December 4, 2023

The big news about the sun is that there isn’t big news. We are blessed, astronomers like to say, to live next to a “boring star”.

But the inhabitants (if any) of the planets orbiting the neighboring star Proxima Centauri, which is only 4.2 light years away, are less fortunate. In April, astronomers announced that a massive flare had erupted from its surface in 2019. For seven seconds when a battery of telescopes was observed on Earth and in space, the little star had increased its output of ultraviolet radiation to one of 14,000 times the most violent such flares ever seen in our galaxy.

This was more than a serious sunburn area. “A person on this planet would have a bad time,” said Meredith MacGregor, an astronomy professor at the University of Colorado who led the global observational effort.

Space weather of this magnitude could sterilize potentially habitable planets and deliver bad news for those looking for life beyond this solar system. Even mild space weather can be disruptive to evolved and colonized creatures. Sunspots and solar storms, which grow and decrease in an 11-year cycle, emit energy that can endanger spacecraft, astronauts, and communication systems.

A new cycle of storms will begin each day, and astrophysicists disagree on how active or threatening it will be. The sun could be about to set records for sunspot numbers and violent storms, or it could slide into a decline like the Maunder Minimum from 1645 to 1715, when sunspots barely appeared – a time known in Europe as the Little Ice Age .

“We live in the atmosphere of a star,” says Scott McIntosh, solar physicist at the National Center for Atmospheric Research in Boulder, Colorado, often. “As a civilization, we take our star for granted.”

Here, 150 million kilometers from the nearest star – the one we call our sun – we exist and mostly thrive on the edge of almost incomprehensible violence and complexity.

The sun is a medium-sized star, a ball of red-hot ionized gas a million miles in diameter. Its great interior spins faster than its exterior, and the outer layers spin faster at the equator than at the poles. The result is a growling nest of magnetic fields that manifest as sunspots and are worse when they break the surface.

Every second, thermonuclear reactions in the center of the sun burn 600 million tons of hydrogen into 596 million tons of helium. The missing four million tons converted into pure energy make up the mortgage payment for all life on earth and perhaps elsewhere in the solar system. As the energy emerges from the sun, it rises through successively cooler and less dense layers of gas and finally 100,000 years later out of the photosphere or surface, where the temperature is only 5,700 Kelvin, or 9,800 degrees Fahrenheit.

The sun is amazingly consistent with these mortgage payments. A few years ago an experiment in Italy confirmed that our star does not seem to have changed its energy output in the last 100,000 years. This is the time it takes for this energy to migrate out of the sun’s core. The researchers were able to calculate how much energy the sun is producing in real time by measuring subatomic particles called neutrinos, which are generated by nuclear reactions in the sun, escape in seconds and reach the earth in just eight minutes. They found that this energy corresponds to the power that was generated 100,000 years ago and is only now detectable.

The action doesn’t stop at the sun’s surface. This cheerful yellow photosphere cooks like oatmeal and is littered with dark magnetic storms (the infamous sunspots) that crackle, swirl, and whip with showers of electrical particles and radiation. The corona, made up of thin, superfast streams of electrified gas and only visible during solar eclipses, extends millions of miles from the glowing surface.

Sometimes things go wrong, even though they are way below Proxima Centauri eruptions so far. When the magnetic fields created by all of the swirling, electrified gas leak onto the sun’s surface, they twist and tangle. Eventually they snap in loops and reconnect, releasing enormous amounts of radiation and charged particles – an explosive solar flare that can be more powerful than millions of hydrogen bombs.

Sometimes these torches blow entire chunks of the Sun’s outer layers into space in events known as coronal mass ejections. The mother of all previously known solar storms occurred on September 1, 1859, when a sunspot hit the earth. Sparks flew from telegraph systems in Europe and North America, causing fires. The aurors that night stretched as far as Hawaii and Cuba and were bright enough for people to read their newspapers by their light.

In 2012, another coronal mass ejection barely missed Earth. A previous study by the National Academy of Sciences concluded that a direct hit from such a storm could cause about $ 2 trillion in damage, shut down the power grid and blind satellites, at least temporarily. Forget about trying to use the internet or your local ATM. Many people would not even be able to flush their toilets without the electricity to operate water pumps, the report said. “I think as a civilization we are being fooled,” said Dr. McIntosh.

Such storms are more likely to occur during the peaks of the Sun’s mysterious 11-year sunspot cycle.

Recently, the sunspot cycles have become weaker. During the last cycle, 101 spots were observed on the sun in 2014, the year of the highest activity. that was well below the historical average of 160 to 240.

Last year, a committee of scientists from NASA and the National Oceanic and Atmospheric Administration predicted that the coming cycle would be similarly anemic, peaking in 2025 of about 115 sunspots.

But Dr. McIntosh and his colleagues made a radically different forecast, of more than 200 sunspots at their peak. The 11-year sunspot cycle, which is based on an analysis of 140 years of solar measurements, refutes a more fundamental 22-year Hale cycle named after its discoverer, George Ellery Hale. During this time, the sun’s magnetic field reverses polarity and then switches back.

Each cycle ends or begins when two magnetic tapes, traveling from opposite, high latitudes of the sun, meet at the equator and destroy each other. On average, each phase of the cycle lasts 11 years but can vary.

Dr. McIntosh and his team found that the longer a cycle lasted, the weaker the next cycle, and vice versa. The current cycle, the 24th since record started, shows all the signs of an end after just over 10 years – shorter than average, which means the next cycle should be strong.

“Sunspot Cycle 25 could be on a scale that rivals the few that have been recorded,” said Dr. McIntosh in late April. On Thursday he and his team waited for the “ignition” to begin. “It’s very, very close,” he wrote in an email. “We’re watching very closely.”

In addition to the health of our planetary infrastructure, astronomers pride themselves on the feeling of understanding the complicated and violent processes behind the relatively calm face of the sun.

“I think the problem with the sun is that we are too close and so there is too much data on the sun,” said Dr. McIntosh. He called it a model breaker: “Your models will eventually fail. That’s one of the reasons the weather is so hard to predict, isn’t it? Because our observations are so detailed, but you know they are difficult to get absolutely right. “

Tony Phillips, an astronomer who runs the website, agreed in an email. “In my experience, people who really understand something can just explain it,” he said. “It strikes me that almost no one in the solar cycle forecasting business can explain their favorite dynamo model in a way that lay people can ‘get’ it.”

The situation reminded him of the proverbial blind people trying to create an elephant theory, one of which was solely focused on feeling the animal’s trunk.

“Scott and Bob stand by and shout, ‘Hey, you’re ignoring most of the elephant,'” he said. “In other words, the solar cycle has more to offer than conventional models usually assume. And so, according to Scott, they are doomed to misunderstand the big picture. “

Jay Pasachoff, an astronomer at Williams College who has spent his life observing the corona during solar eclipses, said he didn’t attach much importance to such predictions. In an email he told of a meeting in the last cycle that had “amusing conversations”.

The conversation, as he recalled, was, “The next cycle will be stronger than the average, the next cycle will be weaker than the average, the next cycle will either be stronger than the average or weaker than the average, the next cycle will neither be stronger above average nor weaker than average. “

He added, “So my plan is to wait and see.”

Potential dangers aside, understanding how the sunspot cycle actually works is critical, “from a purely human perspective, if you are to understand stars,” said Dr. McIntosh. “And if you think about it, the Earth’s magnetic field is mostly why we are likely to have life on Earth.”

He pointed out that Mars has neither an atmosphere nor a magnetic field. “If your planet doesn’t have a magnetic field, you can have the atmosphere you want,” he said, “but your local friendly neighborhood star could wipe it off right away.”

Indeed, astrophysicists suggest that such a fate befell Mars, which was once warmer and wetter than it is today.

Proxima Centauri, a small star known as the M dwarf, is home to at least two exoplanets, one of which is Earth-sized and close enough to the star to be habitable if not immersed in radiation. Dr. MacGregor offered a glimmer of hope for life in such neighborhoods.

“Recent work has shown that ultraviolet light can be very important in catalyzing life – converting complex molecules into amino acids and ultimately into unicellular organisms,” she said. “Because M-dwarfs are so small and cold, they don’t generate as much UV radiation unless they flare up. Perhaps there is a sweet spot where a star flares enough to ignite life, but not so much that it instantly destroys it! “