Dark matter, a mysterious substance that makes up about 85% of the mass of the Universe, remains invisible. It cannot be seen by telescopes, because it has virtually no interaction with light. However, its gravitational influence is visible everywhere: it shapes galaxies, bending space-time. The hunt for this dark component of the cosmos is one of the most challenging tasks of modern astrophysics.
But now astronomers are proposing a revolutionary search method that challenges established beliefs about the complete “invisibility” of dark matter. The study, published in the journal Physical Review Letters, hypothesizes: clusters of dark matter may act as cosmic “lampshades,” dimming the light of stars behind them. This effect, although very faint, can be detected by modern telescopes.
“Dark matter might form large clumps or clouds, often called MACHOs. There may be enough dark matter in these MACHOs that their weak interactions with light collectively block light from passing through the cloud, like how a lampshade blocks some but not all light from getting through,” explains Melissa Diamond of Queen’s University (Canada).
MACHO or WIMP
The nature of dark matter remains a major mystery of cosmology. The most popular theory is the weakly interacting massive particles (WIMPs) that have not been detected so far. The new work focuses on an alternative candidate, massive astrophysical compact halo objects (MACHOs). Unlike exotic WIMPs, MACHOs are hypothesized to be composed of ordinary but extremely dense matter: neutron stars, black holes, or very dim stars. Their dimness is due to the lack of radiation, especially if they are isolated on the outskirts of galaxies. Importantly, dark matter can be a mixture of different components, including both MACHO and WIMP.
Previously, MACHO was attempted to be detected through gravitational microlensing, a phenomenon where the gravity of a massive object bends and amplifies the light of the star behind it. However, this method has limitations: if the object is not massive enough or its substance is too sparse, the lensing effect will be too weak for detection.
“This is where the ‘lampshade’ effect becomes key. The advantage of this technique is that it works for dark matter objects that are difficult or impossible to find by other available methods,” Diamond said.
Finding dark matter
Most importantly, you can start searching now. You don’t need new telescopes to do it. Astronomers can analyze the vast amounts of data already collected by projects like the Optical Gravitational Lensing Experiment (OGLE).
“This technique allows us to make new use of existing data and search for new types of MACHOs that are inaccessible to classical microlensing studies,” Diamond emphasizes. The hunt for “dark lampshades” opens a new window into the exploration of the universe’s most mysterious matter.
We previously reported on how the asteroid Bennu disproved the existence of the fifth fundamental force of nature.
According to Space
