Neomi Lewis ‘21
Astronomers and cosmologists continue the elusive search to understand the nature and existence of dark matter, a substance that is believed to be pervasive throughout the universe, including near our own planet. An international group of astrophysicists have published work in the journal Physical Review Letters this January that suggests that we may be able to better decipher the speed of dark matter moving near Earth by using the speed of old stars as guides.
Dark matter is believed to comprise around 26.8% of matter in the Universe, but it is still a hypothetical substance that is not observable using traditional means of observation such as through electromagnetic radiation. It has been hypothesized to play a significant role in several astronomical phenomena and provide important keys to various questions, including determining the age and ultimate fate of the Universe. Like its mysterious name suggests, much is unknown about dark matter, and its very existence is still disputed by some.
However, there are several theories on how to corroborate the properties of dark matter. Jonah Herzog-Arbeitman, an undergraduate who is part of a research team at Princeton, suggests using the oldest stars we know for clues explained: “Our hypothesis was that there’s some subset of stars that, for some reason, will match the movements of the dark matter.” Herzog-Arbeitman’s team used Eris, a computer simulation which uses supercomputers to replicate the physics of the galaxy. The theory then first started to seem like a legitimate one when the team was able to match the velocities of groups of dark matter with that of stars with low metallicity (with lighter metals in their composition, these stars are generally older because heavier elements take more time to form). To describe this, Lina Necib at the California Institute of Technology said, “The dark matter and these old stars have the same initial conditions: they started in the same place and they have the same properties, so at the end of the day, it makes sense that they’re both acted on only through gravity.”
Being able to approximate the speeds of dark matter is especially important because it helps corroborate the validity of other major experiments performed with dark matter. One primary way that dark matter is being detected is through “direct detection,” a process in which physicists try to force dark matter to interact directly with very dense materials like xenon. These processes have not yielded strong evidence and researchers from this team believe that this may be because dark matter does not have the right kind of velocity and kinetic energy to cause significant reactions.
However, the data produced by the Eris simulation has not yet been verified by real-world astronomy so there is still uncertainty is determining the relevant velocities. But it does not seem like this will take very long because the European Space Agency’s Gaia telescope has been recording information about the Milky Way since July 2014. The wealth of data that will include data on nearly a billion stars will almost definitely help take this exciting theory forward.
- J. Herzog-Arbeitman, et. al. Empirical determination of dark matter velocities using metal-poor stars 120, (2018).
- Image retrieved from: https://commons.wikimedia.org/wiki/File:Dark_Matter_Cloud.png