NGC 6624

NGC 6624
The globular cluster NGC 6624. Credit Hubble Space Telescope
Observation data (J2000 epoch)
ClassVI
ConstellationSagittarius
Right ascension18h 23m 41s
Declination−30° 21′ 39″
Distance25.8 ± 1.1 kly (7.91 ± 0.34 kpc)
Apparent magnitude (V)7.6
Apparent dimensions (V)8.8 arcminutes[1]
Physical characteristics
Metallicity = -0.56 ± 0.27[2] dex
Other designationsESO 457-11, GCl 93, CD−30 15631, CPD−30 5486, HD 168943[3]
See also: Globular cluster, List of globular clusters
The 4U 1820-30 system, consisting of a neutron star and a white dwarf, compared to the Earth and the Sun (bottom). The neutron star is tied with PSR J1748−2446ad as the fastest rotating pulsar known, both making 716 revolutions per second.

NGC 6624 is a globular cluster in the constellation Sagittarius. It was discovered on 24 June 1784 by the astronomer William Herschel. It is given an apparent magnitude of 7.6 to 8.5.[4] Six pulsars are known in NGC 6624. The first of these to be discovered was PSR J1823-3021A. This globular cluster also contains 4U 1820-30, a low-mass X-ray binary with an orbital period of only 11.5 minutes, consisting of a neutron star and a white dwarf. Astronomers using the NICER instrument have found evidence that the neutron star is spinning at 716 Hz (times per second), or 42,960 revolutions per minute, the same velocity as the fastest known spinning neutron star PSR J1748−2446ad and the only one in such a system.[5][6]

NGC 6624 is visible as a hazy spot with a small telescope, and appears as a star-like object with binoculars. Its core appears significantly condensed.[1] It is located 0.8 degrees southeast of the star Delta Sagittarii,[7] and is about 1.17 kpc (3.8 kly) from the Galactic Center.[2]

Map showing location of NGC 6624

References

  1. ^ a b O'Meara, Steve (2007). Steve O'Meara's Herschel 400 Observing Guide. Cambridge: Cambridge University Press. p. 236. ISBN 978-0-521-85893-9.
  2. ^ a b Sofue, Yoshiaki (1998-08-31). The Central Regions of the Galaxy and Galaxies. Netherlands: Kluwer Academic Publishers. p. 37. ISBN 978-0-7923-5061-3.
  3. ^ "NGC 6624". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-02-19.
  4. ^ It is given a diameter of 6 to 8.5 arcminutes, and class VI with stars magnitude 14 and dimmer. It is less than a degree southeast of star Delta Sagittarii. O'Meara, Stephen James (2007). Deep Sky Companions: Hidden Treasures. Cambridge University Press. p. 452. ISBN 978-1-139-46373-7.
  5. ^ Jaisawal, Gaurava K.; Bostancı, Z. Funda; Boztepe, Tuğba; Güver, Tolga; Strohmayer, Tod E.; Ballantyne, David R.; Beck, Jens H.; Göğüş, Ersin; Altamirano, Diego; Arzoumanian, Zaven; Chakrabarty, Deepto; Gendreau, Keith C.; Guillot, Sebastien; Ludlam, Renee M.; Ng, Mason (2024-11-01). "A Comprehensive Study of Thermonuclear X-Ray Bursts from 4U 1820–30 with NICER: Accretion Disk Interactions and a Candidate Burst Oscillation". The Astrophysical Journal. 975 (1): 67. Bibcode:2024ApJ...975...67J. doi:10.3847/1538-4357/ad794e. ISSN 0004-637X.
  6. ^ Starr, Michelle (2024-11-06). "Wild Star Discovered Spinning an Incredible 716 Times Per Second". ScienceAlert. Retrieved 2024-11-10.
  7. ^ Bakich, Michael E. (2010). 1001 Celestial Wonders to See Before You Die: The Best Sky Objects for Star Gazers. Patrick Moore's Practical Astronomy Series. Springer. p. 249. doi:10.1007/978-1-4419-1777-5. ISBN 978-1-4419-1776-8.
  • Robert Burnham, Jr, Burnham's Celestial Handbook: An observer's guide to the universe beyond the solar system, vol 3, p. 1557


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