A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity,with a higher concentration of stars towards its center. It 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".
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.
RR Lyrae variables are periodic variable stars,commonly found in globular clusters. They are used as standard candles to measure (extra) galactic distances,assisting with the cosmic distance ladder. This class is named after the prototype and brightest example,RR Lyrae.
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 through the Milky Way between 300 and 900 million years ago.
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 15 or M15 is a globular cluster in the constellation Pegasus. It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier's catalogue of comet-like objects in 1764. At an estimated 12.5±1.3 billion years old,it is one of the oldest 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 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.
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 currently belongs to the Milky Way,although it was likely stolen from a dwarf galaxy that collided with the Milky Way. NGC 2808 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 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".
NGC 6535 is a globular cluster of stars located at a distance of 22,200 light years from Earth in the equatorial constellation of Serpens,and is listed in the New General Catalogue. Its discovery is usually attributed to astronomer John Russell Hind in 1852. However,Wolfgang Steinicke has uncovered evidence that William Herschel's first discovery was actually NGC 6535,which he observed on 24 August 1780.
Georges Meylan is a Swiss astronomer,born on July 31,1950,in Lausanne,Switzerland. He was the director of the Laboratory of Astrophysics of the Swiss Federal Institute of Technology (EPFL) in Lausanne,Switzerland,and now a professor emeritus of astrophysics and cosmology at EPFL. He is still active in both research and teaching.
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.
Robert Michael Rich is an American astrophysicist. He obtained his B.A. at Pomona College in 1979 and earned his Ph.D. from the California Institute of Technology in 1986 under thesis supervisor Jeremy Mould. He was a Carnegie Fellow at Carnegie/DTM until 1988,when he became an assistant professor of astronomy at Columbia University;during this period,he was the doctoral advisor to Neil deGrasse Tyson. After two years (1996-1998) as a senior research scientist at Columbia,he joined the University of California,Los Angeles as a research astronomer in 1998. As of 2024,he remains affiliated with UCLA as a researcher emeritus/adjunct professor emeritus of astronomy and astrophysics.
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.
Luigi Rolly Bedin,is an Italian astrophysicist and researcher at the National Institute of Astrophysics of the Padua Astronomical Observatory. His research focuses on stellar populations in open and globular clusters,exoplanets and nearby brown dwarfs. He is the discoverer with his team of the dwarf spheroidal galaxy Bedin I. He is a member of the International Astronomical Union.
