Our sun was a bit of a latecomer to the star birthday party in the early days of the Milky Way. Astronomers say it only formed when the stellar version of a "baby boom" had almost fizzled out.
The peak of star formation in the Milky Way galaxy occurred 10 billion years ago, but the sun didn't form until 5 billion years ago.
To better understand the history of star formation in our galaxy, scientists used the Hubble Space Telescope and ground-based observatories to survey almost 2,000 spiral galaxies with similarities to the Milky Way.
The greater the distance to a galaxy, the further astronomers can see into the past of the universe, due to the length of time it takes light from any one galaxy to reach us.
Every billion light years of distance between a galaxy we're looking at and us means we're really looking that many billions of years into the past — so galaxies at different distances show how they evolve over time, astronomers explain in a study published in The Astrophysical Journal.
"This study allows us to see what the Milky Way may have looked like in the past," said Casey Papovich of Texas A&M University, lead author of the study. "It shows that these galaxies underwent a big change in the mass of its stars over the past 10 billion years, bulking up by a factor of 10, which confirms theories about their growth."
The majority of that bulking-up occurred in the first 5 billion years following the galaxies' beginnings, he explained, with galaxies like our Milky Way experiencing a stellar "baby boom" that saw stars being created at a clip 30 times faster than what's happening now. By the time our sun appeared, star formation rates in the galaxy had slowed to a trickle.
Missing most of the party, surprisingly, may have had some advantages, though — elements heavier than hydrogen and helium were more abundant at the end of the star-forming boom, as more massive stars ended their lives early.
The heavier elements with which they enriched the Milky Way would have served as the building blocks of planets in our solar system, and even helped to kick-start life on Earth.
Star formation in a galaxy and its growth in total stellar mass show a strong correlation, Papovich said — so when star formation slows, so does the galaxy's overall growth.
"I think the evidence suggests that we can account for the majority of the buildup of a Milky Way-like galaxy through its star formation," he said — even accounting for "late to the party" types like our sun.
