Event Horizon Telescope (Episode 2: Challenges EHT face)

Lectures (Video)

Main Content

Advantages EHT has

• Extremely High Resolution
  • Very Long Baseline Interferometry
    • The EHT used a technique called Very Long Baseline Interferometry (VLBI) to achieve resolutions on the order of 20 microarcseconds, or about 2.78 x 10^(-10) degrees.
  • Short Wavelengths
    • By utilizing short wavelengths of around 1.3 mm, the EHT was able to take advantage of the inverse relationship between wavelength and angular resolution.
  • Global Telescope Network
    • Careful integration of data from a network of VLBI telescopes around the world was critical to satisfying the need for such high-resolution imaging.

Challenges EHT face

• Synchronizing Telescopes Worldwide
  • Atomic Clock Alignment
    • With telescopes scattered across the globe, up to 10,000 km apart, the EHT team had to carefully align atomic clocks using GPS to within picoseconds (10^-12 seconds).
  • Precision Measurement
    • This level of accuracy was necessary to ensure that the light-travel time differences between the telescopes were measured to within a millimeter.
  • Simultaneous Observations
    • Achieving this level of synchronization was critical for the telescopes to capture the same celestial event simultaneously, enabling the formation of a high-resolution image.
• Overcoming Atmospheric Opacity
  • Atmospheric Challenges
    • The 1.3 mm wavelength used by the EHT is susceptible to degradation by atmospheric water vapor, which can cause opacity and degrade image quality.
  • Site Selection
    • To minimize the impact of weather, the EHT team carefully selected observational sites that maximized the number of clear weather periods for simultaneous image capture.
  • Intricate Data Handling
    • The EHT had to devise intricate methods for transporting and processing the large volumes of data generated by the observations, including shipping data physically via plane or ship.
• Analyzing Petabytes of Data
  • Data Transport Challenges
    • The EHT observations generated about a petabyte of data, which had to be transported physically due to internet bandwidth limitations.
  • Computational Complexity
    • Analyzing such large volumes of data required advanced algorithms and powerful hardware to process the varied and time-variable signals from targets like Sagittarius A*.
  • Collaborative Effort
    • The EHT project involved a global team of scientists and engineers working together to overcome these immense technical challenges and produce the first-ever image of a black hole.