Scientists find elusive gas from post-starburst galaxies hiding within plain sight

A clear understanding of the procedures that govern the development of stars and galaxies is key to providing context to the universe and our place in it

Scientists have discovered that post-starburst galaxies condense their gas rather than expelling it, begging problem: What’s actually keeping them from forming stars?

Post-starburst galaxies were previously thought to spread all of their gas and dust— the fuel required for creating new stars— in violent bursts of energy, and with extraordinary speed. Now, new information from the Atacama Large Millimeter/submillimeter Array (ALMA) reveals these galaxies don’t scatter all of their star-forming fuel after all. Instead, after their supposed finish, these dormant galaxies hold onto and compress large amounts of highly-concentrated, turbulent gas. But contrary to expectation, they’re not really using it to form stars.

In most galaxies, scientists expect gas to be dispersed in a way similar to starlight. But for post-starburst galaxies, or PSBs, this isn’t the case. PSBs are different from other galaxies because they are created in the aftermath of violent collisions, or mergers in between galaxies. Galaxy mergers usually trigger massive bursts of  star formation , but in PSBs, this episode slows down and near-completely stops almost as soon as it begins. As a result, scientists previously thought that little or no star-forming fuel was left in these galaxies’ central star-forming factories. And until now, the belief was that the particular molecular gases had been redistributed to radii well beyond the galaxies, either through stellar processes or by the effects of black holes. The new outcomes challenge this theory.

“ We’ve reputed for some time that large amounts associated with molecular gas remains near PSBs but haven’t been able to say where, which in turn, offers prevented us from understanding why these galaxies stopped forming stars. Now, we have discovered a considerable amount of remaining gasoline within the galaxies and that remaining gas is very compact, ” said Adam Smercina, a good astronomer at the University associated with Washington and the principal detective of the study. “ Could compact gas should be developing stars efficiently, it isn’t. In fact , it is less than 10-percent as efficient as similarly compact gas is expected to end up being. ”

Scientists Find Elusive Gas From Post-starburst Galaxies Hiding in Plain Sight
Scientists studying post-starburst galaxies, or PSBs, discovered that they don’t behave as expected. PSBs were previously believed to scatter their gas because they become dormant. New findings have revealed that these galaxies actually hang onto this gas and compact it near to their particular centers. PSB 0379. 579. 51789 is the one exception in the study. Here, radio stations data of the galaxy overlaid on optical images from your Hubble Space Telescope expose that while the galaxy did hold onto its star-forming energy, the collection of gas is located off-center. Credit: ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO/AUI/NSF)

In addition to being compact enough to make stars, the fuel in the observed dormant— or even quiescent— galaxies had an additional surprise in store for the team: it was often centrally-located, even though not always, and was amazingly turbulent. Combined, these two characteristics led to more questions than answers for researchers.

“ The rates of star formation in the PSBs we observed are lower than in other galaxies, although there appears to be plenty of energy to sustain the process, ” said Smercina. “ In cases like this, star formation may be suppressed due to turbulence in the gas, much like a strong wind can suppress a fire. However , star formation can also be enhanced by turbulence, just like wind can fan flames, so knowing what is generating this turbulent energy, and how exactly it is contributing to dormancy, is a outstanding question of this work. ”

Decker French, an astronomer at the College of Illinois, and a co-author of the research added, “ These results raise the issue of what energy sources are present in these galaxies to push turbulence and prevent the fuel from forming  new stars . One chance is energy from the accretion disk of the central supermassive black holes in these galaxies. ”

A clear understanding of the processes that govern the formation of  stars   and galaxies is key to providing context to the galaxy and our place in this. The discovery of violent, compact gas in otherwise dormant galaxies gives researchers one more clue to solving the mystery of how  galaxies   in particular live, evolve plus die over the course of billions of yrs. And that means additional future research with the help of ALMA’s 1 . 3mm receiver, which views the otherwise invisible with stark clarity.

Scientists Find Elusive Gas From Post-starburst Galaxies Hiding in Plain Sight
Post-starburst galaxies were previously believed to expel all of their molecular gas, the behavior that caused them to stop forming stars. New observations have revealed that these galaxies actually hold onto and condense star-forming fuel close to their centers, and then avoid the use of it to form stars. Here, radio data of PSB 0570. 537. 52266 overlaid on optical images in the Hubble Space Telescope, display the dense collection of gas near the center of the galaxy. Credit: ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO/AUI/NSF)

J. D. Smith, a good astronomer at the University of Toledo, and a co-author from the research said, “ There is much about the evolution of a typical galaxy we don’t understand, and the transition from their vibrant star-forming lives into quiescence is one of the least understood periods. Although post-starbursts were very common within the early universe, today they are quite rare. This means the nearest examples are still billions of light-years away, require events foreshadow the potential outcome of a collision, or merger, between the Milky Way Universe and the Andromeda Galaxy various billion years from now. Only with the incredible solving power of ALMA can we peer deep into the molecular reservoirs left behind ‘ after the fall. ‘”

Smercina added, “ It’s often the case that we because astronomers intuit the solutions to our own questions ahead of observations, but this time, we all learned something completely unexpected about the universe. ”

The results of the study are published today in  The Astrophysical Diary.

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