Tantalizing signals from a handful of recent high-energy searches for dark matter are more likely the product of conventional astrophysics than the first tentative detections of the universes missing mass, say skeptical astrophysicists.

A decade ago, no [one] would make these claims without first checking and re-checking that it couldnt be from some normal astrophysical source, Stacy McGaugh, an astrophysicist at Case Western Reserve University in Cleveland, told Forbes. Nowadays, the attitude seems to be that if you dont immediately recognize what it is, it must be dark matter; [with] no penalty for crying wolf over and over again. Even so, the theoretical stakes remain high.

Thats because for the better part of a century, cosmological cold dark matter has been needed to explain the gravitational dynamics of much of the cosmos visible matter; including the rotation rates of massive galaxies like our own.

Clusters of galaxies like this one, MCS J0416.1-2403 located in the constellation of Eridanus, have long been theorized to be bound by cosmological dark matter. Credit: ESA/Hubble, NASA, HST Frontier Fields; Acknowledgement: Mathilde Jauzac (Durham University, UK and Astrophysics & Cosmology Research Unit, South Africa) and Jean-Paul Kneib (cole Polytechnique Fdrale de Lausanne, Switzerland)

By a very large margin, the matter we do see directly in galaxies does not produce enough gravity to hold the galaxies together; dark matter is invoked to provide the extra gravity needed, Mordehai Milgrom, a physicist at Israels Weizmann Institute, told Forbes. That is, Milgrom says, if the standard laws of physics are used to calculate gravity as we know it.

And because non-baryonic (or exotic) dark matter is theorized to only interact with normal matter primarily via gravity, dark matters detection has inherently been problematic. Even so, most cosmologists accept the idea that normal dark matter may make up as much as 85 percent of the universes missing mass.

The need to invoke dark matter at all stems either from the product of unseen exotic particles that lie well beyond the ken of known physics or is the result of new physics in which gravity behaves differently on the largest scales. Neither scenario is easily tested.

For decades, however, experimental physicists have used both laboratory and astronomical observations from ground and space to search for this missing component.

One of the most recent, as noted this month in the journal Physical Review Letters, involves x-ray emissions from both the Perseus galaxy cluster and the nearby Andromeda galaxy.

Using the European Space Agencys XMM-Newton telescope, researchers from Switzerlands EPFL Laboratory of Particle Physics and Cosmology and Leiden University in The Netherlands report that this observed excess of x-ray photons may represent signals of decay by sterile neutrinos. That is, heretofore unverified, hypothetical dark matter particles.

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New Doubt About Dark Matter