Astronomers find first ‘dark galaxy’

(New Scientist) Astronomers have found the first “dark galaxy” – a black cloud of hydrogen gas and exotic particles, devoid of stars. The gloomy galaxy lurks two million light years from Earth.

Joshua Simon, Timothy Robishaw and Leo Blitz of the University of California, Berkeley, observed a cloud of hydrogen gas called HVC 127-41-330 using the Arecibo radio telescope in Puerto Rico.

It appears to be rotating so fast it would fall apart unless it contains a strong, hidden source of gravity. The researchers therefore argue that the cloud must be at least 80 per cent dark matter, the hypothetical invisible substance whose gravity is supposed to explain why many objects in the cosmos move as fast as they do.

If they are right, this could resolve a problem in dark matter theory. In our local group of galaxies, we know of only about 35 dwarf galaxies, but simulations of galaxy formation using dark matter suggest there should be about 500.

If most of these dwarfs are dark galaxies with no stars, that would explain why we have missed them until now. The reason HVC 127-41-330 and its kind are dark may be because they have too small. Without enough mass, their gravitational forces would be too weak to cram gas together densely enough to form any stars.