Upgrading interferometric measurement technology with new guiding star lasers

The European Southern Observatory (ESO) team has recently made significant breakthroughs in the field of interferometric measurement technology. With the help of four newly installed lasers at the Paranal Observatory in Chile, the research team has successfully created a guiding star, marking a new era in interferometric measurement technology.

The successful generation of the laser guided star is an important component of the ESO GRAVITY+project and a major upgrade to the observatory's four eight meter telescope system.

GRAVITY+ is itself a large and complex upgrade to the ESO's Very Large Telescope Interferometer (VLTI), which has been revealing hidden details of stars and astronomical objects for many years.

Unique facility: GRAVITY+

"This is a very important milestone for a facility that is completely unique in the world," said Antoine Mérand, VLTI Programme Scientist.

VLTI combines light from several individual telescopes of the Paranal site's Very Large Telescopes, either the four eight-meter Unit Telescopes (UT) or the four smaller Auxiliary Telescopes. The installation of a laser at each of the previously unequipped UTs is a key achievement of this long-term project, transforming the VLTI into the most powerful optical interferometer in the world, noted ESO.

GRAVITY+ also encompasses infrastructural changes to the telescopes and upgrades to the VLTI underground tunnels, where the light beams are brought together.

ESO's original GRAVITY interferometer had operated since 2016, incorporating a cryogenically cooled Beam Combining Instrument for generating interferometric fringes from the received stellar light, and infra-red adaptive optics to compensate for atmospheric disturbance.

Correcting atmospheric blur anywhere on the sky

Guide stars are a vital element in ground-based observations, whereby lasers stimulate a point light source in the local atmosphere that can then be used as a reference point for an adaptive optics operation to remove the effects of atmospheric turbulence.

Until now adaptive optics corrections for the VLTI have been done by using bright reference stars that needed to be close to the target, limiting the number of objects that can be observed. The installation of a laser at each of the UTs means that a guide star is now created 90 kilometers above Earth's surface, enabling the correction of atmospheric blur anywhere on the sky.

This unlocks the whole southern sky to the VLTI and enhances its observing power dramatically, noted the ESO team. Astronomers will now be able to study distant active galaxies and directly measure the mass of the supermassive black holes that power them, as well as observe young stars and the planet-forming discs around them.

In addition, the VLTI’s improved capabilities will drastically increase the amount of light that can travel through the system, making the facility up to 10 times more sensitive. This allows observations of isolated stellar black holes, free-floating planets that do not orbit a parent star and stars closest to the Milky Way's supermassive black hole Sgr A*.

A first target for the team's test observations was a cluster of massive stars at the center of the Tarantula Nebula, a star-forming region in our neighboring galaxy the Large Magellanic Cloud. These revealed that a bright object in the nebula, thought to be an extremely massive single star, is actually a binary of two stars close together.

"The VLTI with GRAVITY has already enabled so many unpredicted discoveries," said Principal Investigator Frank Eisenhauer from project partner the Max-Planck Institute for Extraterrestrial Physics (MPE). "We are excited to see how GRAVITY+ will push the boundaries even further."

Source: optics.org