Event horizon telescope captures the highest-resolution black hole images from Earth

In a groundbreaking achievement, the Event Horizon Telescope (EHT) Collaboration has conducted the highest-resolution observations ever achieved from Earth, detecting light at 345 GHz from the centers of distant galaxies. This milestone marks the first time that the EHT has successfully imaged black hole environments at this frequency, allowing researchers to observe cosmic phenomena with unprecedented detail.

By utilizing very long baseline interferometry (VLBI), a technique that combines multiple telescopes around the globe to create a “virtual” Earth-sized telescope, the EHT is now capturing data that promises sharper and more detailed insights into black holes and their complex surroundings.

VLBI works by linking telescopes located far apart, effectively increasing the "baseline" and thus the resolution of observations. The first fringe detections at 345 GHz—a frequency far higher than the EHT’s prior 230 GHz observations—have provided a clearer view of light bending near supermassive black holes, like those at the centers of M87 and the Milky Way’s Sagittarius A*. The angular resolution achieved through this 870-micrometer wavelength imaging is almost 50% greater than at 1.3 mm, delivering a 14 microarcsecond fringe spacing that surpasses previous observational limits.

This sharper imaging capability is especially valuable for understanding the unique behavior of black holes. When the EHT first imaged black holes in 2019, it achieved impressive results at 230 GHz but reached the limits of clarity at that wavelength. The introduction of 345 GHz observations offers a finer “color vision,” allowing scientists to differentiate between the effects of black hole gravity, the hot gas encircling these cosmic giants, and the magnetic fields launching powerful jets.

“At 345 GHz, our images will be sharper and more detailed,” said Alexander Raymond, co-lead on the paper and former researcher at the Center for Astrophysics (CfA). “This, in turn, will likely reveal new properties, both those that were previously predicted and maybe some that weren’t.”

Achieving the high resolution possible with VLBI at 345 GHz, however, presented unique challenges. Although observing single telescopes at this frequency had been feasible, adapting VLBI to 345 GHz required advances in technology. At this frequency, atmospheric water vapor absorbs radio waves much more intensely than at lower frequencies, significantly weakening signals from distant black holes.

To combat this, the EHT collaboration enhanced its bandwidth, which allowed researchers to capture wider swaths of the radio spectrum. Furthermore, researchers had to wait for near-perfect weather conditions across all telescope sites, each of which operates at high altitudes to minimize atmospheric interference.

The success of these new observations was also dependent on the quality and locations of the telescopes within the EHT array. High-altitude sites such as the Atacama Large Millimeter/submillimeter Array (ALMA) and the Submillimeter Array (SMA) in Hawaiʻi are instrumental in mitigating atmospheric opacity and ensuring stability during measurements.

“The most powerful observing locations on Earth exist at high altitudes, where atmospheric transparency and stability are optimal,” explained Nimesh Patel, an astrophysicist at CfA and SMA project engineer. Patel recounted the recent winter conditions at Maunakea, where icy roads had to be cleared minutes before opening the array to ensure data collection during brief windows of stable weather.

Expanding EHT’s capabilities to the 870-micrometer range has opened doors for several scientific advancements. In addition to clearer images, these observations provide insights into the polarized light around black holes. At higher frequencies, Faraday rotation—a phenomenon that alters the orientation of light’s electric field as it travels through a magnetized medium—becomes less pronounced, enabling a more precise view of black hole magnetic fields.

This is especially significant for understanding the magnetic environment surrounding Sagittarius A*, which is influenced by interstellar scattering that diminishes with higher frequencies. By reducing these scattering effects, the EHT can now observe structures as intricate as photon rings, which form when light orbits around the black hole’s event horizon. This is the first step toward observing these rings, an outcome expected to yield unprecedented insights into black hole dynamics.

The achievement also sets the stage for creating time-lapse “movies” of black hole environments. Since Sagittarius A* has a dynamic timescale of about 200 seconds, simultaneous observations at 1.3 mm and 870 micrometers could soon allow real-time imaging of material moving around the event horizon.

For M87*, which evolves over a longer timescale of about three days, images collected over consecutive days could be combined to form detailed time-lapse visualizations of its active surroundings. Developing such time-lapse imagery relies on future upgrades to the EHT’s global array, which includes plans for the next-generation EHT (ngEHT) project.

This ambitious endeavor aims to expand the EHT’s telescope network, adding new antennas in optimal locations worldwide to achieve coverage at multiple frequencies between 100 and 345 GHz. With these enhancements, the array will gather ten times more high-quality data, empowering scientists to capture both sharper and more detailed images.

Beyond imaging the black holes at M87 and Sagittarius A*, the enhanced 870-micrometer capabilities also allow the EHT to observe other active galactic nuclei (AGN) jets with greater precision. The finer resolution makes it possible to study jet formation and acceleration closer to black holes, as well as to investigate features like limb-brightening, which occurs in the jet's inner regions.

Janssen and colleagues, for example, noted that jets often show increased brightness near their edges, a phenomenon poorly understood due to the limited resolution of prior observations. With the new 870-micrometer capabilities, scientists can now study these and other features of AGN jets with the level of detail needed to clarify how these jets originate and propagate across galactic distances.

The ngEHT project’s advancements could also help astrophysicists build a high-fidelity “movie” of accretion and jet launching mechanisms. Multifrequency synthesis (MFS), a technique that combines data from different frequencies, will allow astronomers to map black hole environments in detail over time.

For Sagittarius A*, the MFS technique can provide a real-time glimpse into the black hole's turbulent surroundings, capturing kinematic changes near the event horizon. In the case of M87*, a longer-period dynamical timescale means that high-fidelity images collected over multiple days can be stitched together to create time-lapse footage, offering fresh insights into this supermassive black hole’s activity.

This technological leap forward represents more than just an improvement in resolution—it is a testament to the determination and collaborative spirit within the EHT project, which has transformed ground-based black hole observation. By surmounting the technical hurdles of observing at higher frequencies, the EHT has redefined the boundaries of what is possible in astrophysical research.

“The EHT’s successful observation at 345 GHz is a major scientific milestone,” said Lisa Kewley, Director of CfA and SAO. “By pushing the limits of resolution, we’re achieving the unprecedented clarity in the imaging of black holes we promised early on, and setting new and higher standards for the capability of ground-based astrophysical research.”

This step forward represents a major achievement for scientists seeking to unlock the mysteries of black holes and their dynamic environments. With the arrival of 345 GHz imaging, the EHT has ushered in a new era of astrophysical discovery that promises sharper, clearer, and more comprehensive views of the universe’s most unique entities.

Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.

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