m5 – globular cluster
Lupe Rioné, Amateur astronomer (Spain)
The Serpent Constellation
24,500 light years
165 light years
Globular clusters: Globular clusters are concentrations of thousands to millions of stars joined gravitationally. They all orbit in the halo of a galaxy, although some of them can be located near the center of the Milky Way.
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Continuing with the objects of the Messier Catalog, today we talk about the M5 Globular Cluster, also listed as NGC 5904. Although all globular clusters look similar, they differ in size, number, and types of stars they house. In addition to the distance at which they are located. Globular clusters are as old as our own Milky Way, and their study has always been crucial to understanding the formation of galaxies and their evolution.
The globular cluster M5 is probably one of the most interesting because it is one of the oldest, largest, and brightest clusters. It is located in the constellation of The Serpent (Serpens) at a distance of approximately 24,500 light years, and although it has a diameter of 165 light years, its gravitational influence is much greater.
History and Discovery
M5 was discovered in 1702 by the German astronomer Gottfried Kirch and his wife, while they were observing a comet. At first, they thought it was a nebula. The same thing happened to Charles Messier, who observed it in 1764 and included it in his catalog as M5, saying; “I have seen a beautiful nebula in the Constellation of the Serpent… the nebula does not contain any stars… it is round…” It was justified that he was not able to distinguish it as a globular cluster, since his telescope was not large enough to resolve the object in detail.
Who did determine the nature of this object was William Herschel. In 1791, the astronomer counted as many as 200 stars in the cluster, further stating “that the center is so compressed that it is impossible to distinguish the stars in the nucleus”.
M5 globular cluster. Credit: NASA/Hubble/ STScl
M5 cluster. Credit: Adam Block, MT. Lemmon Sky Center, University of Arizona
M5 is the brightest cluster that can be observed from the Northern Hemisphere, almost as bright as the Hercules cluster (M13). Located in the Serpent Constellation, just between the constellations Libra and Boyero, it can be distinguished as a weak object, even in the city. Like the globular cluster M3, we can turn to the star Arthur and jump to Antares to find it. With an apparent magnitude of 5.6, it can be distinguished from a star with binoculars. Already, with a telescope of about 150-200 mm in diameter we can distinguish many individual stars.
M5 is one of the largest known globular clusters, and astronomers estimate that it is one of the oldest, with an age of about 13 billion years. Estimating that it can hold about 500,000 stars, the cluster is located in the halo of our galaxy, at a distance of about 24,000-25,000 light-years; a distance that becomes greater because it moves away from us at a speed of about 52 km/second. With a diameter of about 160 light-years, it is one of the largest known globular clusters, and its gravitational influence is more than 400 light-years. We call gravitational influence the area of space where any object is attracted by the cluster’s gravity, rather than the galaxy’s gravity.
Zoomed M5 image: NASA/ESA
M5 Credit: Velillacanoj@gmail.com. Telescope TS102f5.2 and camera Atik 41ex
It contains a large number of red and blue giant stars in an extremely dense core. There are 105 known variable stars, of which 97 are of the RR Lyrae type. RR Lyrae type stars, also known as “cluster variables,” are somewhat similar to cepheid variables and can be used to measure distances because their relationship between periods and luminosities is well known. The brightest variable of M5 varies from magnitude 10.6 to 12.1 over a 26-day period.
In addition, M5 is known to contain a dwarf nova. This body is not a small supernova. It is a type of variable star formed by a binary system. One of the stars is a white dwarf, accompanied by a giant star that loses matter due to the gravitational pull of the dwarf star. This causes the giant star to undergo abrupt brightness changes, even in a single day. On top of that, M5 contains two pulsars with rotation periods measured in milliseconds. All these characteristics make it an extraordinary object, very attractive to be observed and photographed.
Location of M5. Credit: ESO, IAU and Sky &Telescope
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