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NASA/Jet Propulsion Laboratory-Caltech

Stars crowd into the core of the Milky Way galaxy. 

Milky Way galaxy may have formed ‘inside-out’

by Laura L. Calderone
Jan 28, 2014


University of Cambridge

Scientists at the University of Cambridge studied star’s metallicity -  how many complex chemical elements are in a star -  to determine the ages. Stars with fewer elements were older and found in the inner part of the galaxy. Scientists who wrote the study theorize our sun may have formed in the inner part of the galaxy and migrated to the outer part of the galaxy.

The Milky Way galaxy may have been formed inside out, according to recent research from scientists at Cambridge University.

This perspective takes scientists one step closer to understanding the formation of the Milky Way galaxy.

Scientists using data from the Gaia-ESO Survey and the Very Large Telescope in Chile found that stars on the inside of the Milky Way galaxy are older than stars on the outside.

“We have started to actually understand the time sequence of the event which led to the formation of the disk, the galactic disk, and consequently to the formation of our solar system as it is,” said Maria Bergemann, a post-doc at the University of Cambridge and leader of the study. Our solar system orbits the galactic center of the Milky Way in one of the outer arms.

The researchers of the study released earlier this month and published in the journal Astronomy and Astrophysics used the metallicity - the chemical elements other than hydrogen and helium - of stars to determine their ages.


Study authors leading the telescope survey are Cambridge physics professor Gerry Gilmore and physicist Sofia Randich with the Arcetri Astrophysical Observatory in Florence, Italy.

“The higher level of the elements inside the solar circle suggests this area contained more stars that ‘lived fast and die young’ in the past,” according to a press release from Cambridge.

Stars that have fewer elements are older and have higher levels of magnesium.


“There are many more old stars, stars with enhanced magnesium ratios, inside the galactic disk, closer to the galactic center than outside,” said Bergemann. “We see that actually the disk becomes younger as we move out and this is what we call the inside-out picture of galaxy formation.”

The Milky Way, our galaxy, has a disk-like shape.

“It’s the shape and distribution of material. You don’t want to visualize a perfect disk,” said Robert McNees, a physics professor at Loyola University Chicago. He said the galaxy shape can be thought of as being like the shape of a quarter, but doesn’t fully conform to a perfect disk.

McNees said this theory indicates the galaxy formed starting from the inside.

“It’s not an all at once thing,” McNees said.

This exploratory research is still in its early stages, but offers strong support for the inside-out formation theory, Bergemann said.

The data set also opens up some questions about our sun, which is not representative of where it is located, based on the data. It is possible the sun migrated from an older, more “inner,” part of the galactic disk to its current location, she said.

“We are there – our solar system is there – at this location in the galaxy for some reason,” Bergemann said.

More research needs to be done in the coming years, but the current exploratory data set will help with future research using the Gaia-ESO Survey.

“Galactic structure information is interesting because the stuff we don’t understand participates in the structure and formation of the galaxy,” McNees said.

There are many mysteries to the universe, such as dark matter and dark energy, McNees said. Much of the matter we understand is still limited. Studies like these can provide new insight into the universe, he said.

Bergemann’s sights are set farther than the boundaries of the Milky Way. She plans to use more data to find similar galaxies and stellar populations.

“Maybe there are other systems which were similar to our stellar system, which would host planets, which could also potentially host life.” Bergemann said.