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I've read this article, titled, "Voyager Mission Finds a New Type of Electron Burst at The Edge of Our Solar System". They state that,

Carried to the fringes of our Solar System by the shock waves of solar eruptions known as coronal mass ejections, these energised particles appear to accelerate even beyond the borders of our Sun's powerful winds.

"The idea that shock waves accelerate particles is not new," notes astrophysicist Don Gurnett from the University of Iowa. 

He says similar processes have been observed within the borders of our Solar System where solar wind is most powerful.

I would think that everything slows down, maybe not so much in the vacuum of space, but why would these particles continue accelerating?

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  • $\begingroup$ Atoms are small. The gravitational pull is small compared to the momentum transfer received by the Sun's light accelerating them outward - but gravity is also small compared to any other effect acting on them, like magnetic fields etc - and those play an important role at the shock front of the heliosphere, too $\endgroup$
    – planetmaker
    Dec 4, 2020 at 23:45
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    $\begingroup$ But that does not explain why an Object X gains momentum and reaches its max speed at the heliosphere. $\endgroup$
    – KingsInnerSoul
    Dec 7, 2020 at 3:52

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I would think that everything slows down, maybe not so much in the vacuum of space, but why would these particles continue accelerating?

Well, there is no such thing as a perfect vacuum, first of all. All of the space surrounding the Sun is filled with an ionized gas -- called a plasma -- that flows out from the sun at supersonic speeds. This supersonic wind is called the solar wind.

Sometimes the sun emits large blobs of plasma called coronal mass ejection (CME). If these propagate much faster than the solar wind, they can generate a shock wave on their leading edge. These are not hydrodynamic shocks, but magnetized shocks. Magnetized shocks can accelerate/energize charged particles to extremely high energies (e.g., see discussion and references at https://physics.stackexchange.com/a/618127/59023).

So as to why the particles get accelerated, it's due to a CME shock running into the termination shock of the heliosphere. You can think of this like two walls moving closer together and between them is a ping pong ball bouncing off of them. If the walls move together quickly, the ping pong ball can gain a lot of momentum/energy.

He says similar processes have been observed within the borders of our Solar System where solar wind is most powerful.

This is just PR-related phrasing that is not conducive to actually conveying relevant information. The solar wind is more dense closer to the sun but by the orbit of Mercury, the solar wind speed is relatively constant all the way out past Pluto.

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  • $\begingroup$ What's the particles' behavior at the heliosphere due to the termination shock? Are they mostly forced out of the heliosphere zone, away from the sun? Or do they mostly get pushed back towards the sun? Is there a vertical spike wave effect that gets created? Does the CME shock gets reflected backwards from the heliosphere? $\endgroup$
    – KingsInnerSoul
    Aug 31, 2021 at 16:19
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    $\begingroup$ @KingsInnerSoul - Most eventually make it out into the heliosheath and mingle around there for a long time. Some come back into the solar wind, but the convectional electric field they "see" (due to their not being in the reference frame of the majority of charged particles) drives them away from the sun, in general. So unless they have a lot of energy, they tend to stay at or outside of the termination shock once they get there. $\endgroup$
    – honeste_vivere
    Aug 31, 2021 at 16:22

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