Why Event Horizon Telescope Overwhelmed James Webb in Seeing Black Holes

For many, the dream of directly imaging a black hole seemed almost impossible until the Event Horizon Telescope (EHT) project brought us unprecedented images of the supermassive black hole in the center of Messier 87 (M87). However, the success of the EHT was not simply due to advanced computational techniques or timing of observations; the critical difference in capability lies in the sheer size of the telescopes used. This article delves into why a huge telescope like the EHT was necessary to observe a black hole, in contrast to the James Webb Space Telescope (JWST).

Understanding the Scale: Why Size Matters

The question often raised is, if the James Webb Space Telescope (JWST) has a much larger mirror and advanced technology, why couldn't it achieve similar images of a black hole? The answer lies in the fundamental nature of telescopes and the characteristics of black holes.

The Role of Aperture: Larger Mirror, Sharper Resolution
A critical factor in the resolution of a telescope is its aperture or the diameter of its primary mirror. The larger the aperture, the more light a telescope can collect and the finer the details it can resolve. The JWST boasts a primary mirror with a diameter of 6.5 meters. In comparison, the EHT, which is a global array of radio telescopes, has an effective aperture over 10,000,000 meters. This vast difference in size means that the EHT can capture much finer details, including the event horizon of a black hole.

While the JWST is optimized for capturing light in the infrared, optical, and near-ultraviolet regions of the electromagnetic spectrum, these wavelengths are not suitable for directly observing a black hole. Black holes are, for practical purposes, black due to their intense gravitational pull, which stops light from escaping. What we observe around a black hole is the accretion disk and other phenomena, not the black hole itself, but these are still details that require extremely high resolution.

Fundamental Limitations: Observable Phenomena and Wavelength

Fundamental Observable Phenomena
The phenomena observable around a black hole, such as the accretion disk, jets, and other high-energy emissions, are what make a black hole detectable. For instance, the supermassive black hole in M87 was first detected due to its intense X-ray emissions, a feat that neither the JWST nor even the Hubble Space Telescope can do alone.

Limitations of the James Webb Space Telescope
While the JWST is one of the most advanced telescopes ever built, its primary focus is on long-wavelength infrared light. This means it is highly effective in studying very distant galaxies, exoplanets, and the early universe. It cannot detect the types of short-wavelength phenomena that provide the most visual evidence of a black hole's presence, such as the accretion disk and the plasma jets emanating from it.

Historical Context and Future Prospects

The Case of Cygnus X-1
Before the advent of the Hubble or even the James Webb, Cygnus X-1 provided strong evidence for the existence of black holes. X-ray observations by satellites and early telescopes confirmed that this object exhibited all the characteristics of a black hole, including mass and behavior, without needing to directly image the black hole itself.

Imaging Capabilities and Future Projects
The success of the EHT in imaging a black hole is groundbreaking, but it doesn’t mean that more advanced instruments like the James Webb won't contribute to our understanding of the universe. The James Webb Space Telescope is set to observe distant galaxies and study exoplanets, while other future projects, such as the planned starshade mission, aim to directly image exoplanets and analyze their atmospheres. Each telescope serves its unique purpose and none can replace the roles of others.

Understanding the limitations and strengths of each telescope is crucial for advancing our knowledge in astrophysics. Whether it’s through the direct imaging by the Event Horizon Telescope or through the detailed observations of the James Webb Space Telescope, both technologies are essential for exploring the mysteries of the universe.