<blockquote>
<p>I would think that everything slows down, maybe not so much in the vacuum of space, but why would these particles continue accelerating?</p>
</blockquote>
<p>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 <a href="https://en.wikipedia.org/wiki/Plasma_(physics)" rel="noreferrer">plasma</a> -- that flows out from the sun at supersonic speeds.  This supersonic wind is called the <a href="https://en.wikipedia.org/wiki/Solar_wind" rel="noreferrer">solar wind</a>.</p>
<p>Sometimes the sun emits large blobs of plasma called <a href="https://en.wikipedia.org/wiki/Coronal_mass_ejection" rel="noreferrer">coronal mass ejection (CME)</a>.  If these propagate much faster than the solar wind, they can generate a <a href="https://en.wikipedia.org/wiki/Shock_wave" rel="noreferrer">shock wave</a> 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 <a href="https://physics.stackexchange.com/a/618127/59023">https://physics.stackexchange.com/a/618127/59023</a>).</p>
<p>So as to why the particles get accelerated, it's due to a CME shock running into the <a href="https://en.wikipedia.org/wiki/Heliosphere#Termination_shock" rel="noreferrer">termination shock</a> of the <a href="https://en.wikipedia.org/wiki/Heliosphere" rel="noreferrer">heliosphere</a>.  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.</p>
<blockquote>
<p>He says similar processes have been observed within the borders of our Solar System where solar wind is most powerful.</p>
</blockquote>
<p>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.</p>

CC BY-SA 4.0
2021-08-31T16:19:39.580Z
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?
KingsInnerSoul
CC BY-SA 4.0
2021-08-31T16:22:30.277Z
@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.
honeste_vivere
CC BY-SA 4.0
2021-08-31T15:48:48.740Z
2021-08-31T15:48:48.740Z
honeste_vivere
<p>I've read <a href="https://www.sciencealert.com/the-voyager-probes-have-detected-a-new-type-of-electron-burst-in-interstellar-space" rel="nofollow noreferrer">this</a> article, titled, &quot;Voyager Mission Finds a New Type of Electron Burst at The Edge of Our Solar System&quot;. They state that,</p>
<blockquote>
<p>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.</p>
<p>&quot;The idea that shock waves accelerate particles is not new,&quot;
notes astrophysicist Don Gurnett from the University of Iowa. </p>
<p>He says similar processes have been observed within the borders of our
Solar System where solar wind is most powerful.</p>
</blockquote>
<p>I would think that everything slows down, maybe not so much in the vacuum of space, but why would these particles continue accelerating?</p>

CC BY-SA 4.0
2020-12-04T23:45:19.210Z
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
planetmaker
CC BY-SA 4.0
2020-12-07T03:52:38.207Z
But that does not explain why an Object X gains momentum and reaches its max speed at the heliosphere.
KingsInnerSoul
<the-sun><space><sun-rays>
Why is the solar wind most powerful near the heliosphere?
KingsInnerSoul
# Why is the solar wind most powerful near the heliosphere?

(Asked by: username_0 on 2020-12-04)

I've read [this](https://www.sciencealert.com/the-voyager-probes-have-detected-a-new-type-of-electron-burst-in-interstellar-space) 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?

**Tags:** the-sun, space, sun-rays
> **Comments:**
> **username_1**: 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  
> **username_0**: But that does not explain why an Object X gains momentum and reaches its max speed at the heliosphere.  

---

## 1 answers

### Answer by username_2 on 2021-08-31. Score: 5 | Accepted answer

> 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](https://en.wikipedia.org/wiki/Plasma_(physics)) -- that flows out from the sun at supersonic speeds. This supersonic wind is called the [solar wind](https://en.wikipedia.org/wiki/Solar_wind).

Sometimes the sun emits large blobs of plasma called [coronal mass ejection (CME)](https://en.wikipedia.org/wiki/Coronal_mass_ejection). If these propagate much faster than the solar wind, they can generate a [shock wave](https://en.wikipedia.org/wiki/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](https://en.wikipedia.org/wiki/Heliosphere#Termination_shock) of the [heliosphere](https://en.wikipedia.org/wiki/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.

> **Comments:**
> **username_0**: 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?  
> **username_2**: @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.  

---

