We know that dark matter is difficult to observe… in fact, we can only indirectly observe the stuff. Gravitational lensing and WMAP “Haze” are two possible ways to observe large-scale dark matter, but what about the small-scale stuff? New research suggests that some types of dark matter may be in the form of cold, primordial clumps of elementary particles and there’s a possibility we’ve been accidentally been observing them for years…
The elementary particles in question are quarks so cold that they haven’t boiled off into the cosmos to form protons and neutrons (baryons). They never evolved past the quark-hadron phase transition only 10-5 seconds after the Big Bang, and so are destined to float around in space as a type of dark matter.
New research suggests that these non-baryonic clumps of quarks and gluons may be observed in our own solar system and may have some very special qualities. They have resisted degradation for the past 14 billion years, and they pass through the cold of space without breaking up. It is theorised these clumps will also have a very high reflectivity due to the huge plasma frequency the quark “plasma” will possess.
The reflectivity of astronomical bodies is measured by a ratio of the amount of light falling on the surface of an object to the amount of light reflected. This ratio is known as the “albedo”. For example, a metallic asteroid may have a fairly high (for an asteroid) albedo of A~0.1 (i.e. 10% of sunlight is reflected). A clump of quark stuff will have a near-perfect reflectivity of A~1.
The brightness of an observed asteroid is an indication of its size. If a clump of reflective quark matter floats by, it is possible that an anomalous reading of its size will be observed, giving the impression that the observation is a larger asteroid rather than a quark nugget.
Interestingly, current observational techniques will allow us to observe a quark nugget only 1 meter in diameter at a distance of the Moon from the Earth.
But how do you distinguish a highly reflecting quark nugget from a real asteroid? Analyse its spectrum. If the reflected light from the observed “asteroid” reveals the signature of heavy elements in similar abundances as other asteroid observations, then it’s a case of: “if it looks like an asteroid, and it tastes like and asteroid, then it is an asteroid”. But should the reflection resemble the spectrum of the Sun, then it is likely it is a reflection from a quark nugget: “If it looks like an asteroid, but it tastes like the Sun, then it might be a quark nugget!”.
In a point against the quark nugget theory, the arXiv Blog points out an important factor. If the quark nugget has been around for as long as it has, it may not be very reflective. The gravitational pull of the matter in the nugget will attract baryonic dust, so would the nugget be disguised not only like an asteroid, but also… well, dark matter? Unless there is some other explanation (such as some repulsion effect on “normal” matter), then the likelihood of observing these nuggets may only be an outside chance.
Keep a careful eye on those asteroid observations; it could be a dust-covered quark nugget…
Original source: arXiv