SPACE / COSMOS
Hubble Space telescope unveils the first images of ongoing star cluster mergers near the center of dwarf galaxies
University of Oulu, Finland
A new study reports the first direct observation of merging star clusters in the nuclear region of dwarf galaxies. This detection confirms the feasibility of this formation route for nuclei in dwarf galaxies, which has long been debated. The study was published in Nature science journal, and led by Postdoctoral Researcher Mélina Poulain from the University of Oulu, Finland.
Dwarf galaxies are the most abundant type of galaxies that populate the Universe. Composed of 100 times fewer stars than the Milky Way, or even less, they are the building blocks of more massive galaxies. Thus, understanding their formation is key to comprehend galaxy evolution.
A notable fraction of dwarf galaxies host a compact star cluster at their centers, typically made of hundreds of thousands to hundreds of millions of stars. Known as nuclear star clusters, these are the densest type of stellar systems in the Universe. The formation of such extreme objects has been under debate for several decades. In dwarf galaxies, they are believed to form from the merger of smaller star clusters, called globular clusters, after they migrate to the galaxy center. However, no such merger of globular clusters has been directly observed to confirm the theory, until now.
Witnessing rare features
While studying observations of a large sample of nearly 80 dwarf galaxies from the Hubble Space telescope, which were led by Prof. Francine Marleau at the University of Innsbruck, Austria, a group of ten researchers from the international MATLAS collaboration noticed a handful of galaxies with an unusual looking nuclear star cluster. Some showed a couple of star clusters close together, while others had a feature similar to a faint stream of light attached to the nuclear star cluster.
“We were surprised by the streams of light that were visible near the center of the galaxies, as nothing similar has been observed in the past”, explains Mélina Poulain.
A thorough analysis of the features has shown that they have similar properties to globular clusters already detected in dwarf galaxies. This suggests that the observations witness the growth of the nuclear star cluster by the dramatic cannibalization of globular clusters at the cores of those galaxies.
Observations reproduced in simulations
To confirm the origin of the faint streams of light, ultra-high resolution complementary simulations were implemented to model the merging process. This portion of the work, led by Dr. Rory Smith at the Universidad Técnica Federico Santa María in Santiago, Chile, set up various mergers between star clusters with differing masses, dynamics, and numbers of clusters involved. Results confirm that the observed light streams are created with two star clusters with significant mass differences merge. The larger the mass ratio, the longer the stream. The process typically lasts a short amount of time, less than 100 million years, and the features produced are visible for even less time, which explains the difficulty of catching such a phenomenon.
The new study is part of Poulain’s research project, funded by the Research Council of Finland. The study was published on 9 April 2025 in the prestigious journal Nature: Reference
Learn more about space physics and astronomy research at the University of Oulu
Journal
Nature
Article Title
Evidence of star cluster migration and merger in dwarf galaxies
Article Publication Date
9-Apr-2025
Research suggests our closest neighboring galaxy may be being torn apart
Is the nearest galaxy to ours being torn apart? Research suggests so
Nagoya University
image:
Velocities of massive star candidates within the SMC shown as vectors.
The colors of the arrows represent the direction of motion. Relative to the LMC, located at the bottom left of the image, most red arrows show movement towards the LMC, whereas most light blue arrows show movement away from the LMC, suggesting they are being pulled apart.
view moreCredit: Credit: Satoya Nakano
A team led by Satoya Nakano and Kengo Tachihara at Nagoya University in Japan has revealed new insights into the motion of massive stars in the Small Magellanic Cloud (SMC), a small galaxy neighboring the Milky Way. Their findings suggest that the gravitational pull of the Large Magellanic Cloud (LMC), the SMC’s larger companion, may be tearing the smaller one apart. This discovery reveals a new pattern in the motion of these stars that could transform our understanding of galaxy evolution and interactions. The results were published in The Astrophysical Journal Supplement Series.
“When we first got this result, we suspected that there might be an error in our method of analysis,” Tachihara said. “However, upon closer examination, the results are indisputable, and we were surprised.”
The SMC remains one of the closest galaxies to the Milky Way. This proximity allowed the research team to identify and track approximately 7,000 massive stars within the galaxy. These stars, which are over eight times the mass of our Sun, typically survive for only a few million years before exploding as supernovae. Their presence indicates regions rich in hydrogen gas, a crucial component of star formation.
“The stars in the SMC were moving in opposite directions on either side of the galaxy, as though they are being pulled apart,” Tachihara said. “Some of these stars are approaching the LMC, while others are moving away from it, suggesting the gravitational influence of the larger galaxy. This unexpected movement supports the hypothesis that the SMC is being disrupted by the LMC, leading to its gradual destruction.”
Another surprising finding was the absence of rotational movement among the massive stars. Unlike in our Milky Way where interstellar gas rotates along with the stars, the study revealed a distinct pattern. Typically, young massive stars move together with the interstellar gas from which they were born, as they have not yet had time to decouple from its motion. However, the massive stars in the SMC do not follow a rotational pattern, indicating that the interstellar gas itself is also not rotating.
“If the SMC is indeed not rotating, previous estimates of its mass and its interaction history with the Milky Way and LMC might need to be revised,” Nakano, a collaborator on the study who also made a video explaining the findings, explained. “This could potentially change our understanding of the history of the three-body interaction between the two Magellanic Clouds and the Milky Way.”
The study has broader implications for understanding the dynamics of interactions between neighboring galaxies, particularly in the early universe. Astronomers consider the SMC to be an ideal model for studying the universe's infancy because it shares many conditions with primordial galaxies, such as low metallicity and weak gravitational potential. Therefore, the researchers' discoveries about the SMC and LMC interacting may resemble processes that shaped galaxies billions of years ago, providing valuable insights into their evolution over cosmic time. The group’s findings could create a new understanding of these processes.
“We are unable to get a ‘bird's-eye view’ of the galaxy in which we live,” Tachihara noted. “As a result, the SMC and the LMC are the only galaxies in which we can observe the details of stellar motion. This research is important because it allows us to study the process of star formation in connection with the motion of stars throughout the galaxy.”
Journal
The Astrophysical Journal Supplement Series
ByAFP
April 9, 2025
The satellites will be positioned hundreds of miles above the Earth
Charlotte CAUSIT
The US retail giant Amazon is preparing to launch Wednesday its first full batch of Project Kuiper satellites, marking a crucial milestone in the battle with Elon Musk’s Starlink to provide high-speed internet.
The 27 satellites will be launched from Cape Canaveral, Florida at 7:00 pm (2300 GMT) aboard an Atlas V rocket operated by the United Launch Alliance (ULA), a joint venture between Boeing and Lockheed Martin.
Like Starlink, the service is designed to provide internet access to even the most remote and underserved areas around the world, including war zones or disaster-struck areas.
The satellites will be positioned hundreds of miles above the Earth, where they will form the foundations of Project Kuiper — a constellation that Amazon says will include more than 3,200 satellites.
Amazon, owned by billionaire Jeff Bezos, has said the internet service will go live this year.
The project’s pricing has not yet been revealed, but Amazon has promised it will be in line with its existing reputation as a low-cost retailer.
With this launch, Amazon is going into direct competition with SpaceX’s Starlink and other satellite internet providers.
The Musk-owned SpaceX launched the first batch of its more than 6,750 operational Starlink satellites in 2019 and is by far the sector’s biggest player, boasting over five million customers worldwide.
Starlink has provided internet access to several disaster and war zones, including Morocco after a devastating 2023 earthquake there, as well as on the frontlines in Ukraine in its war with Russia.
– High competition –
Unlike traditional internet services that rely on fewer satellites that are situated more than 35,000 kilometers (22,000 miles) from Earth, those offered by Musk and soon Bezos use a low Earth orbit of between 550 and 1,300 kilometers (350-810 miles).
This allows them to relay data more rapidly to Earth, enabling internet access in areas without landline connections by copper or fiber optic cable.
“Cost, complexity, and geography can make it difficult to install traditional, ground-based fiber and wireless connectivity solutions in these areas,” Amazon says.
A lower orbit, however, means so-called LEO satellites are only reachable from a smaller area, meaning more are needed for full global coverage and launches are more regular.
Still, it provides a large potential market for Amazon — one in which it is hoping to become a key player by catching up with its main competitor.
Amazon is planning to boost satellite launches in the coming months and years, with more than 80 flights ordered by firms including ULA, Bezos’s space company Blue Origin and even Musk’s SpaceX.
These satellites will be gradually dispatched to the low Earth orbit, which is increasingly populated by Starlink as well as other emerging actors including Europe’s OneWeb and China’s Guowang.
Some have voiced fears the growing number of satellites could lead to congestion and possible collisions, as well as disturbances for astronomical observations.
The role of private hands in space has also raised political questions, particularly given the role of Musk as a key advisor to US President Donald Trump.
Musk has cast doubt on the future of Starlink in Ukraine, where it is essential for military operations in Kyiv’s war with Russia that Trump wants to see ended.
He said in March, however, that “no matter how much I disagree with the Ukraine policy, Starlink will never turn off its terminals.”
Trump’s NASA chief pick says will ‘prioritize’ Mars mission
By AFP
April 9, 2025
Jared Isaacman, an e-payments billionaire, is a close ally of Elon Musk who has flown to space twice with SpaceX as a private astronaut
NASA will prioritize sending astronauts to Mars, President Donald Trump’s pick to lead the US space agency said Wednesday, shifting focus beyond a long-planned return to the Moon — but insisting both were achievable.
Though NASA’s “Artemis” Moon mission was announced in Trump’s first term, he has since openly mused about heading straight to Mars, prompting concerns that China or others could fill the gap on the lunar surface.
The notion has gained traction as Elon Musk — the world’s richest person and SpaceX chief who has long eyed a human mission to Mars — became a key Trump ally and advisor.
“We will prioritize sending American astronauts to Mars,” businessman Jared Isaacman told the Senate committee overseeing his appointment.
“And along the way, we will inevitably have the capabilities to return to the Moon and determine the scientific, economic and national security benefits for maintaining a presence on the lunar surface,” he said.
Musk founded his successful space company with the idea of making humanity a multiplanetary species.
Isaacman, an e-payments billionaire, is a close Musk ally who has flown to space twice with SpaceX as a private astronaut.
He did not appear to view a bid for Mars as incompatible with the Artemis mission, telling senators he did not see any “tough trades here.”
“I absolutely want to see us return to the Moon,” he said, adding that he did not think NASA would have to make “a binary decision of Moon versus Mars, or Moon has to come first versus Mars.”
“I think we could be paralleling these efforts and doing the near impossible, which is exactly why the American taxpayers funded NASA in the first place,” he said.
A “first step” would be a return to the Moon, he said, adding: “we should be doing both.”
Texas Senator Ted Cruz underscored the strategic value of the Moon when it came to US national security back on Earth.
“We must stay the course — an extreme shift in priorities at this stage would almost certainly mean a red moon, ceding ground to China for generations to come,” the Republican, whose state hosts NASA’s massive Johnson Space Center, told the hearing.
“I am hard pressed to think of a more catastrophic mistake we could make in space than saying to Communist China, ‘the Moon is yours,'” Cruz continued.
But Isaacman insisted both a moonshot and a Mars-shot were possible.
“We can chart a course for Mars in line with the president’s vision to return to the Moon before the Chinese can get there,” he said.
Isaacman has also reportedly intervened at the last moment to prevent NASA from suffering the deep cuts made at other agencies by Musk’s so-called Department of Government Efficiency.
Do “completely dark” dark matter halos exist?
University of California - San Diego
Every galaxy is thought to form at the center of a dark matter halo – a region of gravitationally bound matter that extends far beyond the visible boundaries of a galaxy. Stars are formed when gravity within dark matter halos draws in gas, but astrophysicists don’t yet know whether star-free dark matter halos exist.
Now Ethan Nadler, a computational astrophysicist at UC San Diego, has calculated the mass below which halos fail to form stars. This work was done using analytic predictions from galaxy formation theory and cosmological simulations.
"Historically, our understanding of dark matter has been linked to its behavior in galaxies. A detection of completely dark halos would open up a new window to study the universe," stated Nadler.
Previously, this threshold for star formation was thought to be between 100 million to 1 billion solar masses due to cooling of atomic hydrogen gas. Nadler’s research shows that star formation can occur in halos down to 10 million solar masses through molecular hydrogen cooling.
With the Rubin Observatory coming online later this year and JWST already making unprecedented observations of our universe, there will soon be new data to test these predictions and reveal whether completely dark halos exist. This may have far-reaching consequences for cosmology and the nature of dark matter.
The study, titled "The Impact of Molecular Hydrogen Cooling on the Galaxy Formation Threshold," was published April 8, 2025 in Astrophysical Journal Letters and was led by Ethan Nadler.
Journal
The Astrophysical Journal Letters
Method of Research
Data/statistical analysis
Article Title
The Impact of Molecular Hydrogen Cooling on the Galaxy Formation Threshold
Article Publication Date
8-Apr-2025
