A Curious Galaxy That Is Very Young But Looks Very Old Is Puzzling Astronomers

A picture of ALESS 073.1 just 1.2 billion years after the Big Bang. Image Credit: Cardiff University

Astronomers have found a galaxy that is challenging our theories of how galaxies form and evolve. The light from ALESS 073.1 comes to us all the way from just 1.2 billion years after the Big Bang, which actually makes it a young galaxy, only it doesn’t look like one. Observations show a mature and established galaxy, an unexpected and baffling discovery.

In the new study published in Science, astronomers took one of the sharpest direct images of a primordial galaxy ever produced, allowing them to study the galaxy in detail. ALESS 073.1 has a well established and massive core of stars at its center, a so-called bulge, and a uniformly rotating disk of stars around it. These are features are expected to take billions of years to form.

"We discovered that a massive bulge, a regular rotating disk, and possibly spiral arms were already in place in this galaxy when the Universe was just 10% of its current age," lead author Dr Federico Lelli from Cardiff University said in a statement. "In other words, this galaxy looks like a grown adult, but it should be just a little child. A galaxy like ALESS 073.1 just defies our understanding of galaxy formation."

The whole process of galaxy formation must be more rapid than previously thought to explain how ALESS 073.1 can look the way it does. Researchers recently reported the discovery of a young galaxy with a rotating disk in the early universe, which is something that has begun challenging the current models. But the massive bulge is an extra surprise. The bulge – a tightly packed group of stars – is a feature usually expected to have grown over a long period of time thanks to repeated galaxy mergers or by processes internal to the galaxy. Either option will have to have been very rapid. Half of all the stars in ALESS 073.1 are located in the bulge.

"This spectacular discovery challenges our current understanding of how galaxies form because we believed these features only arose in "mature" galaxies, not in young ones," said co-author Dr Timothy Davis, also from Cardiff University.

The exquisite resolution of the observations was due to the Atacama Large Millimeter/submillimeter Array (ALMA). The observatory looks at wavelengths beyond the visible and can study some of the most distant objects we have ever discovered.

To truly understand how galaxies evolve we need more eyes on the distant and early universe. Luckily these should be forthcoming in the next decade. Future observatories such as the Extremely Large Telescope and the James Webb Space Telescope will hopefully be able to add more insights on this particularly weird object and perhaps even find more.

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