Here on Earth, we often say form follows function. A long-necked giraffe can eat leaves from treetops. The airfoil edge of a racing yacht can cut through the air while generating speed. We can look at forms and see how the shape is designed for action or at least artistry. 

When we look out at the universe, we are confronted by shapes that aren’t generated through the interactive design of evolution or engineering. When we see a spiral galaxy with a strong bar-like structure in the center, we don’t see something whose shape is designed with purpose; rather we see something shaped by gravity and light whose shape may have consequences, and as astronomers, when we see these shapes we make it our job to figure out both how they formed and what they do. 

We’ve known for a long time that bars are associated with a spiral galaxy having a companion galaxy. The exact details of how that companion makes a gorgeous bar of stars is a matter for computer simulations. Understanding what is going on is complicated by the obscuring dust and glowing gas that makes it impossible to peer into a galaxy using the colors of light our eyes see. 

In a new study appearing in Astronomy & Astrophysics, researchers led by Eduardo González-Alfonso have switched to using infrared light. What we’re learning now is that a bar can act as a highway to funnel gas and dust from the outer parts of the galaxy into the core, where it can trigger star formation and feed the central supermassive black hole.  In this new study of the barred spiral NGC1300, astronomers used infrared telescopes to look through that dust and gas to map the densities and temperatures of material within the galaxy. Specifically, they looked at this galaxy’s water vapor and the specific colors of light it gives off. Since movement actually changes the color of light a bit, with things appearing redder as they move away and bluer as they approach, they could map the motions of the water vapor using these color shifts. 

Their work focused on the inner 450 light-years of the galaxy and showed the galaxy has three components: a warm envelope, a nuclear disk, and a tiny, much warmer compact core. This region is starbursting at a rate of eighteen solar masses of new stars a year, while material is also streaming into the system’s black hole. It is unclear how much of this is a snapshot of the galaxy at this moment and how much is a long-term aspect of this structure. Our galaxy is weakly barred and just not this interesting, but it might have been in the past and could be again in the future.

More Information

Center for Astrophysics press release

“A proto-pseudobulge in ESO 320-G030 fed by a massive molecular inflow driven by a nuclear bar,” Eduardo Gonzalez-Alfonso et al., 2021 January 7, Astronomy & Astrophysics