A brand new method for figuring out the ages of stars within the Milky Means has given us tighter constraints for an historical galactic collision.
By intently inspecting the interior oscillations and chemical composition of 95 crimson big stars, a crew of astronomers led by the College of Birmingham within the UK has decided that the Milky Means’s biff with a mysterious small galaxy often called Gaia-Enceladus, or the Gaia Sausage, came about round 10 billion years in the past.
Additionally they discovered that lots of the stars within the Milky Means had already fashioned previous to this merger; now, these unique stars can principally be discovered within the thick disk of the galaxy, the bigger of the Milky Means’s two disk buildings.
“The chemical composition, location and movement of the celebrities we are able to observe right this moment within the Milky Means include valuable details about their origin,” defined astronomer Josefina Montalbán of the College of Birmingham within the UK.
“As we enhance our data of how and when these stars have been fashioned, we are able to begin to higher perceive how the merger of Gaia-Enceladus with the Milky Means affected the evolution of our galaxy.”
The continued Gaia survey, which is mapping the Milky Means in 3D, has revealed these collisions within the motions of the celebrities; and, so far as we are able to inform to this point, the most important of the galaxies slurped up by the Milky Means was the Gaia Sausage.
For extra granular element about this incident, although, you want greater than the motions of the celebrities, as revealing as these could be. Understanding the ages and chemical compositions may help too, since they may help decide the place the celebrities have been born.
A star’s chemical composition can assist work out its age – youthful stars have extra heavy components than older ones, or larger metallicity, since metals did not exist earlier than stars got here alongside and solid them through nuclear fusion and supernova explosions. These compositions are decided utilizing spectroscopy, searching for adjustments in particular wavelengths that point out sure components are current.
Spectroscopy is a reasonably useful gizmo; however for even larger accuracy, the analysis crew turned to asteroseismology.
Asteroseismology is the research of the oscillation frequencies of stars, or pulsations of their gentle depth pushed by inside acoustic waves. These oscillations are intently linked to the properties of the star’s inside, comparable to its density and acoustic profile; in flip, these are associated to the star’s mass and age.
Now-retired planet-hunting telescope Kepler was optimized to seek for adjustments in star brightness, since that’s a technique we are able to detect exoplanets orbiting them. It collected asteroseismological knowledge on a complete bunch of stars; from these, Montalbán and her crew picked a bunch of crimson big stars with low metallicity, since these are long-lived and intrinsically shiny, which makes them glorious for mapping star ages.
They then carried out an asteroseismological evaluation of 95 of them, specializing in the person stars as an alternative of averaging out their properties.
The spectroscopy revealed that a few of the stars originated within the Gaia Sausage, and the asteroseismology revealed these have been throughout the identical age, about 10 billion years previous, or barely youthful, than the celebrities that fashioned proper right here within the Milky Means.
This means the Milky Means had already fashioned a great variety of its stars, and was doing so effectively, earlier than the merger with the Gaia Sausage. This helps earlier findings that the Milky Means-Gaia Sausage infall came about round 10 billion years in the past, the researchers mentioned.
“We’ve got proven the large potential of asteroseismology together with spectroscopy to ship exact, correct relative ages for particular person, very previous, stars,” mentioned astronomer Andrea Miglio, of the College of Bologna in Italy.
“Taken collectively, these measurements contribute to sharpen our view on the early years of our Galaxy and promise a shiny future for Galactic archeoastronomy.”
The analysis has been printed in Nature Astronomy.