At the 229th Meeting of the American Astronomical Society held recently, astronomers of the SDSS/APOGEE project announced the results of a study that included more than 150,000 stars in the Milky Way. Each star was analyzed to determine the amount of nearly two dozen chemical elements, including carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur, the ones that form life’s building blocks.
We know that almost all the elements heavier than hydrogen are generated in stars and scattered through space when they explode in supernovas. A part of these elements is absorbed in the formation of new generations of stars, a small part ends up forming planets and on Earth the living beings that inhabit it. In stars, the traces of elements heavier than hydrogen and helium can be detected by a spectrographic analysis to detect those elements’ “signatures”, unique to each one like fingerprints.
The SDSS (Sloan Digital Sky Survey) international collaboration has been conducting a series of astronomical research projects over the years. Years ago these projects produced astronomical photographs that brought fame to the collaboration. However, since 2008, the projects started being spectroscopic investigations that provide other types of data.
For this research, the astronomers who worked at it used the APOGEE (Apache Point Observatory Galactic Evolution Experiment) spectrograph mounted on the Sloan Foundation Telescope at Apache Point Observatory, New Mexico to examine the chemical composition of more than 150,000 stars in the Milky Way. This instrument carries out detections at infrareds because they allow to see stars in a much larger area of the galaxy than visible light. That’s because infrareds pass through interstellar dust while visible light tends to be blocked.
The catalog created through this project has many purposes. Knowing the composition of stars will help astronomers better understand the Milky Way’s history and structure. For example, it was found that the inner area of the Milky Way stars contain more heavy elements. Those stars are older, which means that a greater amount of those elements was created first in the inner part of the galaxy than in the outer areas. This means that the center of the Milky Way there were conditions for the development of life forms similar to the Earth’s ones long before on Earth.
The processes that create the different elements occur in specific types of stars because they evolve in different ways and at different speeds. The consequence is that the analysis of the abundance of these elements can help astronomers to reconstruct the history of those processes and compare the results with the models of galaxy formation and evolution developed through other types of investigation.
An important result is also the possibility to study the distribution of the elements that form the building blocks of life on Earth. Carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur are the six most common elements on Earth and make up more than 97% of the mass of a human being’s body so finding areas in the Milky Way where they’re common could indicate potential system hosting life forms similar to those on Earth. A part of the stars examined was also studied by NASA’s Kepler space telescope and 90 of them could have rocky planets.
The image (courtesy Dana Berry/Skyworks Digital Inc.; SDSS collaboration) shows the spectral signatures and the distribution of carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur in the Milky Way examined in this investigation and their concentrations in the human body. These elements are actually present throughout the human body because first of all they’re part of DNA but have other functions as well so they can be present in particular in certain organs.
This survey is very interesting for the possible implications regarding the development of life forms similar to those on Earth but it’s only an initial stage for possible further research. In fact, the collected data were released and are available online in the so-called Data Release 13 of the SDSS project.
