Dark matter may be massive The physics community has searched for thirty years and found no evidence that dark matter is made of tiny, exotic particles. Theoretical physicists from Case Western Reserve University suggested that scientists look for candidates in the familiar realm of Standard Theory, which will obviously be more massive. Dark matter is invisible matter that, when interacting with ordinary matter, creates a gravitational pull, which, among other things, prevents spinning galaxies from flying apart. Physicists estimate the content of dark matter in the Universe at 27% (ordinary matter is about 5%). Instead of WIMPs, weakly interacting massive particles, or axions, weakly interacting low-mass particles, dark matter can consist of macroscopic objects, from a few grams to the size of a good asteroid. It could also be as dense as a neutron star or the nucleus of an atom, writes Phys.org. Physics professors Glenn Starkman and David Jacobs from the University of Cape Town have published a paper that can be considered a guide to the search for dark matter. The macros, as Starkman and Jacobs call them, will not only be different from dwarf WIMPs and axions, but they will also be different in important ways. They could potentially be assembled from Standard Model particles and would not require new physics to explain their existence. “We've been looking for WIMPs for a long time and haven't seen them,” Starkman says. “We expected to see WIMPs at the Large Hadron Collider, and we don’t have them.” WIMPs and axions remain possible dark matter candidates, but there are good reasons to keep looking elsewhere, theorists say. “Society partially abandoned the idea that dark matter could be made from ordinary materials in the late 1980s,” Starkman says. “We wonder if this was correct and how do we know that dark matter is not made of very ordinary things like quarks and electrons?” After sources of ordinary matter, including hot Jupiters, white dwarfs, neutron stars, stellar black holes, black holes at the centers of galaxies, and mass neutrinos, were eliminated from the list of possible candidates, physicists turned to exotic matter. Matter that lies somewhere between ordinary and exotic matter, akin to neutron stars or large nuclei, remains, Starkman said. “We say related because they are heavily laced with strange quarks, which tend to be very short-lived.” While strange quarks are extremely unstable, Starkman points out that neutrons are also extremely unstable. But in helium, being associated with stable protons, neutrons remain stable. “This opens up the possibility that stable strange black matter that was born in the young universe and dark matter are nothing more than a mixture of strange nuclear matter or other bound states of quarks, or baryons, that are themselves made of quarks.” Such dark matter would fit into the Standard Model. The macros would have to assemble from ordinary and strange quarks, or baryons, before the strange quarks or baryons decay, and at temperatures above 3.5 trillion degrees Celsius, comparable to the temperature at the center of a massive supernova. Quarks would have to assemble with 90 percent efficiency, leaving only 10 percent for the protons and neutrons found in the Universe today. The limits for possible dark matter would be: Minimum 55 grams. If the dark matter were smaller, it would be detected by Skylab detectors or it would leave traces in the mica sheets. Maximum 10^24 grams. Above this limit, macros would be so massive that they would bend light, which could not go unnoticed. Thus, the range between 10^17 and 10^20 grams per centimeter should be excluded from the search, theorists say. Dark matter in this range would be massive enough for gravitational lensing and would influence individual photons of gamma-ray bursts, which would not escape scientists. If dark matter is in a certain range, there are reasons why it hasn't been noticed yet. With a mass of 10^18 grams, dark matter macros would hit the Earth once every billion years. At a lower ma yt3.ggpht.c