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Leiden physicists reinforce dark matter candidacy for conspicuous signal

After finding evidence for a possible emission line at 3.5 keV in the Andromeda galaxy and the Perseus cluster last year, an international team of scientists has found the same signal when looking at the center of the Milky Way. This discovery provides strong support to connect this emission line with the decay of dark matter, possibly answering one of the most important questions in modern astrophysics. Lead author Alexey Boyarksy from the Leiden Institute of Physics and his colleagues publish their results today in Physical Review Letters as an Editor’s Choice article. It is already online in pre-print on ArXiv.

We have known for decades that there is a lot of mass missing in the Universe—as much as eighty percent of the Universe’s mass is a total mystery. We can’t see it, we can’t explain it, but we know it’s there, based of movements of galaxies. The enigmatic nature of this dark matter has grown to be one of the biggest mysteries in science. Leiden physicist Alexey Boyarsky and his fellow researchers might just have found what so many scientists are after. Last year, they spotted an X-ray signal in the Andromeda galaxy and the Perseus cluster at an energy of 3.53 keV with the XMM-Newton space telescope, which they couldn’t directly link to any known source of normal matter. Around the same time, a group at Harvard University saw the exact same signal in the combined spectra of 73 galaxy clusters. In both observations the signal is real with more than 99.3 percent certainty. The question remains: where does it come from?

In a new study, the researchers looked at XMM-Newton data taken from the center of the Milky Way. With 99.9987 percent certainty, they saw an emission line at 3.539 keV. In addition, the signal strength abides upper and lower limits that were imposed by the two previous studies. It is stronger than the signal from other galaxies, which are farther away. And because the physicists didn’t detect a signal in the Milky Way’s thin halo, the signal from the center shouldn’t be stronger than a certain level, otherwise the halo should also give off a detectable signal.

In their publication, the scientists conclude that although it is hard to completely exclude a normal matter origin, it is even harder to find a known substance that can account for the observations in the different astronomical objects. The 3.53 keV signal could indeed come from decaying dark matter. Boyarsky has booked more time on the XMM-Newton telescope to study X-rays from a dwarf galaxy that is known for having few chemical elements. If his group finds the same signal again, the suspect emission line has little alibi left. Boyarsky: ‘Of course it is not guaranteed that we find the signal in the dwarf galaxy. We did what we could, and now we can either get lucky or unlucky. If we do find it there as well, that would be very, very strong evidence of dark matter. Then many further observations will follow.’

‘Checking the dark matter origin of 3.53 keV line with the Milky Way center’, Alexey Boyarsky, Jeroen Franse, Dmytro Iakubovskyi, Oleg Ruchayskiy.

Erik Arends
Physics Outreach Officer
arends [at]
+31 (0)71 527 5471
Twitter: @LeidenPhysics

Publ. 14-10-2015 10:36
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