Galaxies begin as energetic spiral galaxies that are full of gas and dust, and are rich in color — perfect for forming bright new stars. As galaxies evolve, some of them turn into cosmic graveyards where new stars are no longer being formed. The mechanism that produces this dramatic transformation has remained a mystery — until now.
An international team of scientists now claim to have solved this long-standing mystery in astronomy. The team, led by the University of Tokyo and involved the University of Oxford, identified the potential cause using optical imaging spectroscopy from the Sloan Digital Sky Survey-IV Mapping Nearby Galaxies at Apache Point Observatory (SDSS-IV MaNGA).
The team discovered an unexpectedly common new phenomenon in a new class of galaxies dubbed “red geysers,” which may explain how the process works. Red geysers are galaxies that host low-energy supermassive black holes that drive intense interstellar winds.
These winds have so much heat and intensity they suppress star formation throughout whole galaxies. They do this by heating up the ambient gas and prevent it from cooling and condensing into stars. Lead author Dr. Edmond Cheung explains in a statement:
“Stars form from the gas, but in many galaxies stars were found not to form despite an abundance of gas. It was like having deserts in densely clouded regions.
“We knew quiescent galaxies needed some way to suppress star formation, and now we think the red geysers phenomenon may represent how typical quiescent galaxies maintain their quiescence.”
A galaxy dubbed Akira was chosen to be studied as it was a perfect example of “red geysers” (red refers to the color of galaxies lacking young blue stars, and geyser referring to the irregular wind outbursts from the supermassive black hole). The researchers found Akira had an intriguing and complex pattern of warm gas, which implies the existence of an out-flowing wind from the supermassive black hole at its center.
The researchers believe that the fuel for Akira’s supermassive black hole was most likely coming from its interaction with a smaller galaxy, called Tetsuo. The out-flowing wind proved to have enough energy to heat the surrounding gas, which could ultimately prevent any future star formation. Co-author Dr. Michele Cappellari explained in a statement:
“Stars form from the gas, a bit like the drops of rain condense from the water vapour. And in both cases one needs the gas to cool down, for condensation to occur. But we could not understand what was preventing this cooling from happening in many galaxies.
“But when we modelled the motion of the gas in the red geysers, we found that the gas was being pushed away from the galaxy centre, and escaping the galaxy gravitational pull.”
Dr. Kevin Bundy, from the University of Tokyo, and overall leader of the collaboration said:
“The discovery was made possible by the amazing power of the ongoing MaNGA galaxy survey.
“The survey allows us to observe galaxies in three dimensions, by mapping not only how they appear on the sky, but also how their stars and gas move inside them.”
Like global warming on Earth, galactic warming has long-term consequences for red geyser galaxies. Cheung explains:
“You can think of these winds as super-heating the atmospheres of galaxies, as soon as any gas starts to cool; it gets blasted by this wind, like water droplets turning to steam.”
The MaNGA survey is currently in the process of mapping the details of 10,000 nearby galaxies, charting not only the supermassive black holes at galaxy centers, but also their edges as well. The survey is the largest of its kind, Renbin Yan from the University of Kentucky and a team member said in a statement:
“Since MaNGA studies so many galaxies, our snapshots can reveal even the quickest changes to galaxies, and that’s how we found Akira.”
The team hypothesizes that this phenomenon is very common in dormant galaxies. If their theory proves to be right, our very own Milky Way galaxy may not be safe from galactic warming.