Author/s: Méndez-Abreu, J., de Lorenzo-Cáceres, A., Gadotti, D. A., Fragkoudi, F., van de Ven, G., Falcón-Barroso, J., Leaman, R., Pérez, I., Querejeta, M., Sánchez-Blazquez, P., Seidel, M.
Reference: 2018 MNRAS 482 L118 | Link
The complexity of the shapes and structures found within spiral galaxies has fascinated astronomers for decades, and is a key to the understanding of their evolution. One example of this complexity is the galaxy NGC 1291. de Vaucouleurs discovered in this galaxy for the first time a system in which there are two stellar bars, and he identified a pattern, which he termed “lens-bar-nucleus”, which is repeated in the outer and the inner part of the galaxy. This structure in the form of a Russian doll composed of two bars is basic for understanding the internal evolution of the galaxies, and how they fuel the supermassive black holes at their centres. It is in this same galaxy where we have discovered for the first time that there is a peanut-shaped structure in the inner bar. These structures are caused by vertical motions of the stars in the bar, and they are so called because of their boxy or peanut shape when the galaxy is observed sideways on. However until now this type of structures had been detected only in the outer bars of double-barred galaxies, or in individual bars such as that in the Milky Way. This work has been carried out within the international TIMER project using observations performed on the MUSE spectrograph on the Very Large Telescope (VLT) at the European Southern Observatory (ESO), and have shown that peanut-shaped structures can also form inside inner bars. This is important because it shows that some galaxies are like Russian dolls, with internal structures the same as external structures except for their smaller size. These results also show that inner bars follow the same evolutionary path as the outer bar and it implies that they can be stable structures which last for thousands of millions of years. This means that they have a long time in which to take gas into the centre of the galaxy, and supports the idea that they “feed” supermassive black holes, although this has not been confirmed by observations.