NGC 6397

NGC 6397
A Hubble Space Telescope (HST) image of NGC 6397. Credit: HST/NASA/ESA.
Observation data (J2000 epoch)
Class	IX^[1]
Constellation	Ara
Right ascension	17^h 40^m 42.09^s^[2]
Declination	–53° 40′ 27.6″^[2]
Distance	7.2 kly (2.2 kpc)^[3]
Apparent magnitude (V)	+6.68^[4]
Apparent dimensions (V)	32′.0
Physical characteristics
Mass	7004450000000000000♠4.5×10⁴^[5] M_☉
Radius	34 ly^[6]
V_HB	14.2
Metallicity	${\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}$ = –1.76^[7] dex
Estimated age	13.4 ± 0.8 Gyr^[3]
Notable features	Second closest globular to Earth
Other designations	GCl 74,^[4] Lacaille III.11, Dunlop 366, Bennett 98, Caldwell 86

NGC 6397, also known as Caldwell 86, is a globular cluster in the constellation Ara. It is located about 7,200 light-years from Earth, making it one of the two nearest globular clusters to Earth (the other one being Messier 4). The cluster contains around 400,000 stars,^[3] and can be seen with the naked eye under good observing conditions.^[8]

NGC 6397 is one of the at least 20 globular clusters of the Milky Way Galaxy that have undergone a core collapse,^[3] meaning that the core has contracted to a very dense stellar agglomeration.

Astronomical research

Estimating the age of the Milky Way

In 2004, a team of astronomers^[3] focused on the cluster to estimate the age of the Milky Way Galaxy. The team consisted of Luca Pasquini, Piercarlo Bonifacio, Sofia Randich, Daniele Galli, and Raffaele G. Gratton. They used the UV-Visual Echelle Spectrograph of the Very Large Telescope at Cerro Paranal to measure the beryllium content of two stars in the cluster. This allowed them to deduce the time elapsed between the rise of the first generation of stars in the entire Galaxy and the first generation of stars in the cluster. This, added to the estimated age of the stars in the cluster, gives an estimate for the age for the Galaxy: about 13.6 billion years, which is nearly as old as the universe itself.

Lower mass limit for stars

In 2006, a study of NGC6397 using the Hubble Space Telescope was published that showed a clear lower limit in the brightness of the cluster's population of faint stars. The authors deduce that this indicates a lower limit for the mass necessary for stars to develop a core capable of fusion: roughly 0.083 times the mass of the Sun.^[9]

References

↑ Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin (849): 11–14, Bibcode:1927BHarO.849...11S.
1 2 Goldsbury, Ryan; et al. (December 2010), "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters", The Astronomical Journal, 140 (6): 1830–1837, arXiv:1008.2755, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830.
1 2 3 4 5 "How Old is the Milky Way ?". Results for NGC 6397. Retrieved 2006-09-26.
1 2 "SIMBAD Astronomical Object Database". Results for NGC 6397. Retrieved 2006-11-16.
↑ Marks, Michael; Kroupa, Pavel (August 2010), "Initial conditions for globular clusters and assembly of the old globular cluster population of the Milky Way", Monthly Notices of the Royal Astronomical Society, 406 (3): 2000–2012, arXiv:1004.2255, Bibcode:2010MNRAS.406.2000M, doi:10.1111/j.1365-2966.2010.16813.x. Mass is from M_PD on Table 1.
↑ distance × sin( diameter_angle / 2 ) = ~34 ly. radius
↑ Forbes, Duncan A.; Bridges, Terry (May 2010), "Accreted versus in situ Milky Way globular clusters", Monthly Notices of the Royal Astronomical Society, 404 (3): 1203–1214, arXiv:1001.4289, Bibcode:2010MNRAS.404.1203F, doi:10.1111/j.1365-2966.2010.16373.x.
↑ Dunlop, Storm (2005). Atlas of the Night Sky. Collins. ISBN 0-00-717223-0.
↑ "HST analysis of faint stars in NGC6397". Results for NGC 6397. Retrieved 2006-09-26.

External links

New General Catalogue 6000 to 6499

NGC 6000 NGC 6001 NGC 6002 NGC 6003 NGC 6004 NGC 6005 NGC 6006 NGC 6007 NGC 6008 NGC 6009 NGC 6010 NGC 6011 NGC 6012 NGC 6013 NGC 6014 NGC 6015 NGC 6016 NGC 6017 NGC 6018 NGC 6019 NGC 6020 NGC 6021 NGC 6022 NGC 6023 NGC 6024 NGC 6025 NGC 6026 NGC 6027 NGC 6028 NGC 6029 NGC 6030 NGC 6031 NGC 6032 NGC 6033 NGC 6034 NGC 6035 NGC 6036 NGC 6037 NGC 6038 NGC 6039 NGC 6040 NGC 6041 NGC 6042 NGC 6043 NGC 6044 NGC 6045 NGC 6046 NGC 6047 NGC 6048 NGC 6049 NGC 6050 NGC 6051 NGC 6052 NGC 6053 NGC 6054 NGC 6055 NGC 6056 NGC 6057 NGC 6058 NGC 6059 NGC 6060 NGC 6061 NGC 6062 NGC 6063 NGC 6064 NGC 6065 NGC 6066 NGC 6067 NGC 6068 NGC 6069 NGC 6070 NGC 6071 NGC 6072 NGC 6073 NGC 6074 NGC 6075 NGC 6076 NGC 6077 NGC 6078 NGC 6079 NGC 6080 NGC 6081 NGC 6082 NGC 6083 NGC 6084 NGC 6085 NGC 6086 NGC 6087 NGC 6088 NGC 6089 NGC 6090 NGC 6091 NGC 6092 NGC 6093 NGC 6094 NGC 6095 NGC 6096 NGC 6097 NGC 6098 NGC 6099 NGC 6100 NGC 6101 NGC 6102 NGC 6103 NGC 6104 NGC 6105 NGC 6106 NGC 6107 NGC 6108 NGC 6109 NGC 6110 NGC 6111 NGC 6112 NGC 6113 NGC 6114 NGC 6115 NGC 6116 NGC 6117 NGC 6118 NGC 6119 NGC 6120 NGC 6121 NGC 6122 NGC 6123 NGC 6124 NGC 6125 NGC 6126 NGC 6127 NGC 6128 NGC 6129 NGC 6130 NGC 6131 NGC 6132 NGC 6133 NGC 6134 NGC 6135 NGC 6136 NGC 6137 NGC 6138 NGC 6139 NGC 6140 NGC 6141 NGC 6142 NGC 6143 NGC 6144 NGC 6145 NGC 6146 NGC 6147 NGC 6148 NGC 6149 NGC 6150 NGC 6151 NGC 6152 NGC 6153 NGC 6154 NGC 6155 NGC 6156 NGC 6157 NGC 6158 NGC 6159 NGC 6160 NGC 6161 NGC 6162 NGC 6163 NGC 6164 NGC 6165 NGC 6166 NGC 6167 NGC 6168 NGC 6169 NGC 6170 NGC 6171 NGC 6172 NGC 6173 NGC 6174 NGC 6175 NGC 6176 NGC 6177 NGC 6178 NGC 6179 NGC 6180 NGC 6181 NGC 6182 NGC 6183 NGC 6184 NGC 6185 NGC 6186 NGC 6187 NGC 6188 NGC 6189 NGC 6190 NGC 6191 NGC 6192 NGC 6193 NGC 6194 NGC 6195 NGC 6196 NGC 6197 NGC 6198 NGC 6199 NGC 6200 NGC 6201 NGC 6202 NGC 6203 NGC 6204 NGC 6205 NGC 6206 NGC 6207 NGC 6208 NGC 6209 NGC 6210 NGC 6211 NGC 6212 NGC 6213 NGC 6214 NGC 6215 NGC 6216 NGC 6217 NGC 6218 NGC 6219 NGC 6220 NGC 6221 NGC 6222 NGC 6223 NGC 6224 NGC 6225 NGC 6226 NGC 6227 NGC 6228 NGC 6229 NGC 6230 NGC 6231 NGC 6232 NGC 6233 NGC 6234 NGC 6235 NGC 6236 NGC 6237 NGC 6238 NGC 6239 NGC 6240 NGC 6241 NGC 6242 NGC 6243 NGC 6244 NGC 6245 NGC 6246 NGC 6247 NGC 6248 NGC 6249 NGC 6250 NGC 6251 NGC 6252 NGC 6253 NGC 6254 NGC 6255 NGC 6256 NGC 6257 NGC 6258 NGC 6259 NGC 6260 NGC 6261 NGC 6262 NGC 6263 NGC 6264 NGC 6265 NGC 6266 NGC 6267 NGC 6268 NGC 6269 NGC 6270 NGC 6271 NGC 6272 NGC 6273 NGC 6274 NGC 6275 NGC 6276 NGC 6277 NGC 6278 NGC 6279 NGC 6280 NGC 6281 NGC 6282 NGC 6283 NGC 6284 NGC 6285 NGC 6286 NGC 6287 NGC 6288 NGC 6289 NGC 6290 NGC 6291 NGC 6292 NGC 6293 NGC 6294 NGC 6295 NGC 6296 NGC 6297 NGC 6298 NGC 6299 NGC 6300 NGC 6301 NGC 6302 NGC 6303 NGC 6304 NGC 6305 NGC 6306 NGC 6307 NGC 6308 NGC 6309 NGC 6310 NGC 6311 NGC 6312 NGC 6313 NGC 6314 NGC 6315 NGC 6316 NGC 6317 NGC 6318 NGC 6319 NGC 6320 NGC 6321 NGC 6322 NGC 6323 NGC 6324 NGC 6325 NGC 6326 NGC 6327 NGC 6328 NGC 6329 NGC 6330 NGC 6331 NGC 6332 NGC 6333 NGC 6334 NGC 6335 NGC 6336 NGC 6337 NGC 6338 NGC 6339 NGC 6340 NGC 6341 NGC 6342 NGC 6343 NGC 6344 NGC 6345 NGC 6346 NGC 6347 NGC 6348 NGC 6349 NGC 6350 NGC 6351 NGC 6352 NGC 6353 NGC 6354 NGC 6355 NGC 6356 NGC 6357 NGC 6358 NGC 6359 NGC 6360 NGC 6361 NGC 6362 NGC 6363 NGC 6364 NGC 6365 NGC 6366 NGC 6367 NGC 6368 NGC 6369 NGC 6370 NGC 6371 NGC 6372 NGC 6373 NGC 6374 NGC 6375 NGC 6376 NGC 6377 NGC 6378 NGC 6379 NGC 6380 NGC 6381 NGC 6382 NGC 6383 NGC 6384 NGC 6385 NGC 6386 NGC 6387 NGC 6388 NGC 6389 NGC 6390 NGC 6391 NGC 6392 NGC 6393 NGC 6394 NGC 6395 NGC 6396 NGC 6397 NGC 6398 NGC 6399 NGC 6400 NGC 6401 NGC 6402 NGC 6403 NGC 6404 NGC 6405 NGC 6406 NGC 6407 NGC 6408 NGC 6409 NGC 6410 NGC 6411 NGC 6412 NGC 6413 NGC 6414 NGC 6415 NGC 6416 NGC 6417 NGC 6418 NGC 6419 NGC 6420 NGC 6421 NGC 6422 NGC 6423 NGC 6424 NGC 6425 NGC 6426 NGC 6427 NGC 6428 NGC 6429 NGC 6430 NGC 6431 NGC 6432 NGC 6433 NGC 6434 NGC 6435 NGC 6436 NGC 6437 NGC 6438 NGC 6439 NGC 6440 NGC 6441 NGC 6442 NGC 6443 NGC 6444 NGC 6445 NGC 6446 NGC 6447 NGC 6448 NGC 6449 NGC 6450 NGC 6451 NGC 6452 NGC 6453 NGC 6454 NGC 6455 NGC 6456 NGC 6457 NGC 6458 NGC 6459 NGC 6460 NGC 6461 NGC 6462 NGC 6463 NGC 6464 NGC 6465 NGC 6466 NGC 6467 NGC 6468 NGC 6469 NGC 6470 NGC 6471 NGC 6472 NGC 6473 NGC 6474 NGC 6475 NGC 6476 NGC 6477 NGC 6478 NGC 6479 NGC 6480 NGC 6481 NGC 6482 NGC 6483 NGC 6484 NGC 6485 NGC 6486 NGC 6487 NGC 6488 NGC 6489 NGC 6490 NGC 6491 NGC 6492 NGC 6493 NGC 6494 NGC 6495 NGC 6496 NGC 6497 NGC 6498 NGC 6499

Astronomical catalog List of NGC objects

Caldwell catalogue

List	C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 C26 C27 C28 C29 C30 C31 C32 C33 C34 C35 C36 C37 C38 C39 C40 C41 C42 C43 C44 C45 C46 C47 C48 C49 C50 C51 C52 C53 C54 C55 C56 C57 C58 C59 C60 C61 C62 C63 C64 C65 C66 C67 C68 C69 C70 C71 C72 C73 C74 C75 C76 C77 C78 C79 C80 C81 C82 C83 C84 C85 C86 C87 C88 C89 C90 C91 C92 C93 C94 C95 C96 C97 C98 C99 C100 C101 C102 C103 C104 C105 C106 C107 C108 C109

See also	Messier Catalogue Catalogue of Nebulae and Clusters of Stars New General Catalogue Index Catalogue Revised New General Catalogue Herschel 400 Catalogue

Book:Caldwell catalogue Category:Caldwell objects Portal:Astronomy Commons:Caldwell objects

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