(© MPS/Alexey Chizhik)
Solar flares are huge eruptions of radiation that blast out of the Sun – sometimes several times a day – and at their strongest, they can release the energy equivalent of a billion hydrogen bombs.
Our planet's magnetic field and atmosphere, together with tens of millions of miles of space, protect us from these bursts and other space weather.
However, distant stars similar to the Sun have generated so-called superflares, hundreds or thousands of times more energetic than what's been observed in our Solar System.
Could those superflares also potentially erupt from our own Sun – and have they been occurring throughout Earth's history, in the billions of years before we had the instruments required to measure them?
(© MPS/Alexey Chizhik)
That's the question researchers led by a team from the Max Planck Institute for Solar System Research (MPS) in Germany wanted to ask.
In a new study published in Philosophical Transactions of the Royal Society A, the researchers analyzed the 300 strongest solar flares measured between 2010 and 2016, and the energy they produced.
"Of course, we knew that no superflares had occurred during the observation period, but the statistical relationship we found between the released energy and the size of the active region should hold true for more powerful events as well," says astrophysicist Natalie Krivova, from MPS.
By studying the corresponding active regions on the Sun for each flare – the intense magnetic disturbances that eruptions emerge from, which often include dark sunspots – the researchers were able to calculate how energy corresponded to active region size.
They then went back to some of the largest sunspots recorded on the Sun – records that go back much further, around four centuries. One sunspot stands out: the giant sunspot observed in 1947, which covered around 0.6 percent of the visible solar disk.
A sunspot that size, with a diameter some 40 times that of Earth, could theoretically produce a flare reaching the lower end of the superflare range seen on other stars.
That's the question researchers led by a team from the Max Planck Institute for Solar System Research (MPS) in Germany wanted to ask.
In a new study published in Philosophical Transactions of the Royal Society A, the researchers analyzed the 300 strongest solar flares measured between 2010 and 2016, and the energy they produced.
"Of course, we knew that no superflares had occurred during the observation period, but the statistical relationship we found between the released energy and the size of the active region should hold true for more powerful events as well," says astrophysicist Natalie Krivova, from MPS.
By studying the corresponding active regions on the Sun for each flare – the intense magnetic disturbances that eruptions emerge from, which often include dark sunspots – the researchers were able to calculate how energy corresponded to active region size.
They then went back to some of the largest sunspots recorded on the Sun – records that go back much further, around four centuries. One sunspot stands out: the giant sunspot observed in 1947, which covered around 0.6 percent of the visible solar disk.
A sunspot that size, with a diameter some 40 times that of Earth, could theoretically produce a flare reaching the lower end of the superflare range seen on other stars.
(Mount Wilson Observatory)
"Our Sun has superflare potential," says Krivova.
"It can produce massive sunspots that, in principle, can serve as the starting point for the most extreme bursts of radiation."
This fits with the evidence we have of extreme solar particle events (ESPEs), storms of radiation way beyond anything that's been directly observed in history. We haven't seen these events, but there are signs of them in tree-ring records.
We therefore know Earth has been hit by ESPEs – and the new study suggests that superflares may well have caused them.
Krivova is also the senior author on another related study, also recently published in Philosophical Transactions of the Royal Society A, which looks in more detail at the relationship between ESPEs and superflares. The prevailing hypothesis is that superflares can trigger ESPEs, but only if conditions are right for energetic particles to escape into space.
Returning to the first paper, the researchers say the relationship between ESPEs and superflares is something for future studies to build on. More detailed modeling, investigating how sunspots can combine together and the magnetic field conditions that keep superflares confined, will be important here.
While the direct impact on human health would be limited, future solar storms have the potential to cause significant disruption to the technology and infrastructure we rely on in the modern day, which means understanding when and how our Sun might ramp up to a superflare level is an important field of research.
"Our goal was to provide constraints on the maximum possible flare energies that could arise from the most extreme sunspot groups in the historical record," write the researchers in their published paper.
"We emphasize that this analysis does not address the probability or expected frequency of such events."
"Our Sun has superflare potential," says Krivova.
"It can produce massive sunspots that, in principle, can serve as the starting point for the most extreme bursts of radiation."
This fits with the evidence we have of extreme solar particle events (ESPEs), storms of radiation way beyond anything that's been directly observed in history. We haven't seen these events, but there are signs of them in tree-ring records.
We therefore know Earth has been hit by ESPEs – and the new study suggests that superflares may well have caused them.
Krivova is also the senior author on another related study, also recently published in Philosophical Transactions of the Royal Society A, which looks in more detail at the relationship between ESPEs and superflares. The prevailing hypothesis is that superflares can trigger ESPEs, but only if conditions are right for energetic particles to escape into space.
Returning to the first paper, the researchers say the relationship between ESPEs and superflares is something for future studies to build on. More detailed modeling, investigating how sunspots can combine together and the magnetic field conditions that keep superflares confined, will be important here.
While the direct impact on human health would be limited, future solar storms have the potential to cause significant disruption to the technology and infrastructure we rely on in the modern day, which means understanding when and how our Sun might ramp up to a superflare level is an important field of research.
"Our goal was to provide constraints on the maximum possible flare energies that could arise from the most extreme sunspot groups in the historical record," write the researchers in their published paper.
"We emphasize that this analysis does not address the probability or expected frequency of such events."
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