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Hey, did anybody notice there is a massive spooky ghost galaxy right next door to us?  Well, actually the answer turns out to be “no: not really…not until November of last year.”  It was only in November of 2018 that astronomers discovered Antlia 2, a galaxy which is a mere 130,000 light-years away from the Milky Way–which really is right next door in terms of cosmic distances (to contextualize this number, the diameter of the Milky Way itself is between 150,000 and 200,000 light years).

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Ant2, as it is affectionately (?) called, is closer than the Large Magellanic Cloud, a dwarf galaxy with 30 billion stars which is 163,000 light years away and is generally regarded as our closest galactic neighbor. How did we miss this thing?  And why are we calling it a ghost galaxy (aside from the fact that that sounds impossibly cool)?

Antlia 2 is a weird sort of celestial object.  It has the lowest “surface brightness” of any known galaxy and is approximately 100 times more diffuse than any known ultra diffuse galaxy.  Gee! that is really extremely diffuse.  Antlia 2 is also a dark matter galaxy: the exiguous stars of which it consists are insufficient to hold it together without a great deal of unknown mystery mass.  The ghost galaxy may be more than 99 percent dark matter.  Additionally, Ant2 (insomuch as it exists) is hidden by the occlusion cloud above the spiral of the Milky Way.  Only with the advanced astrometry readings of the European Space Agency’s satellite observatory Gaia were astronomers finally able to pinpoint this dark shadow in the sky above the southern constellation Antlia (which itself is named after an 18th century air pump).

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What the jazz? This post is making less sense than usual, but I am not making any of it up…

I worry that this post is too abstruse for comfort.  It concerns an all-but-invisible phantom galaxy made of unknown dark matter. The only reason we even found it to begin with is that astronomers were on the lookout for a hidden galaxy.  Some unknown mass must have caused the stylish ruffles in the spiral arms of our own bright & lively Milky Way.  Thus the fashion sensibility of space topologists helped us to find Antlia 2.  Remind me about this thing in October.  I want to draw some ghost galaxies to celebrate Halloween this year!

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