What do you call a galaxy without stars? It’s a question that puzzled many, until radio astronomers revealed the discovery of the darkest galaxy ever not quite seen, a cloud of hydrogen gas resembling our own Milky Way galaxy in many aspects, such as its mass and rotation, but with no discernible stars. This revelation opens the doors to a new mystery in the universe – the existence of dark galaxies.
Defining Dark Galaxies
Dark galaxies are entities whose stars are so sparse and faint that their light cannot be discerned other than as a thin, transparent haze that doesn’t seem to contain any stars at all. Initially referred to as “low surface-brightness galaxies” or “ultra-diffuse galaxies,” these elusive entities challenge long-held views about the formation and evolution of galaxies. As astronomers continue to probe deeper into the skies with more powerful and smarter eyes, dark galaxies have begun popping up more frequently, contributing to the expanding cosmic lexicon that already includes terms like “dark matter” and “dark energy.”
The Accidental Galaxy
Discovering these dim ghosts is no easy task, as they are hard to find and even harder to study. It often requires hours or days of observation to bring their visible starlight into focus. For instance, in a study involving a variety of telescopes, Dr. Karen O’Neil mistyped the coordinates to the galaxy she intended to observe, resulting in the telescope pointing to a different part of the sky than intended. This fortunate error led to the discovery of a galaxy made only out of gas – the J0613+52 galaxy, about 270 million light-years away. It is swimming amid two billion solar masses worth of primordial hydrogen from the Big Bang, but it’s not forming any stars, possibly because the gas is too diffuse to clump together into the clouds that become stars. The absence of nearby galaxies with a gravitational influence further inhibits the clumping process, presenting a unique opportunity for astronomers to study a nearby galaxy made up of primordial gas.
A Diminutive Nube
In a separate discovery, Spanish astronomers led by Mireia Montes revealed the existence of another nearly starless galaxy they called Nube, which is Spanish for “cloud.” The discovery of Nube further adds to the mystery of dark galaxies, defying present knowledge about how a galaxy with such extreme characteristics can exist. With the parallel discoveries of J0613+52 and Nube, the cosmic landscape takes on a new dimension, prompting questions about the origins and nature of these elusive entities.
The discovery of dark galaxies unveils a new layer of complexity in our understanding of the universe. Their existence challenges conventional theories about galaxy formation and evolution, necessitating further exploration and study to unravel the enigma of galaxies without stars. As astronomers continue to peer deeper into the cosmos
, it is likely that more secrets and surprises await, adding to the richness and diversity of the cosmic tapestry.