NGC 6256

NGC 6256
NGC 6256 as seen through the Hubble Space Telescope
Observation data (J2000 epoch)
ConstellationScorpius
Right ascension16h 59m 32.68s[1]
Declination−37° 07′ 17.1″[1]
Distance22 kly (6.8 kpc)[2]
Apparent magnitude (V)11.3[3]
Apparent dimensions (V)7′[4]
Physical characteristics
Absolute magnitude−7.15[citation needed]
Estimated age13.0±0.5 Gyr[2]
Other designationsNGC 6256, GCL 49.1, ESO 391-SC6 and vdB-Hagen 208[5]
See also: Globular cluster, List of globular clusters

NGC 6256 is a globular cluster of stars in the southern constellation of Scorpius. It was discovered by the Scottish astronomer James Dunlop on Aug 2, 1826.[6] In J. L. E. Dreyer's New General Catalogue annotation it is described as, "very faint, very large, very gradually bright in the middle, well resolved clearly consisting of stars."[7] The cluster is located at a distance of 22 thousand light-years (6.8 kpc) from the Sun.[2]

This is an ancient cluster with an estimated age of about 13 billion years; it was formed during the very early stages of assembly of the Milky Way galaxy. The cluster is orbiting within the galactic bulge with a low orbital eccentricity. It is heavily reddened by extinction due to interstellar gas and dust.[2] The structure is very concentrated at the center, showing a post core collapse morphology.[8]

The HR diagram for this cluster displays two sequences of blue straggler stars, which are the products of stellar mergers. The bluer sequence is well-defined and narrow, most likely being generated over a short time span. The redder sequence is more sparse, being the result of a continuous process of formation. It is hypothesized that the bluer sequence was formed around the time of the cluster's core collapse about one billion years ago; an event that made stellar collisions more likely.[9]

The cluster contains a millisecond X-ray pulsar, designated IGR J16597-3704.[10]

  1. ^ a b Cite error: The named reference Di_Criscienzo_et_al_2006 was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference Cadelano_et_al_2020 was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference O'Meara 2013 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference SEDS was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference CSeligman was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Terzan_Lelievre_1973 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Ortolani_et_al_1999 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Cadelano_et_al_2022 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Tetarenko_et_al_2018 was invoked but never defined (see the help page).