How The Milky Way Grew

“The Milky Way grew up by growing out,” Melissa Ness, an astronomer at the Max Planck Institute for Astronomy in Heidelberg, Germany, said at a news conference.

Ness and her colleagues developed a computer program that analysed the light emitted by red giants —bright stars that started out like the sun but exhausted their hydrogen fuel — to determine the stars’ masses and ages. Although scientists were pretty sure that galaxies grow outward, this new census of the galactic interior to the outskirts will help researchers chart that development in impressive detail.

Most stars don’t easily divulge their ages. Red giants are slightly more helpful because their age depends on their mass. Ness and her colleagues hit on a clever trick to figure out masses and ages by encompassing data from two telescopes.

The researchers trained a computer program to learn how the amount of light emitted at different wavelengths by the Kepler stars varied depending on the stars’ mass. Once the algorithm had determined that relationship, the researchers simply plugged in Sloan light measurements to determine the masses, and thus the ages, of about 70,000 galactic red giants. The ages are accurate to within about 40 percent, which Pasquato says is admirable because of the difficulties in ageing stars. As expected, the Milky Way’s oldest stars reside in the centre of the galaxy, while the youngest generation lives in the distant suburbs.

This year, a new Sloan telescope in Chile will begin scanning the Southern Hemisphere skies, potentially adding many more red giants to the galactic age catalogue.

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