X-ray signal from outer space points to dark matter

For years, high-energy radiation from space has been teasing scientists with inconclusive hints of dark matter. But a definitive answer may be at hand. A team of physicists says that certain galactic x-rays could be a sign of decaying dark matter, and that an upcoming satellite mission should prove or disprove their claim.

Dark matter makes up about 80% of matter in the universe, but no one knows exactly what it is. Most theorists suspect it consists of so-called weakly interacting massive particles (WIMPs)—undiscovered subatomic particles that give off so little light that we can’t see them, though they still interact with other matter through gravity and the weak nuclear force. But laboratory experiments haven’t spotted them, and the most likely evidence from space—gamma rays that putative WIMPs would give off while annihilating one another in the centers of galaxies—are swamped by cascades of gamma rays from other sources such as hot gas.

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> For years, high-energy radiation from space has been teasing scientists with inconclusive hints of dark matter.

True. Some experiments support the observations of Pamela and Fermi. Other experiments find nothing.

> Boyarsky’s group reports a similar 3.5 keV peak in x-rays from the core of the Milky Way.

Not good enough. Need independent confirmation. I don’t see any obvious link between that peak and either dark matter or the peak at 130 GeV found by Fermi in the same direction.

> The ultimate test could also start next year, when JAXA is scheduled launch a new x-ray satellite called ASTRO-H. ASTRO-H will be able to plot the shape of the 3.5-keV peak in much more detail than current satellites can.

That’s just a very minor part of what Astro-H will be doing. Let’s see:

Four instruments together covering wavelengths from soft X-ray (from 0.3 keV) to soft gamma-ray (to 500 keV). The only spectrometer is at the soft X-ray end and includes the 3.5 keV region.

The telescope unfolds to a total length of 14 metres.

The soft X-ray telescope is essentially a direct copy (slightly improved) of the one already on the Suzaku spacecraft, which has been operating since 2005. It will be known as SXI (for sexy). It will have a bigger field of view than Chandra. The hard X-ray telescope HXI will have a smaller field of view than that, it aims to rival NuStar in power.

All three of the soft X-ray, hard X-ray and soft gamma ray have their equivalent instruments on the Suzaku spacecraft, so Astro-H can best be seen as an upgrade and replacement for Suzaku.

The scientific goals of Astro-H are: observing black holes, active galactic nucleii, supernovae, galaxy clusters, etc.

This is an interesting slide: