Strange objects lurk in our weird Universe, hiding secretively in bewitching darkness, making themselves difficult to see. Dark galaxies are just such mysterious objects, that can hide themselves very well in our Universe’s most secretive places because they have no, or very few, stars to shed light on their shadowy, ghostly presence. However, they still may reveal themselves if they host large quantities of glaring gas. Indeed, since 2015, astronomers have managed to discover literally thousands of these very faint, phantom-like systems concealing themselves within and around several clusters of galaxies. How these strange systems are born remains a tantalizing puzzle to be solved. In November 2016, a team of researchers proposed that intense periods of star-birth, as well as blast waves created in the wake of supernova explosions, could be the culprits that made these dim galaxies switch off their stellar lights.
Not all galaxies are bright with the sparkling flames of a myriad of stars. Indeed, astronomers have recently observed many extremely faint, diffuse galaxies, with too few stars to light their magnificent galactic fires. However, how these faint galaxies came to be is not precisely known. They could be an entirely new and surprising type of galaxy that challenges current theories about how galaxies are born–or, alternatively, they might be galactic nonconformists that started out exactly like the ho-hum herd of galaxies we are familiar with, but experienced a sea-change as a result of being shaped by their environment into systems that travel to the beat of a different drum. Once astronomers reported their observations of the first collection of dark galaxies early in 2015 which–like footprints in the snow–pointed them in the direction of where to hunt, they started discovering dark galactic denizens in a large number of nearby galaxy clusters. In only a little over a year, astronomers went from knowing of none, to knowing of over a thousand of these strange beasts, inhabiting the galactic zoo.
The newly discovered treasure trove of dark galactic denizens of the Cosmos presents an intriguing mystery to be solved. Any galaxy as large as our own Milky Way should be able to readily give birth to a host of lovely stellar babies. However, it is still not known how massive the dark galaxies really are. Perhaps these ghostly systems are galactic failures–just as massive as our own Galaxy–that were mysteriously deprived of the ability to create lovely star-babies. Alternatively, the dark galaxies may be light-weights that have been stretched thin, like a blob of tugged-on taffy, by either external or internal events. In either case, with so few stars, dark galaxies must possess immense amounts of invisible matter in order to resist being ripped apart by the merciless gravity exerted by other nearby galaxies.
Expect The Unexpected
Mysteries are seductive. Once bitten by the bug of trying to solve one, the hapless victim of her own curiosity cannot rest until she finally figures the bewitching, bewildering, and bothersome thing out.The dim galaxies are just as faint as dwarf galaxies, but are spread out over an area that is just as large as our own large spiral Milky Way Galaxy. It is a mystery how galaxies so very dim–hosting up to 1000 times fewer stars than our own Galaxy–could still be equally large. The new research, conducted by scientists from the Niels Bohr Institute in Copenhagen, Denmark, has provided a plausible solution to this mystery. Their new research shows that if a large number of supernovae explode during the star-birthing process within a galaxy, it can result in both the stars and the dark matter being launched unceremoniously outwards. This would cause the galaxy to expand. The new research is published in the scientific journal, Monthly Notices of the Royal Astronomical Society.
There is nothing quite like a good scientific mystery to lure a scientist into a trap woven of the twisted threads of bequiling imagination. As a result of the many detections of these galactic nonconformists, the desire became intense to figure out exactly how many of these baffling celestial beasts there really are–and where they might be hiding.
Telescopes constructed to spot dim objects revealed the presence of a plentiful treasure of large but empty galaxies, dubbed ultra-diffuse galaxies (UDGs). The surging flood of new discoveries started in New Mexico, with a telescope poised in a park approximately 110 kilometers from Roswell, a city that sings a terrible siren’s song to those who are tantalized by tales of UFOs. Named the Dragonfly telescope, this remarkable, but relatively tiny, example of technology revealed dim galaxies that had been missed by other observatories. Bigger telescopes are generally considered to be better than their smaller kin. This is because a comparatively large lens or mirror can snare more light–thus observing dimmer objects. However, even the big guys have a limit–unwanted light. This unwanted, scattered light shows itself in the form of faint “ghosts”–blobs that can veil faint detail in images of space or even mimic very dim galaxies.
Alas, large dark galaxies look a lot like these ghosts–which is why they had been missed. But Dragonfly was designed to keep those interfering blobs of light in check and, as a result, scientific detectives pointed Dragonfly at the Coma Cluster of galaxies. The Coma Cluster is populated by thousands of galaxies, and it is located approximately 340 million light-years from Earth. This is considered to be close to Earth–by cosmological standards. Coma is densely packed with constituent galaxies, and is a favorite hunting ground for those who seek to find rare beasts in the celestial zoo.