Galaxies from the Depths: Light from the Primordial Universe

Distant Galaxies

Galaxies (massive systems of stars, gas, and dark matter) from the depths of the universe are direct witnesses to the primordial universe. Observing them allows us to reconstruct the formation of the first structures and cosmic evolution over billions of years.

The study of distant galaxies relies on instruments sensitive to different wavelengths, from visible to infrared. Space telescopes such as the Hubble Space Telescope (1990–present) and the James Webb Space Telescope (2021–present) provide deep images of the sky.

Key methods include spectroscopy (measurement of the spectral shift of emission lines) to determine the redshift (measurement of cosmological redshift) of galaxies, and multi-band photometry to estimate their mass, age, and star formation activity.

High-Redshift Galaxies

Galaxies with a high redshift (>6) are seen as they were less than a billion years after the Big Bang. Their study helps us understand:

• cosmic reionization (process by which the universe becomes transparent to ultraviolet photons),
• the formation of the first massive stars,
• the gradual accumulation of dark matter (hypothetical invisible matter with gravitational influence) in galactic halos.

N.B.:
The redshift z corresponds to a measurement of spectral shift and allows estimating cosmological distance using the formula \( d \approx \frac{c}{H_0} \times z \) for low values of z, where c is the speed of light and \(H_0\) is the Hubble constant.

Comparison of Nearby and Distant Galaxies