Scientists found evidence of strong winds suppressing stellar growth in several dwarf galaxies. Photo by SDSS/UCR
Oct. 14 (UPI) -- Study by study, scientists are beginning to uncover the effects of supermassive black holes on the evolution of the galaxies where they reside. New research suggests their impacts on galaxy growth are most dramatic in dwarf galaxies.
Until now, most studies have focused on black holes located in the center of large galaxies. One recent study showed the Milky Way's resident supermassive black hole has produced explosive activity as recently as a few million years ago.
The new research suggests black holes in dwarf galaxies, the most common type of galaxy in the cosmos, are just as influential.
"Our findings now indicate that their effect can be just as dramatic, if not more dramatic, in dwarf galaxies in the universe," Gabriela Canalizo, a professor of physics and astronomy at the University of California, Riverside, said in a news release.
The findings, recently published the Astrophysical Journal, showed strong winds blowing from supermassive black holes curtail stellar formation inside the dwarf galaxies where they reside.
Scientists used the Sloan Digital Sky Survey to identify 50 dwarf galaxies, 29 of which featured supermassive black holes in their centers. Next, researchers used ground-based telescopes to identify powerful winds blowing from six of the supermassive black holes.
"Using the Keck telescopes in Hawaii, we were able to not only detect, but also measure specific properties of these winds, such as their kinematics, distribution, and power source -- the first time this has been done," Canalizo said. "We found some evidence that these winds may be changing the rate at which the galaxies are able to form stars."
Large galaxies are built from dozens of smaller galaxies that merged over time. With each new merger, the massive galaxies take on new features. Smaller galaxies remain untainted.
"Dwarf galaxies are, therefore, useful in understanding how galaxies evolve. Dwarf galaxies are small because after they formed, they somehow avoided merging with other galaxies," said Christina Manzano-King, a doctoral student in Canalizo's lab. "Thus, they serve as fossils by revealing what the environment of the early universe was like. Dwarf galaxies are the smallest galaxies in which we are directly seeing winds -- gas flows up to 1,000 kilometers per second -- for the first time."
The friction created as large amounts of material and sucked into supermassive black holes causes radiative energy to be released. This energy release pushes ambient gas from the galaxy's center towards its periphery.
"What's interesting is that these winds are being pushed out by active black holes in the six dwarf galaxies rather than by stellar processes such as supernovae," said Manzano-King. "Typically, winds driven by stellar processes are common in dwarf galaxies and constitute the dominant process for regulating the amount of gas available in dwarf galaxies for forming stars."
Though winds can sometimes condense the gas ahead of them, increasing star formation, the powerful winds in the six surveyed dwarf galaxies were strong enough to push gas all the way to the outskirts of the galaxy and into intergalactic space. Stars need gas to form.
"In these six cases, the wind has a negative impact on star formation," said Laura V. Sales, an assistant professor of physics and astronomy. "Theoretical models for the formation and evolution of galaxies have not included the impact of black holes in dwarf galaxies. We are seeing evidence, however, of a suppression of star formation in these galaxies. Our findings show that galaxy formation models must include black holes as important, if not dominant, regulators of star formation in dwarf galaxies."
