ^ a b c Karachentsev, Igor D.; Karachentseva, Valentina E.; Huchtmeier, Walter K.; Makarov, Dmitry I. (2003). "A Catalog of Neighboring Galaxies". The Astronomical Journal. 127 (4): 2031–2068. Bibcode:2004AJ....127.2031K. doi:10.1086/382905.
  4. ^ [1] NASA's Sombrero Galaxy Overview and Wallpaper
  5. ^ a b c "M 104". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-09-24.
  6. ^ [2] Famous Sombrero Galaxy Shows Surprising Side
  7. ^ a b G. R. Kepple; G. W. Sanner (1998). The Night Sky Observer's Guide. Vol. 2. Willmann-Bell. p. 451. ISBN 978-0-943396-60-6.
  8. ^ a b c d e f g h K. G. Jones (1991). Messier's Nebulae and Star Clusters (2nd ed.). Cambridge University Press. ISBN 978-0-521-37079-0.
  9. ^ a b c d e f g G. J. Bendo; B. A. Buckalew; D. A. Dale; B. T. Draine; R. D. Joseph; R. C. Kennicutt Jr.; et al. (2006). "Spitzer and JCMT Observations of the Active Galactic Nucleus in the Sombrero Galaxy (NGC 4594)". The Astrophysical Journal. 645 (1): 134–147. arXiv:astro-ph/0603160. Bibcode:2006ApJ...645..134B. doi:10.1086/504033.
  10. ^ Bajaja, E.; Van Der Burg, G.; Faber, S. M.; Gallagher, J. S.; et al. (1984). "The distribution of neutral hydrogen in the Sombrero galaxy, NGC 4594". Astronomy & Astrophysics. 141: 309–317. Bibcode:1984A&A...141..309B.
  11. ^ Bajaja, E.; Dettmar, R.-J.; Hummel, E.; Wielebinski, R. (1988). "The large-scale radio continuum structure of the Sombrero galaxy (NGC 4594)". Astronomy & Astrophysics. 202: 35–40. Bibcode:1988A&A...202...35B.
  12. ^ J. S. Young; S. Xie; L. Tacconi; P. Knezek; et al. (1995). "The FCRAO Extragalactic CO Survey. I. The Data". The Astrophysical Journal. 98: 219–257. Bibcode:1995ApJS...98..219Y. doi:10.1086/192159.
  13. ^ L. C. Ho; A. V. Filippenko; W. L. W. Sargent (1997). "A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies". The Astrophysical Journal. 112 (2): 315–390. arXiv:astro-ph/9704107. Bibcode:1997ApJS..112..315H. doi:10.1086/313041.
  14. ^ a b J. Kormendy; R. Bender; E. A. Ajhar; A.Dressler; et al. (1996). "Hubble Space Telescope Spectroscopic Evidence for a 1 X 10 9 M☉ Black Hole in NGC 4594". The Astrophysical Journal. 473 (2): L91–L94. Bibcode:1996ApJ...473L..91K. doi:10.1086/310399.
  15. ^ a b de Bruyn, A. G.; Crane, P. C.; Price, R. M.; Carlson, J. B. (1976). "The radio sources in the nuclei of NGC 3031 and NGC 4594". Astronomy & Astrophysics. 46: 243–251. Bibcode:1976A&A....46..243D.
  16. ^ Hummel, E.; van der Hulst, J. M.; Dickey, J. M. (1984). "Central radio sources in spiral galaxies – Starburst or accretion". Astronomy & Astrophysics. 134: 207–221. Bibcode:1984A&A...134..207H.
  17. ^ A. Thean; A. Pedlar; M. J. Kukula; S. A. Baum; et al. (2000). "High-resolution radio observations of Seyfert galaxies in the extended 12-μm sample - I. The observations". Monthly Notices of the Royal Astronomical Society. 314 (3): 573–588. arXiv:astro-ph/0001459. Bibcode:2000MNRAS.314..573T. doi:10.1046/j.1365-8711.2000.03401.x.
  18. ^ T. Di Matteo; C. L. Carilli; A. C. Fabian (2001). "Limits on the Accretion Rates onto Massive Black Holes in Nearby Galaxies". The Astrophysical Journal. 547 (2): 731–739. arXiv:astro-ph/0005516. Bibcode:2001ApJ...547..731D. doi:10.1086/318405.
  19. ^ S. Pellegrini; G. Fabbiano; F. Fiore; G. Trinchieri; et al. (2002). "Nuclear and global X-ray properties of LINER galaxies: Chandra and BeppoSAX results for Sombrero and NGC 4736". Astronomy & Astrophysics. 383 (1): 1–13. arXiv:astro-ph/0111353. Bibcode:2002A&A...383....1P. doi:10.1051/0004-6361:20011482.
  20. ^ S. Pellegrini; A. Baldi; G. Fabbiano; D.-W. Kim (2003). "An XMM-Newton and Chandra Investigation of the Nuclear Accretion in the Sombrero Galaxy (NGC 4594)". The Astrophysical Journal. 597 (1): 175–185. arXiv:astro-ph/0307142. Bibcode:2003ApJ...597..175P. doi:10.1086/378235.
  21. ^ a b M. Krause; R. Wielebinski; M. Dumke (2006). "Radio polarization and sub-millimeter observations of the Sombrero galaxy (NGC 4594). Large-scale magnetic field configuration and dust emission". Astronomy & Astrophysics. 448 (1): 133–142. arXiv:astro-ph/0510796. Bibcode:2006A&A...448..133K. doi:10.1051/0004-6361:20053789.
  22. ^ a b K.-I. Wakamatsu (1977). "Radial distribution and total number of globular clusters in M104". Publications of the Astronomical Society of the Pacific. 89: 267–270. Bibcode:1977PASP...89..267W. doi:10.1086/130114.
  23. ^ W. E. Harris; H. C. Harris; G. L. H. Harris (1984). "Globular clusters in galaxies beyond the local group. III NGC 4594 (the Sombrero)". The Astronomical Journal. 89: 216–223. Bibcode:1984AJ.....89..216H. doi:10.1086/113504.
  24. ^ a b T. J. Bridges; D. A. Hanes (1992). "The globular cluster system of NGC 4594 (the Sombrero)". The Astronomical Journal. 103: 800–814. Bibcode:1992AJ....103..800B. doi:10.1086/116102.
  25. ^ S. S. Larsen; D. A. Forbes; J. P. Brodie (2001). "Hubble Space Telescope photometry of globular clusters in the Sombrero galaxy" (PDF). Monthly Notices of the Royal Astronomical Society. 327 (4): 1116–1126. arXiv:astro-ph/0107082. Bibcode:2001MNRAS.327.1116L. doi:10.1046/j.1365-8711.2001.04797.x.
  26. ^ H. C. Ford; X. Hui; R. Ciardullo; G. H. Jacoby; K. C. Freeman (1996). "The Stellar Halo of M104. I. A Survey for Planetary Nebulae and the Planetary Nebula Luminosity Function Distance". The Astrophysical Journal. 458: 455–466. Bibcode:1996ApJ...458..455F. doi:10.1086/176828.
  27. ^ E. A. Ajhar; T. R. Lauer; J. L. Tonry; J. P. Blakeslee; et al. (1997). "Calibration of the Surface Brightness Fluctution Method for use with the Hubble Space Telescope". The Astronomical Journal. 114: 626–634. Bibcode:1997AJ....114..626A. doi:10.1086/118498.
  28. ^ J. L. Tonry; A. Dressler; J. P. Blakeslee; E. A. Ajhar; et al. (2001). "The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances". The Astrophysical Journal. 546 (2): 681–693. arXiv:astro-ph/0011223. Bibcode:2001ApJ...546..681T. doi:10.1086/318301.
  29. ^ Jensen, Joseph B.; Tonry, John L.; Barris, Brian J.; Thompson, Rodger I.; et al. (2003). "Measuring Distances and Probing the Unresolved Stellar Populations of Galaxies Using Infrared Surface Brightness Fluctuations". The Astrophysical Journal. 583 (2): 712–726. arXiv:astro-ph/0210129. Bibcode:2003ApJ...583..712J. doi:10.1086/345430.
  30. ^ a b R. B. Tully (1988). Nearby Galaxies Catalog. Cambridge University Press. ISBN 978-0-521-35299-4.
  31. ^ P. Fouque; E. Gourgoulhon; P. Chamaraux; G. Paturel (1992). "Groups of galaxies within 80 Mpc. II – The catalogue of groups and group members". Astronomy & Astrophysics. 93: 211–233. Bibcode:1992A&AS...93..211F.
  32. ^ a b G. Giuricin; C. Marinoni; L. Ceriani; A. Pisani (2000). "Nearby Optical Galaxies: Selection of the Sample and Identification of Groups". The Astrophysical Journal. 543 (1): 178–194. arXiv:astro-ph/0001140. Bibcode:2000ApJ...543..178G. doi:10.1086/317070.
  33. ^ A. Garcia (1993). "General study of group membership. II – Determination of nearby groups". Astronomy & Astrophysics. 100: 47–90. Bibcode:1993A&AS..100...47G.
  34. ^ Hau, George K. T.; Spitler, Lee R.; Forbes, Duncan A.; Proctor, Robert N.; Strader, Jay; Mendel, J. Trevor; Brodie, Jean P.; Harris, William E. (2009). "An ultra-compact dwarf around the Sombrero galaxy (M104): the nearest massive UCD". Monthly Notices of the Royal Astronomical Society: Letters. 394 (1): L97–L101. arXiv:0901.1693. Bibcode:2009MNRAS.394L..97H. doi:10.1111/j.1745-3933.2009.00618.x.
  35. ^ a b S. J. O'Meara (1998). The Messier Objects. Cambridge University Press. ISBN 978-0-521-55332-2.

External links

Coordinates: Sky map 12h 39m 59.4s, −11° 37′ 23″

Dust lane

A dust lane is a relatively dense obscuring band of interstellar dust, observed as a dark swath against the background of a brighter object, especially a galaxy. These dust lanes can usually be seen in spiral galaxies (e.g., the Milky Way) when viewed from the edge. Due to the dense and relatively thick nature of this dust, light from the galaxy is reduced by several magnitudes. In the Milky Way, this reduction of light makes it impossible to see the light from the central bulge of the galaxy from Earth. This dust, as well as the gasses also found within these lanes, mix together and combine to form stars and planets.

Herschel 400 Catalogue

The Herschel 400 catalogue is a subset of William Herschel's original Catalogue of Nebulae and Clusters of Stars, selected by Brenda F. Guzman (Branchett), Lydel Guzman, Paul Jones, James Morrison, Peggy Taylor and Sara Saey of the Ancient City Astronomy Club in St. Augustine, Florida, United States c. 1980. They decided to generate the list after reading a letter published in Sky & Telescope by James Mullaney of Pittsburgh, Pennsylvania, USA.In this letter Mr. Mullaney suggested that William Herschel's original catalogue of 2,500 objects would be an excellent basis for deep sky object selection for amateur astronomers looking for a challenge after completing the Messier Catalogue.

The Herschel 400 is a subset of John Herschel's General Catalogue of Nebulae and Clusters published in 1864 of 5,000 objects, and hence also of the New General Catalogue.

The catalogue forms the basis of the Astronomical League's Herschel 400 club. In 1997, another subset of 400 Herschel objects was selected by the Rose City Astronomers of Portland, Oregon as the Herschel II list, which forms the basis of the Astronomical League's Herschel II Program.

Kappa Virginis

Kappa Virginis (κ Virginis, abbreviated Kappa Vir, κ Vir), also named Kang, is a solitary star in the zodiac constellation of Virgo. It has an apparent visual magnitude of 4.18, which is sufficiently bright to be seen with the naked eye. Based upon stellar parallax measurements, the distance to this star is about 255 light-years.

List of black holes

This is a list of black holes (and stars considered probable candidates) organized by size (including black holes of undetermined mass); some items in this list are galaxies or star clusters that are believed to be organized around a black hole. Messier and New General Catalogue designations are given where possible.

List of spiral galaxies

A spiral galaxy is a type of galaxy characterized by a central bulge of old Population II stars surrounded by a rotating disc of younger Population I stars. A spiral galaxy maintains its spirals arms due to density wave theory.

Low-ionization nuclear emission-line region

A low-ionization nuclear emission-line region (LINER) is a type of galactic nucleus that is defined by its spectral line emission. The spectra typically include line emission from weakly ionized or neutral atoms, such as O, O+, N+, and S+. Conversely, the spectral line emission from strongly ionized atoms, such as O++, Ne++, and He+, is relatively weak. The class of galactic nuclei was first identified by Timothy Heckman in the third of a series of papers on the spectra of galactic nuclei that were published in 1980.

M104

M104 or M-104 may refer to:

Sombrero Galaxy, called M104 by Messier number

M104 group of galaxies

HMS Walney (M104), a British warship

M104 Wolverine, a military armored bridge

M104 155mm Cartridge, a U.S. Army chemical artillery shell

M104 (New York City bus), a New York City Bus route in Manhattan

Mercedes-Benz M104 engine

M-104 highway (Michigan), a road in the United States

a Y-chromosome mutation, also called P22

NGC 3079

NGC 3079 is a barred spiral galaxy about 50 million light-years away, and located in the constellation Ursa Major. A prominent feature of this galaxy is the "bubble" forming in the very center (see picture below). The Supermassive black hole at the core has a mass of 2.4+2.4−1.2×106 M☉.

NGC 6027a

NGC 6027a is a spiral galaxy that is part of Seyfert's Sextet, a compact group of galaxies, which is located in the constellation Serpens. In optical wavelengths, it has a strong resemblance to Messier 104, the Sombrero Galaxy, with which it shares a near equivalent orientation to observers on Earth.

NGC 681

NGC 681 (also known as the Little Sombrero Galaxy) is an intermediate spiral galaxy in the constellation of Cetus, located approximately 66.5 million light-years from Earth. The name Little Sombrero Galaxy is a reference to a much larger and earlier observed sombrero-like galaxy designated M104, or the Sombrero Galaxy.

NGC 7742

NGC 7742 also known as Fried Egg Galaxy is a face-on unbarred spiral galaxy in the constellation Pegasus.

The galaxy is unusual in that it contains a ring but no bar. Typically, bars are needed to produce a ring structure. The bars' gravitational forces move gas to the ends of the bars, where it forms into the rings seen in many barred spiral galaxies. In this galaxy, however, no bar is present, so this mechanism cannot be used to explain the formation of the ring. O. K. Sil'chenko and A. V. Moiseev proposed that the ring was formed partly as the result of a merger event in which a smaller gas-rich dwarf galaxy collided with NGC 7742. As evidence for this, they point to the unusually bright central region, the presence of highly inclined central gas disk, and the presence of gas that is counterrotating (or rotating in the opposite direction) with respect to the stars.Two Type II supernovae, SN 1993R and SN 2014cy, have been detected in NGC 7742.

NGC 7814

NGC 7814 (also known as UGC 8 or Caldwell 43) is a spiral galaxy about 40 million light-years away in the constellation Pegasus. The galaxy is seen edge-on from Earth. It is sometimes referred to as "the little sombrero", a miniature version of Messier 104. The star field behind NGC 7814 is known for its density of faint, remote galaxies as can be seen in the image here – in the same vein as the Hubble Deep Field.

Pi Virginis

Pi Virginis (π Vir, π Virginis) is a binary star in the zodiac constellation of Virgo. It is visible to the naked eye with an apparent visual magnitude of 4.64. The distance to this star, based upon parallax measurements, is roughly 380 light years.

This is a spectroscopic binary system with a stellar classification of A5V. They have an orbital period of 283 days with an eccentricity of 0.27. The mass ratio of the two stars is about 0.47, with the primary having an estimated mass of around 2.2 times that of the Sun. The primary is a cool metallic-lined Am star.

Sombrero

Sombrero (Spanish pronunciation: [somˈbɾeɾo]; Spanish for "hat", literally "shadower") in English refers to a type of wide-brimmed hat from Mexico, used to shield from the sun. It usually has a high pointed crown, an extra-wide brim (broad enough to cast a shadow over the head, neck and shoulders of the wearer, and slightly upturned at the edge), and a chin string to hold it in place. In Spanish, sombrero refers to any wide-brimmed hat; in Mexico the hat is called Sombrero de charro.

Sombrero (disambiguation)

A sombrero is a type of wide-brimmed hat.

Sombrero may also refer to:

Sombrero Key (reef), a coral reef in the Florida Keys National Marine Sanctuary

Sombrero, Anguilla, a British overseas island in the Lesser Antilles

Sombrero Galaxy, a spiral galaxy in the constellation Virgo

Sombrero (film), a 1953 film starring Ricardo Montalbán, Pier Angeli, Vittorio Gassman and Cyd Charisse

Sombrero Festival, an annual celebration held jointly by Matamoros, Tamaulipas, Mexico, and Brownsville, Texas, United States

Sound of Pig

Sound of Pig was a cassette culture label started in the early 1980s by Al Margolis in New York City. Featuring his projects If, Bwana and Sombrero Galaxy, plus a number of international artists, Sound of Pig released hundreds of original cassettes throughout the 1980s.

Spitzer Infrared Nearby Galaxies Survey

The Spitzer Infrared Nearby Galaxies Survey (SINGS) was a survey of 75 galaxies using the Spitzer Space Telescope, carried out between 2003 and 2006.

One of the telescope's six Legacy Science Projects, SINGS collected a comprehensive set of spectroscopic data in the infrared region, which, in conjunction with measurements at other wavelengths, was intended to provide insights into star formation and other processes occurring within these galaxies.

Unbarred spiral galaxy

An unbarred spiral galaxy is a type of spiral galaxy without a central bar, or one that is not a barred spiral galaxy. It is designated with an SA in the galaxy morphological classification scheme.

The Sombrero Galaxy is an unbarred spiral galaxy.

Barless spiral galaxies are one of three general types of spiral galaxies under the de Vaucouleurs system classification system, the other two being intermediate spiral galaxy and barred spiral galaxy. Under the Hubble tuning fork, it is one of two general types of spiral galaxy, the other being barred spirals.

Virgo (constellation)

Virgo is one of the constellations of the zodiac. Its name is Latin for virgin, and its symbol is ♍. Lying between Leo to the west and Libra to the east, it is the second-largest constellation in the sky (after Hydra) and the largest constellation in the zodiac. It can be easily found through its brightest star, Spica.

List
See also
Messier
NGC
PGC
UGC
GC

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