An international team of astronomers has discovered a previously unknown component of the Milky Way – a thin disk of variable stars hidden in the galactic bulge. The observations, made using the ESO's Visible and Infrared Survey Telescope for Astronomy (VISTA) telescope conflict with current theories regarding the composition of the center of our galaxy.
As we understand it, the Milky Way is a barred spiral galaxy, with four main spiral arms extending from a galactic core with a supermassive black hole known as Sagittarius A at its heart. Earth sits roughly two thirds out from the center of the Milky Way in the Orion Spur, an offshoot of the Perseus spiral arm.
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Our view to the galactic center is obscured by vast choking clouds of dust and gas, which hamper our efforts to form a unified view of the Milky Way. Therefore, the potential discovery of a new galactic component in spite of these impediments is of great importance in understanding the characteristics and evolution of the vast cosmic structure that we call home.
Astronomers used the VISTA telescope's infrared imaging capabilities to peer through the clouds of dust and gas that would ordinarily mask the interior of our galaxy, capturing multiple shots of the central region of the Milky Way in order to search for variable stars known as Cepheids.
Cepheids are stars that fluctuate dramatically in observable brightness of the course of days, or months, as they expand and contract. It has been discovered that, by observing the rhythmic fluctuations of one of the unusual stellar bodies, that astrophysicists can estimate the star's age.
Variable stars like Cephids are particularly useful tools for astronomers attempting to trace out vast galactic structures, as the relatively well understood precise nature of the pulsations allow scientists to accurately discern their distance relative to Earth.
In all, VISTA sampled 655 Cephids in the galactic bulge, of which 35 were found to belong to a subgroup known as Classical Cepheids, which in turn where discovered to be significantly younger than their more prevalent cousins.
“All of the 35 classical Cepheids discovered are less than 100 million years old" states co-author of a paper on the research, Dante Minniti, of the Universidad Andres Bello, Santiago, Chile. "The youngest Cepheid may even be only around 25 million years old, although we cannot exclude the possible presence of even younger and brighter Cepheids,”
The team then used the accurately defined positions of the Cepheids to trace out the position of a thin disk of younger stars residing in the central bulge – an entirely new component for our galactic model.
Furthermore, the relative youth of these stars shakes up the current model we have the Milky Way, which dictates that the galactic bulge consists of enormous quantities of very ancient stars. Instead, the results of the study hint at a previously undetected source creating new, young stars for the past 100 million years.
Moving forward, the team hopes to establish whether the newly detected stars where born in their presently observed locations, or whether they migrated inward from regions outside of the galactic bulge.
A paper detailing the discovery has been published in The Astrophysical Journal. The findings are illustrated in the video below.