Why aren’t there enough stars and dark matter in the galaxies we observe (particularly the many dwarf galaxies)? Good question. It’s been bothering cosmologists for decades. It bothers physicists too; they can’t see or measure dark matter, since whatever it is, it doesn’t affect the usual electromagnetic suspects. Yet dark matter is thought to account for up to 75% of all matter in the universe; so when areas that should have dark matter don’t have enough…well, there’s a gap in the model somewhere. Lots of models have been proposed, although what is now called the ‘cold dark matter theory’ retains its popularity. A new variation of this theory has just appeared, from the work of an international team.
The difference in this model might be twofold: A more realistic set of variables, such as the inclusion of star formation as a major piece of the model, and millions of hours on the world’s fastest supercomputers to run the simulations. What came out of the simulations was a bang, not a Big Bang, but many very large bangs caused by the earliest stars going supernova and exploding. Those explosions not only blew whole star systems out of galaxies, but also in turn caused the resident dark matter to drift away (having no gravity left to keep it around). In the end, the simulations resulted in formation of the many dwarf galaxies now observed, including their insufficiency of stars and dark matter.
“Most previous work included only a simple description of how and where stars formed within galaxies, or neglected star formation altogether,” said Fabio Governato, a University of Washington research associate professor of astronomy and lead author of the Nature paper.
“The cold dark matter theory works amazingly well at telling where, when and how many galaxies should form,” Governato said. “What we did was find a better description of processes that we know happen in the real universe, resulting in more accurate simulations.”
“There is a theory which states that if ever anyone discovers exactly what
the Universe is for and why it is here, it will instantly disappear and be
replaced by something even more bizarre and inexplicable. There is another
theory which states that this has already happened.”
— Douglas Adams