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File:Hoag's object.jpg

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Afrikaans: 'n Bykans perfekte ring van warm, blou sterre omwentel die geel kern van 'n ongewone ringsterrestelsel bekend as Hoag se Voorwerp. Hierdie beeld van NASA se Hubble-ruimteteleskoop vergun ons 'n gesig wat meer detail van die voorwerp onthul as enige foto tot nog toe. Die beeld kan leidrade aan sterrekundiges verskaf vir ontrafeling van die ontstaansproses van so 'n vreemde voorwerp.

Die hele sterrestelsel is sowat 120 000 ligjaar wyd, wat naamlik effens groter as die Melkweg is. Die blou ring, wat oorheers word deur opeenhopings van jong, massiewe sterre, staan in sterk kontras met die geel kern van meestal ouer sterre. Die skynbare gaping tussen hierdie twee sterbevolkings kan egter wel 'n paar stergroepe bevat wat amper te vaag is om te sien. Vreemd genoeg kan 'n voorwerp in die een-uur-posisie van die gaping gesien word wat 'n treffende ooreenkoms met Hoag se voorwerp toon. Die voorwerp is waarskynlik 'n agtergrond-sterrestelsel.

Ringvormige sterrestelsels kan op verskillende maniere ontstaan. Een moontlike scenario is 'n botsing met 'n ander sterrestelsel. Soms beweeg die tweede sterrestelsel deur die eerste, wat 'n "spatsel" van stervorming agterlaat. Maar in Hoag se Voorwerp is daar geen teken van 'n geskikte tweede sterrestelsel nie. Die vermoede bestaan dan dat die blou ring van sterre die verskeurde oorblyfsels kan wees van 'n sterrestelsel wat verbygeskram het. Sommige sterrekundiges beraam dat die ontmoeting ongeveer 2 tot 3 miljard jaar gelede plaasgevind het.

Hierdie ongewone sterrestelsel is in 1950 deur die sterrekundige Art Hoag ontdek. Hoag het die rookringagtige voorwerp vir 'n planetêre newel aangesien, d.w.s. die gloeiende oorblyfsels van 'n sonagtige ster. Hy het hierdie moontlikheid egter vinnig in twyfel getrek en die vermoede uitgespreek dat die geheimsinnige voorwerp 'n sterrestelsel kan wees. Waarnemings in die 1970's het hierdie voorspelling bevestig, hoewel etlike besonderhede van Hoag se sterrestelsel steeds 'n raaisel bly.

Die sterrestelsel is 600 miljoen ligjare weg in die konstellasie Serpens Caput, d.i. die Slang se Kop. Die Hubble-ruimteteleskoop se Wide Field and Planetary Camera 2 het hierdie beeld op 9 Julie 2001 geneem.
English: A nearly perfect ring of hot, blue stars pinwheels about the yellow nucleus of an unusual ring galaxy known as Hoag's Object. This image from NASA's Hubble Space Telescope captures a face-on view of the galaxy's ring of stars, revealing more detail than any existing photo of this object. The image may help astronomers unravel clues on how such strange objects form.

The entire galaxy is about 120,000 light-years wide, which is slightly larger than our Milky Way Galaxy. The blue ring, which is dominated by clusters of young, massive stars, contrasts sharply with the yellow nucleus of mostly older stars. What appears to be a "gap" separating the two stellar populations may actually contain some star clusters that are almost too faint to see. Curiously, an object that bears an uncanny resemblance to Hoag's Object can be seen in the gap at the one o'clock position. The object is probably a background ring galaxy.

Ring-shaped galaxies can form in several different ways. One possible scenario is through a collision with another galaxy. Sometimes the second galaxy speeds through the first, leaving a "splash" of star formation. But in Hoag's Object there is no sign of the second galaxy, which leads to the suspicion that the blue ring of stars may be the shredded remains of a galaxy that passed nearby. Some astronomers estimate that the encounter occurred about 2 to 3 billion years ago.

This unusual galaxy was discovered in 1950 by astronomer Art Hoag. Hoag thought the smoke-ring-like object resembled a planetary nebula, the glowing remains of a Sun-like star. But he quickly discounted that possibility, suggesting that the mysterious object was most likely a galaxy. Observations in the 1970s confirmed this prediction, though many of the details of Hoag's galaxy remain a mystery.

The galaxy is 600 million light-years away in the constellation Serpens. The Wide Field and Planetary Camera 2 took this image on July 9, 2001.
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Autore NASA and The Hubble Heritage Team (STScI/AURA); Acknowledgment: Ray A. Lucas (STScI/AURA)
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File:Hoags Object.jpg

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This file is in the public domain because it was created by NASA and ESA. NASA Hubble material (and ESA Hubble material prior to 2009) is copyright-free and may be freely used as in the public domain without fee, on the condition that only NASA, STScI, and/or ESA is credited as the source of the material. This license does not apply if ESA material created after 2008 or source material from other organizations is in use.

The material was created for NASA by Space Telescope Science Institute under Contract NAS5-26555, or for ESA by the Hubble European Space Agency Information Centre. Copyright statement at hubblesite.org or 2008 copyright statement at spacetelescope.org.

For material created by the European Space Agency on the spacetelescope.org site since 2009, use the {{ESA-Hubble}} tag.

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