This animation sketches an approach to a very young, newborn star of solar mass, which is surrounded by a flat, cold circumstellar disk of dust and gas. Our planetary system once originated in a disk like this. Stars like these are called T Tauri stars, and they are found inside cold, molecular interstellar clouds in our galaxy. Since our solar system presently moves through a rather empty region of space, the most nearby molecular clouds are relatively distant, typically 500 light years away. Therefore these disks appear as very small objects in the sky when seen from the earth.
In the animation the angles corresponding to 1 arcsecond, 0.1 arcsecond and further down to 0,001 arsecond as resolved from the earth are marked and compared to where the orbits of Pluto, Jupiter and Venus would fall at the distance of 500 light years. 1 arcsecond of spatial resolution is what can be achieved with a single telescope from the ground, but subarcsecond resolutions are nowadays retrieved through special techniques including vibrating optics or with two or several interacting telescopes forming an interferometer. With the Hubble Space Telescope resolutions slightly better than 1 arcsecond is reached, but to resolve structures smaller than 0.001 arcseconds, as marked in the final close up, we will need future special interferometers placed in space. It is within this smaller limit that most of the observed activity of T Tauri stars originates. Strong energetic eruptions, possibly due to surface flares, to blobs of gas falling into the star along dipole magnetic field lines or even to magnetic energy released in the disk which is rotating differentially and build up stresses between layers moving at different velocities. The dipole magnetic field, it is thought, truncates the disk and creates an inner gap.
