Electric Dark Matter?

Is it possible that dark matter, or at least some of it, has an electric charge? That would explain a lot if it did.

Published on 6th Jun, 2018

Hello Space Fans and welcome to another edition of Space Fan News. In this episode, astronomers from Harvard are proposing a new model of dark matter that help explain some observations taken with radio telescopes as part of the EDGES project: the Experiment to Detect the Global Epoch of Reionization Signature. The observations were strange and astronomers are proposing that, to help explain them, perhaps a fraction of dark matter has an electric charge. I wish I had time to tell you about all the amazing collaborations and projects going on in astronomy from all over the world, here are just so many of them. Oh wait, I do, that’s why we have SFN… Anyway, there is this really cool experiment going on right now that I just found out about called EDGES, the Experiment to Detect the Global Epoch of Reionization Signature. It’s primary instrument is a radio telescope located in a radio quiet zone at the Murchison Radio Astronomy Observatory in Western Australia and is a collaboration between Arizona State University and MIT’s Haystack Observatory. A radio quiet zone is an area where radio transmissions are restricted in order to protect a radio telescope or a communications station from radio frequency interference. Kind of like a dark-sky initiative for radio telescopes and are usually in sparsely populated areas.. This radio telescope is looking at a time in cosmic history when neutral hydrogen gas from the early universe became ionized for the first time due to ultraviolet radiation from the first stars. Back in February, scientists from this project said they had detected the radio signature from the first generation of stars, and possible evidence for interaction between dark matter and normal matter. Some astronomers quickly challenged the EDGES claim, but other astronomers immediately began looking at the theoretical basis of these observations and did what astronomers do, started constructing mathematical models to explain the observations. To understand the EDGES observations, let’s start with some basics. The very first stars in the universe were very massive, hot, and bright in the ultraviolet. These stars only lived a few tens of millions of years or so. According to the commonly accepted early universe scenario, this UV light interacted with the cold hydrogen atoms lying between these first star which enabled them to absorb the leftovers from the Big Bang, the Cosmic Microwave Background (CMB). This absorption should have led to a drop in brightness in the CMB during this period, which was around 200 million years after the Big Bang. The EDGES observation did show this absorption, although it has to be confirmed, but the temperature of the hydrogen gas during this period was half of what was expected, making the absorption twice what is should have been. Now if it’s true that what EDGES measured was in fact the absorption of the CMB by the first stars in the universe, then why are these stars absorbing so much? At the time when CMB radiation is being absorbed, any free electrons or protons associated with ordinary matter would have been moving at their slowest possible speeds (since later on they were heated by X-rays from the first black holes). Scattering of charged particles is most effective at low speeds. So, any interactions between normal matter and dark matter during this time would have been the strongest if some of the dark matter particles are charged. This interaction would cause the hydrogen gas to cool because the dark matter is cold, potentially leaving an observational signature like that claimed by the EDGES project. Only small amounts of dark matter with weak electrical charge can both explain the EDGES data and avoid disagreement with other observations. If most of the dark matter is charged, then these particles would have been deflected away from regions close to the disk of our own Galaxy, and prevented from re-entering. Something that conflicts with observations showing that large amounts of dark matter are located close to the disk of the Milky Way. It’s possible that in the early universe, when free electrons and protons were recombining into neutral Hydrogen, at time just prior to reionization, maybe the same thing was happening to dark matter. Maybe whatever makes up neutral dark matter came together from an as yet unknown charged dark matter particle but not all of it recombined. So as you can imagine, there’s a lot of checking, confirming, arguing and reconfirming going on right now, but some astronomers are excited about the idea that the elusive dark matter, whatever it is, some of it anyway, might actually carry a charge. I’ll keep you posted. That’s it for this episode Space Fans, thanks to all Patreon Patrons who keep SFN on the intertubes. These guys in particular, they’ve been with me for a while. Thanks to all of you for watching and as always, Keep Looking Up! Https://www.cfa.harvard.edu/news/2018-08