Supermassive black holes can impede star formation in dwarf galaxies

Phenomena known as red geysers had been thought to occur only in larger galaxies.
By Laurel Kornfeld | Jan 10, 2018
Supermassive black holes at the centers of dwarf galaxies can prevent new stars from forming in their galaxies by spewing powerful winds known as red geysers, according to a study presented by astronomers of the Sloan Digital Sky Survey (SDSS) at a meeting of the American Astronomical Society (AAS) in National Harbor, Maryland, on Tuesday, January 9.

The study was conducted using data collected by SDSS's Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, which created detailed maps of 17 galaxies at a time using more than 1,000 optical fibers.

This technology enables scientists to observe the entirety of a galaxy in detail.

Red geysers are produced when gases fall into supermassive black holes. These gases heat up to several million degrees, glow brightly, and produce strong winds that travel thousands of miles per second across the galaxies.

According to MaNGA Principal Investigator Kevin Bundy of the University of California at Santa Cruz, "We called these features 'red geysers' because the sporadic wind outbursts reminded us of a geyser, and because the end of star formation has left the galaxy with only red stars."

MaNGA, which for the first time allows scientists to see the effects of black holes across entire galaxies, surprisingly found red geysers in 10 percent of the dwarf galaxies studied.

Scientists had expected to see the "geysers" in large galaxies but not in smaller dwarf galaxies, which constitute the majority of galaxies in the universe.

"Dwarf galaxies outnumber galaxies like the Milky Way fifty to one. So if we want to tell the full story of galaxies, we need to understand how dwarf galaxies work," emphasized Samantha Penny of the University of Portsmouth's Institute of Cosmology and Gravitation.

In any galaxy, star formation can end via several mechanisms. Galaxies can run out of the gases needed to make new stars; gases can be sucked out of a galaxy when it interacts with another galaxy; gases can heat up to a point that they can no longer collapse into new stars, or active supermassive black holes can suppress star formation.

"This discovery shows that even isolated dwarf galaxies can stop forming stars if they host an active supermassive black hole. That's not what's written in our textbooks on galaxy evolution. It was a real surprise to see it even once, much less in one out of every ten galaxies we looked at," said research team member Karen Masters of both the University of Portsmouth and Haverford College.



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