Artist's impression of the Milky Way. Its hot halo appears to be stripping away the star-forming atomic hydrogen from its companion dwarf spheroidal galaxies.  Image credit: NRAO/AUI/NSF
Artist’s impression of the Milky Way. Its hot halo appears to be stripping away -forming hydrogen from its companion dwarf spheroidal galaxies. Image credit: NRAO/AUI/NSF

Excerpt from
earthsky.org

Astronomers have discovered that our nearest galactic neighbors are devoid of star-forming gas, and that our Milky Way is to blame.

New observations by large radio telescopes reveal that within a well-defined boundary around our , dwarf galaxies are completely devoid of hydrogen gas. Beyond this , dwarf galaxies are teeming with star-forming material. 

The Milky Way galaxy is actually the largest member of a compact clutch of galaxies that are bound together by gravity. Swarming around our home galaxy is a menagerie of smaller dwarf galaxies, the smallest of which are the relatively nearby dwarf spheroidals, which may be the leftover building blocks of galaxy formation.

Further out are a number of similarly sized and slightly misshaped dwarf irregular galaxies, which are not gravitationally bound to the Milky Way and may be relative newcomers to our galactic neighborhood.

Kristine Spekkens is an assistant professor at the Royal Military College of Canada and lead author on a paper published in the Astrophysical Journal Letters. She said:

“Astronomers wondered if, after billions of years of interaction, the nearby dwarf spheroidal galaxies have all the same star-forming ‘stuff’ that we find in more distant dwarf galaxies.”

Previous studies have shown that the more distant dwarf irregular galaxies have large reservoirs of neutral hydrogen gas, the fuel for star formation. These past observations, however, were not sensitive enough to rule out the presence of this gas in the smallest dwarf spheroidal galaxies. 

Spekkens said:

“What we found is that there is a clear break, a point near our home galaxy where dwarf galaxies are completely devoid of any traces of neutral atomic hydrogen.”

 Bottom line: New observations by large radio telescopes reveal that within a well-defined boundary around our galaxy, dwarf galaxies are completely devoid of star-making hydrogen gas. Astronomers say our Milky Way is to blame.

Known Milky Way satellite galaxies.  Click here for more about this diagram.
Neighboring galaxies to our own Milky Way (Descriptions below)

 

(kpc) DISCOVERY PAPER
Canes Major 7.2 Martin et al. 2004, A dwarf galaxy remnant in Canis Major: the fossil of an in-plane accretion on to the Milky Way
Segue 3 17 Belokurov et al. 2010, Big Fish, Little Fish: Two New Ultra-Faint Satellites of the Milky Way
Segue 1 23 Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way
Sagittarius 24 Ibata, Gilmore & Irwin, 1994, A dwarf galaxy in Sagittarius 1995, Sagittarius: the nearest dwarf galaxy
Segue 2 34.7 Belokurov et al. 2009, The discovery of Segue 2: a prototype of the of satellitesof satellites
Bootes II 43 Walsh, Jerjen & Willman, 2007, A Pair of Bootes: A New Milky Way Satellite
Coma 44 Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
Willman 1 (SDSSJ1049+5103) 45 Willman et al. 2005, A New Milky Way Companion: Unusual Globular Cluster or Dwarf Satellite?
Bootes III 46 Grillmair 2009, Four New Stellar Debris Streams in the Galactic Halo
LMC 50.8
SMC 59.7
Bootes 60 Belokurov et al. 2006, A Faint New Milky Way Satellite in Bootes
Ursa Minor 66 A.G. Wilson of the Lowell Observatory in 1955, Sculptor-Type Systems in the Local of Galaxies
Sculptor (Scl) 79 discovered in 1938 by Harlow Shapley, A Stellar System of a New Type
Draco 82 A.G. Wilson of the Lowell Observatory in 1955, Sculptor-Type Systems in the Local Group of Galaxies
Sextans 89 Mike Irwin, M.T. Bridgeland, P.S. Bunclark and R.G. McMahon, 1990 A new satellite galaxy of the Milky Way in the constellation of Sextans
Ursa Major (UMa) 100 Willman et al. 2005, A New Milky Way Dwarf Galaxy in Ursa Major
Carina 103 Cannon, R. D., Hawarden, T. G., & Tritton, S. B., 1977, A new Sculptor-type dwarf elliptical galaxy in Carina
Hercules 140 Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
Fornax 140 discovered in 1938 by Harlow Shapley, described in “Two Stellar Systems of a New Kind”, Nature, Vol. 142, p. 715
Canes Venatici II 150 Sakamoto & Hasegawa 2006, Discovery of a Faint Old Stellar System at 150 kpc
Leo IV 160 Belokurov et al. 2007, Cats and Dogs, Hair and A Hero: A Quintet of New Milky Way Companions
Pisces II 182 Belokurov et al. 2010, Big Fish, Little Fish: Two New Ultra-Faint Satellites of The Milky Way
Leo II (Leo B) 208 Robert G. Harrington and Albert George Wilson, 1950, Two New Stellar Systems in Leo
Canes Venatici 220 Zucker et al. 2006 A New Milky Way Dwarf Satellite in Canes Venatici
Leo I 254 Robert G. Harrington and Albert George Wilson, 1950, Two New Stellar Systems in Leo