Звездано јато

С Википедије, слободне енциклопедије
Глобуларно јато M15 у чијем центру се налази и црна рупа

Звездано јато је бројнији (барем пар десетина чланова) систем звезда у галаксији које су гравитациони везане. Битно за звездана јата јесте чињеница да су звезде у једном јату настале готово истовремено, што значи да имају исти хемијски састав.

Подела[уреди | уреди извор]

Постоје две врсте звезданих јата:

  • Збијена (глобуларна, кугласта, затворена) јата

Збијена јата[уреди | уреди извор]

Збијена (или глобуларна, кугласта, затворена) звездана јата су велики системи звезда који садрже од неколико стотина па до више стотина хиљада чланова. То су веома стари системи које су настајали заједно са формирањем галаксија. Што значи да им старост иде и до 13 милијарди година, па се у њима налазе веома старе звезде. Налазе се у халоу галаксије и гравитационо су изузетно стабилна.

Расејана јата[уреди | уреди извор]

Расејана или отворена јата су мања од глобуларних јата. Садрже до неколико стотина звезда. То су млади системи звезда са младим звездама, старости до неколико милиона година. Гравитационо су нестабилна и временом звезде полако напуштају систем, и због тога се временом расипају. Налазе се само у диску галаксије. Врло често се налазе у маглини гаса од које је и настало јато (види слику десно).

Отворени кластер[уреди | уреди извор]

The Pleiades, an open cluster dominated by hot blue stars surrounded by reflection nebulosity

Open clusters are very different from globular clusters. Unlike the spherically distributed globulars, they are confined to the galactic plane, and are almost always found within spiral arms. They are generally young objects, up to a few tens of millions of years old, with a few rare exceptions as old as a few billion years, such as Messier 67 (the closest and most observed old open cluster) for example.[1] They form H II regions such as the Orion Nebula.

Establishing precise distances to open clusters enables the calibration of the period-luminosity relationship shown by Cepheids variable stars, which are then used as standard candles. Cepheids are luminous and can be used to establish both the distances to remote galaxies and the expansion rate of the Universe (Hubble constant). Indeed, the open cluster NGC 7790 hosts three classical Cepheids which are critical for such efforts.[2][3]

Embedded cluster[уреди | уреди извор]

The embedded Trapezium cluster seen in X-rays which penetrate the surrounding clouds
Star cluster NGC 3572 and its surroundings

Embedded clusters are groups of very young stars that are partially or fully encased in an Interstellar dust or gas which is often impervious to optical observations. Embedded clusters form in molecular clouds, when the clouds begin to collapse and form stars. There is often ongoing star formation in these clusters, so embedded clusters may be home to various types of young stellar objects including protostars and pre-main-sequence stars. An example of an embedded cluster is the Trapezium Cluster in the Orion Nebula. In ρ Ophiuchi cloud (L1688) core region there is an embedded cluster.[4]

The embedded cluster phase may last for several million years, after which gas in the cloud is depleted by star formation or dispersed through radiation pressure, stellar winds and outflows, or supernova explosions. In general less than 30% of cloud mass is converted to stars before the cloud is dispersed, but this fraction may be higher in particularly dense parts of the cloud. With the loss of mass in the cloud, the energy of the system is altered, often leading to the disruption of a star cluster. Most young embedded clusters disperse shortly after the end of star formation.[5]

The open clusters found in the Galaxy are former embedded clusters that were able to survive early cluster evolution. However, nearly all freely floating stars, including the Sun,[6] were originally born into embedded clusters that disintegrated.[5]

Globular cluster[уреди | уреди извор]

The globular cluster Messier 15 photographed by HST

Globular clusters are roughly spherical groupings of from 10 thousand to several million stars packed into regions of from 10 to 30 light-years across. They commonly consist of very old Population II stars – just a few hundred million years younger than the universe itself – which are mostly yellow and red, with masses less than two solar masses.[7] Such stars predominate within clusters because hotter and more massive stars have exploded as supernovae, or evolved through planetary nebula phases to end as white dwarfs. Yet a few rare blue stars exist in globulars, thought to be formed by stellar mergers in their dense inner regions; these stars are known as blue stragglers.

Super star cluster[уреди | уреди извор]

Super star clusters are very large regions of recent star formation, and are thought to be the precursors of globular clusters. Examples include Westerlund 1 in the Milky Way.[8]

Intermediate forms[уреди | уреди извор]

Messier 68, a loose globular cluster whose constituent stars span a volume of space more than a hundred light-years across

In 2005, astronomers discovered a new type of star cluster in the Andromeda Galaxy, which is, in several ways, very similar to globular clusters although less dense. No such clusters (which also known as extended globular clusters) are known in the Milky Way. The three discovered in Andromeda Galaxy are M31WFS C1[9] M31WFS C2, and M31WFS C3.

These new-found star clusters contain hundreds of thousands of stars, a similar number to globular clusters. The clusters also share other characteristics with globular clusters, e.g. the stellar populations and metallicity. What distinguishes them from the globular clusters is that they are much larger – several hundred light-years across – and hundreds of times less dense. The distances between the stars are thus much greater. The clusters have properties intermediate between globular clusters and dwarf spheroidal galaxies.[10]

How these clusters are formed is not yet known, but their formation might well be related to that of globular clusters. Why M31 has such clusters, while the Milky Way has not, is not yet known. It is also unknown if any other galaxy contains this kind of clusters, but it would be very unlikely that M31 is the sole galaxy with extended clusters.[10]

Another type of cluster are faint fuzzies which so far have only been found in lenticular galaxies like NGC 1023 and NGC 3384. They are characterized by their large size compared to globular clusters and a ringlike distribution around the centres of their host galaxies. As the latter they seem to be old objects.[11]

Star cloud[уреди | уреди извор]

Scutum Star Cloud with open cluster Messier 11 at lower left

Technically not star clusters, star clouds are large groups of many stars within a galaxy, spread over very many light-years of space. Often they contain star clusters within them. The stars appear closely packed, but are not usually part of any structure.[12] Within the Milky Way, star clouds show through gaps between dust clouds of the Great Rift, allowing deeper views along our particular line of sight.[13] Star clouds have also been identified in other nearby galaxies.[14] Examples of star clouds include the Large Sagittarius Star Cloud, Small Sagittarius Star Cloud, Scutum Star Cloud, Cygnus Star Cloud, Norma Star Cloud, and NGC 206 in the Andromeda Galaxy.

Nomenclature[уреди | уреди извор]

In 1979, the International Astronomical Union's 17th general assembly recommended that newly discovered star clusters, open or globular, within the Galaxy have designations following the convention "Chhmm±ddd", always beginning with the prefix C, where h, m, and d represent the approximate coordinates of the cluster centre in hours and minutes of right ascension, and degrees of declination, respectively, with leading zeros. The designation, once assigned, is not to change, even if subsequent measurements improve on the location of the cluster centre.[15] The first of such designations were assigned by Gosta Lynga in 1982.[16][17]

Референце[уреди | уреди извор]

  1. ^ Brent A. Archinal; Steven J. Hynes (2003). Star Clusters. Willmann-Bell. ISBN 978-0-943396-80-4. 
  2. ^ Sandage, Allan (1958). „Cepheids in Galactic Clusters. I. CF Cass in NGC 7790”. The Astrophysical Journal. 128: 150. Bibcode:1958ApJ...128..150S. doi:10.1086/146532. 
  3. ^ Majaess, D.; Carraro, G.; Moni Bidin, C.; Bonatto, C.; Berdnikov, L.; Balam, D.; Moyano, M.; Gallo, L.; Turner, D.; Lane, D.; Gieren, W.; Borissova, J.; Kovtyukh, V.; Beletsky, Y. (2013). „Anchors for the cosmic distance scale: The Cepheids U Sagittarii, CF Cassiopeiae, and CEab Cassiopeiae”. Astronomy & Astrophysics. 560: A22. Bibcode:2013A&A...560A..22M. S2CID 55934597. arXiv:1311.0865Слободан приступ. doi:10.1051/0004-6361/201322670. 
  4. ^ Greene, Thomas P; Meyer, Michael R (1995). „An Infrared Spectroscopic Survey of the rho Ophiuchi Young Stellar Cluster: Masses and Ages from the H-R Diagram”. Astrophysical Journal. 450: 233. Bibcode:1995ApJ...450..233G. doi:10.1086/176134. 
  5. ^ а б Lada, Charles J.; Lada, Elizabeth A. (2003). „Embedded Clusters in Molecular Clouds”. Annual Review of Astronomy and Astrophysics. 41 (1): 57—115. Bibcode:2003ARA&A..41...57L. ISSN 0066-4146. S2CID 16752089. arXiv:astro-ph/0301540Слободан приступ. doi:10.1146/annurev.astro.41.011802.094844. 
  6. ^ Gounelle, M.; Meynet, G. (2012-08-27). „Solar system genealogy revealed by extinct short-lived radionuclides in meteorites”. Astronomy & Astrophysics. EDP Sciences. 545: A4. Bibcode:2012A&A...545A...4G. ISSN 0004-6361. S2CID 54970631. arXiv:1208.5879Слободан приступ. doi:10.1051/0004-6361/201219031. 
  7. ^ Dinwiddie, Robert; Gater, Will; Sparrow, Giles; Stott, Carole (2012). Stars and Planets. Nature Guide. DK. стр. 14, 134—137. ISBN 978-0-7566-9040-3. 
  8. ^ „Young and Exotic Stellar Zoo: ESO's Telescopes Uncover Super Star Cluster in the Milky Way”. ESO. 2005-03-22. Архивирано из оригинала на датум 2017-12-01. Приступљено 2017-11-27. 
  9. ^ „@1592523”. u-strasbg.fr. Приступљено 28. 4. 2018. 
  10. ^ а б A. P. Huxor; N. R. Tanvir; M.J. Irwin; R. Ibata (2005). „A new population of extended, luminous, star clusters in the halo of M31”. Monthly Notices of the Royal Astronomical Society. 360 (3): 993—1006. Bibcode:2005MNRAS.360.1007H. S2CID 6215035. arXiv:astro-ph/0412223Слободан приступ. doi:10.1111/j.1365-2966.2005.09086.x. 
  11. ^ A. Burkert; J. Brodie; S. Larsen 3 (2005). „Faint Fuzzies and the Formation of Lenticular Galaxies”. The Astrophysical Journal. 628 (1): 231—235. Bibcode:2005ApJ...628..231B. S2CID 11466131. arXiv:astro-ph/0504064Слободан приступ. doi:10.1086/430698. 
  12. ^ Patrick Moore (2005). The Observer's Year: 366 Nights in the Universe. Springer. стр. 199. ISBN 1-85233-884-9. 
  13. ^ Bob King (2016-07-13). „Paddle the Milky Way's Dark River”. skyandtelescope.org. Приступљено 2020-09-29. 
  14. ^ Bob King (2016-10-05). „Resolving Andromeda - How to See Stars 2.5 Million Light-Years Away”. skyandtelescope.org. Приступљено 2020-09-20. 
  15. ^ XVIIth General Assembly (PDF) (14–23 August 1979). Montreal, Canada: International Astronomical Union. лето 1979. стр. 13. Архивирано (PDF) из оригинала на датум 18. 1. 2015. Приступљено 18. 12. 2014. 
  16. ^ Lynga, G. (октобар 1982). „IAU numbers for some recently discovered clusters”. Bulletin d'Information du Centre de Données Stellaires. 23: 89. Bibcode:1982BICDS..23...89L. 
  17. ^ „Dictionary of Nomenclature of Celestial Objects”. Simbad. Centre de données astronomiques de Strasbourg. 1. 12. 2014. Архивирано из оригинала на датум 8. 10. 2014. Приступљено 21. 12. 2014. 

Литература[уреди | уреди извор]

Спољашње везе[уреди | уреди извор]