astro.wikisort.org - Galaxy

Willman 1 is an ultra low-luminosity dwarf galaxy or a star cluster.[3] Willman 1 was discovered in 2004.[4] It is named after Beth Willman of Haverford College, the lead author of a study based on the Sloan Digital Sky Survey data. The object is a satellite of the Milky Way, at ~120,000 light-years away.[1] Willman 1 has an elliptical shape with the half-light radius of about 25 pc.[2] Its heliocentric velocity is approximately −13 km/s.[3]

Willman 1
Observation data (J2000 epoch)
Constellation	Ursa Major
Right ascension	10h 49m 22.3s[1]
Declination	+51° 03′ 03.6″[1]
Distance	124 ± 23 kly (38 ± 7 kpc)[2]
Apparent magnitude (V)	15.2 ± 0.4[a]
Characteristics
Type	extreme dSph or unusual star cluster[1]
Apparent size (V)	4.6+0.4 −0.8′[2]
Other designations
SDSS J1049+5103[1]

As of 2007, it was declared the least massive galaxy known, opening up a new category of ultra-low-mass galaxies, lower than the then-theoretical minimum of 10 million solar masses thought to be needed to form a galaxy.[5]

As of 2016, it is the third dimmest likely galaxy known, after Segue 1 and Virgo I, and is over ten million times less luminous than the Milky Way. It has an absolute magnitude of −2.7 ± 0.7.[2] Observations indicate its mass is about 0.4 million solar masses, which means that Willman's 1 mass to light ratio is around 800.[3] A high mass to light ratio implies that Willman 1 is dominated by dark matter. It is difficult, however, to estimate the mass of such faint objects because any mass estimate is based on an implicit assumption that an object is gravitationally bound, which may not be true if the object is in a process of disruption.[3]

The stellar population of Willman 1 consists mainly of old stars formed more than 10 billion years ago.[1] The metallicity of these stars is also very low at [Fe/H] ≈ −2.1, which means that they contain 110 times less heavy elements than the Sun.[3]

Notes

References

Inline

General

Preceded by

Least massive galaxy known 2007 – 2013 500,000MSun

Succeeded by Segue 2

На других языках

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[de] Willman 1

Willman 1 ist eine Ultralichtschwache Zwerggalaxie möglicherweise auch ein Kugelsternhaufen[3]. Sie wurde benannt nach Beth Willman vom Haverford College, der führenden Autorin einer Studie basierend auf Daten des Sloan Digital Sky Survey. Die Galaxie ist ein Trabant der Milchstraße und etwa 120 kpc entfernt[1]. Willman 1 besitzt eine elliptische Form mit einem Halblichtradius von etwa 25 pc[6] und einer heliozentrischen Fluchtgeschwindigkeit von näherungsweise −13 km/s[3].

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- [en] Willman 1

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[es] Willman 1

Willman 1 una galaxia enana de luminosidad ultrabaja o un cúmulo de estrellas. Willman 1 fue descubierta en 2004. Lleva el nombre de Beth Willman, investigadora del Haverford College, autora principal de un estudio basado en los datos de Sloan Digital Sky Survey.[1]

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[ru] Виллман 1

Виллман 1 — это карликовая галактика крайне низкой светимости или звёздное скопление[5]. Она названа в честь Бета Виллмана из Хаверфордского колледжа, ведущего автора исследования, основанного на данных, полученных Слоановским цифровым обзором неба. Она является спутником Млечного Пути и располагается на расстоянии ~120.000 световых лет от Земли[2]. Виллман 1 имеет эллиптическую форму с радиусом около 25 пк. Его скорость относительно Солнечной системы примерно −13 км/с[1][5].

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