NRC crafts a new brain for the ALMA telescope

- Ottawa, Ontario

The world's largest radio telescope, the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile's high desert, is about to get a new brain.

Over the next 5 years, the Herzberg Astronomy and Astrophysics Research Centre at the National Research Council of Canada (NRC) will be working with the U.S. National Science Foundation (NSF) National Radio Astronomy Observatory (NRAO), Massachusetts Institute of Technology (MIT) Haystack Observatory and a Canadian industry partner to upgrade ALMA's "brain"―its central correlator. This essential system combines data from the telescope's 66 massive radio antennas to produce high-resolution images of dust and gas that form the building blocks of galaxies, stars, planets and even life itself.

ALMA's board of directors has just approved the NRC, NRAO and MIT Haystack Observatory plan for the first major upgrade to the central correlator since the telescope array first started observing in 2011. A substantial portion of the US$33 million budget for this will go to Canadian industry to build and program the hardware.

The new correlator is a critical part of a larger initiative, the US$100 million ALMA2030 Roadmap Wideband Sensitivity Upgrade (WSU). Today, ALMA's correlators are among the world's fastest supercomputers. Over the next 10 years, the upgrade will double and eventually quadruple their overall observing speed. In some cases, the upgraded central correlator will speed observations by a factor of 52.

The project will improve the sensitivity, flexibility and efficiency of the telescope while costing only a fraction of the US$1 billion originally invested in the instrument. This amazing improvement builds on decades of digital research and development at the NRC―today one of the world's leading correlator groups.

"The ability to do spectral scans efficiently at such high resolution is unprecedented and will keep ALMA at the forefront of scientific discovery," says Luc Simard, Director General of the NRC's Herzberg Astronomy and Astrophysics Research Centre.

A close up of the TALON-DX signal processing board, which has the NRC-CNRC Canada logo engraved on one corner.

The TALON-DX signal processing board, a critical part of the correlator and beamformer in a radio telescope, which makes data accessible to astronomers.

Upgrading the correlator, also known as the ALMA TALON Central Signal Processor (AT.CSP), is a collaborative effort, with the NRC leading the hardware and firmware development, NRAO leading the software work and the MIT Haystack Observatory providing development to allow the correlator to produce data for Very Long Baseline Interferometry (VLBI). This technique allows global networks of telescopes to operate together to produce measurements with an angular resolution equivalent to an Earth-sized telescope.

"AT.CSP, coupled with ALMA's wideband upgrade, will provide a significant boost to the sensitivity and flexibility of ALMA's VLBI capabilities. We are very much looking forward to the exciting new opportunities for ultra-high-resolution science this will enable for the study of objects like black holes, distant galaxies and dying stars, right within our local Universe," says Lynn Matthews, MIT Haystack Principal Research Scientist.

Collaborations drive frontier research

In its first decade of operation, ALMA worked to unveil the mysteries of planet formation, protoplanetary disks―rotating discs of dense gas and dust surrounding a newly formed star―and the unseen gas and dust that drive the formation of cosmic objects. During that time, the NRC contributed Band 3 receiver cartridges, used for ALMA commissioning and calibration and for a wide variety of science observations. The NRC also constructed a correlator for the NSF's Karl G. Jansky Very Large Array (VLA), the world's largest centimetre-wave radio telescope at the time. The next decade will see several upgrades under the WSU initiative. The first 2 projects will be the Second Generation ALMA Correlator and the Digital Transmission System (DTS).

"The Second Generation ALMA Correlator will allow vastly more instantaneous spectral information from radio sources to be imaged, increasing the number of spectral channels from 32,000 to 600,000," says Brent Carlson, the NRC's Principal Investigator for the correlator project. "This will virtually drown scientists in data for the foreseeable future."

The DTS is a collaboration between the National Astronomy Observatory of Japan (NAOJ) and NRAO. It will act as an expanded information highway, increasing the amount of data that can travel from ALMA's upgraded receivers to the new correlator.

The central correlator and DTS are expected to be ready for on-sky testing by 2026. In addition, upon completion, ALMA2030 will realize upgrades to the Operations Support Facility, systems and support, and receivers. These and other components provided by NRAO, the European Southern Observatory (ESO) and NAOJ will ensure that the ALMA telescope continues to lead frontier research for decades to come.

"Our longstanding working partnership with the NRC has not only helped to keep ALMA in the forefront of radio astronomy, but also to provide scientists with critical research resources," says Crystal Brogan, ALMA-North America Program Scientist and ALMA Development Program Coordinator at NRAO. "Its new central correlator will allow astronomers around the world to probe the origins of the most distant galaxies, the emergence of chemical complexity in the Universe, and the formation of planets with unprecedented detail."

NRC's experience with correlators shines through

Among its countless contributions to astronomy and astrophysics, the NRC has a long history of developing digital correlators for radio astronomy.

The first were correlators for telescopes at the NRC's observatory in Penticton, British Columbia, starting in the early 1970s. In the 1990s, the NRC began developing correlators for international radio telescopes, including the S2 correlator for the Japanese-led space radio telescope, the VLBI Space Observatory Programme (VSOP). Others included the Auto Correlation Spectral Imaging System (ACSIS) correlator for the James Clerk Maxwell Telescope and the correlator for the Jansky Very Large Array (JVLA) in the 2000s.

Over the past decade, the NRC and a Canadian industry partner led the SKAO Central Signal Processor consortium and developed a correlator design for the SKA mid-frequency telescope that became the foundation of the ALMA correlator design. The JVLA and ALMA radio array interferometers, or measurement instruments, are world-leading science facilities, and the NRC is providing correlators for both these systems. The NRC has firmly established key intellectual leadership in correlator signal processing and development, transferring this knowledge to Canadian industry for application in related areas.

In January 2023, Canada announced its intention to proceed to full membership in the international SKAO radio astronomy observatory. The Herzberg Astronomy and Astrophysics Research Centre at the NRC will represent Canada in the governance of the SKAO and will work with domestic and international partners to deliver key observatory systems.

ALMA is a vital component of worldwide VLBI networks, including the Global Millimeter VLBI Array (GMVA) and the Event Horizon Telescope (EHT). VLBI combines the sensitivity of other telescopes around the world to produce the sharpest images ever made. In 2019, for example, ALMA made history by enabling the EHT to produce the famous image of a black hole containing 6.5 billion solar masses in the nearby Messier 87 galaxy. The AT.CSP coupled with the WSU upgrade will provide another significant boost to the sensitivity and flexibility of ALMA's VLBI capabilities.

A black hole inside an orange, glowing, circular mass.

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