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Messier 79

Globular Cluster M79 (NGC 1904), class V, in Lepus

[m79.jpg]
Right Ascension 05 : 24.2 (h:m)
Declination -24 : 31 (deg:m)
Distance 42.6 (kly)
Visual Brightness 7.7 (mag)
Apparent Dimension 9.6 (arc min)

Discovered 1780 by Pierre Méchain.

Globular cluster Messier 79 (M79, NGC 1904) is a nice globular cluster in an unusual place for this kind of objects, in the hemisphere opposite to the Galactic Center, in the inconspicuous constellation Lepus.

M79 was found by Pierre Méchain on October 26, 1780, and reported his discovery to his friend and colleague, Charles Messier, who determined its position and included it in his catalog on December 17, 1780. It was first resolved into stars and recognized as a globular cluster by William Herschel in about 1784.

M79 is a beautiful globular cluster at a quite unusual location in the sky: Most globulars are grouped around the Galactic center, but this is one of the few which are situated in the other hemisphere, i.e. it is beyond us for hypothetical observers in the central stellar bulge of our Milky Way galaxy. It is little over 40,000 light years from us, but about 60,000 light years from the galactic center.

At this distance, M79's apparent diameter of 9.6 minutes of arc corresponds to a linear extension of about 118 light years. This cluster is slightly elliptical, extended at position angle 45 deg. It is receding from us at about 200 km/sec.

As of July 2013, this cluster contains only 12 or 13 known variables, according to Clement (2013, 2018): 10 RR Lyrae stars (6 of type RR0, 4 of RR1), 1 semi-regular variable, and 1 long-term variable (the star M79-V7), perhaps a long-period type II Cepheid (type CW); 1 star (M79-V8) is of uncertain type and to be confirmed. Up to March 2018, this number has increased to 33 (+ 1 former candidate): 11 RR Lyraes (6 RR0, 4 RR1, 1 uncertain), 1 type II Cepheid (CW), 10 semi-regulars + 3 quetionable, each 1 long-term, 1 eclipsing, and 1 variable of unknown type. Current state of variable star research in M79 is presented in Kopacki (2015), and slightly earlier in Kains et.al. (2012).

Holger Baumgardt et.al. (2023) investigated astrometrical data from the GAIA satellite, and from the position and velocity, derived M79's simulated orbit. They found that M79 is at a distance of 42.6 kly (13.08 kpc) from us, and 62.2 kly (19.09 kpc) from the Galactic Center; at that distance, it is currently the most outlying Messier globular cluster from Galactic Center (slightly further out than M53 and M54). It is moving in an orbit with period of about 220 Myr. It is currently approaching its apogalacticum at 63.8 kly (19.57 kpc) from GC which it is to reach in about 20 Myr. About 90 Myr ago, it has passed its last perigalacticum, when it comes very close to the Galactic Center, at only 970 ly (0.97 kly, 0.30 kpc); this is the nearest perigalacticum of all Messier globular clusters! So notably, this currently most outlying Messier globular is also that which comes closest at its perigalacticum passage. The authors also found an age of 11.7 Gyr for M79 from fitting of its Color-Magnitude Diagram (CMD), a half-mass radius of 14 ly (4.33 pc), and a mass of 180,000 solar masses from the velocity dispersion of its member stars.

Globular cluster M79 has a considerably dense core, which is thought to have possibly undergone a core collapse process, as have the globulars M15, M30, M70, and possibly also M62.

The position of M79 is given erroneously in many older references, including the Sky Catalogue 2000.0 and the NGC 2000.0: at RA 05:24.5 Dec -24:33 instead of the correct values, RA 05:24.2 Dec -24:31 (J2000.0), a notion of the present author. The source of the error is currently researched.

In 2003, it was found that M79 is perhaps a rather new immigrant into the globular cluster system of our Milky Way: It may come from, or still be a member, of the remnant globular cluster system of the Canis Major Dwarf galaxy, a dwarf spheroidal galaxy which is currently undergoing a very close encounter with our Galaxy, and in progressive state of dissolution. Together with M79, three more globular clusters are suspected to have immigrated from the Canis Major Dwarf: NGC 1851, NGC 2298, and NGC 2808.

About 0.5 degrees to the SW of M79 lies the 5.5 mag star ADS 3954 with its 7th mag companion, separated by 3".

  • Historical Observations and Descriptions of M79
  • UIT images of M79 (visible and UV) from the Astro-1 Space Shuttle mission (STS-35)
  • More images of M79
  • Amateur images of M79

  • Multispectral Image Collection of M79, SIRTF Multiwavelength Messier Museum
  • Marco Castellani's data for M 79
  • Christine Clement's Catalog of Variable Stars in M79
  • Holger Baumgardt's Fundamental Data for M79 (NGC 1904)
  • SIMBAD Data of M79
  • NED Data of M79
  • Publications on M79 (NASA ADS)
  • Observing Reports for M79 (IAAC Netastrocatalog)
  • NGC Online data for M79

    References


    Hartmut Frommert
    Christine Kronberg
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    Definitive Version: May 23, 2014
    Last Modification: June 2, 2024