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Astronomers have revolutionized our understanding of a collection of stars in the northern sky called the Pleiades. They used data from NASA's TESS (Transiting Exoplanet Survey Satellite) and other observatories as NASA explores the secrets of the universe for the benefit of all, from the Moon to Mars and beyond.
By examining the rotation, chemistry, and orbit around the Milky Way of members of several different nearby stellar groups, the scientists identified a continuum of more than 3,000 stars arcing across 1,900 light-years. This Greater Pleiades Complex triples the number of stars associated with the Pleiades and opens new approaches for discovering similar dispersed star clusters in the future.
"The Pleiades are very well studied - we often use them as a benchmark in astronomical observations," said Andrew Boyle, a graduate student at the University of North Carolina at Chapel Hill. "When I started this research, I didn't expect the cluster to balloon to the size that it did. It really touches on a human note. In the Northern Hemisphere, we've been looking up at the Pleiades and telling stories about them for thousands of years, but there's so much more to them than we knew."
A paper about the result, led by Boyle, published Wednesday, Nov. 12, in the Astrophysical Journal.
The Pleiades is a bright cluster of stars, also known as Messier 45. This loose grouping of about 1,000 members was born roughly 100 million years ago from the same molecular cloud, a cold dense patch of gas and dust.
About six of the stars in the cluster are visible to the unaided eye during evenings from October to April in the northern constellation Taurus. This collection has also been known since antiquity as the Seven Sisters, although the seventh star is no longer visible.
Boyle and his team initially identified over 10,000 stars that could be related to the Pleiades. These stars were orbiting at a similar rate around our Milky Way galaxy according to data from ESA's (European Space Agency) Gaia satellite.
They narrowed down that collection using stellar rotation data from TESS.
NASA's TESS mission scans a wide swath of the sky for about a month at a time, looking for variations in the light from stars to spot orbiting planets. This technique also allows TESS to identify and monitor asteroids out to large distances, determining their spin and refining their shape. Such observations improve our understanding of asteroids in our solar system, which can aid in planetary defense.
Scientists can also use TESS data to determine how fast the stars are rotating by looking at regular fluctuations in their light caused when dark surface features called star spots come in and out of view. Because stellar rotation slows as stars age, the researchers were able to pick out the stars that were about the same age as the Pleiades.
The team also looked at the chemical abundances in potential members using data from ground-based missions like the Sloan Digital Sky Survey, which is led by a consortium of institutions.
"The core of the Pleiades is chemically distinct from the average star in a few elements like magnesium and silicon," said Luke Bouma, a co-author and fellow at the Carnegie Science Observatories in Pasadena, California. "The other stars that we propose are part of the Greater Pleiades are chemically distinct in the same way. The combination of these three major lines of evidence - Milky Way orbits, ages, and chemistry - tells me that we're on the right path when making these connections."
The team members think that all the stars in the Greater Pleiades Complex formed in a tighter collection, like the stars in the young Orion cluster, about 100 million years ago. Over time, the cluster dispersed due to the explosive forces of internal supernovae and from the tidal forces of our galaxy's gravity.
The result is a stream of stars arcing across the sky from horizon to horizon.
Boyle and Bouma are now working on what they call the TESS All-Sky Rotation Survey. This database will allow researchers to access the rotation information for over 8 million stars to discover even more hidden stellar connections like the Greater Pleiades Complex.
"Thanks to TESS, this team was able to shed new light on a fixture of astronomy," said Allison Youngblood, the TESS project scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "From distant stars and planets to asteroids in our solar system and machine learning models here on Earth, TESS continues to push the boundaries of what we can accomplish with large datasets that capture just a part of the complexity of our universe."
NASA's Goddard Space Flight Center, Greenbelt, Md.
