Messier 79 (also known as M79 or NGC 1904) is a

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are 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 membe ...

in the southern constellation Lepus. It was discovered by

Pierre Méchain Pierre François André Méchain (; 16 August 1744 – 20 September 1804) was a French astronomer and surveyor who, with Charles Messier, was a major contributor to the early study of deep-sky objects and comets. Life Pierre Méchain was born i ...

in 1780 and is about 42,000

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s away from

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

and 60,000 light years from the

Galactic Center The Galactic Center or Galactic Centre is the rotational center, the barycenter, of the Milky Way galaxy. Its central massive object is a supermassive black hole of about 4 million solar masses, which is called Sagittarius A*, a compact rad ...

. Like

Messier 54 Messier 54 (also known as M54 or NGC 6715) 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. It is easily found in the sky, being close ...

(the other extragalactic globular on Messier's list), it is believed to not be native to the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

galaxy at all, but instead to the putative

Canis Major Dwarf Galaxy The Canis Major Overdensity (''CMa Overdensity'') or Canis Major Dwarf Galaxy (''CMa Dwarf'') is a disputed dwarf irregular galaxy in the Local Group, located in the same part of the sky as the constellation Canis Major. The supposed small gal ...

, which is currently experiencing a very close encounter with our galaxy. This is, however, a contentious subject as astronomers are still debating the nature of the Canis Major dwarf galaxy itself. The cluster is being disrupted by the

galactic tide A galactic tide is a tidal force experienced by objects subject to the gravitational field of a galaxy such as the Milky Way. Particular areas of interest concerning galactic tides include galactic collisions, the disruption of dwarf or satellit ...

, trailing a long

tidal tail A tidal tail is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy. Tidal tails occur as a result of galactic tide forces between interacting galaxies. Examples of galaxies with tidal tails include the ...

Color-magnitude diagram

This color-magnitude diagram was made using near-infrared images of the cluster in J and K bands. J-band magnitude is plotted along the y-axis and J to K dominant color is plotted along the x-axis. Such a diagram is made rapidly with specialized code for crowded-field photometry.This diagram was made by

Astromundus Astromundus was a 2-years Erasmus Mundus masters course in Astronomy and Astrophysics. It was offered by a consortium of 5 partner universities of four different European countries. Partner universities were University of Innsbruck in Austria, Uni ...

students attending lectures and a workshop by Peter Stetson, the writer of DAOPHOT, standard code for crowded-field photometry. Date: June 2011,

University of Rome Tor Vergata Tor Vergata University of Rome, also known as the University of Rome II ( it, Università degli Studi di Roma "Tor Vergata"), is a public university, public research university located in Rome, Italy. Located in the southeastern suburb of Rome, the ...

From this, it is evident that most of the bright stars in this cluster are red giants. The elongated branch is the

red giant branch The red-giant branch (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass sta ...

. Some of the stars in the diagram, including those extending outward from the red giant branch toward the upper left, are actually foreground stars that are not members of the cluster. Altogether three regions of the Hertzsprung-Russell diagram are present here: the low-mass end of the

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

, the complete red giant branch and the

horizontal branch The horizontal branch (HB) is a stage of stellar evolution that immediately follows the red-giant branch in stars whose masses are similar to the Sun's. Horizontal-branch stars are powered by helium fusion in the core (via the triple-alpha process) ...

. Compared to optical bands, in infrared bands the lower main sequence is shallower and the horizontal branch is steeper (the blue end is fainter and the red end is brighter).

References

External links

Messier 79, SEDS Messier pages

Messier 79, Galactic Globular Clusters Database page
* {{DEFAULTSORT:Messier 79 Messier 079 Messier 079 Messier 079

079 79 may refer to: * 79 (number) * one of the years 79 BC, AD 79, 1979, 2079 * ''79 A.D.'', a 1962 historical epic film * Eruption of Mount Vesuvius in 79, a catastrophic volcanic eruption in Italy See also

* * List of highways numbered {{Num ...

Messier 079 Astronomical objects discovered in 1780