Terzan 5

Terzan 5

An ESO image of Terzan 5
Observation data (J2000 epoch)
Class G2[1]
Constellation Sagittarius
Right ascension 17h 48m 05s[2]
Declination −24° 46′ 48″[2]
Distance 17.9 ± 2.9 kly (5.5 ± 0.9 kpc[3][note 1])
Apparent magnitude (V) 12.8[1]
Apparent dimensions (V) 1′40″ (half-mass diameter)[5]
Physical characteristics
Mass 106 M☉ (2 × 1036 kg)
Radius 3.9 ly[note 2]
VHB 22.5[4]
Estimated age 12 Gyr[6]
Notable features Possibly the core of a disrupted dwarf galaxy
Other designations Ter 5, IRC–20385
See also: Globular cluster, List of globular clusters

Terzan 5 is a heavily obscured globular cluster belonging to the bulge (the central star concentration) of the Milky Way galaxy.[4] It was one of six globulars discovered by French[7] astronomer Agop Terzan in 1968[8] and was initially labeled Terzan 11. The cluster was cataloged by the Two-Micron Sky Survey as IRC–20385.[9] 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 moves towards the Sun with the speed of around 90 km/s.[6]

The absolute magnitude of Terzan 5 is at least MV=−7.5, meaning that its luminosity is about 100,000 times more than that of the Sun, and is close to the average absolute magnitude for galactic globular clusters.[1] The small core of Terzan 5 has one of the highest star densities in the galaxy. Its volume mass density exceeds 106 M☉/pc3,[5] while its volume luminosity density exceeds 105.5 L☉/pc3, where M☉ and L☉ are the Sun's mass and luminosity, respectively. The cluster also has one of the highest metallicities among Milky Way's globular clusters—[Fe/H]=−0.21.[3]

In 2009 it was discovered that Terzan 5 consists of at least two generations of stars with ages of 12 and 6 billion years and slightly different metallicities, possibly indicating that it is the core of a disrupted dwarf galaxy, not a true globular cluster.[6] There are only a few other globular clusters in Milky Way that contain stars with different ages. Among them are M54 and Omega Centauri, the former being the core of Sagittarius Dwarf Elliptical Galaxy. The cluster also contains around 1300 core helium burning horizontal branch (HB) stars,[6] including at least one RR Lyrae variable star.[5]

Contents

Pulsars and X-ray sources

Terzan 5 is known to contain at least 25 millisecond radio pulsars. The first such object, PSR B1744-24A, discovered in 1990, has the period of 11.56 ms. The population of pulsars inside Terzan 5 includes PSR J1748–2446ad, the fastest known millisecond pulsar, which is spinning at 716 Hz (the rotation period is 1.40 ms).[10]

Terzan 5 also contains an X-ray burster, discovered in 1980, known as Terzan 5 or XB 1745-25.[11] It also contains around 50 weaker X-ray sources, many of which are likely Low-mass X-ray binaries (LXMB) or cataclysmic variables.[12]

The large number of X-ray sources and millisecond pulsars may be a direct consequence of the high density of the cluster's core, which leads to a high rate of star collisions, and to formation of close binaries, including binary systems which contain a neutron star.[12]

Gallery

Notes

  1. ^ The distance estimates have historically varied from as close as 2.3 kpc to as far as 14.6 kpc.[4] The recent estimates generally range from 5.5 to 8.7 kpc.[3]
  2. ^ Based on the half-mass radius of 55″[5] and the known distance of 5.5 kpc. The dense core of the cluster has the radius of 7.9″.[5]

References

  1. ^ a b c Racine, René (1975). "UBV photometry of faint globular clusters". The Astronomical Journal 80 (12): 1031–36. Bibcode 1975AJ.....80.1031R. doi:10.1086/111835. 
  2. ^ a b "SIMBAD Astronomical Database". Results for Terzan 5. http://simbad.u-strasbg.fr/Simbad. Retrieved 2009-12-04. 
  3. ^ a b c Ortolani, S.; Barbuy, B.; Zoccali, M.; Renzini, A.; Renzini, A. (2007). "Distances of the bulge globular clusters Terzan 5, Liller 1, UKS 1 and Terzan 4 based on HST NICMOS photometry". Astronomy and Astrophysics 470 (3): 1043–49. arXiv:0705.4030. Bibcode 2007A&A...470.1043O. doi:10.1051/0004-6361:20066628. 
  4. ^ a b c Ortolani, S.; Barbuy, B.; Bica, E. (1996). "NTT VI photometry of the metal rich and obscured bulge globular cluster Terzan 5". Astronomy and Astrophysics 308: 733–37. Bibcode 1996A&A...308..733O. 
  5. ^ a b c d e Cohn, Haldan N.; Lugger, Phyllis M.; Grindlay, Jonathan E.; Edmonds, Peter D. (2002). "Hubble Space Telescope/NICMOS observations of Terzan 5: stellar content and structure of the core". The Astrophysical Journal 571 (2): 818–29. arXiv:astro-ph/0202059. Bibcode 2002ApJ...571..818C. doi:10.1086/339874. 
  6. ^ a b c d Ferraro, F.R.; Dalessandro, E.; Mucciarelli, A.; Beccari, G; Rich, RM; Origlia, L; Lanzoni, B; Rood, RT et al. (2009). "The cluster Terzan 5 as a remnant of a primordial building block of the Galactic bulge". Nature 462 (7272): 483–486. arXiv:0912.0192. Bibcode 2009Natur.462..483F. doi:10.1038/nature08581. PMID 19940920. 
  7. ^ Gottlieb, Steve (August 1, 2000). Sky and Telescope 100 (2): 112. ISSN 0037-6604. 
  8. ^ Terzan, Agop (1968). "Six nouveaux amas stellaires (Terzan 3-8) dans la region DU centre de la Voie lactee et les constellations DU Scorpion et DU Sagittaire.". C.R. Acad. Sci. 267 (Ser. B): 1245–1248. Bibcode 1968CRASB.267.1245T 
  9. ^ King, I.R. (1972). "The identity and aliases of the stellar system Terzan 5". Astronomy and Astrophysics 19: 166. Bibcode 1972A&A....19..166K. 
  10. ^ Hessels, Jason W. T.; Ransom, Scott M.; Stairs, Ingrid H.; Freire, PC; Kaspi, VM; Camilo, F (2006). "A Radio Pulsar Spinning at 716 Hz". Science 311 (5769): 1901–04. arXiv:astro-ph/0601337. Bibcode 2006Sci...311.1901H. doi:10.1126/science.1123430. PMID 16410486. 
  11. ^ Makishima, K.; Ohashi, T.; Inoue, H.; Koyama, K.; Matsuoka, M.; Murakami, T.; Oda, M.; Ogawara, Y. et al. (1981). "Discovery of two new burst sources in the globular clusters Terzan 1 and Terzan 5". The Astrophysical Journal 247: L23–25. Bibcode 1981ApJ...247L..23M. doi:10.1086/183581. 
  12. ^ a b Heinke, C.O.; Wijnands, R.; Cohn, H.N.; Lugger, P. M.; Grindlay, J. E.; Pooley, D.; Lewin, W. H. G. (2006). "Faint X-ray sources in the globular cluster Terzan 5". The Astrophysical Journal 651 (2): 1098–1111. arXiv:astro-ph/0606253. Bibcode 2006ApJ...651.1098H. doi:10.1086/507884.