By Stephen Beech via SWNS
Potentially deadly solar “superflares” are far more common than previously thought, according to a new study.
Unusually strong solar storms earlier this year triggered “Northern Lights” auroras at much lower latitudes than usual.
But even more dramatic “superflares” – when sun-like stars hurl huge amounts of radiation into space – could happen as frequently as once a century, say scientists.
And our own Sun, too, is capable of such outbursts.
Previous studies had suggested “superflare” events occurred only once every 1,000 years or even less frequently.
Researchers say evidence of the most violent solar “tantrums” can be found in prehistoric tree trunks and in samples of millennia-old glacial ice.
However, from those indirect sources, the frequency of superflares can’t be determined.
And direct measurements of the amount of radiation reaching Earth from the Sun have only been available since the beginning of the space age.
But scientists explained that another way to learn about our Sun’s long-term behavior is to turn to the stars.
Modern space telescopes observe 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.
An international research team analyzed the data from 56,450 sun-like stars as seen by NASA’s space telescope Kepler between 2009 and 2013.
Study co-author Prof. Dr. Sami Solanki, of the Max Planck Institute for Solar System Research (MPS), Germany, said: “We cannot observe the Sun over thousands of years.
“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.”
Prof. Dr. Alexander Shapiro, from the University of Graz, Austria, said: “In their entirety, the Kepler data provide us with evidence of 220,000 years of stellar activity.”
He explained that careful selection of the stars to be taken into account was “crucial” to the study as they should be particularly close “relatives” of the Sun.
The team only admitted stars whose surface temperature and brightness were similar to the Sun’s.
They 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.
The team subsequently identified 2,889 superflares on 2,527 of the 56,450 observed stars.
The findings, published in the journal Science, mean that, on average, one sun-like star produces a superflare around once per century.
Co-author Dr. Allan Sacha Brun, of the University of Paris-Cité, France, said: “High-performance dynamo computations of these solar-type stars easily explain the magnetic origins of the intense release of energy during such superflares.”
First author Dr. Valeriy Vasilyev of MPS, said: “We were very surprised that sun-like stars are prone to such frequent superflares.”
Earlier surveys by other research groups had found average intervals of 1,000 years or even 10,000 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 neighbours in the telescope images.
Longer average time intervals between extreme solar events have also been suggested by studies looking for evidence of violent solar storms impacting Earth.
Previously, researchers were able to identify five extreme solar particle events and three candidates within the past 12,000 years, leading to an average occurrence rate of once per 1,500 years.
The most violent is believed to have occurred in the year 775 AD.
However, scientists say it is quite possible that more such violent particle events and also more superflares occurred on the Sun in the past.
Study Co-author Prof. Ilya Usoskin, of the University of Oulu, Finland, said: “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.”
He added: “This requires further investigation.”
The new study does not reveal when the Sun will throw its next fit.
But co-author Dr. Natalie Krivova, of MPS, said: “The new data are a stark reminder that even the most extreme solar events are part of the Sun’s natural repertoire.”
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, scientists say satellites would be at particular risk.
The research team say the most important preparation for strong solar storms is reliable and timely forecasting.
They pointed out that, from 2031, the European Space Agency’s probe Vigil will help with 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.
MPS scientists are currently developing the Polarimetric and Magnetic Imager for the Vigil mission.
