As a nine-year-old growing up in northern California, Andrew West would stay up late looking at the crystal-clear skies through the telescope his parents had bought him, wondering just what was out there.
Now, as an assistant professor of astronomy at the College of Arts & Sciences, West is still searching for answers to that question. His research into red dwarfs—the small, dim stars that make up approximately 70 percent of stars in the Milky Way—has generated new ways to date stars and new insights that can help astronomers in their search for planets that may harbor life.
In contrast to other types of stars, red dwarfs are understudied, as they are impossible to see from Earth with the naked eye and give off between one thousand and ten thousand times less light than stars like our sun. They are the smallest, least massive, least luminous, and coldest of all stars.
There are hundreds of billions of red dwarfs in the Milky Way, but West studies just those in Earth’s neighborhood. Still, this leaves him a dizzying number of possible subjects. The spectroscopic catalog of stars that he and his colleagues at Boston University and other institutions published in 2011—with input from a number of BU graduate and undergraduate students—contains detailed spectroscopic images of approximately 70,000 red dwarfs.
West has developed two processes for age-dating red dwarfs. The first involves studying the strength of the stars’ magnetic fields. Younger stars tend to have stronger magnetic fields due to their faster rotations, which cause more stellar activity in the form of stellar flares. This activity suggests that there may be a lower probability of life existing on the planets orbiting those stars.
Red dwarfs can last in this early, so-called active state, for as long as eight billion years, West discovered. To put that in perspective, our sun’s active state probably lasted around 100 million years after the star was initially formed. Red dwarfs are in an active state for much longer because they are inefficient at slowing down their rotation. Once red dwarfs leave their active state, they can still give off energy for hundreds of billions or potentially hundreds of trillions of years—making their lifetimes far older than the current age of the universe.
West’s second method for dating stars entails analyzing the horizontal plane of the galaxy in slices—a technique called galactic stratigraphy. The youngest stars tend to concentrate around the center of the plane (roughly where Earth is located). However, farther away from the center of the Milky Way’s horizontal axis, the stars tend to be older because as they age stars interact with each other, sometimes throwing each other into off-kilter orbits. By combining both methods, West can more effectively determine the age of stars than was previously possible.
“Astronomers who study the deep universe call red dwarfs ‘vermin’ or ‘zits.’ But I say that one man’s trash is another’s treasure.”
West’s discovery that red dwarfs can remain in an active state for up to eight billion years will greatly strengthen astronomers’ efforts to pinpoint planets that are most likely to harbor life. Because stars in active states give off large amounts of radiation, it is more difficult for life to form or survive on planets in those stars’ orbits. This means that astronomers searching for life-harboring solar systems might rule out systems where the star is a younger red dwarf.
Because red dwarfs include some of the oldest stars in the galaxy, observing them allows West and other astronomers to learn more about the chemical content of the galaxy as far back as 10 billion years ago. Our galaxy is composed mainly of hydrogen and helium, but at that time, there was almost no carbon, oxygen, or nitrogen present. Through nuclear fusion, massive stars turn hydrogen and helium into these heavier elements. Over successive generations of stars forming and then dying as explosive supernovae, they dispersed more carbon, oxygen, and nitrogen into the interstellar medium, allowing for the formation of planets.
West’s study of red dwarfs can offer much valuable information about the age of stars, their chemical composition, and the formation of the galaxy. But to many astronomers, such as those studying the “deep universe” beyond our galaxy, red dwarfs are more distractions than the main event.
“Any image of the deep universe has these little red dots on it that represent red dwarfs in the foreground,” explains West. “Astronomers who study the deep universe call red dwarfs ‘vermin’ or ‘zits.’ But I say that one man’s trash is another’s treasure.”