A group of astrophysicists from the University of Vienna led by Núria Miret-Roig discovered that two approaches to estimating a star’s age measure distinct things: Thus, isochronous measurement establishes the star’s birthdate, whereas dynamical monitoring informs when stars in the examined star clusters “leave their nest,” or roughly 5.5 million years later.
Image of the Rho Ophiuchi cloud complex, the closest star-forming region to Earth. This study reveals that the newly born stars in Rho Ophiuchi have not yet begun to drift apart and that the progenitor cloud is still holding them together. Image Credit: NASA, ESA, CSA, STScI, Klaus Pontoppidan (STScI)
The research has been published in the journal Nature Astronomy and allows one to determine the early phases of a star’s life.
Even though it is a key parameter in astrophysics, measuring a star’s age is still somewhat challenging. Up until now, the most accurate estimates have been found for “star clusters,” which are collections of stars of the same age that share a common ancestor. As part of an ongoing research project at the University of Vienna’s Institute of Astrophysics, the ages of six very young and close star clusters have now been determined.
It was discovered that isochronous measurement and dynamic tracing, two of the most trustworthy techniques for estimating a star’s age, differed consistently and methodically: Compared to the isochronous measurement, the stars were approximately 5.5 million years younger using the dynamic tracing method.
When the Clock Starts Ticking
This indicates that the two measurement methods measure different things.
Núria Miret-Roig, Study First Author and Astrophysicist, University of Vienna
The new analysis indicates that the dynamic backtracking “clock” only starts to run when a star cluster starts to grow after emerging from its parent cloud, but the isochronous “clock” starts to run from the moment of star formation.
This finding has significant implications for our understanding of star formation and stellar evolution, including planet formation and the formation of galaxies, and opens up a new perspective on the chronology of star formation. For example, the length of the so-called ‘embedded phase,’ during which baby stars remain within the parental gas cloud, can be estimated.
João Alves, Study Co-Author and Professor, University of Vienna
Measuring How Long Baby Stars Stay in the Nest
Alves added, “This age difference between the two methods represents a new and much-needed tool to quantify the earliest stages in a star’s life. Specifically, we can use it to measure how long the baby stars take before they leave their nest.”
The observations were made possible by combining high-resolution data from the Gaia special mission with ground-based radial velocities (from the APOGEE catalog, for example).
“This combination allows us to trace the positions of stars back to their birthplace with the accuracy of 3D velocities,” Miret-Roig added.
This examination of the entire solar neighborhood will be made possible by upcoming and new spectroscopic surveys like SDSS-V, 4MOST, and WEAVE.
Puzzling Difference
Miret-Roig further stated, “Astronomers have been using isochronous ages for as long as we have known how stars work, but these ages depend on the particular stellar model we use. The high-quality data from the Gaia satellite has now allowed us to measure ages dynamically, independently of the stellar models, and we were excited to synchronize the two clocks.”
However, a persistent and perplexing discrepancy between the two age determination techniques was revealed during the computations.
“And eventually we reached a point where we could no longer blame the discrepancy on observational errors—that is when we realized that the two clocks were most likely measuring two different things,” Miret-Roig noted.
The study involved an analysis of six young and close star clusters, with ages ranging from 50 million years to 490 light years. It was determined that the embedded phase’s time scale was around 5.5 million years (plus or minus 1.1 million years) and that it might have varied depending on the star cluster's mass and the quantity of stellar feedback.
Miret-Roig expects that by applying this new technique to other young and nearby star clusters, fresh insights into the process of star formation and star drifting apart could be revealed.
Miret-Roig concluded, “Our work paves the way for future research into star formation and provides a clearer picture of how stars and star clusters evolve. This is an important step in our endeavor to understand the formation of the Milky Way and other galaxies.”
Journal Reference
Miret-Roig, N., et al. (2023) Insights into star formation and dispersal from the synchronization of stellar clocks. Nature Astronomy. doi:10.1038/s41550-023-02132-4