ESO 461-36

ESO 461-36 - A dwarf galaxy isolated in the Local Void.

The vast majority of galaxies exist in clusters. These clusters are joined on larger scales by filaments and sheets of galaxies, between which, gigantic galactic voids are nearly entirely free of galaxies. These voids are often hundreds of million of light years across. Only rarely does a lonely galaxy break the emptiness.

As expected of galaxies within the void, ESO 461-36 is exceptionally isolated with no other galaxies discovered within 10 million light years. What is surprising for such a lonely galaxy is that when astronomers compared the stellar disc of the galaxy with a mapping of hydrogen gas, the gas disc was tilted by as much as 55°. The team proposes that this may be due to a bar within the galaxy acting as a funnel along which gas could accrete onto the main disc. Another option is that this galaxy was recently involved in a small scale merger. The tidal pull of even a small satellite could potentially draw the gas into a different orbit.

This disc of gas is also unusually extended, being several times as large as the visual portion of the galaxy. While intergalactic space is an excellent vacuum, compared to the space within voids it is a relatively dense environment. This extreme under-density may contribute to the puffing up of the gaseous disc, but with the rarity of void galaxies, there is precious little to which astronomers can compare.

Compared with other dwarf galaxies, ESO 461-36 is also exceptionally dim. To measure brightness, astronomers generally use a measure known as the mass to light ratio in which the mass of the galaxy is divided by the total luminosity. Typical galaxies have mass to light ratios between 2 and 10. Common dwarf galaxies can have ratios into the 30′s. But ESO 461-36 has a ratio of 89, making it among the dimmest galaxies known.