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Can We Cool The Dark Matter? | An Astronomical Puzzle

[Estimated read time: 3 minutes]
  • Researchers introduced a new model, in which dark matter consists of charged particles.  
  • This would allow dark matter to radiate energy and create compact objects like dark galaxies or dark stars.  

The universe is full of things that we still don’t understand. One of such mysterious things is dark matter that occupies around 27% of the universe. Although dark matter has never been observed, its presence would explain several otherwise puzzling observations.

So far, we know dark matter doesn’t interact or emit electromagnetic radiations, like light, and therefore, it’s invisible to the electromagnetic spectrum. However, it influences the large structure of the universe, affects the cosmic microwave background and the formation of galaxies.

The distribution of baryons (subatomic particle made up of three quarks) and dark matter is very different – while a notable amount of baryons have radiated away much of their energy and fallen deep into the potential wells, the dark matter resides in extended halos.

Because of this difference, scientists long ago came up with a conclusion that dark matter particles cannot cool and collapse on any scale.

What they suggested is dark matter cannot cool off by radiating energy, and even it could, they may come together to form compact objects in a similar manner baryonic matter creates galaxies, stars and planets. However, dark matter doesn’t behave like this – it resides only in diffuse halos.

The Contradictory Model

What if galaxies consist of condensed dark matter in a bunch, and we just have not discovered them yet?

Researchers at Rutgers University have proposed a new model that allows the dark matter to cool. The model forecasts the substructure of hundreds of thousands of dark matter sprinkled throughout the galaxy, without denying the fact that most of those create a halo.

Reference: Physics Review Letters | doi:10.1103/PhysRevLett.120.051102

The baryonic matter cooled down and interactions between charged particles led to the creation of cosmic structures. If dark matter also carry particles that contains similar charge to baryonic particle, perhaps it could cool.

Image credit: Medium

In the new model, the dark matter consists of two types of charged particle – something similar to electrons and protons. These particles are capable of radiating energy, which enables dark matter to create gravitationally collapsed objects with unique mass scales lesser than that of a Milky-Way-like galaxy.

Dark matter cooling is obstructed and it’s stuck in a halo, above some critical mass of dark matter particle present in the galaxy. Below that mass, an enough dense dark matter blob could assemble together to form a compact object.

The model opens the possibility that dark matter and the galaxy play host to a notable number of collapsed substructures. Such structures are not well studied yet, but they are potentially interesting.

Other researchers have also worked in the same area, but they didn’t manage to explain why galactic halos do not collapse.

Read: How Can We Find The Speed Of Dark Matter?

What’s Next?

This is just a natural starting point that opens many interesting avenues for further studies. There are still lots of things to cover in future –

  • Is such behavior generic for models of dark matter with interactions?
  • What about the final states of the collapse?
  • What’s the utmost size of collapsing dark matter halos?
  • Is there a way to identify and exclude these collapsed objects?