Terzan 5
{{ Infobox globular cluster |
| name = Terzan 5
| image = 300px
| caption = Hubble image of Terzan 5
| credit =
| epoch = J2000
| constellation = Sagittarius
| ra = {{RA|17|48|05}}{{cite simbad | title=Cl Terzan 5 | accessdate=2009-12-04}}
| dist_pc =5.9 ± 0.5 kpc
| dist_ly = 18.8 ± 1.6 kly{{#tag:ref|The distance estimates have historically varied from as close as 2.3 kpc to as far as 14.6 kpc. The recent estimates generally range from 5.5 to 8.7 kpc.|group=note}}
| size_v = 1′02″ (half-mass diameter)
| mass_kg = 4{{E-sp|36}}
| radius_ly =2.7 ly{{#tag:ref|Based on the half-mass radius of 31″ and the known distance of 5.9 kpc. The dense core of the cluster has the radius of 9.0″.|group=note}}
| age = 12 Gyr
| notes = Possibly the core of a disrupted dwarf galaxy
| names = Ter 5, IRC–20385
| metal_fe = −0.21
}}
Terzan 5 is a heavily obscured globular cluster belonging to the bulge (the central star concentration) of the Milky Way galaxy. It was one of six globulars discovered by French{{Cite journal
| last1 = Gottlieb
| first1 = Steve
| journal = Sky and Telescope
| volume = 100
| issue = 2
| title = Deep-Sky Notebook: A Tour of Obscure Summer Globular Clusters
| issn = 0037-6604
| page = 112
| date = August 1, 2000
}} astronomer Agop Terzan in 1968{{Cite journal
| last1 = Terzan
| first1 = Agop
| date = 1968
| title = Six nouveaux amas stellaires (Terzan 3-8) dans la region DU centre de la Voie lactee et les constellations DU Scorpion et DU Sagittaire.
| journal = C. R. Acad. Sci.
| issue = Ser. B
| volume = 267
| pages = 1245–1248
| bibcode = 1968CRASB.267.1245T
}} and was initially labeled Terzan 11. The cluster was cataloged by the Two-Micron Sky Survey as IRC–20385. 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 is moving towards the Sun with a speed of around 90 km/s.
Physical properties
The absolute magnitude of Terzan 5 is at least {{nowrap|MV{{=}}−7.5}}. Its bolometric luminosity is about 800,000 times that of the Sun, while its mass is about 2 million solar masses.{{Cite journal | last1 = Lanzoni | first1 = B. | last2 = Ferraro | first2 = F. R. | last3 = Dalessandro | first3 = E. | last4 = Mucciarelli | first4 = A. | last5 = Beccari | first5 = G. | last6 = Miocchi | first6 = P. | last7 = Bellazzini | first7 = M. | last8 = Rich | first8 = R. M. | last9 = Origlia | first9 = L. | doi = 10.1088/0004-637X/717/2/653 | last10 = Valenti | first10 = E. | last11 = Rood | first11 = R. T. | last12 = Ransom | first12 = S. M. | title = New Density Profile and Structural Parameters of the Complex Stellar System Terzan 5 | journal = The Astrophysical Journal | volume = 717 | issue = 2 | pages = 653 | year = 2010 |arxiv = 1005.2847 |bibcode = 2010ApJ...717..653L | s2cid = 118665166 }} The small core of Terzan 5—about 0.5 pc in size—has one of the highest star densities in the galaxy. Its volume mass density exceeds {{nowrap|106 {{Solar mass}}/pc3}}, while its volume luminosity density exceeds {{nowrap|105.5 {{Solar luminosity}}/pc3}}, where {{Solar mass}} and {{Solar luminosity}} are the Sun's mass and luminosity, respectively. The cluster also has one of the highest metallicities among the Milky Way's globular clusters—
In 2009 it was discovered that Terzan 5 consists of at least two generations of stars with ages of 12 and 4.5 billion years and slightly different metallicities, possibly indicating that it is the core of a disrupted dwarf galaxy, not a true globular cluster. There are only a few other globular clusters in the Milky Way that contain stars with different ages. Among them are M54, Omega Centauri and Liller 1. The latter, like Terzan 5, is thought to be a fossil fragment from the assembly of the galactic bulge.{{cite journal|date=2021|author1=Ferraro, F. R.|author2=Pallanca, C.|author3=Lanzoni, B.|author4=Crociati, C.|author5=Dalessandro, E.|author6=Origlia, L.|author7=Rich, R. M.|author8=Saracino, S.|author9=Mucciarelli, A.|author10=Valenti, E.|author11=Geisler, D.|author12=Mauro, F.|author13=Villanova, S.|author14=Moni Bidin, C.|author15=Beccari, G.|title=A new class of fossil fragments from the hierarchical assembly of the Galactic bulge|journal= Nature Astronomy|volume=5|issue=3 |pages=311–318|doi=10.1038/s41550-020-01267-y|arxiv=2011.09966|bibcode=2021NatAs...5..311F|s2cid=227054148 }} The cluster also contains around 1300 core helium burning horizontal branch (HB) stars, including at least one RR Lyrae variable star.
Pulsars and X-ray sources
Terzan 5 is known to contain 49 millisecond radio pulsars as of December 2023,{{Cite web |title=Pulsars in Globular Clusters |url=https://www3.mpifr-bonn.mpg.de/staff/pfreire/GCpsr.html#Terzan5 |access-date=2023-12-20 |website=www3.mpifr-bonn.mpg.de}} the largest MSP population among all globular clusters in the Galaxy; their true number may be as high as 200. 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).
Terzan 5 also contains an X-ray burster, discovered in 1980, known as Terzan 5 or XB 1745-25. It also contains around 50 weaker X-ray sources, many of which are likely Low-mass X-ray binaries (LMXB) or cataclysmic variables.
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.
In addition to discrete X-ray sources Terzan 5 produces a diffuse non-thermal X-ray emission and high (a few GeV) and ultra-high (0.5–24 TeV) energy gamma-rays. The high energy gamma rays probably originate in the magnetosphere of abundant millisecond pulsars, while ultra-high energy gamma rays likely result from the inverse Compton scattering by the relativistic electron emitted by the pulsars off the cosmic microwave background radiation.{{Cite journal | last1 = Abramowski | first1 = A. | last2 = Acero | first2 = F. | last3 = Aharonian | first3 = F. | last4 = Akhperjanian | first4 = A. G. | last5 = Anton | first5 = G. | last6 = Balzer | first6 = A. | last7 = Barnacka | first7 = A. | last8 = Barres De Almeida | first8 = U. | last9 = Becherini | first9 = Y. | last10 = Becker | first10 = J. | last11 = Behera | first11 = B. | last12 = Bernlöhr | first12 = K. | last13 = Bochow | first13 = A. | last14 = Boisson | first14 = C. | last15 = Bolmont | first15 = J. | last16 = Bordas | first16 = P. | last17 = Brucker | first17 = J. | last18 = Brun | first18 = F. | last19 = Brun | first19 = P. | last20 = Bulik | first20 = T. | last21 = Büsching | first21 = I. | last22 = Carrigan | first22 = S. | last23 = Casanova | first23 = S. | last24 = Cerruti | first24 = M. | last25 = Chadwick | first25 = P. M. | last26 = Charbonnier | first26 = A. | last27 = Chaves | first27 = R. C. G. | last28 = Cheesebrough | first28 = A. | last29 = Chounet | first29 = L. -M. | last30 = Clapson | first30 = A. C. | display-authors = 1 | title = Very-high-energy gamma-ray emission from the direction of the Galactic globular cluster Terzan 5 | doi = 10.1051/0004-6361/201117171 | journal = Astronomy & Astrophysics | volume = 531 | pages = L18 | year = 2011 |arxiv = 1106.4069 |bibcode = 2011A&A...531L..18H | s2cid = 59036124 }}
Gallery
File:Commotion in a Crowded Cluster.jpg|Hubble image of the ancient globular cluster Terzan 5
File:The unusual cluster Terzan 5.jpg|Terzan 5 is one of the bulge's primordial building blocks, most likely the relic of the very early days of the Milky Way.{{cite web|title=The unusual cluster Terzan 5|url=http://www.eso.org/public/images/eso1630a/|website=www.eso.org|access-date=9 September 2016}}
Notes
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References
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