Four lasers were directed into the skies above the European Southern Observatory's (ESO) Paranal facility in Chile. Each laser creates an artificial star, which astronomers use to measure and then adjust for the blur generated by Earth's atmosphere.
Four lasers for the VLTI. Image Credit: European Southern Observatory
The striking launch of these lasers, one from each of Paranal's eight-metre telescopes, marks a crucial milestone in the GRAVITY+ project, which is a vast and complicated upgrade to ESO's Very Large Telescope Interferometer (VLTI). GRAVITY+ expands the VLTI's observation power and sky coverage beyond what was previously achievable.
This is a very important milestone for a facility that is completely unique in the world.
Antoine Mérand, Astronomer, European Southern Observatory
Mérand is also a VLTI Program Scientist.
The VLTI uses interferometry to combine light from several VLT telescopes, either the four eight-meter Unit Telescopes (UTs) or the four smaller Auxiliary Telescopes. With an emphasis on GRAVITY, a highly effective VLTI instrument that has been used to image exoplanets, view nearby and distant stars, and conduct in-depth investigations of faint objects circling the Milky Way's supermassive black hole, GRAVITY+ is an update to the VLTI.
GRAVITY+ also includes adjustments to the telescopes' infrastructure as well as enhancements to the VLTI underground tunnels that connect the light beams. The installation of a laser at each of the previously unequipped UTs is a significant milestone in this long-term effort, which will convert the VLTI into the world's most powerful optical interferometer.
The VLTI with GRAVITY has already enabled so many unpredicted discoveries, we are excited to see how GRAVITY+ will push the boundaries even further.
Frank Eisenhauer, GRAVITY+ Principal Investigator, Max-Planck Institute for Extraterrestrial Physics (MPE)
The sequence of enhancements has been happening for a few years and includes updated adaptive-optics technology (a system to adjust for blur created by the Earth's atmosphere) as well as enhanced state-of-the-art sensors and deformable mirrors. Until now, the VLTI's adaptive-optics adjustments have been performed by pointing to bright reference stars that must be close to the target, limiting the number of objects that can be seen.
The placement of a laser at each UT creates a brilliant artificial star 90 km above Earth's surface, allowing atmospheric blur to be corrected anywhere in the sky. This allows the VLTI to see the whole southern sky, significantly increasing its observation capability.
This opens up the instrument to observations of objects in the early distant Universe, such as the quasar we observed on the second night where we resolved the hot, oxygen emitting gas very close to the black hole.
Taro Shimizu, Postdoctoral Researcher, Max-Planck-Institute for Extraterrestrial Physic
Shimizu is a member of the instrument consortium.
Astronomers will be able to examine distant active galaxies and directly estimate the mass of the supermassive black holes that fuel them, as well as witness young stars and planet-forming disks around them, thanks to the VLTI telescopes' lasers.
The VLTI's expanded capabilities will significantly increase the amount of light that can pass through the system, making the facility up to ten times more sensitive.
A big goal of GRAVITY+ is to allow for deep observations of faint targets.
Julien Woillez, Astronomer, European Southern Observatory
Woillez is also a GRAVITY+ Project Scientist.
This improved capacity to identify dimmer objects would enable studies of isolated stellar black holes, free-floating planets that do not orbit a parent star, and stars near the Milky Way's supermassive black hole Sgr A*.
The GRAVITY+ and ESO teams at Paranal conducted their first test observations with the new lasers on a cluster of massive stars at the center of the Tarantula Nebula, a star-forming area in the neighboring galaxy, the Large Magellanic Cloud.
These first studies indicated that a bright object in the nebula, previously assumed to be an enormous single star, is actually a binary of two stars close together. This demonstrates the enhanced VLTI's impressive capabilities and research potential.
This upgrade is more than simply an update; it was originally envisioned decades ago. The laser system was proposed in the final report of the “Very Large Telescope Project” in 1986, long before the VLTI existed: “If it could work in practice, it would be a breakthrough,” the report noted. Now, this breakthrough is a reality.