How big can solar flares get and how far do they spread?

As the Sun spits out more and larger storms, videos of flares erupting from its surface help us appreciate their power. When observed, they usually look like they are extinguishing a few solar diameters away, but the truth is quite different. Although the particles accompanying smaller flares can fall back when the Sun's powerful gravity exceeds their speed, some flares can fly far beyond Earth and even the outer planets.

Solar flares are localized bursts of radiation that occur when energy trapped in twisted magnetic fields is suddenly released, accelerating charged particles from the solar plasma.

How far can solar flares travel?

As strong as the Sun's gravitational field is, flares can deliver so much energy that the particles in them can start traveling at speeds that are a large fraction of the speed of light. A combination of the Sun's gravity and the encounter with the thin material in not-so-airless space slows these particles down but can't stop them. As a result, flares can travel to the heliopause, the boundary where the solar wind dies out, and eventually no longer have the power to push the interstellar medium aside.

As we recently learned, the heliopause is anything but spherical. So to answer the second question first: solar flares can travel significantly different distances depending on the direction from which they are fired. We have not yet fully mapped the boundaries of the heliopause, but we know that it is at least 100 to 120 astronomical units (Earth-Sun distance).

A few flares fired by chance in the right direction can probably reach distances of 350 AU or more. A sufficiently powerful flare might even push the limit a little further for a while, like a rhinoceros running into a rubber wall.

On the other hand, a few flares hit the magnetic field of the Earth or another planet that has such a field and are stopped much earlier.

In fact, the most striking thing about a flare is the light it emits, and this will travel forever unless it hits something. We can see Radiation bursts from other stars, suggesting that the radiation burst has somehow traveled many light years to reach us. The Sun's radiation bursts are not as large as those of many other stars, but with the right telescope they could still be seen from hundreds of light years away.

Flares can become less bright so we can no longer see them long before they reach such distances, but that doesn't mean they're gone.

How big can solar flares get?

If you mean the size of a flare literally, multiply the length, as described above, by the area of ​​the flare. This area varies, of course, and can be difficult to measure, but flares can jump from areas on the Sun's surface many times larger than the Earth, and they don't get smaller during their journey.

However, when people talk about flares being big, they are usually talking about their power. The strongest flare that has been accurately measured occurred in 2001. It was a X28.6 according to the scale by which flares are measured, meaning it was 2.9 x 10^-3 Watts per square meter. That may not sound like much, but spread over an area much larger than the Earth, that results in an astonishing amount of power.

Two years later, however, another eruption overwhelmed the detectors of the Geostationary Operational Environmental Satellite. It was estimated to be a magnitude X40 or 45 eruption.

But we know that flares can get much bigger. The Carrington event in the 19th century^th The 19th century incident happened long before we could measure the power of flares, but the effects they caused, including electrocutions of telegraph operators, make it clear that this was on a far greater scale than anything we have experienced in the space age.

Radiation bursts recorded in tree rings may indicate even larger radiation bursts, but this interpretation is controversial.

Whatever the case, it looks like we can only wait and see how strong flares can get.