Supermassive black hole blows away galaxy’s star-building material

Astronomers have discovered a supermassive black hole that blows away star-building gas and dust from its host galaxy’s core. For years, scientists have wondered why nearby galaxies blast away material from their centers, ejecting enough dust and gas to build more than a thousand Sun-sized stars every year. Now they believe they may have found the answer.

Researchers from the University of Maryland (UMD), and colleagues in the UK and Spain, have published their findings in the academic journal Nature.

They say their study provides the first observational evidence that a supermassive black hole in the middle of a large galaxy can power these enormous molecular outflows deep within the galaxy’s core.

A red-filter image of the galaxy the scientists were observing from the University of Hawaii’s 2.2-meter telescope. It shows faint features that may be tidal debris, a sign of a galaxy merger. (Image: NASA GSFC/SDSS/Sylvain Veilleux)

These outflows, which get rid of huge quantities of star-building gas, influence the shape, size and overall fate of the host galaxy.

Supermassive volcano swallowing huge amounts of gas

Lead author, Dr. Francesco Tombesi, an assistant research scientist in UMD’s astronomy department, and colleagues have been studying the galaxy known as IRAS F11119+3257, which has an actively growing supermassive black hole at its center.

 

Unlike the large (but not supermassive) black hole at the center of the Milky Way (our galaxy), this supermassive one is actively consuming huge amounts of gas.

As the dust enters the black hole it creates friction, which in turn emits electromagnetic radiation – including X-rays and visible light.

Black holes that do this are called AGN (active galactic nuclei). Their intense radiation output generates strong winds that blow material away from the center of the galaxy.

These AGN winds, the researchers found, are powerful enough to drive large molecular outflows that end up at the edges of the galaxy’s borders.

First study to confirm AGN wind theory

Theorists have suspected AGN winds are linked to molecular outflows. This study is the first to confirm the theory with observational evidence.

Dr. Tombesi, who also has a joint appointment at NASA’s Goddard Space Flight Center via the Center for Research and Exploration in Space Science and Technology, said:

“This is the first galaxy in which we can see both the wind from the active galactic nucleus and the large-scale outflow of molecular gas at the same time.”

An artist’s impression of an Active Galactic Nucleus. (Image: ESA/NASA, the AVO project and Paolo Padovani)

The scientists analyzed data gathered by the JAXA’s (Japan Aerospace Exploration Agency’s) D-ray satellite Suzaku, the European Space Agency’s Herschel Space Laboratory, and NASA.

Previous studies had independently described molecular outflows and AGN winds in separate galaxies. Tombesi and team wanted to find a galaxy where both could be observed at the same time. As it turned out, IRAS F11119+3257 was the perfect candidate.

Another theory suggested that the molecular outflows could be caused by active star formation near the galactic center. However, the active nucleus’ brightness in this galaxy, which is responsible for approximately 80% of all its radiation, suggested otherwise.

This intense concentration of energy could not be explained by star formation, which led the researchers to conclude that the primary driver had to be the AGN winds.

Supermassive black hole’s impact too huge to ignore

Co-author Marcio, Meléndez, a research associate in UMD’s astronomy department, said:

“The temptation is to ignore the supermassive black hole when studying galactic dynamics and evolution, but our study shows that you can’t because it influences galaxies on the larger scale.”

The researchers only have this one galaxy as a baseline for study, given the limited satellite time available. However, as they have a better understanding of what they are looking for, they believe finding more candidate galaxies in future will be easier.

ASTRO-H, a successor satellite to Suzaku, will be launched by NASA and JAXA within the next year. With its state-of-the-art instruments, the team will be able to study more galaxies like IRAS F11119+3257 in greater detail.

Co-author Sylvain Veilleux, a professor of astronomy at UMD and a fellow at the Joint Space-Science Institute (JSI), said:

“These are not like normal spiral or elliptical galaxies. They’re like train wrecks. Two galaxies collided with each other, and it’s now a single object. This train wreck provided all the material to feed the supermassive black hole that is now driving the huge galactic-scale outflow.”

In addition to Veilleux, Tombesi and Meléndez, co-authors included James Reeves of Keele University in the United Kingdom, Eduardo González-Alfonso of the Universidad de Alcalá in Spain, and Chris Reynolds of UMD (and a JSI fellow).

The study was financed by NASA, the US National Science Foundation, Spain’s Ministerio de Economía y Competitividad, and the UK Science and Technology Facilities Council.

Citation: “Wind from the black-hole accretion disk driving a molecular outflow in an active galaxy,” F. Tombesi, M. Meléndez, S. Veilleux, J. N. Reeves, E. González-Alfonso & C. S. Reynolds. Nature. Published 26 March, 2015. DOI: 10.1038/nature14261.