Galaxies

A large faint companion to the Milky Way

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Science  06 Sep 2019:
Vol. 365, Issue 6457, pp. 996-997
DOI: 10.1126/science.365.6457.996-f

The dwarf galaxy Antlia 2 (bottom left; added artificially to the photo to make its location visible) is large but very faint.

PHOTO: G. TORREALBA (ACADEMIA SINICA, TAIWAN), V. BELOKUROV (CAMBRIDGE, UK AND CCA, NEW YORK, US) BASED ON THE IMAGE BY ESO/S. BRUNIER

The Milky Way is orbited by numerous low-mass dwarf galaxies, which are mostly small and faint. Torrealba et al. have discovered a nearby dwarf galaxy, Antlia 2, which is faint but very large. Combining astrometric, photometric, and spectroscopic data, they determine the distance, mass, and brightness of the galaxy. Because its starlight is spread over a large region, Antlia 2 has the faintest surface brightness of any known galaxy, more than 100 times lower than previously discovered ultra-diffuse galaxies. Its peculiar properties may result from tidal interactions with the Milky Way, implying that Antlia 2 was once even larger.

Mon. Not. R. Astron. Soc. 488, 2743 (2019).

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