Line of Perseus | by Brian Koberlein



5 August 2014

The Perseus cluster is a large galactic cluster consisting of hundreds of galaxies. It’s typically a spotlight of research as a result of it’s each huge and fairly shut (about 240 million gentle years away). Not too long ago we’ve found some fascinating x-rays coming from the area. The outcomes have been revealed the Astrophysical Journal, displaying there may be an unexplained emission line within the x-ray spectrum.

The analysis really targeted on plasma surrounding the cluster, the place the staff noticed x-ray spectra on the lookout for emission strains from varied components. By observing these strains and their strengths, we are able to decide the composition of the plasma. However as a result of x-ray spectra may be faint, the staff added collectively 17 days price of observations. That is much like the best way pictures of the night time sky are sometimes made by including collectively a collection of brief exposures to create a vivid and detailed picture.

The Perseus Cluster.
NASA/CXC/SAO/E.Bulbul, et al
The Perseus Cluster.

After including all of the observations, the staff discovered recognized emission strains from varied components, but additionally discovered an emission line at 3.5 keV that doesn’t correspond to a recognized component. This type of spurious line can seem in summed spectra for a number of causes, comparable to instrument noise or glitches from the best way information is processed, so the staff first made certain these weren’t the trigger. The sign remained, so it appeared real. After this primary discovery, the staff discovered the identical emission line in dozens of different clusters that have been noticed with completely different x-ray telescopes. So it appears clear this can be a real sign.

Since this emission line isn’t attributable to recognized components, what might it’s? One apparent alternative is darkish matter. A big supercluster comparable to Perseus must be loaded with darkish matter, and the interplay of darkish matter particles might produce such a line. It has even been proposed that this x-ray line could possibly be much like the 21cm line of hydrogen, such that the presence and power of this line could possibly be a measure of the quantity of darkish matter in a area.

But it surely hasn’t been confirmed that that is, in truth, a darkish matter sign. One of many issues is that varied darkish matter fashions might produce such a sign, so its existence does little to tell apart one mannequin from one other. One other downside is that alternate options might additionally produce a sign, comparable to colliding black holes. Proper now, the alternate options appear much less seemingly than darkish matter, however they will’t be dominated out.

So as soon as once more we now have a touch of darkish matter with out conclusive proof.

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