A Fierce Storm in a Giant-Barred Spiral Galaxy 11 Billion Years Ago

In the early universe, more than 10 billion years ago, numerous monster galaxies formed stars at a rate over 100 times faster than the Milky Way. Although a few galaxies undergo star formation at a similar pace even in the present-day universe, almost all of them collide or merge with other galaxies. Based on this, scientists assumed that such intense bursts of star formation in monster galaxies are also caused by substantial gas influx at their centers because of galaxy collisions or mergers, and that they evolve into giant elliptical galaxies once the gas is depleted.

Monster galaxies are far from Earth and obscured by massive amounts of dust generated by intense star formation, making them difficult to observe at optical wavelengths. Until recently, their shape and the physical process that drives such bursts of star formation remained largely unknown. However, recent infrared imaging observations with the James Webb Space Telescope have uncovered dust-veiled monster galaxies, revealing the existence of many monster galaxies with a remarkable disk structure. This prompted a new question: Why are monster galaxies that appear to be ordinary disk galaxies experiencing such intense bursts of star formation?

A research team led by Shuo Huang targeted a monster galaxy with a barred spiral structure in the Universe 11.1 billion years ago. The J0107a galaxy, located at a redshift of z=2.467, was serendipitously found in 2014, while the nearby merging galaxy VV114 was observed. The James Webb Space Telescope’s near-infrared images of VV114, released in 2023, revealed that J0107a is an exceptionally massive example of a monster galaxy, with a mass more than ten times that of the Milky Way Galaxy and a star formation rate approximately 300 times that of the Milky Way. Even more surprisingly, J0107a has a perfect barred spiral structure, one of the largest and most distinct of any galaxy in this cosmic epoch. The shape looks more like modern barred spiral galaxies than any previously observed monster galaxies. While more information on gas kinematics is needed to explore the factors behind J0107a's intense star formation, spectroscopic observations of a dust-covered galaxy are incredibly challenging, even with the James Webb Space Telescope.

The research team then used ALMA to observe the emission lines of carbon monoxide and neutral carbon atoms and discovered that J0107a closely resembles modern barred spiral galaxies, such as the Milky Way, in terms of the shape of its bar structure as well as the distribution and movement of the associated gas. On the other hand, the team also found that while the proportion of gas in the bar structure of a modern galaxy is less than 10% of the total mass, that of J0107a is very high at around 50%. The data shows that J0107a's bar structure, which consists of stars and gas with a mass far greater than that of modern galaxies, stirs up the disk, creating a gas flow at a speed of several hundred kilometers per second over a radius of 20,000 light-years around the center of the galaxy, which is equivalent to the distance from the center of the Milky Way to the Solar System. Some of this gas falls into the galaxy's center, resulting in intense star formation. No previous theoretical studies of galaxy formation predicted the existence of a monster galaxy with such a bar structure.

This is the first successful direct observation of a burst of star formation induced by gas inflow from a bar structure in the early universe. The conventional theories of monster galaxy formation and evolution assumed that intense star formation occurs due to galactic collisions and mergers or gravitational instability in their disks, turning them into elliptical galaxies over hundreds of millions of years. Meanwhile, J0107a is assumed to have developed a shape resembling a modern barred spiral galaxy while retaining the extreme physical properties of a monster galaxy over hundreds of millions of years in the early universe, just 2.6 billion years after the Big Bang. The detailed data on gas distribution and kinematics obtained from this observation will provide essential clues to the origin of monster galaxies and inform research into the formation and evolution of bar structures in other galaxies, as we are witnessing the bar structure formation process in the early universe.

Shuo Huang, the research team's leader, says, "The substantial amount of gas required for the growth of giant galaxies is supplied by galactic mergers or inflows from the cosmic web. While no sign of a galactic merger exists, a large gas disk has been detected around J0107a. This gas disk has a diameter of approximately 120,000 light years, which is twice the diameter of the galaxy's main body, visible as stars, and its motion roughly follows that of the galaxy itself. Based on this, we assume it was created from a large amount of gas spiraling toward the galaxy from the cosmic web¹. This is a new picture of a monster galaxy, in which a disk galaxy is formed from a cosmic-scale gas flow, followed by the emergence of a bar structure during the galactic evolution, leading to rapid galactic-scale gas flows and bursts of star formation. We will continue our observational studies with ALMA to investigate this further."

Notes

1. These gas flows are theoretically predicted and called "cold streams." ↩︎

Additional Information

This research was published in Nature on May 21, 2025, by Shuo Huang et al., "Large gas inflow driven by a matured galactic bar in the early Universe" (DOI: 10.1038/s41586-025-08914-2).

Grants-in-Aid support this research from the Japan Society for the Promotion of Science (KAKENHI: Nos. JP22H04939, JP23K20035, JP24H00004) and the ALMA Joint Scientific Research Program (No. 2024-26A).

The National Astronomical Observatory of Japan (NAOJ), an ALMA partner on behalf of East Asia, published the original press release.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan, and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of ALMA's construction, commissioning, and operation.

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