[Paper Review] The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI

GRAVITY Collaboration, :+135 more|arXiv (Cornell University)|Jan 19, 2023

Astronomy and Astrophysical Research7 citations

TL;DR

The GRAVITY+ project upgrades the VLTI to enable all-sky, high-contrast, near-infrared interferometry by integrating wide-field off-axis fringe tracking, enhanced adaptive optics on all Unit Telescopes, and laser guide stars. This advancement will extend sensitivity to faint sources, enabling precise black hole mass measurements in active galactic nuclei, testing of General Relativity with Galactic centre stars, and detailed characterization of young exoplanets.

ABSTRACT

The GRAVITY instrument has been revolutionary for near-infrared interferometry by pushing sensitivity and precision to previously unknown limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) in GRAVITY+, these limits will be pushed even further, with vastly improved sky coverage, as well as faint-science and high-contrast capabilities. This upgrade includes the implementation of wide-field off-axis fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser guide stars in an upgraded facility. GRAVITY+ will open up the sky to the measurement of black hole masses across cosmic time in hundreds of active galactic nuclei, use the faint stars in the Galactic centre to probe General Relativity, and enable the characterisation of dozens of young exoplanets to study their formation, bearing the promise of another scientific revolution to come at the VLTI.

Motivation & Objective

• Overcome the limited sky coverage of current interferometric instruments by enabling observations of sources anywhere in the sky.
• Extend sensitivity to fainter sources by improving wavefront sensing and fringe tracking capabilities.
• Enable high-contrast imaging to detect and characterize low-luminosity objects such as young exoplanets and circumstellar disks.
• Support precision astrometry and spectroscopy of faint, compact objects in the Galactic center to test General Relativity.
• Transform the VLTI into a fully operational, all-sky facility for faint-source science in the near-infrared.

Proposed method

• Implement wide-field off-axis fringe tracking to stabilize interferometric fringes over extended fields of view.
• Integrate new adaptive optics systems on all four Unit Telescopes to correct atmospheric turbulence across a wider sky region.
• Deploy laser guide stars to extend the accessible sky region beyond natural guide star availability.
• Upgrade the VLTI infrastructure to support real-time, high-bandwidth wavefront correction and data reduction.
• Use advanced wavefront sensing and control algorithms to maintain high-contrast imaging performance.
• Integrate new detectors and backend systems to improve sensitivity and spectral resolution in the K-band.

Experimental results

Research questions

• RQ1 Can wide-field off-axis fringe tracking enable stable, high-precision interferometric measurements across the entire sky?
• RQ2 To what extent can laser guide stars extend the accessible sky region for high-contrast observations?
• RQ3 How much does the addition of advanced adaptive optics improve sensitivity to faint sources in the Galactic center?
• RQ4 Can GRAVITY+ achieve sufficient contrast to resolve and characterize young exoplanets around faint stars?
• RQ5 What improvements in astrometric and spectroscopic precision are achievable for testing General Relativity with stars near Sgr A*?

Key findings

• GRAVITY+ will extend the sky coverage of the VLTI to nearly all celestial sources, overcoming the limitations of on-axis guide stars.
• The integration of laser guide stars and off-axis fringe tracking will allow observations of faint targets in regions previously inaccessible to interferometry.
• Enhanced adaptive optics on all Unit Telescopes will significantly improve wavefront correction and sensitivity, especially for faint sources.
• The upgrade will enable high-contrast imaging of young exoplanets with contrast levels suitable for detecting circumplanetary disks and protoplanetary structures.
• The instrument will achieve sub-milliarcsecond astrometry and high-precision radial velocity measurements, crucial for black hole mass measurements in active galactic nuclei.
• The project is expected to enable the detection and characterization of dozens of young exoplanets and hundreds of AGN black hole masses across cosmic time.