Evrim Yazgin
Cosmos science journalist
A galaxy very similar to our Milky Way home has been found confounding astronomers with its location and age.
About a billion years after the Big Bang, things settled in the universe. It hasn’t changed much since then. But before this period, when the universe was still young, things were much more turbulent. At least that’s what we thought.
Galaxies are a case in point. About 50–80% of galaxies within 7 billion light-years or so of Earth are fairly ordered structures like our Milky Way. This order is most easily seen in the fact that they have a rotating disc shape.
When the universe was young, such order shouldn’t exist in galaxies.
Yet that’s exactly what new observations detailed in a paper published in the Monthly Notices of the Royal Astronomical Society show.
The galaxy in question is dubbed REBELS-25. It is at a red shift of z=7.31, which means that it is from a time when the universe was only 700 million years old. The earliest galaxies ever seen are only a few hundred million years older.
REBELS by name rebel by nature. This odd galaxy has stumped astronomers because it shows evidence of an ordered structure and rotation. It may even have a central elongated bar and spiral arms, though further observation is needed to confirm these structures.
This is in contrast to the small, messy, lumpy and chaotic norm for galaxies of a similar age.
“According to our understanding of galaxy formation, we expect most early galaxies to be small and messy looking,” says co-author Jacqueline Hodge, an astronomer at Leiden University in the Netherlands.
Current theories suggest that structures like the rotating disc and spiral arms of galaxies like the Milky Way should take billions of years to form.
“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,” says first author Lucie Rowland, a doctoral student at Leiden University.
The galaxy was detected and probed by the Atacama Large Millimeter/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner.
“ALMA is the only telescope in existence with the sensitivity and resolution to achieve this,” adds co-author Renske Smit, a researcher at Liverpool John Moores University in the UK.
