The conventional wisdom in astronomy classifies red galaxies as “dead” zones, incapable of birthing new stars. This classification stems from the understanding that massive, short-lived blue or white stars expire over time, leaving behind a population dominated by long-lived, low-mass red stars, thus imparting a reddish hue to the galaxy. However, recent research is challenging this long-held belief.

A New Perspective on Star Formation

Emerging evidence suggests that some red galaxies are, in fact, still actively forming stars. The caveat? These galaxies primarily produce low-mass, red stars. This discovery throws a wrench into the gears of current galaxy evolution theory, prompting a reevaluation of how galaxies are categorized and understood.

The Hubble Space Telescope captures both blue and red galaxies. (Source: ESA / Hubble & NASA, J. Dalcanton, Dark Energy Survey / DOE / FNAL / DECam / CTIO / NOIRLab / NSF / AURA Acknowledgement: L. Shatz)

Challenging Customary Classifications

According to the research team, these “red star-forming galaxies” defy the traditional binary classification of galaxies as either “blue, young, active” or “red, old, inactive.” They propose the addition of a third category to account for this enigmatic group. These galaxies appear red not because star formation has ceased, but because they predominantly give birth to low-mass stars with cooler surface temperatures, resulting in a reddish overall appearance.

The Antennae galaxies, a starburst galaxy formed by the merger of NGC 4038 and NGC 4039. (Source: NASA/ESA)

Implications for Understanding the Early Universe

This discovery suggests that star formation and evolution in the early universe might potentially be more intricate than previously understood. It also hints that the number of stars in the universe may have been underestimated. Astronomers have historically viewed galaxy evolution as a linear progression: from vibrant blue galaxies to eventual red galaxies through aging or mergers. The team’s findings indicate that some galaxies may follow an option evolutionary path,characterized by the slow but steady production of new,low-mass red stars.

The results of this study have profound implications and may allow astronomers to reevaluate the timing and scale of the evolution of cosmic star formation.

The team plans to validate this new classification. One group will focus on identifying the characteristics of red star-forming galaxies, while another will analyze data from over 2 billion Milky Way stars collected by the Gaia satellite to study the formation, evolution, and distribution patterns of these galaxies.

A Paradigm Shift in Galaxy Classification

If confirmed, this research could trigger significant revisions to the galaxy classification system, deepening our understanding of the conditions that fostered star formation in the early universe. The evolution of galaxies may not be a simple transition from blue to red, but rather a diverse and complex cosmic narrative.

The evolution process of galaxies is no longer just a single mode from blue to red, but a cosmic evolution image with diversity and complexity.