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A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity,with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars,all orbiting in a stable,compact formation. Globular clusters are similar in form to dwarf spheroidal galaxies,and the distinction between the two is not always clear. Their name is derived from Latin globulus. Globular clusters are occasionally known simply as "globulars".
Star clusters are large groups of stars held together by self-gravitation. Two main types of star clusters can be distinguished:globular clusters are tight groups of ten thousand to millions of old stars which are gravitationally bound,while open clusters are more loosely clustered groups of stars,generally containing fewer than a few hundred members,and are often very young. Open clusters become disrupted over time by the gravitational influence of giant molecular clouds as they move through the galaxy,but cluster members will continue to move in broadly the same direction through space even though they are no longer gravitationally bound;they are then known as a stellar association,sometimes also referred to as a moving group.
A blue straggler is a type of star that is more luminous and bluer than expected. Typically identified in a stellar cluster,they have a higher effective temperature than the main sequence turnoff point for the cluster,where ordinary stars begin to evolve towards the red giant branch. Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry of the stars in the globular cluster M3.
Messier 4 or M4 is a globular cluster in the constellation of Scorpius. It was discovered by Philippe Loys de Chéseaux in 1745 and catalogued by Charles Messier in 1764. It was the first globular cluster in which individual stars were resolved.
The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph),also known as the Sagittarius Dwarf Elliptical Galaxy,is an elliptical loop-shaped satellite galaxy of the Milky Way. It contains four globular clusters in its main body,with the brightest of them—NGC 6715 (M54)—being known well before the discovery of the galaxy itself in 1994. Sgr dSph is roughly 10,000 light-years in diameter,and is currently about 70,000 light-years from Earth,travelling in a polar orbit at a distance of about 50,000 light-years from the core of the Milky Way. In its looping,spiraling path,it has passed through the plane of the Milky Way several times in the past. In 2018 the Gaia project of the European Space Agency showed that Sgr dSph had caused perturbations in a set of stars near the Milky Way's core,causing unexpected rippling movements of the stars triggered when it moved past the Milky Way between 300 and 900 million years ago.
Omega Centauri is a globular cluster in the constellation of Centaurus that was first identified as a non-stellar object by Edmond Halley in 1677. Located at a distance of 17,090 light-years,it is the largest-known globular cluster in the Milky Way at a diameter of roughly 150 light-years. It is estimated to contain approximately 10 million stars,with a total mass of 4 million solar masses,making it the most massive known globular cluster in the Milky Way.
Messier 2 or M2 is a globular cluster in the constellation Aquarius,five degrees north of the star Beta Aquarii. It was discovered by Jean-Dominique Maraldi in 1746,and is one of the largest known globular clusters.
Messier 54 is a globular cluster in the constellation Sagittarius. It was discovered by Charles Messier in 1778 and then included in his catalog of comet-like objects.
Messier 69 or M69,also known NGC 6637,is a globular cluster in the southern constellation of Sagittarius. It can be found 2.5°to the northeast of the star Epsilon Sagittarii and is dimly visible in 50 mm aperture binoculars. The cluster was discovered by Charles Messier on August 31,1780,the same night he discovered M70. At the time,he was searching for an object described by Nicolas-Louis de Lacaille in 1751–2 and thought he had rediscovered it,but it is unclear if Lacaille actually described M69.
Messier 92 is a globular cluster of stars in the northern constellation of Hercules.
47 Tucanae or 47 Tuc is a globular cluster located in the constellation Tucana. It is about 4.45 ± 0.01 kpc (15,000 ± 33 ly) from Earth,and 120 light years in diameter. 47 Tuc can be seen with the naked eye,with an apparent magnitude of 4.1. It appears about 44 arcminutes across including its far outreaches. Due to its far southern location,18°from the south celestial pole,it was not catalogued by European astronomers until the 1750s,when the cluster was first identified by Nicolas-Louis de Lacaille from South Africa.
The Canis Major Overdensity or Canis Major Dwarf Galaxy is a disputed dwarf irregular galaxy in the Local Group,located in the same part of the sky as the constellation Canis Major.
The Fornax Dwarf Spheroidal is an elliptical dwarf galaxy in the constellation Fornax that was discovered in 1938 by Harlow Shapley. He discovered it while he was in South Africa on photographic plates taken by the 24 inch (61 cm) Bruce refractor at Boyden Observatory,shortly after he discovered the Sculptor Dwarf Galaxy.
NGC 3201 is a low galactic latitude globular cluster in the southern constellation of Vela. It has a very low central concentration of stars. This cluster was discovered by James Dunlop on May 28,1826 and listed in his 1827 catalogue. He described it as "a pretty large pretty bright round nebula,4′ or 5′ diameter,very gradually condensed towards the centre,easily resolved into stars;the figure is rather irregular,and the stars are considerably scattered on the south".
NGC 2808 is a globular cluster in the constellation Carina. The cluster belongs to the Milky Way,and is one of our home galaxy's most massive clusters,containing more than a million stars. It is estimated to be 12.5-billion years old.
Terzan 5 is a heavily obscured globular cluster belonging to the bulge of the Milky Way galaxy. It was one of six globulars discovered by French astronomer Agop Terzan in 1968 and was initially labeled Terzan 11. The cluster was cataloged by the Two-Micron Sky Survey as IRC–20385. It is situated in the Sagittarius constellation in the direction of the Milky Way's center. Terzan 5 probably follows an unknown complicated orbit around the center of the galaxy,but currently it is moving towards the Sun with a speed of around 90 km/s.
NGC 121 is a globular cluster of stars in the southern constellation of Tucana. It is the oldest globular cluster in the Small Magellanic Cloud (SMC),which is a dwarf satellite galaxy of the Milky Way. This cluster was first discovered by English astronomer John Herschel on September 20,1835. The compiler of the New General Catalogue,Danish astronomer John Louis Emil Dreyer,described this object as "pretty bright,pretty small,little extended,very gradually brighter middle". The cluster is located at a distance of around 200,000 light-years (60 kpc) from the Sun.
NGC 5053 is the New General Catalogue designation for a globular cluster in the northern constellation of Coma Berenices. It was discovered by German-British astronomer William Herschel on March 14,1784 and cataloged as VI-7. In his abbreviated notation,he described it as,"an extremely faint cluster of extremely small stars with resolvable nebula 8 or 10′diameter,verified by a power of 240,beyond doubt". Danish-Irish astronomer John Louis Emil Dreyer reported in 1888 that the cluster appeared,"very faint,pretty large,irregular round shape,growing very gradually brighter at the middle".
Bedin I is a dwarf spheroidal galaxy located in the constellation Pavo. It is situated around 28.38 million light-years from Earth,behind the globular cluster NGC 6752. Bedin I is possibly one of the oldest galaxies known,having formed around 10–13 billion years ago,and is one of the most isolated dwarf galaxies known,situated around 2.12 million light-years away from NGC 6744,its nearest neighbor with which it may be physically associated. As such,it has been deemed by astronomers as a "fossil" from the early universe. It was accidentally discovered by Italian astronomer Luigi Bedin,whose team was studying white dwarfs in NGC 6752 using the Hubble Space Telescope in September 2018;the discovery was announced in a paper published in January 2019.
The Palomar globular clusters are some of the faintest of all globular clusters in the Milky Way galaxy,and been discovered in the 1950s on the survey plates of the first Palomar Observatory Sky Survey (POSS). In total there are 15 Palomar globular clusters,which include Palomar 1,Palomar 2,Palomar 3,Palomar 4,Palomar 5,Palomar 6,Palomar 7,Palomar 8,Palomar 9,Palomar 10,Palomar 11,Palomar 12,Palomar 13,Palomar 14,and Palomar 15. Some Palomar Globulars,like Palomar 6,Palomar 7,Palomar 9,Palomar 10 and Palomar 11 are clusters of average size located nearby,yet obscured in our line of sight by dust. Other Palomar globulars,like Palomar 3,Palomar 4 and Palomar 14 are giants located in the far outer halo of the Milky Way. Some even originated from a different galaxy,such as Palomar 12 from the Sagittarius Dwarf Spheroidal Galaxy,which is now known as a satellite of the Milky Way. Observation of different Palomar globulars greatly varies in the degree of difficulty depending on the cluster. Some are small and compact,others are very sparse,to the point where they may be hard to distinguish from foreground stars.
References
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- 1 2 "Ata Sarajedini". scholar.google.com.
- 1 2 "1995 Hubble Fellows to Study HST Discoveries".
- 1 2 "NSF Award Search: Award # 0094048 - CAREER: Stellar Populations in the Local Volume". www.nsf.gov.
- 1 2 "Ata Sarajedini, Ph.D. – UFRF Professors".
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- 1 2 "AAS Journals Editorial Board".
- ↑ "Sarajedini, Ata".
- ↑ "Sarajedini appointed associate dean in CLAS - News - University of Florida". news.ufl.edu.
- ↑ "Dean of the Charles E. Schmidt College of Science Announced". www.fau.edu.
- ↑ "Ata Sarajedini, Ph.D., Installed as Inaugural Bjorn Lamborn Endowed Chair in Astrophysics". Florida Atlantic University.
- ↑ "Ata Sarajedini Selected as Chair of Hubble Space Telescope Time Allocation Committee : Florida Atlantic University - Charles E. Schmidt College of Science". physics.fau.edu.
- ↑ "Host". Star Gazers 2.
- ↑ Sarajedini, Ata; Bedin, Luigi R.; Chaboyer, Brian; Dotter, Aaron; Siegel, Michael; Anderson, Jay; Aparicio, Antonio; King, Ivan; Majewski, Steven; Marín-Franch, A.; Piotto, Giampaolo; Reid, I. Neill; Rosenberg, Alfred (March 12, 2007). "The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters without PreviousHubble Space TelescopePhotometry". The Astronomical Journal. 133 (4): 1658–1672. arXiv: astro-ph/0612598 . doi:10.1086/511979.
- ↑ Piotto, G.; Milone, A. P.; Bedin, L. R.; Anderson, J.; King, I. R.; Marino, A. F.; Nardiello, D.; Aparicio, A.; Barbuy, B.; Bellini, A.; Brown, T. M.; Cassisi, S.; Cool, A. M.; Cunial, A.; Dalessandro, E.; D'Antona, F.; Ferraro, F. R.; Hidalgo, S.; Lanzoni, B.; Monelli, M.; Ortolani, S.; Renzini, A.; Salaris, M.; Sarajedini, A.; Marel, R. P. van der; Vesperini, E.; Zoccali, M. (February 5, 2015). "THEHUBBLE SPACE TELESCOPEUV LEGACY SURVEY OF GALACTIC GLOBULAR CLUSTERS. I. OVERVIEW OF THE PROJECT AND DETECTION OF MULTIPLE STELLAR POPULATIONS". The Astronomical Journal. 149 (3): 91. arXiv: 1410.4564 . doi:10.1088/0004-6256/149/3/91.
- ↑ Milone, A. P.; Piotto, G.; Bedin, L. R.; Aparicio, A.; Anderson, J.; Sarajedini, A.; Marino, A. F.; Moretti, A.; Davies, M. B.; Chaboyer, B.; Dotter, A.; Hempel, M.; Marín-Franch, A.; Majewski, S.; Paust, N. E. Q.; Reid, I. N.; Rosenberg, A.; Siegel, M. (April 1, 2012). "The ACS survey of Galactic globular clusters - XII. Photometric binaries along the main sequence". Astronomy & Astrophysics. 540: A16. arXiv: 1111.0552 . doi:10.1051/0004-6361/201016384 – via www.aanda.org.
- ↑ Sollima, A.; Beccari, G.; Ferraro, F. R.; Fusi Pecci, F.; Sarajedini, A. (August 15, 2007). "The fraction of binary systems in the core of 13 low-density Galactic globular clusters*". Monthly Notices of the Royal Astronomical Society. 380 (2): 781–791. arXiv: 0706.2288 . doi:10.1111/j.1365-2966.2007.12116.x.
- ↑ Layden, Andrew C.; Sarajedini, Ata (April 29, 2000). "Photometry of the Globular Cluster M54 and the Sagittarius Dwarf Galaxy: The Age-Metallicity Relation". The Astronomical Journal. 119 (4): 1760–1792. doi:10.1086/301293.
- ↑ Siegel, Michael H.; Dotter, Aaron; Majewski, Steven R.; Sarajedini, Ata; Chaboyer, Brian; Nidever, David L.; Anderson, Jay; Marín-Franch, Antonio; Rosenberg, Alfred; Bedin, Luigi R.; Aparicio, Antonio; King, Ivan; Piotto, Giampaolo; Reid, I. Neill (September 6, 2007). "The ACS Survey of Galactic Globular Clusters: M54 and Young Populations in the Sagittarius Dwarf Spheroidal Galaxy". The Astrophysical Journal. 667 (1): L57–L60. arXiv: 0708.0027 . doi:10.1086/522003.
- ↑ Harbeck, Daniel; Grebel, Eva K.; Holtzman, Jon; Guhathakurta, Puragra; Brandner, Wolfgang; Geisler, Doug; Sarajedini, Ata; Dolphin, Andrew; Hurley-Keller, Denise; Mateo, Mario (December 29, 2001). "Population Gradients in Local Group Dwarf Spheroidal Galaxies". The Astronomical Journal. 122 (6): 3092–3105. arXiv: astro-ph/0109121 . doi:10.1086/324232.
- ↑ Dotter, Aaron; Sarajedini, Ata; Anderson, Jay; Aparicio, Antonio; Bedin, Luigi R.; Chaboyer, Brian; Majewski, Steven; Marín-Franch, A.; Milone, Antonino; Paust, Nathaniel; Piotto, Giampaolo; Reid, I. Neill; Rosenberg, Alfred; Siegel, Michael (December 15, 2009). "THE ACS SURVEY OF GALACTIC GLOBULAR CLUSTERS. IX. HORIZONTAL BRANCH MORPHOLOGY AND THE SECOND PARAMETER PHENOMENON". The Astrophysical Journal. 708 (1): 698–716. arXiv: 0911.2469 . doi:10.1088/0004-637x/708/1/698.
- ↑ "The Hubble Space Telescope UV Legacy Survey of Galactic globular clusters – IX. The Atlas of multiple stellar populations".
- ↑ Dalcanton, Julianne J.; Williams, Benjamin F.; Lang, Dustin; Lauer, Tod R.; Kalirai, Jason S.; Seth, Anil C.; Dolphin, Andrew; Rosenfield, Philip; Weisz, Daniel R.; Bell, Eric F.; Bianchi, Luciana C.; Boyer, Martha L.; Caldwell, Nelson; Dong, Hui; Dorman, Claire E.; Gilbert, Karoline M.; Girardi, Léo; Gogarten, Stephanie M.; Gordon, Karl D.; Guhathakurta, Puragra; Hodge, Paul W.; Holtzman, Jon A.; Johnson, L. Clifton; Larsen, Søren S.; Lewis, Alexia; Melbourne, Jason L.; Olsen, Knut A. G.; Rix, Hans-Walter; Rosema, Keith; Saha, Abhijit; Sarajedini, Ata; Skillman, Evan D.; Stanek, Krzysztof Z. (May 31, 2012). "THE PANCHROMATIC HUBBLE ANDROMEDA TREASURY". The Astrophysical Journal Supplement Series. 200 (2): 18. arXiv: 1204.0010 . doi:10.1088/0067-0049/200/2/18.
- ↑ "AAS Names 21 New Fellows for 2024".
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