The conundrum is called either the dwarf galaxy problem or the missing satellites problem and it’s been haunting astronomers and physicists for decades. But now with the aid of an ultra-high-resolution galaxy modeling, researchers with the Carnegie Institution for Science in the United States believe they have finally solved the mystery.
Galaxies like our own Milky Way are huge – they are comprised of literally hundred of billions of stars. But smaller in size are dwarf galaxies which can hold anywhere between millions to several billion stars. And “holding” is the key to the dwarf galaxy problem, as scientists have known for some time that the gravitational forces keeping galaxies both big and small intact area attributed not only to the presence of regular matter like planets and stars but also in large part due to the existence of dark matter, that as-yet unobserved substance thought to make up over a quarter of the mass and energy in the universe.
Scientists have calculated that the dark matter within the Milky Way should be responsible for the existence of hundreds and perhaps thousands of faintly glowing dwarf galaxies spinning around the periphery of the much larger Milky Way. The problem is we have yet to find more than a few dozen such dwarf galaxies, thus leaving them wondering about these missing satellite mini-galaxies.
One proposed solution states that many more dwarf galaxies do exist but they are overwhelmingly composed of dark matter, rendering them so faint as to be almost undetectable, a theory that was championed a decade ago by researchers who used the W.M. Keck Observatory in Hawaii to study eight new dwarf galaxies and accurately determine their respective masses.
Their results showed that there might just be, in fact, hundreds of dwarf galaxies within the Milky Way but that they are much smaller than previously assumed and filled almost completely with dark matter.
“It seems that very small, ultra-faint galaxies are far more plentiful than we thought,” said Dr. Marla Geha, co-author of the study and a Plaskett Research Fellow at the Herzberg Institute of Astrophysics in Canada. “If you asked me last year whether galaxies this small and this dark existed, I would have said no,” said Dr. Marla Geha, then a Research Fellow at the Canadian National Research Council’s Herzberg Institute of Astrophysics in Victoria, B.C. “I’m astonished that so many tiny, dark matter-dominated galaxies have now been discovered.”
But now, using the most sophisticated and high-resolution simulations ever created, researchers have tracked the development of galaxies such as the Milky Way and determined that in all likelihood, the small number of dwarf galaxies astronomers have already observed on the fringes of the Milky Way may have been correct all along.
The main insight afforded by the new modeling is that it explains how supernovae – explosions of huge stars – can impact their surroundings, to the point where the winds created by their demise are strong enough to blow gas and stars right out of small galaxies of the dwarf variety, effectively preventing them from becoming fully formed.
“We had thought before that perhaps our understanding of dark matter was incorrect in these simulations, but these new results show we don’t have to tinker with dark matter,” says Andrew Wetzel, postdoctoral fellow at Caltech and Carnegie Observatories and lead author of the new study, published in Astrophysical Journal Letters . “When we more precisely model supernovae, we get the right answer.”