Virtual telescope significantly more powerful thanks to laser technology

Four telescopes of the Very Large Telescope Interferometer (VLTI) are now equipped with laser technology, thanks to which the combined instrument can carry out observations with powerful correction mechanisms anywhere in the night sky. This was announced by the European Southern Observatory ( ESO) and the Max Planck Society, which operate the virtual observatory. It consists of four combined 8-meter telescopes, making it even more powerful. An example image makes clear what is now possible. The improved technology is expected to enable more precise analyses of black holes, the center of the Milky Way, and extremely distant quasars, among other things.

Help against turbulence in the air

With the lasers now put into operation, artificial reference stars can be generated separately in the night sky for all four sub-telescopes of the interferometer. Adaptive optics then determines the turbulence in the atmosphere based on the flickering of these guide stars and can compensate for it by deforming the secondary mirrors on the telescope. The result is significantly sharper astronomical images without the negative influences of the Earth's atmosphere. The technology has been successfully used for years; at the VLTI, it is now intended to support imaging of any region of the sky. Until now, correction relied on bright real reference stars near the target, which limited the number of observable objects. The project is running under the name GRAVITY+.

As the responsible parties explain, the laser light excites a small point in a layer of sodium atoms to glow, which are located about 90 km above the Earth's surface. The result is a laser guide star above most of the Earth's atmosphere. The four lasers now put into operation enable the combined telescope array to target the entire southern sky and photograph it with the greatest possible precision. For verification, a cluster of massive stars in a neighboring galaxy of the Milky Way was targeted. Gravity+ then directly showed that an object, previously thought to be a single large star, actually consists of two stars. Further research is to follow.

In interferometry, several observatories are combined, which is long common in radio astronomy, for example, but is much more difficult in optical astronomy. Here, the different images must be physically merged to enable the combination. The effectiveness of the approach became clear in 2021 when a team from the Max Planck Institute for Extraterrestrial Physics published images of the stars orbiting the central black hole of the Milky Way. Even the responsible parties were amazed by the level of detail. It remains to be seen what the improved optics will reveal.

(mho)