NGC 6397

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NGC 6397
P0321a.jpg
A Hubble Space Telescope (HST) image of NGC 6397
Observation data (J2000 epoch)
Class IX [1]
Constellation Ara
Right ascension 17h 40m 42.09s [2]
Declination –53° 40′ 27.6″ [2]
Distance 7.8  kly (2.4  kpc) [3]
Apparent magnitude (V)+6.68 [4]
Apparent dimensions (V)32.0′
Physical characteristics
Mass1.14×105 [5]   M☉
Radius34 ly [6]
VHB14.2
Metallicity  = –1.76 [7] dex
Estimated age13.4 ± 0.8 Gyr [8]
Notable featuresSecond closest globular cluster
Other designationsGCl 74, [4] Lacaille III.11, Dunlop 366, Bennett 98, Caldwell 86
See also: Globular cluster, List of globular clusters

NGC 6397 (also known as Caldwell 86) is a globular cluster in the constellation Ara that was discovered by French astronomer Nicolas-Louis de Lacaille in 1752. [9] It is located about 7,800 light-years from Earth, [3] making it one of the two nearest globular clusters to Earth (the other one being Messier 4). The cluster contains around 400,000 stars, [8] and can be seen with the naked eye under good observing conditions. [10]

Contents

NGC 6397 is one of at least 20 globular clusters of the Milky Way Galaxy that have undergone a core collapse, [8] 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 [8] focused on the cluster to estimate the age of the Milky Way Galaxy. 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. This estimate assumes that the NGC 6397 is not older than the Milky Way.

Lower mass limit for stars

In 2006, a study of NGC 6397 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. [11]

Black holes and white dwarfs

In February 2021, the core of NGC 6397 was reported to contain a relatively dense concentration of compact objects (white dwarfs, neutron stars and black holes), based on the movement of stars near the core derived from data gathered by the Hubble Space Telescope and the European Space Agency's Gaia spacecraft. [12] [13] The respective study argued that black holes could dominate the mass budget of this concentration, if the black holes were not ejected by means of dynamical interactions. Indeed, another group of scientists shortly responded, claiming that because NGC 6397 has undergone core collapse, it should have started dense enough to speed its rates of dynamical interactions, and its original black hole population should be almost entirely gone. [14] This group provided dynamical simulations that showed that a concentration of white dwarfs could explain the first measurement. [15]

Finally, in 2022, a work was published by the former scientists, along with one of the leaders of the latter group, and other experts of Hubble and Gaia data. [5] This new work showed that the fits of the central mass excess in NGC 6397 from observed data agreed remarkably well with numerical simulations accounting for a population of hundreds of massive white dwarfs, and essentially no black holes. [16]

Distant globular clusters

Hubble pictures revealed many distant globular clusters in galaxies far behind NGC 6397.

See also

Related Research Articles

<span class="mw-page-title-main">Globular cluster</span> Spherical collection of stars

A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of member stars, all orbiting in a stable, compact formation. Globular clusters are similar in form to dwarf spheroidal galaxies, and the distinction between the two is not always clear. Their name is derived from Latin globulus. Globular clusters are occasionally known simply as "globulars".

<span class="mw-page-title-main">Messier 87</span> Elliptical galaxy in the Virgo Galaxy Cluster

Messier 87 is a supergiant elliptical galaxy in the constellation Virgo that contains several trillion stars. One of the largest and most massive galaxies in the local universe, it has a large population of globular clusters—about 15,000 compared with the 150–200 orbiting the Milky Way—and a jet of energetic plasma that originates at the core and extends at least 1,500 parsecs, traveling at a relativistic speed. It is one of the brightest radio sources in the sky and a popular target for both amateur and professional astronomers.

<span class="mw-page-title-main">Messier 4</span> Globular cluster in Scorpius

Messier 4 or M4 is a globular cluster in the constellation of Scorpius. It was discovered by Philippe Loys de Chéseaux in 1745 and catalogued by Charles Messier in 1764. It was the first globular cluster in which individual stars were resolved.

<span class="mw-page-title-main">Omega Centauri</span> Globular cluster in the constellation Centaurus

Omega Centauri is a globular cluster in the constellation of Centaurus that was first identified as a non-stellar object by Edmond Halley in 1677. Located at a distance of 17,090 light-years, it is the largest-known globular cluster in the Milky Way at a diameter of roughly 150 light-years. It is estimated to contain approximately 10 million stars, with a total mass of 4 million solar masses, making it the most massive known globular cluster in the Milky Way.

<span class="mw-page-title-main">Messier 30</span> Globular cluster in the constellation Capricornus

Messier 30 is a globular cluster of stars in the southeast of the southern constellation of Capricornus, at about the declination of the Sun when the latter is at December solstice. It was discovered by the French astronomer Charles Messier in 1764, who described it as a circular nebula without a star. In the New General Catalogue, compiled during the 1880s, it was described as a "remarkable globular, bright, large, slightly oval." It can be easily viewed with a pair of 10×50 binoculars, forming a patch of hazy light some 4 arcminutes wide that is slightly elongated along the east–west axis. With a larger instrument, individual stars can be resolved and the cluster will cover an angle of up to 12 arcminutes across graduating into a compressed core about one arcminute wide that has further star density within.

<span class="mw-page-title-main">Messier 54</span> Globular cluster in Sagittarius

Messier 54 is a globular cluster in the constellation Sagittarius. It was discovered by Charles Messier in 1778 and then included in his catalog of comet-like objects.

<span class="mw-page-title-main">Messier 53</span> Globular cluster in the constellation Coma Berenices

Messier 53 is a globular cluster in the Coma Berenices constellation. It was discovered by Johann Elert Bode in 1775. M53 is one of the more outlying globular clusters, being about 60,000 light-years (18.4 kpc) light-years away from the Galactic Center, and almost the same distance from the Solar System. The cluster has a core radius (rc) of 2.18 pc, a half-light radius (rh) of 5.84 pc, and a tidal radius (rtr) of 239.9 pc.

<span class="mw-page-title-main">Messier 62</span> Globular cluster in the constellation Ophiuchus

Messier 62 or M62, also known as NGC 6266 or the Flickering Globular Cluster, is a globular cluster of stars in the south of the equatorial constellation of Ophiuchus. It was discovered in 1771 by Charles Messier, then added to his catalogue eight years later.

<span class="mw-page-title-main">Dwarf galaxy</span> Small galaxy composed of up to several billion stars

A dwarf galaxy is a small galaxy composed of about 1000 up to several billion stars, as compared to the Milky Way's 200–400 billion stars. The Large Magellanic Cloud, which closely orbits the Milky Way and contains over 30 billion stars, is sometimes classified as a dwarf galaxy; others consider it a full-fledged galaxy. Dwarf galaxies' formation and activity are thought to be heavily influenced by interactions with larger galaxies. Astronomers identify numerous types of dwarf galaxies, based on their shape and composition.

<span class="mw-page-title-main">Sculptor Galaxy</span> Intermediate spiral galaxy in the constellation Sculptor

The Sculptor Galaxy is an intermediate spiral galaxy in the constellation Sculptor. The Sculptor Galaxy is a starburst galaxy, which means that it is currently undergoing a period of intense star formation.

<span class="mw-page-title-main">47 Tucanae</span> Globular cluster in the constellation Tucana

47 Tucanae or 47 Tuc is a globular cluster located in the constellation Tucana. It is about 4.45 ± 0.01 kpc (15,000 ± 33 ly) from Earth, and 120 light years in diameter. 47 Tuc can be seen with the naked eye, with an apparent magnitude of 4.1. It appears about 44 arcminutes across including its far outreaches. Due to its far southern location, 18° from the south celestial pole, it was not catalogued by European astronomers until the 1750s, when the cluster was first identified by Nicolas-Louis de Lacaille from South Africa.

<span class="mw-page-title-main">NGC 2419</span> Globular cluster in the constellation Lynx

NGC 2419 is a globular cluster in the constellation Lynx. It was discovered by William Herschel on December 31, 1788. NGC 2419 is at a distance of about 300,000 light years from the Solar System and at the same distance from the Galactic Center.

<span class="mw-page-title-main">NGC 3201</span> Globular cluster in the constellation Vela

NGC 3201 is a low galactic latitude globular cluster in the southern constellation of Vela. It has a very low central concentration of stars. This cluster was discovered by James Dunlop on May 28, 1826 and listed in his 1827 catalogue. He described it as "a pretty large pretty bright round nebula, 4′ or 5′ diameter, very gradually condensed towards the centre, easily resolved into stars; the figure is rather irregular, and the stars are considerably scattered on the south".

<span class="mw-page-title-main">NGC 6752</span> Globular cluster in the constellation Pavo

NGC 6752 is a globular cluster in the constellation Pavo. It is the fourth-brightest globular cluster in the sky, after Omega Centauri, 47 Tucanae and Messier 22, respectively. It is best seen from June to October in the Southern Hemisphere.

<span class="mw-page-title-main">NGC 6934</span> Globular cluster in the constellation Delphinus

NGC 6934 is a globular cluster of stars in the northern constellation of Delphinus, about 52 kilolight-years distant from the Sun. It was discovered by the German-born astronomer William Herschel on 24 September 1785. The cluster is following a highly eccentric orbit through the Milky Way along an orbital plane that is inclined by 73° to the galactic plane. It may share a common dynamic origin with NGC 5466. As of 2018, it has been poorly studied.

<span class="mw-page-title-main">NGC 2808</span> Globular cluster in the constellation Carina

NGC 2808 is a globular cluster in the constellation Carina. The cluster currently belongs to the Milky Way, although it was likely stolen from a dwarf galaxy that collided with the Milky Way. NGC 2808 is one of our home galaxy's most massive clusters, containing more than a million stars. It is estimated to be 12.5-billion years old.

<span class="mw-page-title-main">NGC 1851</span> Globular cluster in the constellation Columba

NGC 1851 is a relatively massive globular cluster located in the southern constellation of Columba. Astronomer John Dreyer described it as not very bright but very large, round, well resolved, and clearly consisting of stars. It is located 39.5 kilolight-years from the Sun, and 54.1 kilolight-years from the Galactic Center. The cluster is following a highly eccentric orbit through the galaxy, with an eccentricity of about 0.7.

<span class="mw-page-title-main">NGC 6352</span> Globular cluster in the constellation Ara

NGC 6352 is a globular cluster of stars in the southern constellation of Ara, located approximately 18.3 kly from the Sun. It was discovered by Scottish astronomer James Dunlop on May 14, 1826. The cluster has a Shapley–Sawyer Concentration Class of XI:. A telescope with a 15 cm (5.9 in) aperture is required to resolve the stars within this loose cluster.

<span class="mw-page-title-main">NGC 5286</span> Globular cluster in the constellation Centaurus

NGC 5286 is a globular cluster of stars located some 35,900 light years away in the constellation Centaurus. At this distance, the light from the cluster has undergone reddening from interstellar gas and dust equal to E(B – V) = 0.24 magnitude in the UBV photometric system. The cluster lies 4 arc-minutes north of the naked-eye star M Centauri. It was discovered by Scottish astronomer James Dunlop, active in Australia, and listed in his 1827 catalog.

<span class="mw-page-title-main">ESO 444-46</span> Galaxy in the constellation Centaurus

ESO 444-46 is a class E4 supergiant elliptical galaxy; the dominant and brightest member of the Abell 3558 galaxy cluster around 640 million light-years away in the constellation Centaurus. It lies within the core of the massive Shapley Supercluster, one of the closest neighboring superclusters. It is one of the largest galaxies in the local universe, and possibly contains one of the most massive black holes known. The black hole's mass is very uncertain, with estimates ranging from as low as 501 million M☉, to as high as 77.6 billion M☉.

References

  1. ↑ Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin, 849 (849): 11–14, Bibcode:1927BHarO.849...11S.
  2. 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, S2CID   119183070.
  3. 1 2 Salazar, Doris Elen (5 April 2018). "Cosmic 'Yardstick' Measures Distance to One of Universe's Oldest Objects". Space.com. Retrieved 5 April 2018.
  4. 1 2 "NGC 6397". SIMBAD . Centre de données astronomiques de Strasbourg . Retrieved 2006-11-16.
  5. 1 2 Vitral, Eduardo; Kremer, Kyle; Libralato, Mattia; Mamon, Gary A.; Bellini, Andrea (2022), "Stellar graveyards: clustering of compact objects in globular clusters NGC 3201 and NGC 6397", Monthly Notices of the Royal Astronomical Society, 514 (1): 806, arXiv: 2202.01599 , Bibcode:2022MNRAS.514..806V, doi:10.1093/mnras/stac1337
  6. ↑ distance × sin( diameter_angle / 2 ) = ~34 ly. radius
  7. ↑ 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, S2CID   51825384.
  8. 1 2 3 4 "How Old is the Milky Way ?". Results for NGC 6397. Archived from the original on 2008-09-05. Retrieved 2006-09-26.
  9. ↑ Jones, K. G. (March 1969). "The search for the nebulae - VI". Journal of the British Astronomical Association. 79: 213–222. Bibcode:1969JBAA...79..213J.
  10. ↑ Dunlop, Storm (2005). Atlas of the Night Sky . Collins. ISBN   978-0-00-717223-8.
  11. ↑ "HST analysis of faint stars in NGC6397". Results for NGC 6397. Retrieved 2006-09-26.
  12. ↑ Vitral, Eduardo; Mamon, Gary A. (2021), "Does NGC 6397 contain an intermediate-mass black hole or a more diffuse inner subcluster?", Astronomy & Astrophysics, 646 (A63): A63, arXiv: 2010.05532 , Bibcode:2021A&A...646A..63V, doi: 10.1051/0004-6361/202039650
  13. ↑ "Hubble Uncovers Concentration of Small Black Holes". ESA. 11 February 2021. Retrieved 21 February 2021.
  14. ↑ Rui, Nicholas Z.; Weatherford, Newlin C.; Kremer, Kyle; Chatterjee, Sourav; Fragione, Giacomo; Rasio, Frederic A.; Rodriguez, Carl L.; Ye, Claire S. (2021), "No Black Holes in NGC 6397", Research Notes of the American Astronomical Society, 5 (3): 47, arXiv: 2103.06273 , Bibcode:2021RNAAS...5...47R, doi: 10.3847/2515-5172/abee77 , S2CID   232185141
  15. ↑ Kremer, Kyle; Rui, Nicholas Z.; Weatherford, Newlin C.; Chatterjee, Sourav; Fragione, Giacomo; Rasio, Frederic A.; Rodriguez, Carl L.; Ye, Claire S. (2021), "White Dwarf Subsystems in Core-Collapsed Globular Clusters", The Astrophysical Journal, 917 (1): 28, arXiv: 2104.11751 , Bibcode:2021ApJ...917...28K, doi: 10.3847/1538-4357/ac06d4 , S2CID   233394452
  16. ↑ "Chasser des trous noirs dans un cimetière d'étoiles". 10 June 2022.
  17. ↑ "Hubble's view of dazzling globular cluster NGC 6397". www.spacetelescope.org. Retrieved 13 April 2018.
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