March 1, 2024

Lukmaan IAS

A Blog for IAS Examination




THE CONTEXT: Astronomers have identified the object AzTECC71 as a dusty star-forming galaxy, which has reappeared as a faint yet distinct galaxy in an image from the James Webb Space Telescope (JWST).


  • This ghostly object was first detected as a glowing blob from ground-based telescopes, then vanished in images from the Hubble Space Telescope, and has now reappeared in the JWST image.
  • The galaxy is shrouded in a dusty veil, making it hard to see through, and is located nearly 1 billion years after the Big Bang.

Significance of the Discovery:

  • The reemergence of this ghostlike galaxy is significant as it sheds light on the presence of heavily dust-obscured, hidden populations of galaxies in the early universe.
  • The discovery challenges the previous notion that such galaxies were extremely rare in the early universe.
  • The findings suggest that these galaxies might be three to 10 times as common as expected, indicating that the early universe was much dustier than previously thought.

The COSMOS-Web Project:

  • The COSMOS-Web collaboration, co-led by an associate professor at UT Austin, aims to map up to 1 million galaxies from a part of the sky the size of three full moons.
  • The project received 250 hours of observing time in JWST’s first year and has been studying the earliest structures of the universe.
  • The team has identified more than a dozen additional candidates in the first half of COSMOS-Web data that have yet to be described in the scientific literature.

Characteristics of Dusty Star-Forming Galaxies

  • Dusty star-forming galaxies are hard to see in optical light because much of the light from their stars is absorbed by a veil of dust and then re-emitted at redder wavelengths.
  • Before JWST, astronomers sometimes referred to them as “Hubble-dark galaxies,” in reference to the previously most-sensitive space telescope.
  • The JWST’s sensitivity allows it to study the optical and infrared properties of these heavily dust-obscured galaxies, providing new insights into their nature and evolution.

Observations and Findings

  • The galaxy AzTECC71 was first detected as an indistinct blob of dust emission by a camera on the James Clerk Maxwell Telescope in Hawaii.
  • The COSMOS-Web team later spotted the object in data collected by another team using the ALMA telescope in Chile, which has higher spatial resolution and can see in the infrared.
  • When they looked in the JWST data in the infrared at a wavelength of 4.44 microns, they found a faint galaxy in exactly the same place.
  • In shorter wavelengths of light, below 2.7 microns, it was invisible.
  • The team estimates that the galaxy is being viewed at a redshift of about 6, which translates to about 900 million years after the Big Bang.


  • The reemergence of the ghostlike dusty galaxy AzTECC71 in the JWST image provides valuable insights into the prevalence of heavily dust-obscured galaxies in the early universe.
  • The discovery has the potential to reshape our understanding of the early universe and the history of galaxy evolution.


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