Lying at a distance of some 130,000 light years , Pyxis is one of the most distant examples of a globular cluster . It is also about 2 billion years younger than other globular clusters with the same metallicity . Together , these characteristics imply that Pyxis was likely formed in a massive dwarf galaxy that the Milky Way then cannibalized . Thus , Pyxis may have an extragalactic origin . One mystery , however , is that the orbits of other known massive dwarf galaxies are inconsistent with the orbit of Pyxis , which is derived from the new proper motion measurements .
The research is part of a much larger effort now underway to study the proper motion of several substructures across the Milky Way ’ s halo . It is also part of a Large and Long Program at Gemini that is targeting other clusters , dwarf galaxies , and individual stars in stellar streams . The paper is published in The Astrophysical Journal .
Seoul National University , received time on Gemini North to observe the object ’ s 2017 close passage when the fragments and associated debris swarm were just over one astronomical unit away .
According to Kim , a variety of hypotheses could explain the history of this body , including rotational breakup , impact cratering , or shattering . The team determined a rotation period ~ 11.36 hours for the largest fragment , which , if the fragment ’ s spin period has been constant after the mass ejection , would , according to Kim , fail to meet the critical spin rate for rotational break up .
The observations also reveal that the largest fragment has a highly-elongated shape with about a 2:1 ratio . Looking at the size distributions of the ejecta and other fragments , the team concludes that the body likely underwent impact shattering in order to produce the observed morphology .
The study ’ s light curve is shown in Figure 9 and presents the largest fragment ’ s double-
Figure 8 . Left : GMOS-South image of the Pyxis field , with the center of the cluster marked with a red star . Right : A zoom of the Pyxis area with GeMS- GSAOI . The field-ofview of GMOS is 5 x 5 arcminutes ; GeMS is 85 x 85 arcseconds .
Figure 9 . Rotational light curve of the largest fragment of P / 2010 A2 . Time-series g0-band photometry over two nights ( upper panel ) and phase based on the best-t doublepeaked period of 11.36 hr ( lower panel ). A sine curve with a period of 11.36 hr was plotted in the upper panel ( gray line ).
Korean Astronomers Dissect a Fragmented Asteroid
In January 2017 , the active and fragmented main belt asteroid P / 2010 A2 made its closest approach to the Earth after its 2010 discovery , when it exhibited a mysterious cometlike dust trail . Prior to this year ’ s passage , the fragments had not yet been characterized , due to the extremely small size (~ 120 meters in diameter ) and faintness of this object .
A Korean team , led by Yoonyoung Kim of
January 2018 / 2017 Year in Review GeminiFocus
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