Using data from the Sloan Digital Sky Survey and a new technique to determine stars’ ages, scientists have proven that the Milky Way’s central disk formed from the inside out.
Inner red stars in the Milky Way go back 13 billion years
Astronomer Melissa Ness of the Institute for Astronomy in Heidelberg, Germany recently revealed her findings a the American Astronomical Society meeting in Kissimmee, Florida. While presenting her findings, Ness told those in attendance that, as expected, our galaxy formed from the inside out. Stars going back 13 billion years were found clustered around the center while outer stars close to the disk’s edge are a mere one billion years old.
“What we’re able to do … is understand how our galaxy has formed in detail, looking at the dispersion of ages, the gradient of the ages, how the ages change as a function of both the height from the (disk’s) plane and the radius,” Ness said. “It’s understanding the details of this inside-out formation that is now possible.”
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Ness and her team began with a sample of 2,000 stars using the recently discovered relationship between a star’s carbon-to-nitrogen concentration ration and a star’s age. In order to “have a look” the team studied optical data collected by NASA‘s Kepler telescope. With the 2,000 star sample, they used the carbon-to-nitrogen ratio to determine the stars’ mass. This information was then fed into a computer model to calculate the mass of all the near 70,000 red giant stars that have been observed in the Sloan’s APOGEE (Apache Point Observatory Galaxy Evolution Experiment) survey.
“This is somewhat revolutionary because ages have previously been considered very hard to get, particularly from stellar spectra. They’re important, but they’re difficult,” Ness said.
“Measuring the individual ages of stars from their spectra and combining them with chemical information offers the most powerful constraints in the galaxy,” she said.
“We hope there will be many follow-up studies,” Ness told Discovery News. “We’ve only just determined the age catalog ourselves.”
History of the Kepler space telescope
While the Kepler spacecraft/telescope was instrumental in producing this first “Space Map” of the Milky Way’s growth, it is perhaps best known for the more than 1,000 exo-planets that scientists have discovered since it went into service including a couple of hundred last week. This is even more incredible given the fact that the thing is “broken.”
The Kepler spacecraft and it’s dorm fridge-sized telescope, named after the Renaissance astronomer Johann Kepler, was launched in March of 2009. It’s sole mission at the time was to seek out new planets and did the job splendidly until 2013 when two of it’s four stabilizing reaction wheels broke making it impossible to precisely focus on its coordinates.
What could be seen as a disaster to NASA turned out to be an opportunity for a number of ambitious astronomers who believed that Kepler could still be quite useful if re-tasked.
In 2014, Barclay and NASA astronomer Steve Howell, believing that the optics on Kepler could still be useful, called on the astronomy community to provide NASA with test targets.
“As we got more and more data we realized that the precision of our observations would really be so much better than we ever expected,” Barclay said.
Howell’s findings led to NASA changing Kepler’s mission and named it K2, which officially began in late 2014.
Now, instead of being directed by NASA, the astronomy community submits requests for Kepler to look at a specific area of space. If NASA agrees it’s worthwhile the request is given an 80 day campaign and Ness’ work wouldn’t have come off without one of these campaigns.