A new survey of stars in the Milky Way shows that the chemical elements needed for life are more concentrated in the inner part of the galaxy than the outer. The finding is giving scientists insight into the history and evolution of the galaxy and how that may impact the prospects for life.
"It is very interesting that the elements in the inner galaxy are so enriched, which means they've had billions of years longer to maybe develop life. The problem is we still only have one version of life that we know of," said Sten Hasselquist, an astronomy graduate student at New Mexico State University.
"The longer time scale is tantalizing," he added.
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The results, released at the American Astronomical Society meeting in Grapevine, Texas, last week are based on infrared observations of more than 150,000 stars made by the Sloan Digital Sky Survey.
The map shows stars in the inner part of the galaxy have greater concentrations of the six elements found in all life - carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur, collectively known as CHNOPS.
"It's a great human interest story that we are now able to map the abundance of all of the major elements found in the human body across hundreds of thousands of stars in our Milky Way," Ohio State University astronomer Jennifer Johnson said in a press release. "This allows us to place constraints on when and where in our galaxy life had the required elements to evolve, a sort 'temporal galactic habitable zone.' "
Astronomers believe all the elements except for hydrogen and helium were synthesized inside stars, with different elements forming inside different stars and on different time scales.
"We can use this information to disentangle the chemical evolution history of a given stellar population," said New Mexico State astronomer Jon Holtzman.
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The Sloan Digital Sky Survey, now in its 17th year, has mapped 35 percent the sky and collected data on more than 4 million astronomical objects. Although best known for its beautiful images, since 2008 the survey had been entirely spectroscopic, meaning it collects data on the brightness of light at different wavelengths, not just optical.
The current stellar chemistry measurements use a spectrograph, called APOGEE, which senses infrared light. The Apache Point Observatory Galactic Evolution Experiment spectrograph is mounted on the 2.5-meter Sloan Foundation Telescope at Apache Point Observatory in New Mexico. A second APOGEE instrument is being added to the Irénée du Pont Telescope at Las Campanas Observatory in Chile.
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