THE DARK MATTER SERIES
EP-2 What Could Not Be Dark Matter?
In the last part, I covered how we got an idea that something like Dark Matter, which is invisible to us, could be established to exist. It is not just a theory, but rather, in this case, it is proven to exist by various observations and the scientific community is now in search of a theory, or particles that could explain the behavior of Dark Matter.
So, what the name Dark Matter suggests is that it is something Dark i.e. it is not visible to us at least(no idea if some alien species there would have found a way to see it!) to us. And the other part suggests that it has something to do with Matter.
So, something Dark and related to Matter……Dark and related to Matter………well we know at least a thing or two that fits this category, don’t we? for example the monsters there in space…..Black-holes.
So, could Black-holes or something related to them is the culprits behind Dark Matter? Well, after all, Science is not that easy! Let’s see what are the things that we can surely rule out as Dark Matter.
For starters, Black-holes cannot be candidates for Dark-Matter, because first of all, Dark Matter does not interact electromagnetically at all whereas although Black-holes are Black, they do emit radiation for sure. Secondly, if Black-holes were Dark Matter, there would have to be a lot of them to generate the gravity that is exerted by Dark Matter and in such large numbers, their effects on nearby Stars would be visible in that the orbits of these Stars would be distorted by their gravity.
Also, from what we know till now, Dark Matter is supposed to form Halo structures surrounding the outer edges of Galaxies. Thus, Black-holes are one of the types of MACHOs, which we will discuss next.
Next, we discuss the idea of why MACHOs (Massive Compact Halo Objects) are not candidates of Dark Matter. But there is plenty of evidence against MACHOs as MACHOs suggest the idea that DM is made up of ordinary matter which is not visible. But if that were the case then there does not seem to be any reason why they would form a Halo instead of disks like normal galaxies.
Another problem about MACHO’s is that BH which account for a large part of MACHO’s, are objects formed from large stars, and the distribution of DM in many cases preludes such large concentrations of mass.
Another possible candidate for DM which is now debunked is primordial Black-holes which would have been in existence from the very early days of the universe. When the matter was first forming, the violent fluctuations in spacetime after the big bang may have been capable of compressing matter to form black holes.
A finding from the University of Berkeley in 2018 analyzing supernovas for gravitational lensing from primordial Black-holes, their findings: no more than 40% of Dark Matter can consist of primordial Black-holes, and probably none of it does.
The viability of old white dwarfs as a component of the Galactic Dark Matter is that while there are some interesting hints, there is no compelling evidence in the current statistics either for or against the scenario. There are enormous problems in fitting the spectra of these cool white dwarfs with the current generation of models.
The second concern is simply that no truly ultracool white dwarfs have as yet been discovered, or, perhaps better put, no white dwarfs are known whose colors and/or spectra suggest that the object’s age is in the range of 12–14 Gyrs.
Thus, here is the list of candidates, which could not form Dark Matter, though they seem to be the first go-to candidates. But due to the structure and different behavior of Dark Matter that we observe, there is plenty of evidence to debunk them as of now.
Next, we will look at some particles and whether they could be the ideal candidates for Dark Matter. Stay Tuned!
