Not just any solar flares, a new kind first described in the 1980s. The kind of solar flares that we see the most pictures and video loops of are fast, dramatic events. These occur when the magnetic field lines of the sun tangle, or cross, then snap and reconnect around sunspots. These outflows of radiation are the ones you hear talk of doom coming from; when strong enough, they can damage satellites and even affect the power and communication infrastructure on the ground.
The new kind of solar flares don't release energy as quickly and then slowly dissipate. Until Chandrayaan-2 began observing these flares, around 100 had been observed. That's 100 since the 1980s. Using Chandrayaan-2's lunar orbiter, a team of researchers detected 1,400 such slow-rising flares in three years.
"There was a consensus in the solar physics community, since the early 2000s, that most solar flares are these rapidly rising intensities, followed by a slow decay," Aravind Bharathi Valluvan, team leader and an astrophysics graduate student at the University of California, San Diego, told Space.com. "However, what my research, along with my team, has shown is that not all solar flares follow that pattern."
Valluvan explained that the solar science community had overlooked slower-rising flares, or "hot thermal" flares because computer algorithms used to detect solar flares in observational data have focused on fast-rising, or "impulsive" flares. Impulsive flares are defined as covering the maximum area they possibly can in under half their lifespan.
"We did not do that, and instead took a more general approach. What we saw is that there are a lot more slow-rising flares, and it's not an insignificant subset. In fact, they form a quarter of all flares," they continued. "So, we need to be studying hot thermal flares as a separate population. Currently, our understanding about these slower type flashes is quite limited."
As is often the case, the more these hot thermal flares are studied the more questions arise. To begin with, the magnetic reconnection process that's believed to generate both impulsive flares and hot thermal flares is rapid, which should give rise to a rapid energy release as well. Which says that it might be the climb of the flare's ejected material through the suns photosphere that's different, instead of the way the flare is created.
Rapid-rising impulse flares are associated with temperatures of around 18 million degrees Fahrenheit (10 million degrees Celsius). But slow-rising flares get their moniker "hot thermal flares" because they are associated with even greater temperatures of up to 54 million degrees Fahrenheit (30 million degrees Celsius).
Another significant conclusion of the the lunar orbiter's observations is that there are no "medium" speed flares between the faster impulse flares and the slower hot thermal flares. Trying to understand that seems like an important step.
There are more things to study. A question researchers puzzle over is why the solar corona is hotter than the sun's "surface," or photosphere. Not just "hotter" but hundreds of times hotter, despite being closer to the sun's fusion core.
"Why is the atmosphere hotter than the surface of the sun? That is something that solar flares have always been hypothesized as a solution for, but we never found evidence for this," Valluvan concluded. "These new types of flashes could be a potential resolution for this coronal heating mystery. And that is one of the things that I am most excited about."
"On July 2nd (2314 UT), giant sunspot AR3354 exploded, producing a long duration
X1-class solar flare. NASA's
Solar Dynamics Observatory (SDO) recorded the extreme ultraviolet flash." From the July 3, 2023 post about that flare.
Typical. Different input yields different result. (GASP!)
ReplyDeleteWhat makes this typical is that so many for so long play follow the leader.
Known since the 1980s yet only now seen in a new light (no pun) because some upstart had the idea to model differently.
Why, in this case, had researchers been so cowed as to not change perspective, try a new lense, dare to ask 'what if?'. It sure seems that way.
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The atm is hotter because of a lack of insulative qualities. Can a densely packed heat source be thought of as insulative? I say, yes.
Also, is temperature the only metric to define 'hotter'? We're talking space, not terrestrial.
I believe temperature is defined as the average molecular speed, thus even a single isolated hydrogen atom has a "temperature".
DeleteThis is not only space, it's an area close enough to the sun to kill people. All measurements are indirect, not some grad student holding a thermometer. Which is pretty much impossible for readings in the millions of degrees, anyway. I mean, what physical object isn't going to be destroyed in that?
DeleteThat "average molecular speed" is measured by the radiation when an electron drops orbitals and gives off a photon.
Part of the problem is the general public doesn't understand that energy is carried in many forms. "Heat" is a measure of thermal energy, i.e., motion. But heat is carried and transferred also by electromagnetic radiation. And then there is the whole black body radiation issue, wherein the inherent heat content of a body is indirectly measured by the black body spectrum it radiates. Tie this all up in a bow wrapped by the argument about whether a hot gas has any black body radiation and you have a right lively debate.
DeleteVery true. You can hold your hand near a hot cup of coffee and feel both convective air currents and long wave infrared radiation.
DeleteYour whole body is an excellent LWIR receiver. Why does 70F on the thermometer feel too cold in the winter and too warm in the summer? My theory is that you are sensing different radiated surface temperatures on your windows and inner walls, despite the air temperature being the same around you.
Deletewhat nuclear reactions are happening in the photosphere? in the solar corona?
ReplyDeletecould this be a partial reason for the temperature difference?
To the best of my knowledge, while the temperatures in the corona might support nuclear reactions, the pressures don't and the photosphere's temperatures are quite a bit lower than the corona's. This is going way back in my reading, but as I understand it, the pressures to achieve fusion are only attainable in the core of a star, so no fusion in the corona, the photosphere, or anywhere outside the densest part of the core.
DeleteAnyone who could provide info that contradicts that is welcome, of course.
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DeleteThere was a recent book that argued that the sun is liquid, not gaseous. Now, I don't know why this elicited such a firestorm of a debate, as I was taught very early on that this was the case. But apparently the prevailing theory at the moment is that the liquid/gas border is well down inside the star.
DeleteIf the surface were liquid and the corona is gaseous, this would explain some of the huge temperature differential. At least, it seems that way to me, depending on the pressures. Think of steam over water at 100C. The temperature of the vapor goes up proportional to the pressure, far higher than the vaporization point. The pressure at the surface of the sun is considerable, given the gravity.
Don't quote me as a physicist here. I haven't modeled it. But it seems possible.
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A large amount of heating is due to the inductive heating of the plasma by the immense and dynamic magnetic fields.
DeleteOn the liquid/gas subject, I tend to go with the idea it's liquid because I also learned that early on. I recall that in the core it's even more complex because the pressures are great enough to separate nuclei from electrons, making it a "lumpy soup", which is about as clumsy a metaphor as I can think of.
DeleteIt has to be that the electrons and nuclei are separated so that positively charged hydrogen nuclei that are repelling each other can get forced close enough to fuse.
Again, as I recall.