In a new study, researchers looked back in time to learn more about the early life of the Milky Way. Of course they can’t actually look back in time, so they did the next best thing. Using catalogues of observations by a variety of telescopes, the researchers looked at galaxies very similar to the Milky Way that are far enough a way to provide a glimpse into their ancient past.
The researchers found that galaxies like ours go through an early baby boom, churning out new stars at a rate 30 times faster than the Milky Way does today. Our sun, however, as not part of that original baby boom. The stellar baby boom peaked 10 billion years ago and our star was born about 5 billion years ago.
However, the late start had some advantages. Heavy elements were more prevalent later in the galaxies life as early, massive stars exploded. Those heavy elements helped to form the planets and provided the building blocks of life.
To paint this picture of the early life of the Galaxy, researchers used multi-wavelength observations ranging from ultraviolet to far infrared light. Data was gathered from the European Space Agency’s Hershel Space Observatory, the NASA Hubble and Spitzer space telescopes and a number of ground based telescopes.
The deeper in space something is, the further back in time we are looking. So, by gathering almost 2,000 images of Milky Way-like galaxies, from a number of telescopes in a variety of wavelengths the new census paints a reasonably complete picture of the evolution of spiral galaxies like our own.
“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 Casey Papovich of Texas A&M University in College Station, in a statement.
Casey is lead author of the paper, published in Astrophysics Journal, that describes the study’s results.
The paper agrees with previous research which showed that Milky Way-like galaxies started as clusters of stars which swallowed large amounts of gas, igniting an explosion of star formation.
The researchers also found a strong correlation between star formation and growth in stellar mass. In other words, when galaxies slow in their rate of star formation they also slow their rate of growth as galaxies.
“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. 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,” said Papovich.
The researchers sifted through more than 24,000 galaxies in the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), taken with Hubble, and the FourStar Galaxy Evolution Survey (ZFOURGE).
The research also raises interesting questions relating to the Fermi Paradox.
The question, raised by physicists Enrico Fermi and Michael H. Hart, asks where all the alien life is. The Sun is a relatively young star and this study supports the idea that there are many much older stars. Even given the issue with heavy elements, some of those stars likely have Earth-like planets and some of those stars are likely to have developed life, even advanced intelligent life.
So, given their multi-billion year head start, where is everyone?
