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{{Short description|Dwarf irregular galaxy, satellite galaxy of the Milky Way}}

factoids

0044.8}}-7243}}1 E20 m>203.7 ± 1.5 light-year (62.44 ± 0.47 parsec>kpc)10.3847/1538-4357/ABBB2B > TITLE=A DISTANCE DETERMINATION TO THE SMALL MAGELLANIC CLOUD WITH AN ACCURACY OF BETTER THAN TWO PERCENT BASED ON LATE-TYPE ECLIPSING BINARY STARS LAST1=GRACZYK LAST2=PIETRZYńSKI LAST3=THOMPSON LAST4=GIEREN LAST5=ZGIRSKI LAST6=VILLANOVA LAST7=GóRSKI LAST8=WIELGóRSKI LAST9=KARCZMAREK LAST10=NARLOCH LAST11=PILECKI LAST12=TAORMINA LAST13=SMOLEC LAST14=SUCHOMSKA LAST15=GALLENNE LAST16=NARDETTO LAST17=STORM LAST18=KUDRITZKI LAST19=KAłUSZYńSKI LAST20=PYCH JOURNAL=THE ASTROPHYSICAL JOURNAL ISSUE=1 ARXIV=2010.08754 S2CID=224706414, free, |z = 0.000527|appmag_v = 2.753|5}}5.78lyabbr=off}}(diameter; 25.0 mag/arcsec2 B-band isophote)HTTPS://UI.ADSABS.HARVARD.EDU/ABS/1991RC3..BOOK.....D > BIBCODE=1991RC3..BOOK.....D TITLE=THIRD REFERENCE CATALOGUE OF BRIGHT GALAXIES FIRST1=GERARD FIRST2=ANTOINETTE FIRST3=HEROLD G. FIRST4=RONALD J. FIRST5=GEORGES FIRST6=PASCAL, TITLE = RARE ASTRONOMICAL SIGHTS AND SOUNDS PAGES = URL = HTTPS://BOOKS.GOOGLE.COM/BOOKS?ID=DF5UDWAAQBAJ, |constellation name = Tucana and Hydrus|notes = Companion dwarf to theMilky WayNew General Catalogue>NGC 292, PGC 3085, Nubecula Minor}}The Small Magellanic Cloud (SMC) is a dwarf galaxy near the Milky Way.APOD, 2006-06-17, The Small Cloud of Magellan, 2008-07-07, Classified as a dwarf irregular galaxy, the SMC has a D25 isophotal diameter of about {{convert|5.78|kpc|ly|sigfig=3|abbr=off}}, and contains several hundred million stars. It has a total mass of approximately 7 billion solar masses.JOURNAL, Bekki, Kenji, Stanimirović, Snežana, Snežana Stanimirović, The total mass and dark halo properties of the Small Magellanic Cloud, Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), 395, 1, 2009-05-01, 0035-8711, 10.1111/j.1365-2966.2009.14514.x, 342–350, 0807.2102, 2009MNRAS.395..342B, 18268139, At a distance of about 200,000 light-years, the SMC is among the nearest intergalactic neighbors of the Milky Way and is one of the most distant objects visible to the naked eye.The SMC is visible from the entire Southern Hemisphere and can be fully glimpsed low above the southern horizon from latitudes south of about 15° north. The galaxy is located across the constellation of Tucana and part of Hydrus, appearing as a faint hazy patch resembling a detached piece of the Milky Way. The SMC has an average apparent diameter of about 4.2° (8 times the Moon's) and thus covers an area of about 14 square degrees (70 times the Moon's). Since its surface brightness is very low, this deep-sky object is best seen on clear moonless nights and away from city lights. The SMC forms a pair with the Large Magellanic Cloud (LMC), which lies 20° to the east, and, like the LMC, is a member of the Local Group. It is currently a satellite of the Milky Way, but is likely a former satellite of the LMC.

Observation history

File:Panoramic Large and Small Magellanic Clouds.jpg|thumb|left|Panoramic Large and Small Magellanic Clouds as seen from ESO's VLT observation site. The galaxies are on the left side of the image.]]File:Tucana IAU.svg|thumb|left|Constellation of (Tucana]]: the SMC is the green shape at the south (bottom) of picture)In the southern hemisphere, the Magellanic clouds have long been included in the lore of native inhabitants, including south sea islanders and indigenous Australians. Persian astronomer Al Sufi mentions them in his Book of Fixed Stars, repeating a quote by the polymath Ibn Qutaybah, but had not observed them himself. European sailors may have first noticed the clouds during the Middle Ages when they were used for navigation. Portuguese and Dutch sailors called them the Cape Clouds, a name that was retained for several centuries. During the circumnavigation of the Earth by Ferdinand Magellan in 1519–1522, they were described by Antonio Pigafetta as dim clusters of stars.BOOK File:Small_Magellanic_Cloud.png|thumb|left|Small Magellanic Cloud as photographed by an amateur astronomer. Unrelated stars have been edited out.]]Between 1834 and 1838, John Frederick William Herschel made observations of the southern skies with his {{convert|14|in|cm|adj=on}} reflector from the Royal Observatory. While observing the Nubecula Minor, he described it as a cloudy mass of light with an oval shape and a bright center. Within the area of this cloud he catalogued a concentration of 37 nebulae and clusters.BOOK In 1891, Harvard College Observatory opened an observing station at Arequipa in Peru. Between 1893 and 1906, under the direction of Solon Bailey, the {{convert|24|in|mm|adj=on}} telescope at this site was used to survey photographically both the Large and Small Magellanic Clouds.BOOK Using this period-luminosity relation, in 1913 the distance to the SMC was first estimated by Ejnar Hertzsprung. First he measured thirteen nearby cepheid variables to find the absolute magnitude of a variable with a period of one day. By comparing this to the periodicity of the variables as measured by Leavitt, he was able to estimate a distance of 10,000 parsecs (30,000 light years) between the Sun and the SMC.BOOK, John R., Gribbin, 1999, The Birth of Time: How Astronomers Measured the Age of the Universe, Yale University Press, 978-0-300-08346-0, registration,weblink This later proved to be a gross underestimate of the true distance, but it did demonstrate the potential usefulness of this technique.JOURNAL Announced in 2006, measurements with the Hubble Space Telescope suggest the Large and Small Magellanic Clouds may be moving too fast to be orbiting the Milky Way.WEB, Press release: Magellanic Clouds May Be Just Passing Through,weblink Harvard University, January 9, 2007,

Features

File:VISTA’s view of the Small Magellanic Cloud.jpg|thumb|VISTA's view of the Small Magellanic Cloud. alt=The SMC contains a central bar structure, and astronomers speculate that it was once a barred spiral galaxy that was disrupted by the Milky Way to become somewhat irregular.WEB,weblinkcosmic_classroom/multiwavelength_astronomy/multiwavelength_museum/smc.html, Small Magellanic Cloud, NASA/Infrared Processing and Analysis Center, IPAC, 2008-07-07, 2015-11-07, https:web.archive.org/web/20151107043237weblink dead, There is a bridge of gas connecting the Small Magellanic Cloud with the Large Magellanic Cloud (LMC), which is evidence of tidal interaction between the galaxies.JOURNAL, Structure and Evolution of the Magellanic Clouds, Mathewson DS, Ford VL, IAU Symposium, 1984, 108, 125, This bridge of gas is a star-forming site.JOURNAL, 10.1051/0004-6361:20031360, Heydari-Malayeri M, 4, Meynadier F, Charmandaris V, Deharveng L, Le Bertre T, Rosa MR, Schaerer D, The stellar environment of SMC N81, 2003, Astron. Astrophys., 411, 3, 427–436, 2003A&A...411..427H, astro-ph/0309126, 8240730, The Magellanic Clouds have a common envelope of neutral hydrogen, indicating they have been gravitationally bound for a long time. In 2017, using the Dark Energy Survey plus MagLiteS data, a stellar over-density associated with the Small Magellanic Cloud was discovered, which is probably the result of interactions between the SMC and LMC.JOURNAL, Adriano Pieres, etal, 2017, A stellar over-density associated with the Small Magellanic Cloud, Monthly Notices of the Royal Astronomical Society, 468, 2, 1349–1360, 1612.03938, 10.1093/mnras/stx507, 2017MNRAS.468.1349P, File:Head in the Clouds (potw2249a).tiff|thumb|right|The Small Magellanic Cloud pictured by the Hubble Space TelescopeHubble Space Telescope

X-ray sources

The Small Magellanic Cloud contains a large and active population of X-ray binaries. Recent star formation has led to a large population of massive stars and high-mass X-ray binaries (HMXBs) which are the relics of the short-lived upper end of the initial mass function. The young stellar population and the majority of the known X-ray binaries are concentrated in the SMC's Bar.HMXB pulsars are rotating neutron stars in binary systems with Be-type (spectral type 09-B2, luminosity classes V–III) or supergiant stellar companions. Most HMXBs are of the Be type which account for 70% in the Milky Way and 98% in the SMC.Coe et al. 2005 The Be-star equatorial disk provides a reservoir of matter that can be accreted onto the neutron star during periastron passage (most known systems have large orbital eccentricity) or during large-scale disk ejection episodes. This scenario leads to strings of X-ray outbursts with typical X-ray luminosities Lx = 1036–1037 erg/s, spaced at the orbital period, plus infrequent giant outbursts of greater duration and luminosity.Negueruela 1998 for a reviewMonitoring surveys of the SMC performed with NASA's Rossi X-ray Timing Explorer (RXTE)Laycock et al. 2005; Galache et al. 2008 see X-ray pulsars in outburst at more than 1036 erg/s and have counted 50 by the end of 2008. The ROSAT and ASCA missions detected many faint X-ray point sources,Haberl & Sasaki 2000 but the typical positional uncertainties frequently made positive identification difficult. Recent studies using XMM-NewtonHaberl et al. 2008; Haberl & Pietsch 2004 and ChandraAntoniou et al. 2009; Edge et al. 2004, and Laycock et al. 2010 have now cataloged several hundred X-ray sources in the direction of the SMC, of which perhaps half are considered likely HMXBs, and the remainder a mix of foreground stars, and background AGN.No X-rays above background were observed from the Magellanic Clouds during the September 20, 1966, Nike-Tomahawk flight.JOURNAL, 4, Chodil G, Mark H, Rodrigues R, Seward FD, Swift CD, X-Ray Intensities and Spectra from Several Cosmic Sources, Astrophys. J., Oct 1967, 150, 10, 57–65, 1967ApJ...150...57C, 10.1086/149312, free, Balloon observation from Mildura, Australia, on October 24, 1967, of the SMC set an upper limit of X-ray detection.JOURNAL, Lewin WHG, Clark GW, Smith WB, Search for X-rays from the Large and Small Magellanic Clouds, 1968, Nature, 220, 5164, 249–250, 1968Natur.220..249L, 10.1038/220249b0, 4187949, An X-ray astronomy instrument was carried aboard a Thor missile launched from Johnston Atoll on September 24, 1970, at 12:54 UTC for altitudes above 300 km, to search for the Small Magellanic Cloud.JOURNAL, Price RE, 4, Groves DJ, Rodrigues RM, Seward FD, Swift CD, Toor A, X-Rays from the Magellanic Clouds, Astrophys. J., Aug 1971, 168, 8, L7–9, 1971ApJ...168L...7P, 10.1086/180773, free, The SMC was detected with an X-ray luminosity of 5{{e|38}} erg/s in the range 1.5–12 keV, and 2.5{{e|39}} erg/s in the range 5–50 keV for an apparently extended source.The fourth Uhuru catalog lists an early X-ray source within the constellation Tucana: 4U 0115-73 (3U 0115-73, 2A 0116-737, SMC X-1).JOURNAL, Forman W, 4, Jones C, Cominsky L, Julien P, Murray S, Peters G, The fourth Uhuru catalog of X-ray sources, Astrophys. J. Suppl. Ser., 1978, 38, 357, 10.1086/190561, 1978ApJS...38..357F, free, Uhuru observed the SMC on January 1, 12, 13, 16, and 17, 1971, and detected one source located at 01149-7342, which was then designated SMC X-1.JOURNAL, Leong C, 4, Kellogg E, Gursky H, Tananbaum H, Giacconi R, X-Ray Emission from the Magellanic Clouds Observed by UHURU, Astrophys. J., Dec 1971, 170, 12, L67–71, 1971ApJ...170L..67L, 10.1086/180842, Some X-ray counts were also received on January 14, 15, 18, and 19, 1971.BOOK, Tananbaum HD, X- and Gamma-Ray Astronomy, UHURU Results on Galactic X-ray Sources, 55, Bradt H, Giacconi R, International Astronomical Union, 9–28, 1973IAUS...55....9T, Dordrecht, Holland, 1973, 10.1007/978-94-010-2585-0_2, 978-90-277-0337-8, The third Ariel 5 catalog (3A) also contains this early X-ray source within Tucana: 3A 0116-736 (2A 0116-737, SMC X-1).JOURNAL, McHardy IM, Lawrence A, Pye JP, Pounds KA, The Ariel V /3 A/ catalogue of X-ray sources. II - Sources at high galactic latitude /absolute value of B greater than 10 deg/, Monthly Notices of the Royal Astronomical Society, Dec 1981, 197, 4, 893–919, 1981MNRAS.197..893M, 10.1093/mnras/197.4.893, free, The SMC X-1, a HMXRB, is at J2000 right ascension (RA) {{RA|01|15|14}} declination (Dec) {{Dec|73|42|22}}.Two additional sources detected and listed in 3A include SMC X-2 at 3A 0042-738 and SMC X-3 at 3A 0049-726.

Mini Magellanic Cloud (MMC)

It has been proposed by astrophysicists D. S. Mathewson, V. L. Ford and N. Visvanathan that the SMC may in fact be split in two, with a smaller section of this galaxy behind the main part of the SMC (as seen from Earth perspective), and separated by about 30,000 ly. They suggest the reason for this is due to a past interaction with the LMC that split the SMC, and that the two sections are still moving apart. They dubbed this smaller remnant the Mini Magellanic Cloud.JOURNAL, Mathewson, D. S., Ford, V. L., Visvanathan, N., The structure of the Small Magellanic Cloud, The Astrophysical Journal, 301, 1986, 664, 0004-637X, 10.1086/163932, 1986ApJ...301..664M, JOURNAL, Crowl, Hugh H., etal, The Line-of-Sight Depth of Populous Clusters in the Small Magellanic Cloud, The Astronomical Journal, 122, 1, 2001, 220–231, 0004-6256, 10.1086/321128, astro-ph/0104227v1, 2001AJ....122..220C, 45263795, In 2023, it was reported that the SMC is indeed two separate structures with distinct stellar and gaseous chemical compositions, separated by around 5 kiloparsecs.JOURNAL, 2312.07750, Murray, Claire E., Hasselquist, Sten, Peek, Joshua E. G., Christina Willecke Lindberg, Almeida, Andres, Choi, Yumi, Craig, Jessica E. M., Denes, Helga, Dickey, John M., Di Teodoro, Enrico M., Federrath, Christoph, Gerrard, Isabella A., Gibson, Steven J., Leahy, Denis, Lee, Min-Young, Lynn, Callum, Yik Ki Ma, Marchal, Antoine, McClure-Griffiths, N. M., Nidever, David, Nguyen, Hiep, Pingel, Nickolas M., Tarantino, Elizabeth, Uscanga, Lucero, van Loon, Jacco Th., A Galactic Eclipse: The Small Magellanic Cloud is Forming Stars in Two, Superimposed Systems, The Astrophysical Journal, 2023, 962, 2, 120, 10.3847/1538-4357/ad1591, free, 2024ApJ...962..120M,

See also

• Large Magellanic Cloud
• Magellanic Clouds
• Objects within the Small Magellanic Cloud:
  • NGC 265
  • NGC 290
  • NGC 346
  • NGC 602

References

{{Reflist|30em}}

External links

{{Commons category}}

• NASA Extragalactic Database entry on the SMC
• SEDS entry on the SMC
• SMC at ESA/Hubble {{Webarchive|url=https://web.archive.org/web/20070927184702weblink |date=2007-09-27 }}
• Astronomy Picture of the Day 2010 January 7 The Tail of the Small Magellanic Cloud - Likely stripped from the galaxy by gravitational tides, the tail contains mostly gas, dust, and newly formed stars.

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