The Voyager 2 probe discovered an increase in space density outside the solar system
In November 2018, the Probe Voyager 2 left the outer edge of the heliosphere after a 41-year journey and entered interstellar space. The latest data sent by the probe revealed interesting information about space outside the solar system. The data collected by the spaceship indicate that the further Voyager 2 moves from the sun, the density of space increases. This is not the first time that an increase in the density of matter has been observed in space. The Travel 1, which entered interstellar space in 2012, found a similar density gradient, but elsewhere in space. New data from Voyager 2 shows that the measurements from Voyager 1 were not only correct, but that the recorded increase in density may be a feature of interstellar space.
The research was done in "The Astrophysical Journal Letters" released. https://iopscience.iop.org/article/10.3847/2041-8213/abae58
Space beyond the heliosphere
On November 5, 2018, the Voyager 2 probe crossed the outer edge of the heliosphere - a protective "bubble" of particles and magnetic fields generated by our sun. At the edge of the heliosphere, called the heliopause, the solar wind loses its speed and the pressure of the galactic winds begins to outweigh the pressure of the solar wind. This limit is about 18 billion kilometers from the sun. As before, the Voyager 1 probe, its twin structure went beyond the heliosphere into what is known as the interstellar center.
Space is generally thought of as a vacuum, but it isn't, at least not entirely. The density of matter in space is extremely low. In the solar system, the solar wind has an average density of protons and electrons of 3 to 10 particles per cubic centimeter of space, but this value decreases with increasing distance from the sun. Scientists have estimated that the average density of space in the Milky Way is about 0,037 particles per cubic centimeter.
The increase in spatial density
Voyager 1 crossed the heliopause on August 25, 2012 at a distance of 121,6 astronomical units from Earth (approximately 18,1 billion km). When the volume density was first measured on October 23, 2013, the result showed 0,055 electrons per cubic centimeter. Voyager 2, which traveled beyond the heliosphere and flew over Jupiter, Saturn, Uranus and Neptune, crossed the heliopause on November 5, 2018 at a distance of 119 astronomical units from Earth (17,8 billion km). Your instruments then showed 0,039 electrons per cubic centimeter, which is very close to the Voyager 1. Both probes found an increase in spatial density outside the heliosphere. After passing several more astronomical units in space, Voyager 1 recorded an increase in density to about 0,13 electrons per cubic centimeter. The Voyager 2 probe took similar measurements, which also showed an increase in density - to about 0,12 electrons per cubic centimeter.
These measurements may seem small, but they are important enough to pique the interest of scientists, especially since it is not clear what is causing them. One theory is that the matter carried by the interstellar winds slows down when it reaches the heliopause, causing something like a traffic jam. This matter is building up on the edge of the heliosphere, and that is what the instruments mounted on both probes recorded. Future measurements made by both Voyager probes carried out during their further journey into interstellar space can help to verify the concept. Even if it can take some time. It is not certain that the Voyager probes can work long enough to solve this problem.