A dwarf dark galaxy has been spotted by astronomers thanks to light from the distant object being magnified by a gravitational lens. This surprise finding was made by researchers using the Atacama Large Millimeter Array (ALMA) observatory in Chile.
Gravitational lensing, a phenomenon first predicted by physicist Albert Einstein, occurs when light passes on either side of a massive object before being recorded by astronomers. This bends the path of light, similar to the action of a glass lens. This effect is sometimes used to examine distant galaxies, which would normally be too far from the Earth for astronomers to study.
In the new ALMA image, light from a distant galaxy, shown in red, is seen arcing around a less distant galaxy, pictured in blue. Distortions in the wave, expressed as a white dot, reveal the presence of a dark dwarf galaxy sitting roughly four billion light years from Earth.
Gravitational lens SDP.81 was the focus of a study by astronomers, testing new high-resolution capabilities of the ALMA observatory. The research team did not discover the dwarf dark galaxy hidden in the image until a year after recording the image.
Dwarf dark matter galaxies are exceedingly hard to detect. This relatively small body contains roughly 0.1 percent of the mass of our own Milky Way galaxy. Techniques used in this new finding could allow astronomers to find other similar concentrations of dark matter spread around the Cosmos.
"We can find these invisible objects in the same way that you can see rain droplets on a window. You know they are there because they distort the image of the background objects," said Yashar Hezaveh of Stanford University.
Dark matter may be difficult to detect, but physics suggests that roughly 80 percent of the matter within the visible universe is of this elusive variety. This bizarre material does not interact with light or other forms of electromagnetic radiation, but does exert a gravitational influence on the space around it.
This dark matter galaxy may exist as a satellite of the more-traditional galaxy creating the lensing effect. Astrophysicists believe a galaxy like our own should be accompanied by thousands of satellite galaxies - instead, astronomers know of just 40 such bodies. If these satellites are mostly dark matter, this could explain the discrepancy.
Analysis of the ring and detection of the dark dwarf galaxy will be published in the Astrophysical Journal.