The early universe was bananas

What does a newborn galaxy look like?

For the longest time, many astrophysicists and cosmologists have assumed that newborn galaxies would look like the orbs and spidery discs in the modern universe.

But according to an analysis of new images from the James Webb Space Telescope, baby galaxies were neither eggs nor discs.

They were bananas. Or pickles, or cigars, or surfboards – choose your own metaphor.

That is the tentative conclusion of a team of astronomers who re-examined images of some 4,000 newborn galaxies observed by Webb at the dawn of time.

“This is both a surprising and unexpected result, though there were already hints of it with Hubble,” said Dr Viraj Pandya, a postdoctoral fellow at Columbia University, referring to the Hubble Space Telescope.

He is the lead author of a paper soon to be published in the Astrophysical Journal under the provocative title, Galaxies Going Bananas. Dr Pandya is scheduled to give a talk about his work on Jan 10 at a meeting of the American Astronomical Society in New Orleans.

Astronomers say that if the result holds, it could profoundly alter their understanding of how galaxies emerge and grow.

It could also offer insight into the mysterious nature of dark matter, an unknown and invisible form of matter that astronomers say makes up a major part of the universe and outweighs atomic matter five to one. Dark matter engulfs galaxies and provides the gravitational nurseries in which new galaxies arise.

The result builds on hints from earlier observations from the Hubble telescope that the earliest galaxies were shaped like pickles, said Dr Joel Primack, an astronomer at the University of California, Santa Cruz, and an author of the new paper.

In an e-mail, Dr Alan Dressler of the Carnegie Observatories, who was not part of Dr Pandya’s work, characterised the result as “important – I do think it is important – extremely important, if it is true”.

“I retain some scepticism about this result, given how hard it is to make such measurement,” he added. “Especially for galaxies that are far away, small and not very bright (I’m talking about the galaxies).”

Dr Pandya’s team analysed the images of galaxies in a patch of sky smaller than a full moon known as the Extended Groth Strip, which has been surveyed by many telescopes, including the Hubble. The images were obtained by an international collaboration called the Cosmic Evolution Early Release Science, or CEERS, survey.

The team plans to extend its observations to other well-studied areas of the cosmos.

“This will let us identify galaxies with different 3D shapes all over the sky” and facilitate much-needed spectroscopic follow-up observations, Dr Pandya wrote in an e-mail.

He and his collaborators investigated the three-dimensional shapes of galaxies by statistically analysing their two-dimensional projections on the sky. If these early galaxies were balls or discs randomly oriented in space, they should occasionally present their full faces, appearing round and circular, to telescopes.

But astronomers are not seeing much of that. Instead, they see lots of cigars and bananas. “They consistently look very linear, with some galaxies showing multiple bright clumps arranged like pearls on a necklace,” Dr Pandya said.

Such oblong galaxies are rare today, but they make up as much as 80 per cent of the galaxies in the CEERS sample, which reaches back to about 500 million years after the Big Bang.

“Their masses are such that they would be the progenitors of galaxies like the Milky Way, implying that our own galaxy may have gone through a similar cigar/surfboard morphological phase in the past,” Dr Pandya said.

In the modern universe, galaxies seem to come in two basic forms: featureless, roundish clouds called ellipticals, and flat, spidery discs like our Milky Way home. Evidently, the earliest newborns did not start out like that. The reason, astronomers suspect, is related to the properties of dark matter, but exactly which or how is unclear.

The leading theory holds that dark matter consists of clouds of exotic subatomic particles left over from the Big Bang. Ordinary matter, drawn by gravity into these clouds, would condense and light up into stars and galaxies, according to computer simulations.

In a popular variant called cold dark matter, these leftover particles would be heavy and slow compared with protons, neutrons and the other, more familiar denizens of the quantum atomic world. According to computer simulations, cold dark matter would clump easily to form the large-scale patterns astronomers see in the sky.

Identifying these slow, heavy particles would shake the world of particle physics and cosmology.

But thus far, experiments in labs like the Large Hadron Collider at Cern – the European Organisation for Nuclear Research – have failed to detect or produce any particles of cold dark matter.

Lately, interest has shifted to other proposed forms of dark matter, including a whole gallery – a “dark sector” – of “dark” particles interacting with one another invisibly through “dark” forces.

In this mix are axions, which in theory are extremely light and act more like waves than particles – “fuzzy dark matter” or “wavy dark matter”, in the vernacular.

In computer simulations of galaxy formation, such waves can interfere with one another, producing knobby filamentary structures instead of the round shapes predicted by cold dark matter.

“Yes, the dark matter connection is tantalising,” Dr Pandya said, adding that the devil was in the messy details of “gastrophysics”, which describes how turbulence, hot gas and magnetic fields interact to light up stars and galaxies.

Prof Jeremiah Ostriker, an emeritus professor of astrophysics at Princeton now affiliated with Columbia University, in recent years has turned his attention to fuzzy dark matter. In 1973, Prof Ostriker conceived the idea of dark matter with his Princeton colleague James Peebles.

He and others have pointed out that fuzzy dark matter would leave its own signature on the sizes and shapes of baby galaxies.

Because of their inherent waviness, axions would not clump as effectively as cold dark matter, so it would be hard for them to produce baby galaxies of less than a billion solar masses. Cold dark matter has no such limitation.

Today’s telescopes are far from sensitive enough to observe such infants, however; a new generation of even bigger instruments may be needed to finish the job.

When Prof Ostriker learnt of Dr Pandya’s work, he remarked that the prospects for fuzzy dark matter were looking better and better.

“Keep up the good work,” he said. NYTIMES