Dark matter percentage

Scientists have struggled for decades to identify the constituent particles of dark matter, but they’ve had little to show for all their efforts. A new study at Case Western Reserve University is now advancing the radical new hypothesis that dark matter may in fact be made not of exotic subatomic particles, but rather of macroscopic objects which would mass anywhere from a tennis ball to a dwarf planet, be as dense as a neutron star, and still be adequately described by the Standard Model of particle physics.

Dark matter constitutes approximately 27 percent of the mass-energy of the Universe, trumping the measly five percent of ordinary matter. Although it can’t be observed directly, we know it must be there because of the strong gravitational effects it exerts on ordinary matter as it distorts incoming light and helps new galaxies form.

The search for the dark matter particle has been fruitless thus far and so, in an effort to leave no stone unturned, researchers Glenn Starkman and David Jacobs have chosen to take a look at the bigger picture, focusing on what the dimensional constraints of a dark matter particle actually are. Over the past 30 years, the search has mainly focused on the space of weakly-interacting particles such as WIMPs and axions. But in expanding their field of view, Starkman and Jacobs have concluded that the objects which interact strongly with both themselves and ordinary matter deserve more attention, not least because they could be accounted for by the currently accepted Standard Model of physics.

"The community had kind of turned away from the idea that dark matter could be made of normal-ish stuff in the late ‘80s, " Starkman said. "We ask, was that completely correct and how do we know dark matter isn’t more ordinary stuff  – stuff that could be made from quarks and electrons?".

When looking at the constraints in terms of mass and cross-section of such hypothetical objects, something immediately jumps to the eye: such objects could be absolutely massive, and as dense as a neutron star or the nucleus of an atom. Which explains the researchers’ nickname for them  –  the "Macros."