The space.com report says "Researchers think that the emission, known as the "3.5 keV line" (keV stands for kilo-electronvolts), is likely made of sterile neutrinos
, which have long been thought of as a candidate for dark matter, study co-author Chris Dessert, of the University of Michigan, told Space.com. "
The report indicates the search did not confirm the candidate for DM. There are many other candidates too like WIMPS, axions, axion like particles or ALP, etc. Scientific American published on this latest DM search effort and noted :
"...Existential Crisis Ultimately, scientists are left scratching their head at the extremely odd behavior of 85 percent of the mass in the universe. Do the new studies discrediting the supposed signals of dark matter in our galaxy make them doubt dark matter exists? “No,” Abazajian says, “particle dark matter is so consistent with what’s been observed, from the subgalaxy scale out to the horizon of the cosmos, that it is, basically, without a doubt, there.” Even though their faith in the existence of dark matter is unshaken, scientists’ hope of finding it may be diminished. Not only is astrophysical evidence elusive, but direct detection experiments aiming to capture the particles responsible have so far failed...", ref - Milky Way Dark Matter Signals in Doubt after Controversial New Papers
Note that there is still evidence in favor of sterile or right handed neutrinos because the best explanation for flavor oscillation and thus each must have different masses requiring at least two left handed neutrinos to have nonzero masses. The existence of left handed neutrinos thus requires the existence of heavy right handed neutrinos. The simplest idealized standard model avoids right handed neutrinos by making all neutrino masses identically zero eliminating them from the equation entirely as this has been confirmed to not be the case symmetry requires that they exist in one form or another
The challenge sterile neutrinos pose is that if they exist, and the existence of Neutrino flavor oscillation says they either *must exist* or otherwise the standard model must be wrong, then they by definition can *never* be detected by the strong, weak or electromagnetic forces.
This is because by definition the weak nuclear force only acts on left handed particles and the weak force is the only force neutrinos can interact by. According to the Standard Model Sterile Neutrinos *must exist* because Neutrino flavor oscillation has been observed. i.e. the only way for the sterile or right handed neutrino not to exist is for all neutrinos to effectively be massless and thus identical.
Thus the only way a sterile neutrino could ever be detected is by decaying into a detectable particle with nonzero charge or color charge.
So the only question left is whether these right handed neutrinos are stable or at least long lived or whether they decay almost instantly. This is where the ambiguity resides because while flavor oscillation among left handed neutrinos tells us that all 3 flavors of neutrinos must have different masses it doesn't tell us what those masses are only that they are all different from each other. If all 3 types of left handed neutrinos have mass then sterile neutrinos would be unstable to at least some degree as their stability depends on this mass.
So while the existence of heavy right handed neutrinos is confirmed we can't know if they are stable or not without directly measuring neutrino masses which is hard.
Work has shown that if one of the 3 left handed neutrinos is stable then its counterpart right handed neutrino must be stable as well so we can not assume that right handed neutrinos are unstable.
The problem of course is that if sterile neutrinos are stable i.e. don't decay they will forever remain undetectable as sterile neutrinos according to the standard model can not interact via the strong or electroweak forces and interact by gravity.
This means the only way they can be confirmed is by directly observing neutrino masses which are ridiculously tiny. This is the same as measuring quantum level gravity and thus is currently beyond our reach.
However theorists show that if Sterile Neutrinos are stable i.e. 1 neutrino flavor is massless then they exist in about the right amounts to account for dark matter and will never be able to be detected by any theoretical means short of creating sterile neutrinos that is measuring the missing energy and momentum.
The continued non detection of alternative types of dark matter proposed to get around the fundamental undetectability required by the standard model by each and every mechanism we try only further strengthens the case for sterile neutrinos this work only weakens the case for unstable sterile neutrinos.
WIMPs the dream child of the unsubstantiated supersymmetry model never had any evidence that it should be correct aside from pure wishful thinking. Supersymmetry has been effectively ruled out by experiments in the LHC kept "alive" by the sunken cost fallacy and the addition of correction terms in terms of orthogonal series functions (like the famous Fourier series) which are directly analogous to the epicycles that allowed the Polemic model of the universe to remain consistent with observations. This model also fails to explain Neutrino flavor oscillation so should have been ruled out last century when epicycles started to get added on top of epicycles.
Looking back towards the one thing that has been affirmed again and again at these scales the Standard Model we only have any theoretical leeway because we don't know what the Neutrino masses are. In principal right handed Neutrinos should be able to be created if they exist thus we either should see their decay or not depending on their stability.
The lack of detections says that if they are being created, and we have no reason to believe they wouldn't be created in the modern universe since left handed neutrinos are created, that they do not have a short lifetime.
This either tells us one of 3 things must be true.
1)Right handed neutrinos exist but they decay instantly or nearly so that the reactions that make them are so improbably rare that they can't be observed within the observable universe since the big bang and thus they can't account for all of dark matter.
2) Right handed Neutrinos exist and the reactions that make them are not super improbably rare and sterile neutrinos are stable or long lived and thus can naturally fully account for all of dark matter.
3) the standard model is wrong despite no evidence for the theory being incorrect and any and all alternatives failing to match experimental evidence.
Of these Occam's razor strongly suggests option 2 is most likely to apply for our universe as we have no reason why the reactions for these should be so absurdly rare that we can detect left handed neutrinos but not right handed ones and option 3 is equivalent to throwing our hands up in the air and saying everything we know is wrong because we don't like what the theory is telling us.
Every non detection only further strengthens this case it is possible axions exist since they emerge from within the less understood strong force components of the standard model that has yet to be combined together with electroweak theory. Either way their existence doesn't matter for the case of sterile neutrinos as we have observed Neutrino flavor oscillation. Axions thus would just be a bonus that could account for dark matter allowing more variability in the amount of sterile neutrinos out there.