An Earth-sized telescope: the new frontier in astronomical observation
Imagine being able to observe the universe with never before seen clarity! Astronomers around the world achieved this using a technique allowing them to obtain the highest possible resolution, opening a new window to explore the mysteries of the cosmos.
In October 2018, telescopes located in Chile, Hawaii and Spain worked together to observe several astronomical sources. These intercontinental observations achieved unparalleled resolution, comparable to viewing a coin from thousands of kilometres away.
The stability and sensitivity of the Event Horizon Telescopes (EHT) were key to this success. Why is this new capability so important? Being able to observe at higher frequencies allows scientists to study black holes in unprecedented detail.This includes the ability to see the event horizon, the “boundaries” of black holes, both in space and time. It's like having a super-powerful magnifying glass to examine these fascinating cosmic objects.
This achievement is not only a technical milestone, but a revolution in our understanding of the universe. With future improvements, astronomers will be able to unravel even more secrets about black holes and other astronomical phenomena, bringing us one step closer to understanding the mysteries of the cosmos.
Telescopes united by the World
Very long base interferometry (VLBI) is a fascinating technique in astronomy that uses a network of independent telescopes, separated by large distances, to simultaneously observe the same astronomical source.
Recently, the first detections of interference were achieved at a wavelength of 870 μm (frequency 345 GHz), marking the lowest wavelength (and highest frequency) VLBI observation to date.
This experiment, carried out with the Event Horizon Telescope (EHT), demonstrated the technical capacity of VLBI since this technique allows obtaining extremely high angular resolution, which improves with the distance between the telescopes and the observation frequency.
The observation wavelength in VLBI has decreased over time. From 3 mm (86 GHz) in 1981 to the first successful observation at 1.3 mm (230 GHz) in 1989. Advances that reflect the technical challenges of making observations at increasingly shorter wavelengths.
What is interferometry
The use of larger telescopes and advanced receivers enabled detections in multiple active galactic nuclei (AGN) and in Sagittarius A* (Sgr A*), the supermassive black hole at the centre of our galaxy.
These advances in the VLBI technique open new possibilities for observing astronomical phenomena with unprecedented precision, allowing scientists to explore the universe in greater detail.
The EHT being the highest resolution terrestrial instrument to date, has developed the ability to observe at 900 microns, which is an important aspect for the next generation of EHT (ngEHT). Imaging event horizon-scale structures in Sgr A* and the M87* black hole.
Observing at these longitudes improves angular resolution by about 50% compared to previous observations, providing a sharper view of the black hole's shadow and its surroundings.
How telescopes are synchronized
Network synchronization in very long base interferometry (VLBI) is crucial for obtaining accurate and consistent data from astronomical observations. Each telescope in a VLBI network operates independently, but all must be perfectly synchronized in time.
Precise timing is essential because even a small discrepancy in timing can result in significant errors in the data obtained. This is achieved using atomic clocks with nanosecond precision.
Errors can arise due to atmospheric and instrumental fluctuations. To correct these errors, a technique called “phase closure” is used, which involves adding the differences between the telescopes, which helps cancel out the errors and improve the precision of the observations.
After successful observations in 2017, tests were conducted in 2018 that included characterization of the system used at the ALMA station to synchronize the network for VLBI.
EHT infrastructure and technology
The EHT, conceived as a common international effort of independent observatories working in the short millimeter range, has directly addressed these challenges and provides key infrastructure for the extension of VLBI to higher frequencies.
The telescopes that make up the EHT network are precision structures located in high altitude and low opacity locations. The cutting-edge instrumentation supporting the operation of these telescopes includes cryogenic receivers and broadband digital systems, to optimize performance.
Tests on different telescopes, including synchronization of network systems, have been successfully tested in recent studies reported in EHT research articles.
These advances in the technology and infrastructure of the world's largest telescope make it possible to overcome the challenges of observation, opening new possibilities for exploring the universe with unprecedented precision.