SPACE/COSMOS
Astronomers close to solving mystery of how universe’s giant galaxies formed
image:
Two antennae galaxies colliding - photo by NASA
view moreCredit: Photo by NASA
Astronomers say they are close to solving an intergalactic mystery about the creation of the universe's biggest galaxies which has puzzled experts for decades.
Scientists have discovered the birth sites of gigantic elliptical galaxies which they claim offer new clues about how they were formed.
The creation of these ancient galaxies, which look like bulging footballs compared to our flat disk-like Milky Way, remains a mystery to astrophysicists.
But now academics from the University of Southampton, working with experts across the world, say their new study may finally unravel the enigma.
Dr Annagrazia Puglisi from Southampton, who co-authored the research, said it is likely that large flows of cold gas and collisions between galaxies in the early universe created these giant systems.
She added: “Two disk galaxies smashing together caused gas – the fuel from which stars are formed – to sink towards their centre, generating trillions of new stars.
“These cosmic collisions happened some eight to 12 billion years ago, when the universe was in a much more active phase of its evolution.
“Our findings take us closer to solving a long-standing mystery in astronomy that will redefine our understanding of how galaxies were created in the early universe.”
The study, published in Nature, was a collaboration between Southampton, the Purple Mountain Observatory in China and the Chinese Academy of Science, among others.
Experts analysed more than 100 star-forming galaxies in the distant universe using the world’s largest radio telescope, known as ALMA, located in Chile’s Atacama desert.
The scientists made the discovery using a new technique which looked at the distribution of light emitted by distant and highly-luminous galaxies, said study lead Dr Qing-Hua Tan from the Purple Mountain Observatory.
She added: “This is the first real evidence that spheroids form directly through intense episodes of star formation located in the cores of distant galaxies.
“Astrophysicists have sought to understand this process for decades.
“These galaxies form quickly – gas is sucked inwards to feed black holes and triggers bursts of stars, which are created at rates ten to 100 times faster than our Milky Way.”
Researchers used the open-source A3COSMOS and A3GOODSS archival projects which enabled them to gather high-quality observations of many distant galaxies.
The scientists say they will combine their findings with data taken from telescopes aboard the JWST and Euclid satellites, as well as the Chinese Space Station, to map the stellar components of galaxies.
Dr Puglisi from Southampton added: “This will give us a more complete picture of early galaxy formation and deepen our understanding of how the universe has evolved since the beginning of time.”
Read more at www.nature.com/articles/s41586-024-08201-6.
ENDS
428 WORDS
Journal
Nature
Method of Research
Observational study
Subject of Research
Not applicable
Article Title
In situ spheroid formation in distant submillimetre-bright Galaxies
Article Publication Date
4-Dec-2024
Astronomers witness the in situ spheroid formation in distant submillimetre-bright galaxies
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Schematic diagram shows how spheroid formation occurs in distant submillimetre-bright galaxies, and how this process connects to the evolution of giant elliptical galaxies in today's Universe. On the far left, we have RGB images from JWST (using F444W for red, F227W for green, and F150W for blue) showcasing examples from our sample of galaxies. The cyan dashed ellipse marks the concentrated region of submm emission, with zoomed-in views highlighting the ALMA submm images. Also shown is a classification of the galaxies' intrinsic shapes. The average shape parameters for our full sample (green ellipse), a subsample of submm-compact galaxies (orange ellipse), and a subsample of submm-extended galaxies (blue ellipse) are compared to local early-type galaxies (red ellipse) and late-type galaxies (represented by purple and cyan spiral shapes).
view moreCredit: Credit: Qing-Hua Tan
An international team of researchers including The University of Tokyo Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) has found evidence showing that old elliptical galaxies in the universe can form from intense star formation within early galaxy cores. This discovery will deepen our understanding of how galaxies evolved from the early Universe, reports a new study in Nature.
Galaxies in today’s Universe are diverse in morphologies and can be roughly divided into two categories: younger, disk-like spiral galaxies, like our own Milky Way, that are still forming new stars; and older, elliptical galaxies, which are dominated by a central bulge, no longer forming stars and mostly lacking gas. These spheroidal galaxies contain very old stars, yet how they formed has remained a mystery—until now.
The discovery of the birth sites of giant, elliptical galaxies – announced in a paper published today in Nature – come from analyzing data from the Atacama Large Millimeter/submillimeter Array (ALMA) on over 100 Submillimeter Bright Galaxies (SMGs) with redshifts dating to the “Cosmic noon” era, when the universe was between around 1.6 and 5.9 billion years old and many galaxies were actively forming stars. This study provides the first solid observational evidence that spheroids can form directly through intense star formation within the cores of highly luminous starburst galaxies in the early Universe, based on a new perspective from the submillimeter band. This breakthrough will significantly impact models of galaxy evolution and deepen our understanding of how galaxies form and evolve across the Universe.
In this study, researchers led by Chinese Academy of Sciences Purple Mountain Observatory Associate Researcher Qinghua Tan, and including Kavli IPMU Professor John Silverman, Project Researcher Boris Kalita, and graduate student Zhaoxuan Liu, used statistical analysis of the surface brightness distribution of dust emission in the submillimeter band, combined with a novel analysis technique. They found that the submillimeter emission in most of sample galaxies are very compact, with surface brightness profiles deviating significantly from those of exponential disks. This suggests that the submillimeter emission typically comes from structures that are already spheroid-like. Further evidence for this spheroidal shape comes from a detailed analysis of galaxies’ 3D geometry. Modeling based on the skewed-high axis-ratio distribution shows that the ratio of the shortest to the longest of their three axes is, on average, half and increases with spatial compactness. This indicates that most of these highly star-forming galaxies are intrinsically spherical rather than disk-shaped. Supported by numerical simulations, this discovery has shown us that the main mechanism behind the formation of these tri-dimensional galaxies (spheroids) is the simultaneous action of cold gas accretion and galaxy interactions. This process is thought to have been quite common in the early Universe, during the period when most spheroids were forming. It could redefine how we understand galaxy formation.
This research was made possible thanks to the A3COSMOS and A3GOODSS archival projects, which enabled researchers to gather a large number of galaxies observed with a high enough signal-to-noise ratio for detailed analysis. Future exploration of the wealth of ALMA observations accumulated over the years, along with new submillimeter and millimeter observations with higher resolution and sensitivity, will allow us to systematically study the cold gas in galaxies. This will offer unprecedented insight into the distribution and kinematics of the raw materials fueling star formation. With the powerful capabilities of Euclid, the James Webb Space Telescope (JWST), and the China Space Station Telescope (CSST) to map the stellar components of galaxies, we will gain a more complete picture of early galaxy formation. Together, these insights will deepen our understanding of how the Universe as a whole has evolved over time.
Journal
Nature
Article Title
In situ spheroid formation in distant submillimetre-bright Galaxies
Article Publication Date
4-Dec-2024
Researchers use data from citizen scientists to uncover the mysteries of a blue low-latitude aurora
Nagoya University
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One of the two photographs that captured blue-dominant aurora and were analyzed in this study.
view moreCredit: Takuya Usami
Colorful auroras appeared around Japan's Honshu and Hokkaido islands on May 11, 2024, sparked by an intense magnetic storm. Usually, auroras observed at low latitudes appear red due to the emission of oxygen atoms. But on this day, a salmon pink aurora was observed throughout the night, while an unusually tall, blue-dominant aurora appeared shortly before midnight.
Smartphone videos and amateur photos captured the event, enabling scientists to combine public data with their own research and study the phenomenon.
In a new study, researchers analyzed the videos and images of the blue-dominant aurora to estimate the area of the phenomenon and confirmed the estimates with spectrophotometers. Published in the journal Earth, Planets and Space, the research was led by Sota Nanjo, a postdoctoral researcher at the Swedish Institute of Space Physics in Sweden, and Professor Kazuo Shiokawa from the Institute for Space-Earth Environmental Research (ISEE) at Nagoya University in Japan.
Nanjo and Shiokawa’s investigation provided the first visualization of the spatial structure of blue-dominant auroras during a storm. The researchers found that the auroras had longitudinal structures that were aligned with magnetic field lines, the first time they had been identified in a low-latitude, blue-dominant aurora. They also found that the aurora spanned about 1200 km in longitude, consisted of three separated structures, and ranged in altitude from 400-900 km.
Nanjo and Shiokawa’s findings may change our understanding of blue auroras. The ring current, a donut-shaped region of charged particles encircling Earth, is believed to be the source of energetic neutral atoms (ENAs) that produce low-latitude auroras, including the red aurora. According to this model, the storm likely energized the ENAs, creating a colorful display of light.
However, the group's discoveries cannot easily be explained by this mechanism. As Shiokawa explains: “In this study, a structure of several hundred kilometers was found in the blue-dominant aurora in the longitudinal direction, which is difficult to interpret by ENA activity only. In addition, ENAs are unlikely to create auroral structures aligned with magnetic field lines, as observed in this study.”
Another possibility was that the aurora was due to resonant scattering of nitrogen molecular ions caused by sunlight irradiation. However, the group's research suggests that a different process occurred, as sunlight only reached down to 700 km, not the 400 km observed by the researchers.
Instead, their results may indicate the intriguing possibility of an unidentified process. “Our findings suggest that nitrogen molecular ions may have accelerated upward by some mechanism and were responsible for the formation of the blue-dominant aurora,” Shiokawa said.
“To date, it is not well understood how nitrogen molecular ions with large molecular weight can exist at such high altitudes,” he continued. “Such ions are not easily able to exist for long periods of time due to their heavy mass and short dissociative-recombination time intervals; however, they are observed at high altitudes. The process is shrouded in mystery.”
Overall, repeated observations of blue-dominant auroras, such as the one observed in Japan, may provide clues to understand the principle behind how nitrogen can be found at these altitudes. As the process of nitrogen molecular ion outflow into the magnetosphere is important in everything from understanding geomagnetic storms and the radiation environment in space, these findings could help us understand the processes that take place hundreds of kilometers above us.
Blue-dominant aurora captured by another photographer was also analyzed in this study.
Credit
Mitsuhiro Ozaki
Journal
Earth Planets and Space
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