ALMA telescope achieves highest resolution observations to date

Using a new calibration method, astronomers have achieved the highest-resolution observations ever with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

During a technical test, a team of experts from the Joint ALMA Observatory (JAO), the National Astronomical Observatory of Japan (NAOJ), the National Radio Astronomy Observatory (NRAO) in the USA, and the European Southern Observatory (ESO) imaged an evolved star with a resolution of 5 milliarcseconds - equivalent to seeing a 10-metre-long bus on the Moon.

ALMA comprises 66 high-precision antennas, each equipped with receivers that allow it to observe radio waves in different frequency ranges or bands. As the maximum separation between antennas increases and as the frequency of the observations increases, ALMA's resolution also increases.

The new images were obtained with a maximum separation between its antennas of 16 km. They were made using the Band 10 receivers, which allow the telescope to observe at frequencies as high as 950 GHz - the highest possible for the array.

The novel calibration technique used to conduct the new observations is referred to as the band-to-band method. In this method, atmospheric fluctuations are compensated for by observing a nearby calibrator in low-frequency radio waves, while the target is observed with high-frequency radio waves.

During a technical test in 2021, the researchers observed R Leporis - a star in the final stages of its evolution in the Milky Way - using a bright galactic core as a calibrator, which, while distant, appears nearby the star in the sky.

Time to celebrate for @almaobs ! 🥳 🎉In a test that imaged the evolved Milky Way star R Leporis, ALMA — in which ESO is a partner — achieved the sharpest observations since it began operations. 1/More info: https://t.co/YBpOilrlQu📷 ALMA (ESO/NAOJ/NRAO)/Y. Asaki et al. pic.twitter.com/8sHm5jVmGZ

— ESO (@ESO) November 15, 2023