| Messier 15 | |
|---|---|
 Deep Broadband (RGB) image of M15 | |
| Observation data (J2000 epoch) | |
| Class | IV[1] |
| Constellation | Pegasus |
| Right ascension | 21h 29m 58.33s[2] |
| Declination | +12° 10′ 01.2″[2] |
| Distance | 35.69 ± 0.43 kly (10.944 ± 0.131 kpc)[3] |
| Apparent magnitude (V) | 6.2[4] |
| Apparent dimensions (V) | 18′.0 |
| Physical characteristics | |
| Mass | 5.6×105[5] M☉ |
| Radius | ~88 ly[6] |
| VHB | 15.83 |
| Metallicity | = –2.37[7] dex |
| Estimated age | 12.0 Gyr[8] |
| Notable features | steep central cusp |
| Other designations | NGC 7078, GCl 120[9] |
![{\displaystyle {\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/4c0821bd80891e071c08e7c7ee8e022baedf522c)
Messier 15 or M15 (also designated NGC 7078 and sometimes known as the Great Pegasus Cluster) is a globular cluster in the constellation Pegasus. It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier's catalogue of comet-like objects in 1764.[citation needed] At an estimated 12.5±1.3 billion years old, it is one of the oldest known globular clusters.[10]
YouTube Encyclopedic
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Sirius Stargazing: Globular Cluster M15
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How to Find Pegasus the Winged Horse Constellation
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Einstein's Cross (galaxy + quasar) in Pegasus Constellation
Transcription
Welcome to Sirius Stargazing. I'm TK and in this episode we're going to look at the Globular Cluster Messier 15 - M15 for short - in the constellation of Pegasus. Now, unlike open or galactic clusters, which populate the sweeping arms of spiral galaxies like the one we live in, globular clusters occupy the galactic halo, which is an enormous, almost spherical cloud of material around the Milky Way's core; an outer component of the galaxy much fainter and less readily detectable than the bright nucleus or disc, which you and I are so familiar with. This is because on average, it's very diffuse, but the globular clusters within it are by contrast incredibly dense; tightly bound spherical ensembles of perhaps millions of suns. In the case of M15, the number is not quite this great, perhaps on the order of a few hundred thousand, but it is remarkable for having an unusually dense core. We know it has undergone a process called 'core-collapse' and today, many astronomers believe that deep in the centre lurks a medium-sized black hole. Because of this, I always think of Messier 15 as a scale model of an elliptical galaxy, and when you see it, it really looks like one, but there are more subtle similarities as well. For example, as with elliptical galaxies, globular clusters like M15 are composed entirely of very ancient stars. Now, in the disc of the Milky Way, we see nebulae where stars are forming, and we see open clusters containing very young stars, but in globular clusters no such star formation is going on any more. In fact, so old are most of the stars in M15, that when they formed there was actually no disc of the Milky Way at all. The galactic thin disc as we know it is a mere 9 billion years old or so, whereas members of M15 exceed 13 billion years, and that means they have been around for most of the history of the known Universe. Find Pegasus on your star atlas or planisphere and look for the star Enif, or Epsilon Pegasi, which marks the tip of its nose. Back-track up its head, and it will bring you to the star Theta Pegasi, and you need to construct an imaginary line between these two. Continue this line back down in the direction Pegasus is facing and past Enif for around half the distance between the two stars you've just found, and you'll come across M15. Knowing whether you've identified it for the first time can be tricky, so use this apparently nearby star as an indicator. It's brighter than the surrounding stars, and it will let you know that M15 is not far away. In poorer conditions, use averted vision to bring out more of the cluster and with practise you should be able to see both the bright and dense core, and the much fainter halo. At first, you might think that M15 looks just like a fuzzy star, but as a more experienced observer, you'll come to see it as being distinctly non-stellar, even at low magnification. Seeing M15 with a wide field-of-view, such as with binoculars, will really give you a good sense of scale. The cluster is about 200 light-years wide, but at best will only appear as a small, nebulous blob, because it's an incredible 34,000 light-years away, floating free from the galaxy's main spiral. Don't let its appearance disappoint you though; the trick to enjoying these deep sky objects is to know what it is you're looking at, and I find it amazing to consider that small blob for what it really is: the accumulated light of so many distant suns. It really leaves one wondering how the night sky would look to us if we lived there. Of course, there would be tens of thousands of bright stars above us, making our constellations either very numerous or at least very complicated, but because so many stars are bound together so very closely, a great number would be visible even during the day. So, Sirius Stargazers like us would never get any sleep. From a star system in M15, our home galaxy would be a truly staggering sight, dominating the sky, its beautiful spiral structure unmistakably clear. Maybe in the distant future, human beings will invent some kind of exotic new spacecraft and travel out of the galaxy to look back at our home, but for the foreseeable future at least, we can only study our neighbouring star cities, and try to infer how our own must appear to the rest of the Universe. For now, we'll keep looking out from the inside. Until next time, clear skies.
Characteristics
M 15 is about 35,700 light-years from Earth,[3] and 175 light-years in diameter.[11] It has an absolute magnitude of −9.2, which translates to a total luminosity of 360,000 times that of the Sun. Messier 15 is one of the most densely packed globulars known in the Milky Way galaxy. Its core has undergone a contraction known as "core collapse" and it has a central density cusp with an enormous number of stars surrounding what may be a central black hole.[12]
Home to over 100,000 stars,[11] the cluster is notable for containing a large number of variable stars (112) and pulsars (8), including one double neutron star system, M15-C. It also contains Pease 1, the first planetary nebula discovered within a globular cluster in 1928.[13][14] Just three others have been found in globular clusters since then.[15]
Amateur astronomy
At magnitude 6.2, M15 approaches naked eye visibility under good conditions and can be observed with binoculars or a small telescope, appearing as a fuzzy star.[11][14] Telescopes with a larger aperture (at least 6 in. (150 mm)) will start to reveal individual stars, the brightest of which are of magnitude +12.6. The cluster appears 18 arc minutes in size (three tenths of a degree across).[11] M15 is around 4° WNW of the brightest star of Pegasus, Epsilon Pegasi.[14]
X-ray sources
Earth-orbiting satellites Uhuru and Chandra X-ray Observatory have detected two bright X-ray sources in this cluster: Messier 15 X-1 (4U 2129+12) and Messier 15 X-2.[16][17] The former appears to be the first astronomical X-ray source detected in Pegasus.
Gallery
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The central square arcminute of M15 imaged using the lucky imaging technique -
Map showing the location of M15 -
M15 photographed by HST. The planetary nebula Pease 1 can be seen as a small blue object to the upper left of the core of the cluster.
See also
References
- ^ Shapley, Harlow; Sawyer, Helen B. (August 1927). "A Classification of Globular Clusters". Harvard College Observatory Bulletin. 849 (849): 11–14. Bibcode:1927BHarO.849...11S.
- ^ a b 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.
- ^ a b Bhardwaj, Anupam; Rejkuba, Marina; Sloan, G. C.; Marconi, Marcella; Yang, Soung-Chul (2021). "Optical and Near-infrared Pulsation Properties of RR Lyrae and Population II Cepheid Variables in the Messier 15 Globular Cluster". The Astrophysical Journal. 922 (1): 20. arXiv:2108.11388. Bibcode:2021ApJ...922...20B. doi:10.3847/1538-4357/ac214d. S2CID 237304172.
- ^ "Messier 15". SEDS Messier Catalog. Archived from the original on 11 July 2022. Retrieved 28 April 2022.
- ^ 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. S2CID 118652005. Mass is from MPD on Table 1.
- ^ distance × sin( diameter_angle / 2 ) = 88 ly radius
- ^ Boyles, J.; et al. (November 2011). "Young Radio Pulsars in Galactic Globular Clusters". The Astrophysical Journal. 742 (1): 51. arXiv:1108.4402. Bibcode:2011ApJ...742...51B. doi:10.1088/0004-637X/742/1/51. S2CID 118649860.
- ^ Koleva, M.; et al. (April 2008). "Spectroscopic ages and metallicities of stellar populations: validation of full spectrum fitting". Monthly Notices of the Royal Astronomical Society. 385 (4): 1998–2010. arXiv:0801.0871. Bibcode:2008MNRAS.385.1998K. doi:10.1111/j.1365-2966.2008.12908.x. S2CID 17571531.
- ^ "M 15". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-16.
- ^ O'Malley, Erin M.; Gilligan, Christina; Chaboyer, Brian (April 2017). "Absolute Ages and Distances of 22 GCs Using Monte Carlo Main-sequence Fitting". The Astrophysical Journal. 838 (2): 162. arXiv:1703.01915. Bibcode:2017ApJ...838..162O. doi:10.3847/1538-4357/aa6574. S2CID 11852378.
- ^ a b c d "M 15". astropix.
- ^ Gerssen J, van der Marel RP, Gebhardt K, Guhathakurta P, Peterson RC, Pryor C (2003). "Evidence for an intermediate-mass black hole in the globular cluster M 15. II. Kinematic analysis and dynamical modeling". Astronomical Journal. Hubble Space Telescope. 125 (1): 376–377. arXiv:astro-ph/0210158. Bibcode:2003AJ....125..376G. doi:10.1086/345574. S2CID 118948032.
- ^ Cohen, J.G.; Gillett, F.C. (1989). "The peculiar planetary nebula in M 22" (PDF). Astrophysical Journal. 346: 803–807. Bibcode:1989ApJ...346..803C. doi:10.1086/168061. S2CID 119770028.
- ^ a b c O'Meara, Stephen James; Levy, David H. (1998), Deep-Sky Companions: The Messier Objects, Cambridge University Press, p. 74, ISBN 978-0521553322.
- ^ "more". SEDS.org. Messier 15.
- ^ Forman W; Jones C; Cominsky L; Julien P; Murray S; Peters G (1978). "The fourth Uhuru catalog of X-ray sources". Astrophysical Journal Supplement Series. 38: 357. Bibcode:1978ApJS...38..357F. doi:10.1086/190561.
- ^ White NE; Angelini L (2001). "The discovery of a second luminous low-mass X-ray binary in the globular cluster M15". Astrophysical Journal Letters. 561 (1): L101–5. arXiv:astro-ph/0109359. Bibcode:2001ApJ...561L.101W. doi:10.1086/324561. S2CID 18877294.
External links
- Messier 15, SEDS Messier pages
- Messier 15, Galactic Globular Clusters Database page
- Globular Cluster Photometry With the Hubble Space Telescope. V. WFPC Study of M15's Central density Cusp
- Wikisky.org SDSS image of M15
- Gretton, Roy; Gray, Meghan. "M15 – Globular Cluster". Deep Sky Videos. Brady Haran.
- Messier 15 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
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This page was last edited on 18 March 2024, at 19:42