Plik:Caldwell 25.jpg
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English: There are about 150 globular star clusters that roam the Milky Way’s halo, which encases the galaxy like a giant, diffuse eggshell. But among them, Caldwell 25 is unusual. Unlike most globular clusters, which are huge, spherical clouds of old stars believed to be among the oldest in the galaxy, Caldwell 25 may not be from our galaxy at all. Located about 300,000 light-years from Earth, this cluster is sometimes called “the Intergalactic Wanderer” because it is so far away — even farther than the Milky Way’s largest satellite galaxies, the Small and Large Magellanic clouds, which are about 160,000 light-years away. Scientists have surmised that the cluster may be part of the remains of a small galaxy that was captured and disrupted by the Milky Way.
Caldwell 25 seems to be fairly similar to other large globular clusters, though its extreme distance makes it difficult to study and compare its properties with other globular clusters in the Milky Way. Usually all the stars in a globular cluster are very similar to one another in composition, since they typically form in the same general area from the same materials. However, Hubble’s observations of Caldwell 25 hint that it has a different story. This interesting cluster hosts two distinct sets of red giant stars that have different amounts of certain elements. Red giants are a type of star that results when a medium-mass star expends the fuel that keeps it burning during most of its lifetime. One of Caldwell 25’s red-giant subsets, found mainly in the central region of the cluster, has a surprisingly high amount of helium. The differences between the two groups has led scientists to question whether the two stellar populations formed together or started out as individual groups that later merged. Caldwell 25 was discovered by astronomer William Herschel on New Year’s Eve of 1788 and is also cataloged as NGC 2419. The cluster is intrinsically bright, but it appears faint because it is so far away. It has a magnitude of 10.4 and is located in the constellation Lynx. In a typical amateur telescope, Caldwell 25 appears as a soft, hazy, circular glow. Because of the cluster’s distance, individual stars are not readily resolved. Observing under clear, winter skies in the Northern Hemisphere will provide the best opportunity to spot Caldwell 25. Southern Hemisphere observers should search for it in the northern sky during the summer. Credit: ESA/Hubble & NASA, S. Larsen et al. For more information about Hubble’s observations of Caldwell 25, see: www.spacetelescope.org/images/potw1908a/ For Hubble's Caldwell catalog site and information on how to find these objects in the night sky, visit: www.nasa.gov/content/goddard/hubble-s-caldwell-catalog |
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Źródło | https://www.flickr.com/photos/144614754@N02/49096538881/ |
Autor | NASA Hubble |
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Ten plik, opublikowany pierwotnie w serwisie Flickr przez NASA Hubble pod adresem https://flickr.com/photos/144614754@N02/49096538881 (kopia archiwalna), został sprawdzony 23 lutego 2020 przez FlickreviewR 2, który potwierdził, że jest on tam dostępny na licencji cc-by-2.0. |
23 lutego 2020
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aktualny | 22:05, 23 lut 2020 | 3916 × 3892 (19,77 MB) | Killarnee | User created page with UploadWizard |
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Dostawca | ESA/Hubble & NASA, S. Larsen et al. |
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Źródło | ESA/Hubble |
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Data i czas utworzenia oryginału | 06:00, 25 lut 2019 |
Komentarz pliku JPEG | Globular clusters like NGC 2419, visible in this image taken with the NASA/ESA Hubble Space Telescope, are not only beautiful, but also fascinating. They are spherical groups of stars which orbit the centre of a galaxy; in the case of NGC 2419, that galaxy is the Milky Way. NGC 2419 can be found around 300 000 light-years from the Solar System, in the constellation Lynx (the Lynx). The stars populating globular clusters are very similar to one another, with similar properties such as metallicity. The similarity of these stellar doppelgängers is due to their formation early in the history of the galaxy. As the stars in a globular cluster all formed at around the same time, they tend to display reasonably homogeneous properties. It was believed that this similarity also extended to the stellar helium content; that is, it was thought that all stars in a globular cluster would contain comparable amounts of helium. However, Hubble’s observations of NGC 2419 have shown that this is not always the case. This surprising globular cluster turns out to be made up of two separate populations of red giant stars, one of which is unusually helium-rich. Other elements within the different stars in NGC 2419 vary too — nitrogen in particular. On top of this, these helium-rich stars were found to be predominantly in the centre of the globular cluster, and to be rotating. These observations have raised questions about the formation of globular clusters; did these two drastically different groups of stars form together? Or did this globular cluster come into being by a different route entirely? |
Użyte oprogramowanie | Adobe Photoshop CC 2019 (Windows) |
Data i czas zeskanowania | 19:02, 11 lis 2018 |
Data ostatniej modyfikacji metadanych | 17:59, 31 gru 2018 |
Data i czas modyfikacji pliku | 17:59, 31 gru 2018 |
Unikalny identyfikator oryginalnego dokumentu | xmp.did:6936c3b7-837a-5e47-b24f-494b117f35d7 |
Słowa kluczowe | NGC 2419 |
Kontakt |
Karl-Schwarzschild-Strasse 2 Garching bei München, None, D-85748 Germany |