The early universe was made of bananas
What does a newborn galaxy look like?
Many astrophysicists and cosmologists have long assumed that newborn galaxies would look like the orbs and spin-like disks known to the modern universe.
But according to an analysis of new images from the James Webb Space Telescope, baby galaxies were neither eggs nor disks. They were bananas. Or pickles, or cigars, or surfboards – choose your own metaphor. That’s the preliminary conclusion of a team of astronomers who reexamined images of some 4,000 newborn galaxies observed by Webb at the dawn of time.
“This is both a surprising and unexpected result, although there was already evidence of this at Hubble,” said Viraj Pandya, a postdoctoral researcher 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 are going bananas.” Dr. Pandya will lecture about his work Wednesday at a meeting of the American Astronomical Society in New Orleans.
If the result holds, astronomers say it could profoundly change their understanding of how galaxies form and grow. It could also provide insight into the mysterious nature of dark matter, an unknown and invisible form of matter that astronomers say makes up a large part of the universe and outweighs atomic matter. Dark matter engulfs galaxies and forms the gravitational nurseries in which new galaxies are formed.
The result builds on evidence from previous Hubble Telescope observations that the earliest galaxies existed were shaped like picklessaid Joel Primack, an astronomer at the University of California, Santa Cruz, and author of the new paper.
In an email, Alan Dressler of the Carnegie Observatories, who was not part of Dr. Pandya, the result as “important – I think it is important – extremely important, if it is true.”
“I remain somewhat skeptical about this result, given how difficult it is to perform such a measurement,” he added. “Especially for galaxies that are far away, small and not very bright (I’m talking about the galaxies).”
The team of Dr. Pandya analyzed images of galaxies in a patch of sky smaller than a full moon, known as the Extended Groth Strip, which has been examined by many other telescopes. including the Hubble telescope. The images were obtained through an international collaboration called the Cosmic Evolution Early Release Science, or CEERS, survey.
The team plans to extend its observations to other well-studied parts of the cosmos. “This will allow us to identify galaxies with different 3D shapes across the entire sky” and enable much-needed follow-up spectroscopic observations, wrote Dr. Pandya in an email.
Galaxies are the city-states of the cosmos. Within the visible universe there are an estimated two trillion of them, each containing as many as a trillion stars. But the visible universe is only a fraction of what is out there. Most of the matter in the cosmos appears to be in the form of dark matter; Whatever dark matter is, it forms the invisible bones of the universe we see.
Astronomers now think that galaxies were formed by random fluctuations in the density of matter and energy during the Big Bang. As space expanded, the denser regions were left behind and dark matter accumulated, pulling normal matter with it. This material eventually collapsed again and lit up as stars and galaxies or disappeared into black holes. The Webb Telescope was designed to explore this formative and mysterious era; with a giant mirror and infrared sensors it can see the most distant, and therefore earliest, galaxies.
Dr. Pandya and his collaborators investigated the three-dimensional shapes of galaxies by statistically analyzing their two-dimensional projections on the sky. If these early galaxies were balls or disks randomly oriented in space, they should occasionally show their full faces, which appear round and circular, to telescopes.
But astronomers don’t see much of that. Instead they see a lot of cigars and bananas.
“They consistently look very linear,” said Dr. Pandya, “where some galaxies show multiple bright clumps, arranged like pearls on a chain.”
Such elongated galaxies are rare today, but they make up as many as 80 percent of the galaxies in the CEERS sample, which dates back to about 500 million years after the Big Bang.
“Their masses are so large that they could be the precursors of galaxies like the Milky Way,” said Dr. Pandya, “implying that our own galaxy may have gone through a similar cigar/surfboard morphological phase in the past.”
In the modern universe, galaxies appear to come in two basic forms: featureless, round clouds called ellipticals, and flat, spin-like disks like our Milky Way House.
Apparently the earliest newborns didn’t start out that way. The reason, astronomers suspect, is related to the properties of dark matter, but which and how exactly is unclear.
The leading theory states that dark matter consists of clouds of exotic subatomic particles left over from the Big Bang. Ordinary matter, drawn into these clouds by gravity, would condense and glow 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 to protons, neutrons and the other, more familiar inhabitants of the quantum atomic world. According to computer simulations, cold dark matter would easily clump together to form the large-scale patterns that astronomers see in the sky.
Identifying these slow, heavy particles would turn the world of particle physics and cosmology upside down. But so far, experiments in labs such as the Large Hadron Collider at CERN have failed to detect or produce particles of cold dark matter. Recently, interest has shifted to other proposed forms of dark matter, including an entire gallery – a ‘dark sector’ – of ‘dark’ particles that interact invisibly through ‘dark’ forces.
Included in this mix are axions, which in theory are extremely light and behave more like waves than particles – ‘faint dark matter’ or ‘wavy dark matter’ in the vernacular. In computer simulations of galaxy formation, such waves can interfere with each other, creating knobby thread-like structures instead of the round shapes predicted by cold dark matter.
“Yes, the dark matter connection is exciting,” said Dr. Pandya, adding that the devil was in the messy details of “gastrophysics,” which describes how turbulence, hot gas and magnetic fields interact to illuminate stars and galaxies.
Jeremiah Ostriker, professor emeritus of astrophysics at Princeton and now at Columbia University, has turned his attention to faint dark matter in recent years. In 1973, Dr. Ostriker developed the idea of dark matter with his Princeton colleague James Peebles.
He and others have pointed out that faint 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, making it difficult for them to produce baby galaxies with masses less than a billion solar masses. Cold dark matter does not have this limitation. However, current telescopes are far from sensitive enough to observe such babies; A new generation of even larger instruments may be needed to get the job done.
When Dr. Ostriker heard about Dr. Pandya’s work, he noticed that the prospects for faint dark matter were looking better and better. “Keep it up.” he said.