The universe is full of mysteries, and one of the most intriguing is the elusive nature of dark matter. A recent discovery has shed some light on this enigmatic substance, but it also raises more questions than answers. A team of astronomers has found a small, dark object that's so impossible to see, it can only be detected by the way its gravity distorts space. This object, with a mass about 1 million times that of our Sun, is the lowest-mass dark object ever found in the Universe. It doesn't emit any light or other radiation, and was detected by the way its gravity distorts space, and therefore distorts any background light passing through or near it. The effect is a well-known phenomenon known as gravitational lensing, and astronomers can use the technique to measure how big the object is. So what is it? The team don't know for sure, but say it could be a clump of dark matter 100 times smaller than any previously detected. Dark matter is an invisible substance that's never been directly detected, but is required to explain what's holding galaxies together. If astronomers count up all the visible matter in a galaxy – the stars, gas and dust – there's not enough gravitational force to stop the galaxy from ripping itself apart as it rapidly rotates. There must be some other 'stuff' holding galaxies together, even though we can't detect it. This is known as dark matter. The other possibility with regards to this dark, mysterious object is that it's a compact, inactive dwarf galaxy. "It’s an impressive achievement to detect such a low mass object at such a large distance from us," says Chris Fassnacht, professor in the Department of Physics and Astronomy at the University of California, Davis, a co-author on the study published in Nature Astronomy. "Finding low-mass objects such as this one is critical for learning about the nature of dark matter." Can dark matter exist in tiny clumps? Objects like these could help astronomers answer this very question. Combining the power of our best telescopes The team behind this discovery used an array of telescopes including the Green Bank Telescope in West Virginia, the Very Long Baseline Array in Hawaiʻi and the European Very Long Baseline Interferometric Network (EVN), which includes radio telescopes in Europe, Asia, South Africa and Puerto Rico. Combining the collective observing power of these telescopes enabled them to effectively create an Earth-sized super-telescope, big enough to capture the subtle ripples in spacetime caused by the object. It's the lowest mass object ever found by the technique, by magnitude of a hundred, suggesting the technique could be used to find similar objects. "Given the sensitivity of our data, we were expecting to find at least one dark object, so our discovery is consistent with the so-called ‘cold dark matter theory’ on which much of our understanding of how galaxies form is based," says lead author Devon Powell at the Max Planck Institute for Astrophysics (MPA), Germany. "Having found one, the question now is whether we can find more and whether the numbers will still agree with the models." This discovery has opened up new avenues of research and has raised more questions than it has answered. The team's findings suggest that dark matter may exist in tiny clumps, but they don't know for sure. The search for dark matter continues, and with each new discovery, we get a little closer to understanding the universe's hidden secrets.
