Record-breaking primeval spinning galaxy contests cosmic evolution theories

The most faraway and thus earliest rotating disk galaxy ever speckled has surprised astrophysicists and could in fact challenge our theories of galactic evolution. Not only does it ostensibly exist too early in the universe to be sturdily spinning, the galaxy also shows hints of spiral arms akin to extremely evolved “modern” galaxies like our own Milky Way. The galaxy, termed REBELS-25, is seen as it was just 700 million years post the Big Bang, at a time when astrophysicists expect galaxies to have been small and messy. Living up to its name, this defiant galaxy has rebelled against that trend by looking orderly rather than chaotic.

REBELS-25 was discovered by a team of astrophysicists employing the Atacama Large Millimeter/submillimeter Array (ALMA), a network of 66 radio telescopes placed in the Atacama Desert region of Northern Chile.

“According to our understanding of galaxy formation, we expect most early galaxies to be small and messy-looking,” said team member Jacqueline Hodge (an astronomer at Leiden University in the Netherlands), in a statement.

A tidy young rebel

Modern galaxies like the Milky Way in the 13.8-billion-year-old cosmos have had billions of years to develop distinctive characteristics and shapes, such as striking spiral arms. In the early cosmos, before this time to organize actually became available, astrophysicists expect to see messy and clumpy galaxies. These early galaxies are likely to have developed the shape of contemporary galaxies over the course of billions of years as they engaged in a succession of mergers and collisions, developing features like disk shapes and spiral arms very slowly. The discovery of REBELS-25, when the cosmos was just 5% of its present age, throws that timescale into real doubt.

“Seeing a galaxy with such similarities to our own Milky Way, that is strongly rotation-dominated, challenges our understanding of how quickly galaxies in the early universe evolve into the orderly galaxies of today’s cosmos,” said study team leader Lucie Rowland (Leiden University), in the same statement.

When astronomers first exposed REBELS-25 with ALMA, the galaxy was already considered interesting because it showed signs of rotation. But, this initial investigation wasn’t high-enough resolution to confirm that this is undeniably the most distant, sturdily rotating galaxy ever seen.

To bare the structure and motion of this early galaxy more precisely, the team kept on studying it with ALMA, but this time at a higher resolution. This exhibited gas in REBELS-25 moving both toward and away from Earth. This is possible owing to a phenomenon called blueshift and redshift.

When a light source is moving in the direction of Earth, the wavelength of this light is compressed. This “shifts” the light toward the short-wavelength “blue end” of the electromagnetic spectrum. Thus, a light source moving toward us is “blueshifted.” On the other hand, if a light source is moving away from us, the wavelength of the light it emanates is stretched, shifting it toward the “red end” of the electromagnetic spectrum.

The new study established that REBELS-25 is a record-breaking galaxy, the earliest and most faraway, strongly rotating galaxy ever seen. “ALMA is the only telescope in existence with the sensitivity and resolution to achieve this,” said team member Renske Smit (Liverpool John Moores University in England), in the same statement.