Tyler O'Neal, Staff Editor CLIENTS

NASA sun data helps new model predict big solar flares

Using data from NASA's Solar Dynamics Observatory, or SDO, scientists have developed a new model that successfully predicted seven of the Sun's biggest flares from the last solar cycle, out of a set of nine. With more development, the model could be used to one day inform forecasts of these intense bursts of solar radiation.

As it progresses through its natural 11-year cycle, the Sun transitions from periods of high to low activity, and back to high again. The scientists focused on X-class flares, the most powerful kind of these solar fireworks. Compared to smaller flares, big flares like these are relatively infrequent; in the last solar cycle, there were around 50. But they can have big impacts, from disrupting radio communications and power grid operations, to at their most severe endangering astronauts in the path of harsh solar radiation. Scientists who work on modeling flares hope that one day their efforts can help mitigate these effects.

Led by Kanya Kusano, the director of the Institute for Space-Earth Environmental Research at Japan's Nagoya University, a team of scientists built their model on a kind of magnetic map: SDO's observations of magnetic fields on the Sun's surface. Their results were published in Science on July 30, 2020. An X-class solar flare flashes on the edge of the Sun on March 7, 2012. This image was captured by NASA's Solar Dynamics Observatory and shows a type of light that is invisible to human eyes, called extreme ultraviolet light.{module INSIDE STORY}

It's well-understood that flares erupt from hot spots of magnetic activity on the solar surface, called active regions. (In visible light, they appear as sunspots, dark blotches that freckle the Sun.) The new model works by identifying key characteristics in an active region, characteristics the scientists theorized are necessary to set off a massive flare.

The first is the initial trigger. Solar flares, especially X-class ones, unleash huge amounts of energy. Before an eruption, that energy is contained in twisting magnetic field lines that form unstable arches over the active region. According to the scientists, highly twisted rope-like lines are a precursor for the Sun's biggest flares. With enough twisting, two neighboring arches can combine into one big, double-humped arch. This is an example of what's known as magnetic reconnection, and the result is an unstable magnetic structure - a bit like a rounded "M" - that can trigger the release of a flood of energy, in the form of a flare.

Where the magnetic reconnection happens is important too, and one of the details the scientists built their model to calculate. Within an active region, there are boundaries where the magnetic field is positive on one side and negative on the other, just like a regular refrigerator magnet.

"It's similar to an avalanche," Kusano said. "Avalanches start with a small crack. If the crack is up high on a steep slope, a bigger crash is possible." In this case, the crack that starts the cascade is magnetic reconnection. When reconnection happens near the boundary, there's potential for a big flare. Far from the boundary, there's less available energy, and a budding flare can fizzle out - although, Kusano pointed out, the Sun could still unleash a swift cloud of solar material, called a coronal mass ejection.

Kusano and his team looked at the seven active regions from the last solar cycle that produced the strongest flares on the Earth-facing side of the Sun (they also focused on flares from part of the Sun that is closest to Earth, where magnetic field observations are best). SDO's observations of the active regions helped them locate the right magnetic boundaries, and calculate instabilities in the hot spots. In the end, their model predicted seven out of nine total flares, with three false positives. The two that the model didn't account for, Kusano explained, were exceptions to the rest: Unlike the others, the active region they exploded from was much larger and didn't produce a coronal mass ejection along with the flare.

"Predictions are the main goal of NASA's Living With a Star program and missions," said Dean Pesnell, the SDO principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Maryland, who did not participate in the study. SDO was the first Living with a Star program mission. "Accurate precursors such as this that can anticipate significant solar flares show the progress we have made towards predicting these solar storms that can affect everyone."

While it takes a lot more work and validation to get models to the point where they can make forecasts that spacecraft or power grid operators can act upon, the scientists have identified conditions they think are necessary for a major flare. Kusano said he is excited to have a promising first result.

"I am glad our new model can contribute to the effort," he said.

ALMA finds possible sign of neutron star in supernova 1987A

Tyler O'Neal, Staff Editor CLIENTS

Two teams of astronomers have made a compelling case in the 33-year-old mystery surrounding Supernova 1987A. Based on observations of the Atacama Large Millimeter/submillimeter Array (ALMA) and a theoretical follow-up study, the scientists provide new insight for the argument that a neutron star is hiding deep inside the remains of the exploded star. This would be the youngest neutron star known to date.

Ever since astronomers witnessed one of the brightest explosions of a star in the night sky, creating Supernova 1987A (SN 1987A), they have been searching for a compact object that should have formed in the leftovers from the blast.

Because particles known as neutrinos were detected on Earth on the day of the explosion (23 February 1987), astronomers expected that a neutron star had formed in the collapsed center of the star. But when scientists could not find any evidence for that star, they started to wonder whether it subsequently collapsed into a black hole instead. For decades the scientific community has been eagerly awaiting a signal from this object that has been hiding behind a very thick cloud of dust. CAPTION This artist's illustration of Supernova 1987A shows the dusty inner regions of the exploded star's remnants (red), in which a neutron star might be hiding. This inner region is contrasted with the outer shell (blue), where the energy from the supernova is colliding (green) with the envelope of gas ejected from the star prior to its powerful detonation. CREDIT NRAO/AUI/NSF, B. Saxton{module INSIDE STORY}

The "blob"

Recently, observations from the ALMA radio telescope provided the first indication of the missing neutron star after the explosion. Extremely high-resolution images revealed a hot "blob" in the dusty core of SN 1987A, which is brighter than its surroundings and matches the suspected location of the neutron star.

"We were very surprised to see this warm blob made by a thick cloud of dust in the supernova remnant," said Mikako Matsuura from Cardiff University and a member of the team that found the blob with ALMA. "There has to be something in the cloud that has heated up the dust and which makes it shine. That's why we suggested that there is a neutron star hiding inside the dust cloud."

Even though Matsuura and her team were excited about this result, they wondered about the brightness of the blob. "We thought that the neutron star might be too bright to exist, but then Dany Page and his team published a study that indicated that the neutron star can indeed be this bright because it is so very young," said Matsuura.

Dany Page is an astrophysicist at the National Autonomous University of Mexico, who has been studying SN 1987A from the start. "I was halfway through my PhD when the supernova happened," he said, "it was one of the biggest events in my life that made me change the course of my career to try to solve this mystery. It was like a modern holy grail."

The theoretical study by Page and his team, published today in The Astrophysical Journal, strongly supports the suggestion made by the ALMA team that a neutron star is powering the dust blob. "In spite of the supreme complexity of a supernova explosion and the extreme conditions reigning in the interior of a neutron star, the detection of a warm blob of dust is a confirmation of several predictions," Page explained.

These predictions were the location and the temperature of the neutron star. According to supernova computer models, the explosion has "kicked away" the neutron star from its birthplace with a speed of hundreds of kilometers per second (tens of times faster than the fastest rocket). The blob is exactly at the place where astronomers think the neutron star would be today. And the temperature of the neutron star, which was predicted to be around 5 million degrees Celsius, provides enough energy to explain the brightness of the blob.

Not a pulsar or a black hole

Contrary to common expectations, the neutron star is likely not a pulsar. "A pulsar's power depends on how fast it spins and on its magnetic field strength, both of which would need to have very finely tuned values to match the observations," said Page, "while the thermal energy emitted by the hot surface of the young neutron star naturally fits the data."

"The neutron star behaves exactly like we expected," added James Lattimer of Stony Brook University in New York, and a member of Page's research team. Lattimer has also followed SN 1987A closely, having published prior to SN 1987A predictions of a supernova's neutrino signal that subsequently matched the observations. "Those neutrinos suggested that a black hole never formed, and moreover it seems difficult for a black hole to explain the observed brightness of the blob. We compared all possibilities and concluded that a hot neutron star is the most likely explanation."

This neutron star is a 25 km wide, extremely hot ball of ultra-dense matter. A teaspoon of its material would weigh more than all the buildings within New York City combined. Because it can only be 33 years old, it would be the youngest neutron star ever found. The second youngest neutron star that we know of is located in the supernova remnant Cassiopeia A and is 330 years old.

Only a direct picture of the neutron star would give definite proof that it exists, but for that astronomers may need to wait a few more decades until the dust and gas in the supernova remnant become more transparent.

Detailed ALMA images

Even though many telescopes have made images of SN 1987A, none of them have been able to observe its core with such high precision as ALMA. Earlier (3-D) observations with ALMA already showed the types of molecules found in the supernova remnant and confirmed that it produced massive amounts of dust.

"This discovery builds upon years of ALMA observations, showing the core of the supernova in more and more detail thanks to the continuing improvements to the telescope and data processing," said Remy Indebetouw of the National Radio Astronomy Observatory and the University of Virginia, who has been a part of the ALMA imaging team.

TiPES outlines techniques to achieve better climate simulation

Tyler O'Neal, Staff Editor CLIENTS

We are changing the Earth system at an unprecedented speed without knowing the consequences in detail. Increasingly detailed, physics-based supercomputer models are improving steadily, but an in-depth understanding of the persisting uncertainties is still lacking. The two main challenges have been to obtain the necessary amount of detail in the models and to accurately predict how anthropogenic carbon dioxide disturbs the climate's intrinsic, natural variability. A path to surmounting both of these obstacles are now laid out in a comprehensive review published in Reviews of Modern Physics by Michael Ghil and Valerio Lucarini from the EU Horizon 2020 climate science project TiPES.

"We propose ideas to perform much more effective climate simulations than the traditional approach of relying exclusively on bigger and bigger models allows. And we show how to extract much more information at much higher predictive power from those models. We think it is a valuable, original, and much more effective way than a lot of things that are being done," says Valerio Lucarini, a professor in mathematics and statistics at the University of Reading, UK and at CEN, the Institute of Meteorology, University of Hamburg, Germany. {module INSIDE STORY}

Such an approach is urgently needed because nowadays climate models generally fail in performing two important tasks.

First, they cannot reduce the uncertainty in determining the mean global temperature at the surface after a doubling of carbon dioxide (CO2) in the atmosphere. This number is called equilibrium climate sensitivity and in 1979 it was computed to 1,5-4 degrees Celsius. Since then the uncertainty has grown. Today it is 1,5-6 degrees in spite of decades of improvement to numerical models and huge gains in computational power over the same period.

Second, climate models struggle to predict tipping points, which occur when a subsystem i.e. a sea current, an ice sheet, a landscape, an ecosystem suddenly, and irrevocably shift from one state to another. These kinds of events are well documented in historical records and pose a major threat to modern societies. Still, they are not predicted by the high-end climate models that the IPCC assessments rely upon.

These difficulties are grounded in the fact that mathematical methodology used in most high-resolution climate calculations does not reproduce well deterministically chaotic behavior nor the associated uncertainties in the presence of time-dependent forcing.

Chaotic behavior is intrinsic to the Earth system as very different physical, chemical, geological and biological processes like cloud formation, sedimentation, weathering, ocean currents, wind patterns, moisture, photosynthesis, etc. range in timescales from microseconds to millions of years. Apart from that, the system is forced mainly by solar radiation which varies naturally over time, but also by anthropogenic changes to the atmosphere. Thus, the Earth system is highly complex, deterministically chaotic, stochastically perturbed, and never in equilibrium.

"What we are doing is essentially extending deterministic chaos to a much more general mathematical framework, which provides the tools to determine the response of the climate system to all sorts of forcings, deterministic as well as stochastic," explains Michael Ghil, professor at Ecole Normale Supérieure and PSL University in Paris, France and at the University of California, Los Angeles, USA.

The fundamental ideas are not that new. The theory was developed decades ago, but as a very difficult mathematical theory which calls for cooperation between experts in different fields to be implemented in climate models. Such interdisciplinary approaches involving the climate science community as well as experts in applied mathematics, theoretical physics, and dynamical systems theory have been slowly emerging. The authors hope the review paper will accelerate this tendency as it describes the mathematical tools needed for such work.

"We present a self-consistent understanding of climate change and climate variability in a well defined coherent framework. I think that is an important step in solving the problem. Because first of all, you have to pose it correctly. So the idea is - if we use the conceptual tools we discuss extensively in our paper, we might hope to help climate science and climate modeling make a leap forward," says Valerio Lucarini.