Spiral galaxies in the universe came into existence 4 billion years earlier than expected: Study

Spiral galaxies in the universe came into existence 4 billion years earlier than expected: Study

A new study has revealed that the number of spiral galaxies in the youth of the universe is much higher than astronomers expected.

The universe is about 13.8 billion years old and contains a variety of galaxies, from spiral to elliptical and with or without bulges. Astronomers previously believed that spiral galaxies formed about 6 billion years ago, but a new study by a group of astronomers from the University of Missouri in the US has thrown this assumption into question. Published on June 11 In Astrophysical Journal Letters,

Young galaxies in the universe are spiral in shape, while older galaxies are of various shapes. Astronomers study them to understand how they formed and evolved. But older galaxies are more difficult to study because the light coming from them is weaker.

not just hot air

A key idea in astronomy is that as the universe cooled from a dense plasma state, it contained more and more hot gases. They formed clumps of matter that eventually turned into galaxies. These early galaxies were irregularly shaped and had no disks. But as they cooled, they formed hot, thick disks that later thinned and eventually became spiral 'arms' – a process that took billions of years.

This theory is now questionable. “Our work shows that this cooling and spiral formation happen around the same cosmic time,” said Vicki Kuhn, a graduate student at the University of Missouri and a member of the study.

Astronomers routinely watch star formation in real time, but since all the galaxies have already formed, they use a kind of astronomical archaeology to study them. “We don't see proto-galaxies,” said Girish Kulkarni of the Tata Institute of Fundamental Research in Mumbai, who was not involved in the study. “Then we study how galaxies evolve. Spiral galaxy fractions are one way to do this biography.”

Looking into the past and forward

The first step is to use light of infrared and optical wavelengths to detect galaxies in the early universe. Because old galaxies are hard to detect, we need powerful telescopes. Ideally, astronomers would like to observe light emitted when the universe was about 500 million years old, when galaxies are thought to have formed.

NASA's James Webb Space Telescope, launched in 2021, has helped astronomers peer deeper into the universe's past than ever before. The University of Missouri team used the telescope to study a cluster of 873 galaxies individually and identified at least 216 spiral galaxies. Some of them date back 1.5 billion years to the birth of the universe.

For the study, all six authors looked at each image to classify it as spiral or non-spiral. Prerana Biswas, a postdoctoral researcher at the Indian Institute of Astrophysics in Bengaluru, who was not involved in the study, said the method is crude but shows the result is free of human bias. Abhijit Borkar, a research scientist at the Institute of Astronomy of the Czech Academy of Sciences in Prague, who was also not involved in the study, agreed.

But while Dr. Biswas said future studies should use automated algorithms to find spiral galaxies, Dr. Borkar said there are few options for such validation. “Even for applying machine learning or neural networks, this is the first step. The only way to improve is to involve a large number of astronomers combing through the data.”

An underestimation comes to light

The researchers then compared the number of spiral galaxies to the number of total galaxies. They found that the proportion of galaxies with spiral shapes increased from about 8% to 48% between 3 billion and 7 billion years after the Big Bang. Previous observations had instead indicated an increase of 5% to 30%. “This is much higher than the previously known number,” Dr. Kulkarni said.

Dr. Borkar was really amazed by the fact that galaxies with spiral arms were fully formed so quickly.

New observations show that there are a greater number of spiral galaxies and that their number has increased as the universe evolved.

Dr Kulkarni explained how astronomers study the formation of galaxies. They develop mathematical models on powerful computers and let them evolve over time. While dark matter and gravity are major influences on the evolution of the universe, they are not enough to cause galaxies to form. So astrophysicists incorporate hotter, denser gases into the simulations. These simulations match what astronomers have observed so far.

As the universe gets older, gases cool and clump together, forming stars. As stars evolve, they give rise to supernovae, which create most of the elements on Earth today. A few black holes also form, and some of them sit at the center of galaxies and exert their influence.

From simple to complex

Given the uncertainty in the parameters of many of these models, astrophysicists also use observations to refine them – and such refinements are often significant.

The Hubble Space Telescope is famous for its clear images of distant celestial bodies and astrophysicists have used it to refine many models. But then some studies found indications that the early universe had many galaxies with disks. Astronomers believe that such galaxies were actively forming new stars.

However, the authors of the current study did not compare their observations to simulations, which confused Dr. Kulkarni.

They also said that the relationship between these sophisticated simulations and existing data may not be easy to understand. All experts agreed that astronomers should carefully re-examine the existing framework of observational data and theoretical studies.

“The earlier scenario was much simpler,” Dr. Borkar said. Now “the theories need to be made more complex.” He said it is possible that while stars are forming in some regions of galaxies, hot gases may simultaneously exist in other regions.

'No one knows'

The new findings could also affect what astronomers understand about the rate of star formation in the universe. For planets like Earth to form around stars, spiral galaxies must keep enough elements heavier than iron in their spiral arms. When heavy stars die and explode as supernovae, they throw these elements into the arms. But if something else hinders star formation — such as the influence of a black hole — then not enough stars will form in the first place.

As the universe got older, spiral galaxies became more numerous, even at the peak of star formation. Over time, the gas in the spiral arms of spiral galaxies became less dense, slowing the formation of more stars. But collisions between galaxies, such as the one predicted to occur between our galaxy and its neighbor Andromeda in about 5 billion years, could restart the process in another lifetime and create an elliptical galaxy as well.

Overall, our view of the universe's cycle of forming galaxies, stars and planets like Earth is becoming more complex. What does this mean for our understanding of galaxy formation? “I can safely say that no one knows,” Dr. Biswas said.

Debdutta Paul is a science writer at the International Centre for Theoretical Sciences, Bengaluru, and a freelance science journalist.

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