SPACE/COSMOS
Superflares once per century
More often than previously thought, sun-like stars hurl huge amounts of radiation into space. The Sun, too, is capable of such outbursts
Max Planck Institute for Solar System Research
image:
Artist's impression of a Sun-like star exhibiting a superflare as seen in visible light
view moreCredit: MPS/Alexey Chizhik
There is no question that the Sun is a temperamental star, as alone this year’s unusually strong solar storms prove. Some of them led to remarkable auroras even at low latitudes. But can our star become even more furious? Evidence of the most violent solar “tantrums” can be found in prehistoric tree trunks and in samples of millennia-old glacial ice. However, from these indirect sources, the frequency of superflares cannot be determined. And direct measurements of the amount of radiation reaching the Earth from the Sun have only been available since the beginning of the space age.
Another way to learn about our Sun’s long-term behavior is to turn to the stars, as is the approach of the new study. Modern space telescopes observe thousands and thousands of stars and record their brightness fluctuations in visible light. Superflares, which release amounts of energy of more than one octillion joules within a short period of time, show themselves in the observational data as short, pronounced peaks in brightness. “We cannot observe the Sun over thousands of years,” Prof. Dr. Sami Solanki, Director at the MPS and coauthor, explained the basic idea behind the investigation. “Instead, however, we can monitor the behavior of thousands of stars very similar to the Sun over short periods of time. This helps us to estimate how frequently superflares occur,” he adds.
Looking for close relatives of the Sun
In the current study, the team including researchers from the University of Graz (Austria), the University of Oulu (Finland), the National Astronomical Observatory of Japan, the University of Colorado Boulder (USA) and the Commissariat of Atomic and Alternative Energies of Paris-Saclay and the University of Paris-Cité, analyzed the data from 56450 sun-like stars as seen by NASA’s space telescope Kepler between 2009 and 2013. “In their entirety, the Kepler data provide us with evidence of 220000 years of stellar activity,” said Prof. Dr. Alexander Shapiro from the University of Graz.
Crucial for the study was the careful selection of the stars to be taken into account. After all, the chosen stars should be particularly close “relatives” of the Sun. The scientists therefore only admitted stars whose surface temperature and brightness were similar to the Sun’s. The researchers also ruled out numerous sources of error, such as cosmic radiation, passing asteroids or comets, as well as non-sun-like stars that in Kepler images may by chance flare up in the vicinity of a sun-like star. To do this, the team carefully analyzed the images of each potential superflare - only a few pixels in size - and only counted those events that could reliably be assigned to one of the selected stars.
In this way, the researchers identified 2889 superflares on 2527 of the 56450 observed stars. This means that on average, one sun-like star produces a superflare approximately once per century.
“High performance dynamo computations of these solar-type stars easily explain the magnetic origins of the intense release of energy during such superflares”, said coauthor Dr. Allan Sacha Brun of the Commissariat of Atomic and Alternative Energies of Paris-Saclay and the University of Paris-Cité.
Surprisingly frequent
“We were very surprised that sun-like stars are prone to such frequent superflares”, said first author Dr. Valeriy Vasilyev from the MPS. Earlier surveys by other research groups had found average intervals of a thousand or even ten thousand years. However, earlier studies were unable to determine the exact source of the observed flare and therefore had to limit themselves to stars that did not have any too close neighbors in the telescope images. The current study is the most precise and sensitive to date.
Longer average time intervals between extreme solar events have also been suggested by studies looking for evidence of violent solar storms impacting Earth. When a particularly high flux of energetic particles from the Sun reaches the Earth's atmosphere, they produce a detectable amount of radioactive atoms such as the radioactive carbon isotope 14C. These atoms are then deposited in natural archives such as tree rings and glacial ice. Even thousands of years later, the sudden influx of high-energy solar particles can thus be deduced by measuring the amount of 14C using modern technologies.
In this way, researchers were able to identify five extreme solar particle events and three candidates within the past twelve thousand years of the Holocene, leading to an average occurrence rate of once per 1500 years. The most violent is believed to have occurred in the year 775 AD. However, it is quite possible that more such violent particle events and also more superflares occurred on the Sun in the past. “It is unclear whether gigantic flares are always accompanied by coronal mass ejections and what is the relationship between superflares and extreme solar particle events. This requires further investigation”, co-author Prof. Dr. Ilya Usoskin from the University of Oulu in Finland pointed out. Looking at the terrestrial evidence of past extreme solar events could therefore underestimate the frequency of superflares.
Forecasting dangerous space weather
The new study does not reveal when the Sun will throw its next fit. However, the results urge caution. “The new data are a stark reminder that even the most extreme solar events are part of the Sun's natural repertoire,” said coauthor Dr. Natalie Krivova from the MPS. During the Carrington event of 1859, one of the most violent solar storms of the past 200 years, the telegraph network collapsed in large parts of northern Europe and North America. According to estimates, the associated flare released only a hundredth of the energy of a superflare. Today, in addition to the infrastructure on the Earth's surface, especially satellites would be at risk.
The most important preparation for strong solar storms is therefore reliable and timely forecasting. As a precaution, satellites, for example, could be switched off. From 2031, ESA’s space probe Vigil will help in the endeavor of forecasting. From its observation position in space, it will look at the Sun from the side and notice sooner than Earth-bound probes when processes that might drive dangerous space weather are brewing up on our star. The MPS is currently developing the Polarimetric and Magnetic Imager for this mission.
Journal
Science
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
Sun-like stars produce superflares roughly one per century
Article Publication Date
13-Dec-2024
NASA successfully integrates Roman mission’s telescope, instruments
image:
The telescope and instruments for NASA’s Nancy Grace Roman Space Telescope were recently integrated together on the observatory’s instrument carrier at the agency’s Goddard Space Flight Center in Greenbelt, Md. Next, the entire system will be joined to the Roman spacecraft.
view moreCredit: NASA/Chris Gunn
NASA’s Nancy Grace Roman Space Telescope team has successfully integrated the mission’s telescope and two instruments onto the instrument carrier, marking the completion of the Roman payload. Now the team at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, will begin joining the payload to the spacecraft.
“We’re in the middle of an exciting stage of mission preparation,” said Jody Dawson, a Roman systems engineer at NASA Goddard. “All the components are now here at Goddard, and they’re coming together in quick succession. We expect to integrate the telescope and instruments with the spacecraft before the year is up.”
Engineers first integrated the Coronagraph Instrument, a technology demonstration designed to image exoplanets — worlds outside our solar system — by using a complex suite of masks and active mirrors to obscure the glare of the planets’ host stars.
Then the team integrated the Optical Telescope Assembly, which includes a 7.9-foot (2.4-meter) primary mirror, nine additional mirrors, and their supporting structures and electronics. The telescope will focus cosmic light and send it to Roman’s instruments, revealing billions of objects strewn throughout space and time. Roman will be the most stable large telescope ever built, at least 10 times more so than NASA’s James Webb Space Telescope and 100 times more than the agency’s Hubble Space Telescope. This will allow scientists to make measurements at levels of precision that can answer important questions about dark energy, dark matter, and worlds beyond our solar system.
With those components in place, the team then added Roman’s primary instrument. Called the Wide Field Instrument, this 300-megapixel infrared camera will give Roman a deep, panoramic view of the universe. Through the Wide Field Instrument’s surveys, scientists will be able to explore distant exoplanets, stars, galaxies, black holes, dark energy, dark matter, and more. Thanks to this instrument and the observatory’s efficiency, Roman will be able to image large areas of the sky 1,000 times faster than Hubble with the same sharp, sensitive image quality.
“It would be quicker to list the astronomy topics Roman won’t be able to address than those it will,” said Julie McEnery, the Roman senior project scientist at NASA Goddard. “We’ve never had a tool like this before. Roman will revolutionize the way we do astronomy.”
The telescope and instruments were mounted to Roman’s instrument carrier and precisely aligned in the largest clean room at Goddard, where the observatory is being assembled. Now, the whole assembly is being attached to the Roman spacecraft, which will deliver the observatory to its orbit and enable it to function once there.
At the same time, the mission’s deployable aperture cover — a visor that will shield the telescope from unwanted light — is being joined to the outer barrel assembly, which serves as the telescope’s exoskeleton.
“We’ve had an incredible year, and we’re looking forward to another one!” said Bear Witherspoon, a Roman systems engineer at NASA Goddard. “While the payload and spacecraft undergo a smattering of testing together, the team will work toward integrating the solar panels onto the outer barrel assembly.”
That keeps the observatory on track for completion by fall 2026 and launch no later than May 2027.
To virtually tour an interactive version of the telescope, visit:
https://roman.gsfc.nasa.gov/interactive
The Nancy Grace Roman Space Telescope is managed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation by NASA’s Jet Propulsion Laboratory and Caltech/IPAC in Southern California, the Space Telescope Science Institute in Baltimore, and a science team comprising scientists from various research institutions. The primary industrial partners are BAE Systems Inc. in Boulder, Colorado; L3Harris Technologies in Rochester, New York; and Teledyne Scientific & Imaging in Thousand Oaks, California.
Technicians install the primary instrument for NASA's Nancy Grace Roman Space Telescope, called the Wide Field Instrument (at left), in the biggest clean room at the agency's Goddard Space Flight Center in Greenbelt, Md. This marked the final step to complete the Roman payload, which also includes a Coronagraph instrument and the Optical Telescope Assembly.
Credit
NASA/Chris Gunn
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