Barnard's Star
Barnard's Star
[A black sky is shown with a yellow spot near the bottom, left of the center. Three smaller red spots at the diagonal from top left to bottom right indicate a moving star over time. Above these red spots lines are connected to a text that starts and ends with many A s, first growing, and at the end getting smaller:] ...AAAAHHi Sun! I was here billions of years before you formed and will shine for trillions of years after you dieEEEEEEAAA...
[Caption below the frame:] Sometimes, I wonder what Barnard's Star is saying to the Sun as it performs its 20,000-year-long high-speed flyby.

Barnard's Star is a very-low-mass red dwarf about 6 light-years away from Earth in the constellation of Ophiuchus . It is the fourth-nearest known individual star to the Sun after the three components of the Alpha Centauri system; it is the closest star to Earth in the Northern Hemisphere. It is a red dwarf with a mass of 0.144 Solar masses, a diameter one fifth that of the Sun, and it is 7–12 billion years old. Because of this low mass the gravitational pressure in the core is much lower and thus the fusion rate is far smaller than in the core of the Sun. In fact this star is so dim that, even though it's one of the nearest, it can't be seen by the naked eye. The low fusion rate also means that the lifespan of small stars is much longer. While huge stars might last a few hundred million years, and the Sun about 10 billion years, a small red dwarf has a lifespan of about a trillion years.
Barnard's Star is the star with the greatest proper motion in the sky. Proper motion is motion in the sky other than that caused by Earth's rotation or orbit. Barnard's star is both very close to the sun (as these things go) and moving now at a speed of more than 140 km/s toward the Sun. It will make its closest approach to the Sun in approximately 10,000 years, at a distance of about 3.75 light-years.
The image on the right shows different stars near the Sun over 100,000 years and it can be seen that none of them are getting closer than 3 light-years. This is a safe distance to our Solar System and the stars will not influence the orbits of the planets or smaller bodies. It's also obvious that much closer approaches never have happened since the Solar System formed 4.5 billion years ago because otherwise the nearly circular orbits of the planets in the same plane wouldn't be possible. Closer encounters have happened in the past by mostly small stars like Scholz's Star which actually passed through the Oort cloud at a distance of 0.82 light-years about 70,000 years ago, and at least one estimate suggests that a star is expected to pass through the Oort Cloud every 100,000 years or so. This distance is still too far away to influence the orbits of the planets, but those encounters cause comets perturbed from the Oort cloud to the inner Solar System roughly 2 million years later.
The comic shows the sizes and the distances not in a proper scale. If the Sun was 1.4 cm (1.4 Mio km in real) in diameter, Barnard's Star would be less than 3 mm at a distance of 356 km. Even Jupiter wouldn't fit into this picture -- at ten times smaller than the Sun, it would be a few pixels, but at a distance of 7.8 m to the Sun and all the other planets would fit into a circle less than 100 meters in diameter. The distances to others stars are far beyond human imagination and at its closest distance a message still takes 3.75 years from Barnard's Star to the Sun.
In regards to "20,000-year-long high-speed flyby", the joke here is suggesting Barnard's Star would need to scream out the maleficent, trolling statement as quickly as possible due to 20,000 years being such a small segment of time relative to the lifespan of the star (and our Sun, for that matter).
The title text emphasizes that this close approach will not be any hazard to the Solar System, but someone is envious of the long lifetime of Barnard's Star or annoyed by its unpleasant behavior (yelling at the sun for 20,000 years would be a minuscule amount of time for the stars, but for humans it would be a vast length of time, and would get annoying very quickly).
[A black sky is shown with a yellow spot near the bottom, left of the center. Three smaller red spots at the diagonal from top left to bottom right indicate a moving star over time. Above these red spots lines are connected to a text that starts and ends with many A s, first growing, and at the end getting smaller:] ...AAAAHHi Sun! I was here billions of years before you formed and will shine for trillions of years after you dieEEEEEEAAA...
[Caption below the frame:] Sometimes, I wonder what Barnard's Star is saying to the Sun as it performs its 20,000-year-long high-speed flyby.
