Two sides of dark matter? Scientists unfold the age-old mystery

dark matter
Composite image of the Perseus galaxy cluster using data from NASA’s Chandra X-ray Observatory, ESA’s XMM-Newton and Hitomi, a Japanese-led X-ray telescope. X-ray: NASA/CXO/Fabian

Researchers have unfolded the nature of dark matter based on observations made by NASA's Chandra X-ray Observatory and two other X-ray telescopes. The finding is expected to solve the mystery of invisible substance which accounts for about 85% of the matter in the Universe.

The studies are based on observations of European Space Agencies' (ESA) XMM-Newton observatory and Japan's Hitomi X-ray telescope along with the Chandra findings.

Joseph Conlon of Oxford University who led the study said, "We expect that this result will either be hugely important or a total dud. I don't think there is a halfway point where you are looking for answer to one of the biggest questions in science."

The mystery unveiled about the spike from the hot gas in Perseus galaxy cluster. The intensity of the spike or the bright line in the electromagnetic emission from the Perseus hot gas has long remained difficult to observe, predict or explain. The researchers have observed about 3.5 kiloelectron volts (keV) energy from the ray of light.

The 3.5 keV emission line, observed from 73 other galaxy clusters using the XMM-Newton, gave away clue to the discovery of the dark matter, which has been shaped by series of confusions and contrary observations by the telescopes.

A research team led by Esra Bulbul of Harvard- Smithsonian Center for Astrophysics in Cambridge made their initial findings of the Perseus galaxy cluster spike in 2014. Another team led by Alexey Boyarsky of Leiden University in the Netherlands reported evidence of emission of 3.5 keV from galaxy M31 based on XMM-Newton observations within a week of Esra Bulbuls' findings.

However, several other astronomers failed to detect the energy line while few other groups succeeded in doing so. The researchers faced difficulty to explain the absorption of X-ray light in the black hole and the emission of the same energy rays from the hot gas far away from it.

The Oxford team suggests that the phenomenon might be caused by dark matter whose particles have two states of energy like the atoms which are separated by 3.5 keV energy band. The scientists believe that observations of absorbed spike line at close angles near the black hole and emitted lines in distant hot gas in the cluster would be the most important clue of the particles nature of the dark matter.

The researchers say that they need further observations of the Perseus cluster and other galaxies to make the final conclusion.

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