Astronomers have taken a census of distant spiral galaxies to help us understand what our Milky Way may have looked like in the distant past, also providing us with a fascinating look into the evolution of our own solar system.
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By surveying nearly 2,000 spiral galaxies - observed by the Hubble Space Telescope and other space and ground-based telescopes - with properties similar to the Milky Way, we've not only gained a valuable insight to how our galaxy looked in the past, we've found out that our sun, in the grand galactic scheme of things, appears to have been a late bloomer.
The further astronomers look into the universe, the longer into the past they can see. As light travels at a finite speed (the speed of light), studying a galaxy 1 billion light-years away corresponds to a time when the universe was 1 billion years younger than it is now. So by surveying Milky Way-like galaxies at different distances from us, we can see how our galaxy may have looked in the past.
And by doing this, astronomers have created a timeline and identified when the Milky Way likely had the most intense period of stellar birth.
"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 in College Station, lead author of the study published in the April 9 edition of The Astrophysical Journal. "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."
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Our sun, however, only started to form about 5 billion years ago, meaning that our star formed when the galaxy was well past its frenzied star birth boom of 10 billion years ago.
But this certainly was no bad thing and may even be a key factor as to why our star system has a rich variety of planets and is probably why the chemistry for life is here in abundance.
Several generations of stars have come and gone, and before the formation of the sun, many stars that formed during the frenzied period of star birth used up their fuel and exploded as supernovae. Supernovae, combined with other energetic stellar events, formed the elements heavier than hydrogen and helium, elements that are essential for the formation of metal rich stars and, by extension, the rocky worlds that orbit them.
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In addition to adding a new understanding to the evolution of our sun, this new census strengthens our knowledge of how spiral galaxies grow.
"I think the evidence suggests that we can account for the majority of the buildup of a galaxy like our Milky Way through its star formation," Papovich said. "When we calculate the star-formation rate of a Milky Way galaxy 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."
The spiral galaxies used for this study were selected from 24,000 candidates identified and studied in wavelengths from the ultraviolet to the far-infrared, using Hubble, NASA's Spitzer Space Telescope, the European Herschel Space Observatory and the Magellan Baada Telescope at the Las Campanas Observatory in Chile.