An international team of researchers has produced the first comprehensive age map of the Milky Way that shows how the galaxy evolved over the course of billions of years.
In a presentation held during the 227th conference of the American Astronomical Society (AAS), Melissa Ness, a researcher from the Max Planck Institute in Germany, described how she and her colleagues were able to create the age map of the galaxy after studying the stars that comprise it.
The researchers believe that the age of red giant stars can be determined based on their masses and composition. Using this theory, they discovered that older stars in the Milky Way can often be found near the center of the galaxy, while younger stars tend to form around the edges of its disk.
Ness said that the location of the stars in the Milky Way is important to understanding how the spiral galaxy was formed.
In order to study the spectra, or light, from the red giant stars, Ness and her team made use of the Sloan Digital Sky Survey (SDSS), which measures a section of the sky using a spectroscope and multi-filter imaging. They then used the data they collected to create the age map of the Milky Way.
"Measuring the individual ages of stars from their spectra and combining them with chemical information offers the most powerful constraints in the galaxy," Ness said.
Determining The Age Of Red Giant Stars In The Milky Way
The Milky Way is well-known for its characteristic spiral arms, which can be seen as a flattened disk consisting of stars and space dust. By sorting out the individual stars in the galaxy based on their age, researchers can get a better understanding on how the Milky Way evolved as a whole.
The researchers were able to do this by examining the link between the age and mass of bright, red giant stars found in the galaxy.
The life course of stars plays an important role in the relationship between the age and mass of red giant stars. Some stars tend to meet their demise in a violent explosion known as a supernova, while other stars do not even have enough mass to be able to produce such as cataclysmic event.
Stars with lesser mass, such as the Solar System's own sun, live out the rest of their existence by swelling up and turning into red giants. These stars may have a larger radii compared to others, but they still only have a relatively low mass.
Ness and her colleagues turned to the SDSS' Apache Point Observatory Galaxy Evolution Experiment (APOGEE) to help them find out the ages and locations of 70,000 individual red giants. However, to determine the age of a star, its mass has to be measured first, which is a feat that has eluded astronomers for years.
The researchers then enlisted the aid of NASA scientists handling the Kepler space telescope. Despite being known more for discovering more than a thousand exoplanets over the years, Kepler also helped astronomers gather information on different stars.
Marie Martig, a researcher from the Swinburne University of Technology in Australia and one of the co-authors of the Max Planck Institute study, carried out a separate research that measured the ages and masses of 2,000 stars that had been previously identified by Kepler scientists.
Martig was able to determine the link between the age, mass and gas abundances of red giant stars after she compared the data collected from the earlier study with those gathered through APOGEE.
Ness, Martig and the other researchers used this recently discovered relationship to identify the mass of the 70,000 stars that APOGEE scientists observed in the Milky Way's disk.
Using the age map of the Milky Way, the scientists successfully charted how the spiral galaxy has developed throughout billions of years. They discovered that the ancient stars were the ones that first populated the galaxy and helped create the growing disk where following generations of stars eventually formed.