29 Noviembre 2023

Scholars from the UNAB Institute of Astrophysics Participate in the Discovery of an Unusual Nebula in Our Galaxy

The director of the Institute of Astrophysics at the Universidad Andrés Bello, Dante Minniti, and Professor Juan Carlos Beamín from the same institution, are part of an international group that discovered a nebula that shines in sync with its newly born star, a phenomenon that has puzzled scientists.

The observations were made using the VISTA telescope in the Antofagasta Region. An international team of astronomers led by Professor Roberto K. Saito from the Universidade Federal de Santa Catarina in Florianópolis, Brazil, which includes Dante Minniti and Juan Carlos Beamín, reported the discovery of another unique object in our Galaxy. This object is a peculiar combination of a variable star and a nebula, which also changes in brightness and is located in a very dark region in the Scorpio constellation, near the center of the Milky Way.

The discovery, published in The Astrophysical Journal Letters, was made possible by the VVVX Survey, a mapping of the Milky Way plane in infrared light with the VISTA telescope at the ESO Paranal Observatory in Chile. Deep images accumulated over more than 12 years allow for the search and monitoring of variable stars, i.e., stars that change in brightness over time. “Tens of thousands of these stars have been discovered, classified according to their brightness fluctuations. However, occasionally, variable objects appear that cannot be easily explained because they do not fit into any known classes,” explains Dante Minniti, director of the UNAB Institute of Astrophysics.

The VVVX Survey has already discovered a dozen unidentified objects named WIT, an acronym for “What Is This?” representing extremely rare astronomical phenomena. Such is the case with this new finding, called WIT-12.

The VISTA telescope at the ESO Cerro Paranal Observatory was fundamental to this discovery. “It is a telescope optimized for infrared observations, which allows us to reveal objects that are very obscured behind dense clouds of interstellar dust,” Minniti explains.

A simple technique was used to analyze the infrared images, generally applied to search for light echoes from supernovas, which involves creating images in colors from different observation periods with the same filter. In this case, composite images taken in 2010, 2011, and 2012 were used, revealing a nebula that changes color, suggesting some variability of interest to astronomers.

Further monitoring of the region revealed a red star located at the center of this nebula that changes in brightness periodically every four years. Spectroscopic observations with the 4m SOAR telescope at Cerro Pachón, in Chile, revealed that this central source is a very young stellar object, periodically illuminating the nebula. But the mystery doesn’t end there, as the study also revealed that the nebula changes color. “One part varies in the same way as the star, while the other does the opposite: when the central star is brighter, that nebula region dims,” indicates Dr. Dante Minniti, an astrophysicist. In other words, it is a nebula that pulsates in sync with its newly born star.

For the UNAB astronomer, discovering such new objects is important because it expands the frontiers of knowledge, revealing previously unknown phenomena that we must study and explain. Although this phenomenon baffles observers – hence its classification as a WIT object – the VVVX Survey team proposes some possible explanations.

It could be a central variable star that produces a light echo reflected in the rear part of the surrounding nebula. “As the nebula is so large, the light from the nearest part reaches us directly, meaning that part of the nebula increases in brightness when the star is brighter. On the other hand, the light that reaches us from the farther part is delayed so much that the star has already dimmed,” says the director of the UNAB Institute of Astrophysics, adding that this effect is known as a light echo and has been observed in explosive phenomena like novas and supernovas, but not in variable stars like WIT-12.

Another possible explanation could be the presence of a bent circumstellar disk that blocks light to some areas of the nebula as it rotates. This phenomenon resembles an “anti-lighthouse,” casting a shadow in a specific direction as it rotates.

Finding a definitive explanation will require more observations and a new search for similar objects, using new technologies that astronomers eagerly anticipate, like the future Vera C. Rubin Observatory currently under construction in Chile.

Escrito por Pamela Alarcón