Although the number of sunspots on our Sun regularly fluctuates in an 11-year cycle, a peculiar 70-year period in which sunspots were extremely rare has baffled scientists for three centuries.
According to a group of researchers at Penn State, a nearby Sun-like star now appears to have interrupted its own cycles and entered a period of uncommon starspots. It may be possible to learn more about what occurred to our own Sun during this “Maunder Minimum” by continuing to monitor this star. This observation may also provide information about the Sun’s stellar magnetic activity, which has the potential to alter Earth’s climate.
In a brand-new publication that is available online in the Astronomical Journal, the star is discussed together with a list of the starspot activity of 58 other Sun-like stars over the course of five decades. As a result of temporarily lower temperatures in the area brought on by the star’s dynamo, which generates its magnetic field, starspots appear as a dark patch on the surface of stars.
Since Galileo and other astronomers first noticed starspots on our Sun in the 1600s, astronomers have been recording changes in starspot frequency and have a solid record of its 11-year cycle. The Maunder Minimum is an exception, which lasted from the middle of the 1600s until the beginning of the 1700s and has baffled astronomers ever since.
“We don’t really know what caused the Maunder Minimum, and we have been looking to other Sun-like stars to see if they can offer some insight,” said Anna Baum, an undergraduate at Penn State at the time of the research and first author of the paper. “We have identified a star that we believe has entered a state similar to the Maunder Minimum. It will be really exciting to continue to observe this star during, and hopefully as it comes out of, this minimum, which could be extremely informative about the Sun’s activity three hundred years ago.”
The research team combined 50–60 years’ worth of starspot data for 59 stars by combining information from several sources. This comprised information from the 1966–1996 Mount Wilson Observatory HK Project, which was created to examine star surface activity, and from planet searches at Keck Observatory, which have been looking for exoplanets since 1996.
A database of stars that appeared in both sources and had additional easily available data that could assist explain starspot activity was developed by the researchers. Additionally, the researchers put a lot of work to clean up the data by standardizing measurements from the various telescopes so that they could be directly compared.
This research is a great example of cross-generational astronomy, and how we continue to improve our understanding of the universe by building upon the many observations and dedicated research of astronomers that came before us. I looked at starspot data from Mount Wilson and Keck Observatory for my thesis when I was a graduate student, Howard looked at starspot data from the California Planet Survey for his master’s thesis, and now Anna has stitched together all the data for a more comprehensive look across the years. We are all excited to continue studying this and other promising stars.
Professor Jason Wright
By seeing at least two whole periods of the cycles, which frequently last more than a decade, the team was able to determine or confirm that 29 of these stars exhibit starspot cycles. Some stars didn’t seem to have cycles at all, which could indicate that they are dying or are rotating too slowly to generate dynamos and are magnetically “dead.” To determine whether some stars have cycles, more investigation is needed on a number of them.
“This continuous, more than 50-year time series allows us to see things that we never would have noticed from the 10-year snapshots that we were doing before,” said Jason Wright, professor of astronomy and astrophysics at Penn State and an author of the paper. “Excitingly, Anna has found a promising star that was cycling for decades but appears to have stopped.”
The star HD 166620 was thought to have a cycle that lasted roughly 17 years, but the researchers claim that it has now entered a phase of low activity and has not exhibited any signals of starspots since 2003.
“When we first saw this data, we thought it must have been a mistake, that we pulled together data from two different stars or there was a typo in the catalog or the star was misidentified,” said Jacob Luhn, a graduate student at Penn State when the project began who is now at the University of California, Irvine.
“But we double and triple checked everything. The times of observation were consistent with the coordinates we expected the star to have. And there aren’t that many bright stars in the sky that Mount Wilson observed. No matter how many times we checked, we always come to the conclusion that this star has simply stopped cycling.”
The scientists intend to keep observing this star during its minimum phase and possibly as it emerges from its minimum and starts to cycle once more. This ongoing study could reveal crucial details regarding the creation of the magnetic dynamos in the Sun and other stars.
“There’s a big debate about what the Maunder Minimum was,” said Baum, who is now a doctoral student at Lehigh University studying stellar astronomy and asteroseismology .
“Did the Sun’s magnetic field basically turn off? Did it lose its dynamo? Or was it still cycling but at a very low level that didn’t produce many sunspots? We can’t go back in time to take measurements of what it was like, but if we can characterize the magnetic structure and magnetic field strength of this star, we might start to get some answers.”
A deeper comprehension of the Sun’s magnetic field and surface activity could have a number of significant ramifications. Strong star activity, for instance, can impair satellites and international communications, and a particularly potent solar storm in 1989 knocked out the electricity infrastructure in Quebec.
Additionally, it has been hypothesized that sunspot cycles and Earth’s climate may be related. The researchers also noted that data from this star might influence our efforts to find planets outside of our solar system.
“Starspots and other forms of surface magnetic activity of stars interfere with our ability to detect the planets around them,” said Howard Isaacson, a research scientist at the University of California, Berkeley, and an author of the paper. “Improving our understanding of a star’s magnetic activity might help us improve our detection efforts.”
Researchers can now do further research using the carefully selected database of the 59 stars and their starspot activity.
“This research is a great example of cross-generational astronomy, and how we continue to improve our understanding of the universe by building upon the many observations and dedicated research of astronomers that came before us,” said Wright.
“I looked at starspot data from Mount Wilson and Keck Observatory for my thesis when I was a graduate student, Howard looked at starspot data from the California Planet Survey for his master’s thesis, and now Anna has stitched together all the data for a more comprehensive look across the years. We are all excited to continue studying this and other promising stars.”
