Using the Atacama Large Millimeter/submillimeter Array (ALMA), a team of researchers from around the globe have found something "unexpected:" compact interstellar clouds hidden within the nearby dwarf irregular galaxy Wolf-Lundmark-Melotte (WLM), according to a press release from the National Radio Astronomy Observatory.
"For many reasons, dwarf irregular galaxies like WLM are poorly equipped to form star clusters," said Monica Rubio, an astronomer with the University of Chile and lead author. "These galaxies are fluffy with very low densities. They also lack the heavy elements that contribute to star formation. Such galaxies should only form dispersed stars rather than concentrated clusters, but that is clearly not the case."
WLM is an isolated dwarf galaxy about 3 million light years away on the edges of the "Local Group" that includes the Milky Way, the Magellanic Clouds, Andromeda, M33 and many smaller galaxies.
"Molecules, and carbon monoxide in particular, play an important role in star formation," Rubio said. "As gas clouds begin to collapse, temperatures and densities rise, pushing back against gravity. That's where these molecules and dust particles come to the rescue by absorbing some of the heat through collisions and radiating it into space at infrared and submillimeter wavelengths."
The cooling effect is what allows gravity to do its job in the collapse which then results in the formation of a star.
WLM and other tiny galaxies have low amounts of heavy elements, so there wasn't enough material to observe that would explain the new star clusters.
"Like a diver being squeezed at the bottom of a deep abyss, these bundles of star-forming gas are under tremendous pressure, even though the surrounding ocean of interstellar gas is much more shallow," said Bruce Elmegreen, a co-author and researcher at the IBM T.J. Watson Research Center. "By discovering that the carbon monoxide is confined to highly concentrated regions within a vast expanse of transitional gas, we could finally understand the mechanisms that led to the impressive stellar neighborhoods we see in the galaxy today."
The study, "Dense cloud cores revealed by CO in the low metallicity dwarf galaxy WLM," has been published in the journal Nature.
The first video from NRAO is an "artist animation revealing an emerging star cluster in the WLM dwarf irregular galaxy. The optical image of the galaxy was taken with the Blanco 4-meter telescope. ALMA data reveal the presence of dense clouds of star-forming dust and gas. The zoom-in illustrates how a collection of stars would appear within one such cloud."
Credit: Animation by B. Saxton (NRAO/AUI/NSF); Optical data: P. Massey/Lowell Observatory and K. Olsen (NOAO/AURA/NSF); ALMA data: M. Rubio et al., Universidad de Chile, ALMA (NRAO/ESO/NAOJ): Fly-in animation by B. Kent (NRAO/AUI/NSF)
This video from NRAO "explains how an irregular dwarf galaxy is able to form star clusters similar to those found in larger galaxies."
Credit: Animation by B. Saxton (NRAO/AUI/NSF), editing by J. Hellerman (NRAO/AUI/NSF); Optical data: P. Massey/Lowell Observatory and K. Olsen (NOAO/AURA/NSF); ALMA data: M. Rubio et al., Universidad de Chile, ALMA (NRAO/ESO/NAOJ); Fly-in animation: B. Kent (NRAO/AUI/NSF)