La «galaxia oscura»

Unos astrónomos afirman haber encontrado la primera «galaxia oscura» -formada por una gigantesca nube de hidrógeno y mucha materia oscura, carente de estrellas (uno creía que las galaxias tenían que tener estrellas por definición de galaxia, pero aparentemente eso es una ingenuidad y la galaxiedad de las galaxias no tiene nada que ver con las estrellas). Se encontraría a 50 millones de años luz, más o menos en dirección Virgo. Aparentemente, los modelos de formación de galaxias predicen que esos objetos deben existir en gran número.

The new galaxy, which consists of a gigantic cloud of hydrogen gas and exotic dark matter, contains enough material to give birth to tens of millions of stars. Yet something is preventing this from happening. Such dark galaxies have been predicted, and could outnumber normal galaxies by as much as a hundred to one, but this is the first time anyone has confidently claimed to have seen one.

Aunque, como suele pasar en ciencia, la cosa no está del todo clara:

When Minchin’s team measured the speed of rotation of the hydrogen gas in VIRGOHI21, they found that it would have to contain about one-tenth of the dark matter of the Milky Way. But if that is so, it should also have a hundred times as much hydrogen gas as they actually detected. Far from being a dwarf, VIRGOHI21 seems to be a giant in its own right.

Merrifield says that the shortfall in the observed amount of hydrogen may mean that what Minchin and his team have seen is not a dark galaxy after all. «Their story doesn’t quite hang together, and I would speculate that they have been fooled by two passing hydrogen clouds.» The difference in speed as one passes the other would give the illusion of rotation, he says.