Small Magellanic Cloud

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Galaxy
Small Magellanic Cloud
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The Small Magellanic Cloud on an image taken by the Gaia Space Telescope
The Small Magellanic Cloud on an image taken by the Gaia Space Telescope
AladinLite
Constellation Toucan
Position
equinox :  J2000.0 , epoch : J2000.0
Right ascension 00 h 52 m 44 s
declination −72 ° 49 ′ 42 ″
Appearance
Morphological type SB (s) m pec  
Brightness  (visual) 1.87 mag
Angular expansion 5.3 ° x 3.4 °
Physical data
Affiliation Local group  
Redshift 0.00053 ± 0.00001  
Radial velocity 158 ± 4 km / s  
distance approx. 200,000  ly  
Metallicity [Fe / H] −0.74
story
Catalog names
NGC  292 • PGC  003085 •

The Small Magellanic Cloud , KMW for short or SMC (from English Small Magellanic Cloud ), Latin Nubecula Minor , is an irregular galaxy of the Local Group . At a distance of about 200,000 light years, it is relatively close to the Milky Way and is located in the night sky on the border between the constellation Toucan and the Little Water Snake . With a diameter of about 7000 light years, it is much smaller than the Milky Way. Like the Large Magellanic Cloud , it is an object of the southern sky and therefore not visible from Central Europe . The inhabitants of the southern hemisphere have always known the Magellanic Clouds, for example they are mentioned in some Aboriginal myths . With the advent of global seafaring at the beginning of the 16th century, the Small Magellanic Cloud was also noticed by Europeans. From the 19th century onwards it found increasing scientific attention. Their character as an object outside the galaxy could only be identified in the 1920s.

Adjacent to the Small Magellanic Cloud are the Magellanic Bridge and the Magellanic Current, two elongated HI regions that connect the two Magellanic Clouds with each other or with the Milky Way. The structure of the Small Magellanic Cloud was significantly influenced by the gravitational influences of the Large Magellanic Cloud and the Milky Way, although it is unclear whether it is gravitationally bound to its neighboring galaxies or just passing by by chance. As one of the closest extragalactic objects, the Small Magellanic Cloud is an important research object for exploring the universe outside the Milky Way.

History of exploration

Location of the Small Magellanic Cloud (Nubecula Minor) at the foot of the Toucan constellation, Uranometria , 1603

Until the 16th century, the Small Magellanic Cloud was unknown in Europe due to its location. In some Aboriginal legends , the two magellanic clouds play a role. While the Large Magellanic Cloud was already described by the Persian astronomer al-Sufi around 964 in the Book of Fixed Stars , the first known European description of the Small Magellanic Cloud dates back to 1515, when it was discovered by the Italian explorer Andrea Corsali on a trip to Kochi was noticed. Corsali's travelogue found its way into the work De Rebus Oceanicis et Novo Orbe by Petrus Martyr von Anghiera . However, the description of the chronicler Antonio Pigafetta , who observed the Magellanic Clouds in January 1521 as part of Ferdinand Magellan's circumnavigation over the South Pacific, gained greater fame . In Johann Bayer's 1603 celestial atlas Uranometria , the Small Magellanic Cloud is listed as Nubecula Minor (small cloud).

In 1837, John Herschel observed the Magellanic Clouds from the Royal Observatory, Cape of Good Hope , Cape Town . He was able to make out 200 individual stars, 37 nebulae and seven star clusters in the Small Magellanic Cloud. Herschel described the two clouds as "remarkable objects" and said that nowhere else in the sky are there as many stars and nebulae in as little space. As early as 1867, Cleveland Abbe concluded that the Magellanic Clouds were galaxies separate from the Milky Way .

In spring 1904, the American astronomer began Henrietta Swan Leavitt in photographs of Boyden Observatory in Arequipa , Peru , to variable stars to be found in the Magellanic Clouds. In a document from 1908, she noted 969 variable stars and noted, based on 16 stars, that brighter stars had a longer period. Four years later, in a publication by Edward Charles Pickering , Leavitt discovered the period-luminosity relationship of Cepheids based on nine other stars from the Small Magellanic Cloud , which made a significant contribution to the further development of distance measurement at great astronomical distances. In 1913, Ejnar Hertzsprung then used this measurement on Cepheids to calculate a first estimate of the distance for the Small Magellanic Cloud, which at 10 kilo parsec (32,600 light years) was, however, still a long way from today's estimate.

During the Shapley-Curtis debate at the beginning of the 1920s, it emerged that the Magellanic Clouds, like the Andromeda Nebula, are objects outside the Milky Way. Harlow Shapley initially advocated the thesis that there is a single galaxy with the Milky Way and that nebulae like the Magellanic Clouds are part of this galaxy. However, investigations by Edwin Hubble on the Andromeda Galaxy showed that it was far outside the Milky Way, which refuted Shapley's thesis. Shapley contributed to much of the early scientific knowledge of Magellanic Clouds in the first half of the 20th century. In 1924, he estimated the distance to the Small Magellanic Cloud to be 31.6 kiloparsecs, which is about 103,000 light years.

structure

The Small Magellanic Cloud is mostly classified as an irregular dwarf galaxy , but it also has features of a barred spiral galaxy . In the middle it has a weak bar with a "wing" on the east side. According to recent studies, based on data from the Gaia space telescope , the "wing" is moving at a speed of 64 ± 10 km / s towards the Large Magellanic Cloud and is thus moving away from the rest of the galaxy, which is evidence of a collision between Large and Small Magellanic Clouds are considered hundreds of millions of years ago. A study by Donald S. Mathewson, VL Ford and N. Visvanathan by the Australian National University in 1985 assumed that the Small Magellanic Cloud had been torn in two by a collision with its larger counterpart two hundred million years ago. It was assumed that there are two galaxies with a distance of about 12 kiloparsecs (≈ 39,000 light years), which lie on a line of sight and move away from each other at 15 km / s. The star distribution in the Small Magellanic Cloud also suggests past interactions with the Large Magellanic Cloud. Stars with an age of 1.5 to 4 billion years are unevenly distributed, in the direction of the Large Magellanic Cloud there are more stars of this age.

Between the Milky Way and the Small Magellanic Cloud there is a high-speed cloud of neutral hydrogen , the Magellanic Current . The Magellanic Bridge , also a HI area , connects the two Magellanic Clouds with each other. The Small Magellanic Cloud has a relatively high star formation rate , which is presumably due to gravitational interactions with the Large Magellanic Cloud and the Milky Way. Over half of the stars that ever formed in the Small Magellanic Cloud were formed over 8.4 billion years ago. Then relatively few stars formed in a quieter phase until about three billion years ago. Since then, the galaxy has been more active again, with upward eruptions 2.4 billion years ago, 0.4 billion years ago and 60 million years ago. It was in relative proximity to the Milky Way on the first two of these climbs.

Location of the Small Magellanic Cloud (SMC) in the constellation Toucan (left)

The galaxy is located in the southern sky on the border between the constellations Toucan and Little Water Snake , which means that it cannot be observed from Central Europe. It can only be observed temporarily south of 17 degrees north latitude . The galaxy is only visible to the naked eye in good weather conditions, because its brightness of around two magnitudes is distributed in the sky over a comparatively large arc angle of just under five degrees, which is roughly ten times the diameter of the moon. Their actual diameter is about 7,000 light years.

Gravitational binding to neighboring galaxies

Position of the Magellanic Clouds relative to the Milky Way. Abbreviations:
GMW - Large Magellanic Cloud
KMW - Small Magellanic Cloud
GSP - Galactic South Pole
MSI - First hydrogen compression in the Magellanic Current
3 - 30 Doradus
W. - Wing of the KMW
The green arrow indicates the direction of rotation of the Magellanic Clouds around the center of the Milky Way.

It is not clear whether the Magellanic Clouds are gravitationally bound to the Milky Way. At first, this was the popular belief. Observations by Nitya Kallivayalil et al. with the Hubble Space Telescope from 2006, however, showed that the two galaxies may only be passing the Milky Way. By comparing the position of stars in the Magellanic Clouds with distant quasars, it was possible to determine a significantly higher proper motion of the two galaxies than had previously been assumed. According to this, the Small Magellanic Cloud moves through space at around 302 km / s. The Small Magellanic Cloud would either pass the Milky Way or the galaxy's mass would be at least twice as large as previously assumed. A possible gravitational binding to the Large Magellanic Cloud was also questioned by Nitya Kallivayalil as well as Roeland P. van der Marel and Charles R. Alcock . Both galaxies are currently moving away from each other at 105 ± 42 km / s.

distance

A research team Dariusz Graczyk identified in 2013 as part of the Araucaria Projects , which is concerned with the measurement of inter-galactic distances, based on four eclipsing binaries later type with an uncertainty of about three percent of a distance of 62.1 ± 1.9 kiloparsec (≈ 202,500 Light years). Previously, RW Hilditch, ID Howarth and TJ Harries had calculated a distance of 60.6 ± 1.0 kpc (≈ 198,000 ly) in 2004 by measuring 50 eclipsing stars of spectral classes O and B.

Dimensions

Jason Harris and Dennis Zaritsky determined 2006 by the examination of the velocity distribution of 2046 red giant a mass of 1.4-1.9  ·  10 9 solar masses (M ☉ ) in a radius of 1.6 kiloparsec (≈ 5200 light-years) as well as of 2 , 7–5.1  ·  10 9 M ☉ in a radius of three kiloparsecs (≈ 9800 light years). Most models give an estimate for the total mass of 1.4–3  ·  10 9 M ☉ . However, this value is strongly dependent on the influence of the postulated dark matter .

Web links

Commons : Small Magellanic Cloud  - collection of images, videos and audio files

References and comments

  1. ↑ a b c d Small Magellanic Cloud (SMC). In: NASA / IPAC Extragalactic Database. Retrieved March 5, 2020 .
  2. ^ A b c Warren H. Finlay: Concise Catalog of Deep-Sky Objects. Springer-Verlag, 2014, ISBN 978-3-319-03169-9 , p. 154.
  3. ^ R. Earle Luck, Thomas J. Moffett, Thomas G. Barnes III, Wolfgang P. Gieren: Magellanic Cloud Cepheids: Abundances . In: Astronomical Journal . Volume 115, Issue 2, pp. 605-635. doi: 10.1086 / 300227
  4. ^ Helaine Selin: Astronomy Across Cultures: A History of Non-Western Astronomy. Springer-Verlag, 2000, ISBN 978-94-010-5820-9 , pp. 79-83 ( available online ).
  5. ↑ Alexander von Humboldt : Critical studies on the historical development of the geographical knowledge of the New World and the progress of nautical astronomy in the 15th and 16th centuries. Volume 2, Berlin 1836 ( p. 175 ).
  6. ^ Helen Sawyer Hogg : Out of Old Books (From Humboldt's Account of the Magellanic Clouds). In: Journal of the Royal Astronomical Society of Canada. Volume 41, p. 357. bibcode : 1947JRASC..41..357S .
  7. ↑ Stephen James O'Meara: Deep-Sky Companions: The Caldwell Objects. Cambridge University Press, Cambridge 2016, ISBN 978-1-107-08397-4 , p. 483.
  8. ^ Johann Bayer: Uranometria . ( available online, p. 110. )
  9. ^ Helen Sawyer Hogg: Out of Old Books (From Humboldt's Account of the Magellanic Clouds). In: Journal of the Royal Astronomical Society of Canada. Volume 41, p. 360. bibcode : 1947JRASC..41..357S .
  10. ^ Paul William Hodge : Magellanic Cloud Studies, Past and Future. In: New Views of the Magellanic Clouds. IAU Symposium # 190, 1999, ISBN 1-58381-021-8 , p. 3. bibcode : 1999IAUS..190 .... 3H .
  11. ↑ D. Wattenberg: The Magellanic Clouds . In: Astronomical News . Volume 237, p. 27. doi: 10.1002 / asna.19292372402 .
  12. ↑ Aparna Vidyasagar: How Henrietta Swan Leavitt Helped Build a Yardstick to Measure the Universe. On: kcet.org of November 14, 2019, accessed on March 10, 2019.
  13. ^ John Gribbin : The Birth of Time: How Astronomers Measured the Age of the Universe . Yale University Press, 1999, ISBN 978-0-300-08914-1 , p. 89.
  14. ↑ Bart J. Bok : Shapley's Researches on the Magellanic Clouds. In: Publications of the Astronomical Society of the Pacific . Volume 77, No. 459, pp. 416-420. bibcode : 1965PASP ... 77..416B .
  15. ↑ Harlow Shapley: The Magellanic Clouds, III. The Distance and Linear Dimensions of the Large Cloud. In: Harvard College Observatory Circular . Volume 268, pp. 1-4. bibcode : 1924HarCi.268 .... 1S .
  16. ^ Richard Taibi: Charles Olivier and the Rise of Meteor Science. Springer-Verlag, 2016, ISBN 978-3-319-83071-1 , pp. 144-145.
  17. ↑ Nick Carne: Confirmed: two galaxies near the Milky Way collided 'recently.' In: Cosmos of October 26, 2018, accessed on March 10, 2020.
  18. ^ Sally Oey et al .: Resolved Kinematics of Runaway and Field OB Stars in the Small Magellanic Cloud . In: The Astrophysical Journal Letters. Volume 867. October 24, 2018. arxiv : 1810.06596 .
  19. ↑ A NEW GALAXY IS SIGHTED IN THE EARTH'S 'BACKYARD'. In: The New York Times of November 8, 1983, accessed March 10, 2020.
  20. ^ DS Mathewson, VL Ford, N. Visvanathan: The Structure of the Small Magellanic Cloud. In: Astrophysical Journal. Volume 301, pp. 664-674. bibcode : 1986ApJ ... 301..664M , doi: 10.1086 / 163932 .
  21. ^ Dougal Mackey et al .: Substructures and Tidal Distortions in the Magellanic Stellar Periphery. In: The Astrophysical Journal Letters . Volume 858, No. 2. doi: 10.3847 / 2041-8213 / aac175 .
  22. ↑ Alessio Mucciarelli: The chemical composition of the Small Magellanic Cloud. In: Astronomical Notes . Volume 335, Ausgust 1. arxiv : 1310.6888 .
  23. ^ Jason Harris, Dennis Zaritsky: The Star Formation History of the Small Magellanic Cloud. In: The Astronomical Journal. Volume 127, pp. 1531-1544, doi: 10.1086 / 381953 .
  24. ^ G. Indu, A. Subramaniam: The recent star-formation history of the Largeand Small Magellanic Clouds. In: Astronomy & Astrophysics. Volume 535, doi: 10.1051 / 0004-6361 / 201117298 .
  25. ^ Larry Sessions: Small Magellanic Cloud orbits Milky Way. On: earthsky.org October 31, 2017, accessed March 31, 2020.
  26. ^ Nola Taylor Redd: Small Magellanic Cloud: A Satellite Dwarf Galaxy Neighbor. From: space.com on December 13, 2018, accessed on March 31, 2020.
  27. ↑ Graphics from stars and space . Issue 5/98
  28. ↑ In 2006 the assumption was about 10 12 solar masses, more recent observations from Gaia suggest about one and a half times this value.
  29. ↑ Magellanic Clouds May Be Just Passing Through. In: Harvard-Smithsonian Center for Astrophysics . dated January 9, 2007 (English).
  30. ↑ Gurtina Besla, Nitya Kallivayalil et al .: Are the Magellanic Clouds on their First Passage about the Milky Way? In: The Astrophysical Journal . Volume 668, pp. 949-967, arxiv : astro-ph / 0703196 .
  31. ↑ Nitya Kallivayalil, Roeland P. van der Marel, Charles Alcock: Is the SMC Bound to the LMC? The HST Proper Motion of the SMC. In: The Astrophysical Journal . Volume 652, pp. 1213-1229, doi: 10.1086 / 508014 .
  32. ^ Dariusz Graczyk et al .: The Araucaria Project. The distance to the Small Magellanic Cloud from late-type eclipsing binaries. November 11, 2013. arxiv : 1311.2340 .
  33. ↑ RW Hilditch, ID Howarth, TJ Harries: Forty eclipsing binaries in the Small Magellanic Cloud: fundamental parameters and Cloud distance. In: Monthly Notices of the Royal Astronomical Society . Volume 357, pp. 304-324, arxiv : astro-ph / 0411672 .
  34. ^ Jason Harris, Dennis Zaritsky: Spectroscopic Survey of Red Giants in the Small Magellanic Cloud. I. Kinematics. In: The Astronomical Journal. Volume 131, No. 5, doi: 10.1086 / 500974 .
  35. ↑ Gurtina Besla: The orbits and Total Mass of the Magellanic Clouds. University of Arizona, 2015, arxiv : 1511.03346 .
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