Dark Matter; Dark Energy; We basically use the term ‘dark’ as a cool sounding version of ‘We have no clue what this is.’ But Dark Matter is a better name than ‘We haven’t a clue’ Matter.
Over the years, Astronomers have been trying to pinpoint what the stuff actually is that seems to permeate the universe and makes up 26.8% of the entire total energy-mass (Compare this to a paltry 4.9% of ordinary matter, ie the stuff we can see).
But now, as per usual, theorists have come up with another possibility for the source of dark matter: moderately sized, ultra-dense objects. We’re talking somewhere from a size just big enough to avoid detection as particles, to the size of a good asteroid, but as dense as a neutron star or the nucleus of an atom. At that density a pea would weigh as much as a mountain.
Over the past decade, the leading candidates for dark matter have been WIMPS, weakly-interacting massive particles. We’ve been looking for them with the Large Hadron Collider at CERN but haven’t found any. If the particles are massive, it would take a huge amount of energy to recreate them in a particle accelerator.
The other possibility for years was MACHOs, Massively-compact halo objects. Things like brown dwarfs, black holes, neutron stars, and failed Jupiters, but all of these have been ruled out.
Physics professor Glenn Starkman and former graduate student David Jacobs at Case Western Reserve University have postulated that dark matter could be the in between objects, such as relatives of neutron stars or large nuclei. One such relative are so-called ‘strange quarks.’ These are extremely unstable, short lived particles seen in particle accelerators. ‘However,’ Starkman points out, ‘so are neutrons, yet they become stable in atomic nuclei.’ Strange quarks may have similar behaviours, meaning they could be in stable chunks left over from the early universe. Dark Matter may just be clumps of strange matter.
Starkman and Jacobs calculated that the macros would have to be assembled from ordinary and strange quarks or baryons at a temperature of 3.5 trillion degrees Celcius (a tad warm) before they can decay, a temperature comparable to the center of a massive supernova. The quarks would have to be assembled with 90 percent efficiency, leaving just 10 percent to form the protons and neutrons found in the universe today. This would allow for the large amount of dark matter compared with observable matter.
After eliminating several candidates for Dark Matter, we arrive at the following constraints:
1. A minimum mass of 55 grams. If dark matter were smaller, it would have been seen in detectors in Skylab or in tracks found in sheets of mica.
2. A maximum of 1024 (a million billion billion) grams. Above this, the dark matter chunks would be so massive they would bend starlight, which has not been seen.
3. At the mass of 1018 grams, dark matter chunks would hit Earth about once every billion years. At lower masses, they would strike Earth more frequently but might not leave a recognizable record or observable mark.
So we keep experimenting and theorizing, in hopes that we only have one possibility left. This is pure science and we are in the middle of this amazing story where we humans begin to understand our entire universe.
“Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.”
– Arthur Conan Doyle