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. Open clusters are more loosely clustered groups of stars, generally containing fewer than a few hundred members, that are often very young. As they move through the galaxy, over time, open clusters become disrupted by the gravitational influence of giant molecular clouds. Even though they are no longer gravitationally bound, they will continue to move in broadly the same direction through space and are then known as stellar associations, sometimes referred to as moving groups.
The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a D25 isophotal diameter of about 46.56 kiloparsecs (152,000 light-years) and is approximately 765 kpc (2.5 million light-years) from Earth. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the princess who was the wife of Perseus in Greek mythology.
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 107 or M107, also known as NGC 6171 or the Crucifix Cluster, is a very loose globular cluster in a very mildly southern part of the sky close to the equator in Ophiuchus, and is the last such object in the Messier Catalogue.
An intermediate-mass black hole (IMBH) is a class of black hole with mass in the range 102–105 solar masses: significantly higher than stellar black holes but lower than the 105–109 solar mass supermassive black holes. Several IMBH candidate objects have been discovered in the Milky Way galaxy and others nearby, based on indirect gas cloud velocity and accretion disk spectra observations of various evidentiary strength.
A galactic halo is an extended, roughly spherical component of a galaxy which extends beyond the main, visible component. Several distinct components of a galaxy comprise its halo:
Messier 12 or M 12 is a globular cluster in the constellation of Ophiuchus. It was discovered by the French astronomer Charles Messier on May 30, 1764, who described it as a "nebula without stars". In dark conditions this cluster can be faintly seen with a pair of binoculars. Resolving the stellar components requires a telescope with an aperture of 8 in (20 cm) or greater. In a 10 in (25 cm) scope, the granular core shows a diameter of 3′ (arcminutes) surrounded by a 10′ halo of stars.
Interacting galaxies are galaxies whose gravitational fields result in a disturbance of one another. An example of a minor interaction is a satellite galaxy disturbing the primary galaxy's spiral arms. An example of a major interaction is a galactic collision, which may lead to a galaxy merger.
NGC 5466 is a class XII globular cluster in the constellation Boötes. Located 51,800 light years from Earth and 52,800 light years from the Galactic Center, it was discovered by William Herschel on May 17, 1784, as H VI.9. This globular cluster is unusual insofar as it contains a certain blue horizontal branch of stars, as well as being unusually metal poor like ordinary globular clusters. It is thought to be the source of a stellar stream discovered in 2006, called the 45 Degree Tidal Stream. This star stream is an approximately 1.4° wide star lane extending from Boötes to Ursa Major.
NGC 5986 is a globular cluster of stars in the southern constellation of Lupus, located at a distance of approximately 34 kilolight-years from the Sun. It was discovered by Scottish astronomer James Dunlop on May 10, 1826. John L. E. Dreyer described it as, "a remarkable object, a globular cluster, very bright, large, round, very gradually brighter middle, stars of 13th to 15th magnitude". Its prograde–retrograde orbit through the Milky Way galaxy is considered irregular and highly eccentric. It has a mean heliocentric radial velocity of +100 km/s. The galacto-centric distance is 17 kly (5.2 kpc), which puts it in the galaxy's inner halo.
In astronomy Westerhout 49 also known as W49, is a strong galactic thermal radio source characteristic of an HII region. It was discovered by Gart Westerhout in 1958.
In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space.
Palomar 14 is a globular cluster located in the constellation Hercules. It is a member of the Palomar Globular Clusters group. Palomar 14 was discovered in 1958 by Sidney van den Bergh and Halton Arp during inspection of the photographic plates from the Palomar Sky Survey. This is a round, diffuse cluster located in the outer halo of the Milky Way galaxy. It is about 3–4 billion years younger than a typical galactic cluster.
Boötes III is an overdensity in the Milky Way's halo, which may be a disrupted dwarf spheroidal galaxy. It is situated in the constellation Boötes and was discovered in 2009 in the data obtained by Sloan Digital Sky Survey. The galaxy is located at the distance of about 46 kpc from the Sun and moves away from it at the speed of about 200 km/s. It has an elongated shape with the radius of about 0.5 kpc. The large size and an irregular shape may indicate that Boötes III in a transitional phase between a gravitationally bound galaxy and completely unbound system.
NGC 1404 is an elliptical galaxy in the Southern constellation Eridanus. It was discovered on November 28, 1837, by the astronomer John Herschel. Based on the tip of the red-giant branch distance indicator, it lies at a distance of approximately 60 million light-years from the Milky Way. It is one of the brightest members of the Fornax Cluster.
NGC 7727 is a peculiar galaxy in the constellation Aquarius. It harbors two galactic nuclei, each containing a supermassive black hole, separated 1,600 light years apart.
Laevens 1 is a faint globular cluster in the constellation Crater that was discovered in 2014. It is also known as Crater, the Crater cluster and PSO J174.0675-10.8774.
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.
