ESO 137-001, Credit: NASA, ESA, CXC

ESO 137-001 by NASA, ESA, CXC

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How do you feed an active galactic nucleus (AGN)? These incredibly energetic, luminous galactic centers host supermassive black holes that accumulate matter, but how? Where does the accreted gas come from? And why aren’t AGNs more common?

Biana Poggianti and colleagues attempt to answer these questions by looking at one type of galaxy known as jellyfish. Jellyfish galaxies occur in galaxy clusters, and they acquired their sobriquet from long “tentacles” of gas and newborn stars that make them resemble their aquatic animal namesakes. The wispy streams of gas are being torn away from the galaxy as it moves through space. This process is known as ram pressure stripping—a drag force experienced by an object moving through a fluid.

As Poggianti and team write in a new paper, “The galaxy loses its gas because the ram pressure overcomes the local binding energy…” begging the question, where does that gas go? They also write that “A prerequisite for AGN activity is… the availability of gas in the galaxy disk to feed the black hole.” Could the loss of gas due to ram pressure stripping and the availability of gas to feed the AGN therefore be related in jellyfish galaxies?

The scientists looked at seven massive jellyfish galaxies to find out. They determined that six of them host an AGN. Looking at the galaxies’ velocity and location within the galaxy cluster, the authors discovered that ram pressure more likely occurs closer to the center of the clusters and at high velocities—a sweet spot where the six jellyfish hosting an AGN are found. The team believes that the same ram pressure responsible for stripping gas from these galaxies could also funnel gas toward the central supermassive black hole, triggering AGN activity.

Could this be true in other types of galaxies affected by ram pressure stripping? The authors write that simulations of this process in galaxies with AGNs do not yet exist to shed more light on these rare, energetic galactic nuclei, but would be very valuable. Anyone ready to expend some supercomputer CPU hours on that?

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