An international team of astronomers has found that Milky Way-like galaxies underwent a stellar ‘baby boom’ in their early history, creating stars at a rate thirty times faster than today.
This illustration depicts a view of the night sky from a hypothetical planet within the young Milky Way Galaxy 10 billion years ago; glowing pink clouds of hydrogen gas harbor countless newborn stars, and the bluish-white hue of young star clusters litter the landscape; the star-birth rate is 30 times higher than it is in our Galaxy today; our Sun, however, is not among these fledgling stars; the Sun will not be born for another 5 billion years. Image credit: NASA / ESA / Z. Levay, STScI.
Scientists don’t have pictures of our Milky Way Galaxy’s early years to trace the history of stellar growth so they studied galaxies similar in mass to our Milky Way, found in deep surveys of the Universe. Stretching back in time more than 10 billion years, the new census contains approximately 2,000 snapshots of Milky Way-like galaxies.
The analysis comprises the most comprehensive galaxy survey yet, and includes data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), taken with the NASA/ESA Hubble Space Telescope.
“This study allows us to see what the Milky Way may have looked like in the past. 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. And most of that stellar-mass growth happened within the first 5 billion years of their birth,” said team leader Dr Casey Papovich of Texas A&M University in College Station.
The findings support the results of a previous study which showed that galaxies like our own began as small groups of stars. The galaxies swallowed large amounts of gas that ignited a firestorm of star birth.
“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,” said Dr Papovich, the first author of the paper published in the Astrophysical Journal (arXiv.org preprint).
“When we calculate the star-formation rate of a Milky Way-like galaxy in the past and add up all the stars it would have produced, it is pretty consistent with the mass growth we expected.”
“To me, that means we’re able to understand the growth of the average galaxy with the mass of a Milky Way galaxy.”
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C. Papovich et al. 2015. ZFOURGE/CANDELS: On the Evolution of M* Galaxy Progenitors from z = 3 to 0.5. ApJ 803, 26; doi: 10.1088/0004-637X/803/1/26
