Can We Make Black Holes Reveal Themselves in Echoes Of Light ?

Relevance: GS – 3 : Science and Technology – developments

Why in the News?

  • Researchers have introduced a new method to study black holes based on their effects on the light flowing around them.
  • The study was published on November 7 in Astrophysical Journal Letters.
  • The research was conducted by astrophysicists from the Institute for Advanced Study in Princeton, New Jersey.
  • George Wong, from the School of Natural Sciences at Princeton University, led the study.
  • The method enables the measurement of black hole properties through light behavior influenced by these massive objects.

Importance of Black Holes

  • Black holes play a critical role in understanding the universe.
  • Their immense gravitational pull traps any object crossing a certain threshold (event horizon).
  • Black holes release enormous energy, impacting the structure of galaxies and the evolution of surrounding stars.

Interaction of Light with Black Holes

  • Light bends when it passes near a massive object like a black hole.
  • Some light takes a direct path to the observer, while other parts loop around the black hole before reaching the same destination.
  • Light from distant sources may arrive on Earth at different times due to these interactions, creating “light echoes.”
  • When two beams of light emitted by the same source reach the earth at different points, the beam to arrive second will be an echo of the beam that arrived first. This phenomenon is thus called a light echo.
  • A light echo occurs when a second beam of light reaches Earth later, mirroring the first.

Can Black Holes Reveal Themselves in Light Echoes?

Measuring Black Hole Properties with Light Echoes

  • The extent and manner in which light circles a black hole depend on the black hole’s:
    • Mass
    • Radius
    • Angular momentum (in the case of spinning Kerr black holes).
  • Scientists can use light echoes as an independent method to determine a black hole’s mass and spin.

Advantages of Light Echo Method

  • Measuring mass and spin is usually challenging due to interference from matter, hot gases, and radiation around black holes.
  • Light is less affected by these factors, offering a clearer signal.
  • Light echoes provide a better signal-to-noise ratio, simplifying the measurement process.

Gravitational Lensing and Light Echoes

  • Any object that bends light is referred to as a lens.
  • Black holes act as gravitational lenses due to their immense gravity, bending light around them.
  • Gravitational lensing can create light echoes, a phenomenon theorized long ago but not directly observed yet.

Proposed Technique: Long-Baseline Interferometry

  • The study suggests using long-baseline interferometry to detect light echoes.
  • This technique relies on the interference created by the non-simultaneous arrival of two light beams, generating a unique signal.
  • Observations could be conducted using one telescope on Earth and another in space.
  • Despite the modest number of instruments, the technique requires extremely precise technical execution.

Motivation for the Study

  • Supermassive black holes in the Milky Way and the nearby M87 galaxy exhibit bright rings of light at 230 GHz frequencies.
  • These rings are shaped by astrophysical forces and the spacetime geometry surrounding black holes.
  • Scientists aim to study these rings in detail using very long baseline interferometry.
  • One goal is to trace the shadow of black holes on these rings to gain insights into the spacetime geometry around them.

Independent of Colour

Focus of the Study

  • The study primarily analyzed the supermassive black hole at the center of the M87 galaxy, a prominent target due to its large apparent size.
  • The findings are applicable to other black holes as well.

Long-Baseline Interferometry

  • The “baseline” in long-baseline interferometry refers to the distance between two telescopes collecting the light.
  • The required baseline should be at least 40 Gλ, where Gλ measures the telescopes’ capacity to collect signals at specific frequencies.

Testing the Technique

  • The Princeton team conducted high-resolution simulations using data from the Event Horizon Telescope.
  • They generated thousands of instantaneous images of light around the M87 black hole, approximately 55 million light-years away.
  • By calculating the time taken for light beams to travel from one side of the black hole to the other, the team linked the delay to the black hole’s mass, angular momentum, and viewing angle.
  • From the simulated data, they inferred the echo delay, supporting the feasibility of their method.

Achromatic Light Echoes and General Relativity

  • According to Einstein’s general theory of relativity, light echoes are expected to be achromatic, meaning they occur independently of light’s frequency.
  • However, since Gλ is inversely proportional to frequency, designing a telescope to detect echoes across multiple frequencies presents technical challenges.
  • Successfully detecting light echoes at various frequencies would validate the new method and offer further confirmation of general relativity’s accuracy in describing black holes.

Associate articles

https://universalinstitutions.com/black-holes-in-webb-implications-for-cosmology/

https://universalinstitutions.com/earth-wide-telescope-confirms-black-holes-shadow-is-real/

Source: https://www.thehindu.com/sci-tech/science/can-we-make-black-holes-reveal-themselves-in-echoes-of-light/article68981587.ece

Mains question

Discuss the phenomenon of light echoes around black holes and their potential role in advancing our understanding of black hole properties. (250 words)