The terms “red galaxies” and “blue galaxies” are often used in astronomy to describe the overall colour characteristics of galaxies, and they are indicative of certain physical properties of these celestial objects.

James Webb Space Telescope (JWST) identified extremely red objects (EROs) in the data. Upon analysis, these objects exhibit striking similarities to blue-excess dust-obscured galaxies (BluDOGs) previously observed in Subaru Telescope data.

Quasars, among the most luminous entities in the universe, are powered by supermassive black holes with masses exceeding a billion times that of the Sun. Despite their prominence in research, the formation mechanisms of quasars remain poorly comprehended.

The dominant hypothesis suggests that quasars originate within galaxies containing gas and dust clouds, concealing the developing quasar until it attains sufficient power to disperse the clouds.

If this hypothesis holds, it becomes crucial to capture the brief window when a quasar emerges from its shroud. Given the fleeting nature of this transition, it is imperative to observe a substantial number of potential pre-quasar candidates, relying on the hope of fortuitously capturing a galaxy precisely as the quasar initiates its breakout.

Examining data from the James Webb Space Telescope (JWST), a set of objects known as extremely red objects (EROs) emerged as potential transitional quasars.

Subsequently, researchers at the Subaru Telescope in Hawai`i noted an intriguing revelation: despite their designation as “red,” EROs exhibit a significant blue component, akin to the blue-excess dust-obscured galaxies (BluDOGs) identified in extensive data from the Subaru Telescope and detailed in a report last year.

Upon analysis, it became apparent that EROs and BluDOGs likely belong to the same category of objects, though certain noteworthy distinctions exist. One plausible explanation is that EROs represent an earlier stage in their evolutionary process compared to BluDOGs. To unravel the genuine relationship among EROs, BluDOGs, and quasars, a more extensive collection of candidates is essential. This enlarged sample is slated for examination by the upcoming generation of astronomical instruments, including the planned Japanese infrared space telescope project known as GREX-PLUS.

A general distinction between red galaxies and blue galaxies:

RED GALAXIES

Older Population: Red galaxies often contain older stellar populations, composed mostly of older stars. These stars have lower temperatures, and their light tends to be more in the red part of the spectrum.

Elliptical Shape: Many red galaxies have an elliptical or spheroidal shape. These shapes are associated with galaxies that have undergone significant mergers or interactions, leading to the redistribution of stellar material.

Low Star Formation: Red galaxies typically exhibit lower rates of ongoing star formation. The majority of their stars formed earlier in the universe’s history.

BLUE GALAXIES

Younger Population: Blue galaxies, on the other hand, often have a higher proportion of younger, hotter stars. These stars emit more blue light, giving the overall galaxy a bluish appearance.

Spiral or Irregular Shape: Blue galaxies are more likely to have a spiral or irregular shape. These shapes suggest ongoing star formation, with material organized in spiral arms or irregular patterns.

Active Star Formation: Blue galaxies tend to have higher rates of current star formation. They may contain regions of intense starburst activity, where new stars are forming at a rapid pace.

The colour of a galaxy provides astronomers with valuable information about its age, composition, and evolutionary history. Observations in different wavelength bands, beyond just the visible light spectrum, help astronomers to further understand the properties of galaxies.

In conclusion, the distinct characteristics of red and blue galaxies, reflecting their age, composition, and evolutionary stage, are discerned through various observational methods. Advanced telescopes such as JWST and Subaru, with their capabilities to capture diverse wavelength ranges, play a crucial role in unraveling the intricate details of these galaxies, ultimately enhancing our understanding of the cosmic tapestry.