‘Fluffy’ molecular clouds may change our understanding of star formation
Stars are born in dense clouds of gas and dust, but new evidence suggests that conditions in the early universe may have shaped their formation in surprising ways.
In a recent study, observations of the Small Magellanic Cloud (SMC) revealed that about 40% of the star-forming clouds in this distant dwarf galaxy exhibit a “fluffy” shape.
This discovery potentially alters our understanding of how many stars – similar to our own Sun – came into being.
Star formation across cosmic history
The research was led by Kazuki Tokuda, a postdoctoral fellow at Kyushu University’s Faculty of Science. The findings may shed new light on the evolution of star formation across cosmic history.
In the Milky Way today, stars generally form within elongated, filamentary molecular clouds.
Astronomers believe our own Solar System originated in such a structure, where a large filament broke apart into smaller cores – often called “stellar eggs.”
Over hundreds of thousands of years, gravity pulled gas into each core to forge a new star.
Conditions of the early universe
Tokuda noted that our understanding of star formation is still developing, and comprehending how stars formed in the earlier universe is even more challenging.
“The early universe was quite different from today, mostly populated by hydrogen and helium. Heavier elements formed later in high-mass stars,” explained Tokuda.
“We can’t go back in time to study star formation in the early universe, but we can observe parts of the universe with environments similar to the early universe.”
The Small Magellanic Cloud meets these conditions. It lies about 20,000 light-years from Earth – very close by cosmic standards – and contains only one-fifth the heavy elements (sometimes called “metals” by astronomers) found in the Milky Way.
This makes the SMC an excellent proxy for conditions that would have been prevalent around 10 billion years ago, when the universe itself contained fewer heavy elements.
Observing fluffy molecular clouds
Despite the SMC’s usefulness, it has proven challenging to gather high-resolution data on its star-forming regions.
Astronomers need to distinguish whether filaments – like those that give rise to stars in the Milky Way – also exist in the SMC, or if some entirely different process might govern star formation there.
Fortunately, new observations from the ALMA radio telescope in Chile offered the resolution needed to analyze molecular clouds in the Small Magellanic Cloud.
“In total, we collected and analyzed data from 17 molecular clouds. Each of these molecular clouds had growing baby stars 20 times the mass of our Sun,” Tokuda said.
“We found that about 60% of the molecular clouds we observed had a filamentary structure with a width of about 0.3 light-years, but the remaining 40% had a ‘fluffy’ shape. Furthermore, the temperature inside the filamentary molecular clouds was higher than that of the fluffy molecular clouds.”
Higher temperatures in the filamentary clouds appear to reflect a more recent formation. After their initial collisions, these clouds start off relatively hot, with weak turbulence.
As the gas cools, the incoming energy from further collisions creates increased turbulence, which can smooth out the filamentary structure – resulting in the “fluffy” clouds that Tokuda’s team observed.
Colossal star-forming factories
The shift from filamentary to fluffy shapes could have profound implications for the stars that eventually emerge. If the filaments remain intact, they tend to fragment along their lengths, producing many stars (some of them low-mass stars like the Sun).
On the other hand, if the clouds lose their structure too quickly and become fluffy, the formation of these stellar cores may be disrupted, potentially affecting how many Sun-like stars (and planetary systems) can form.
The difference in temperature between filamentary and fluffy clouds is likely linked to their age. Initially, all molecular clouds formed as filamentary structures with high temperatures, primarily due to the impact of cloud collisions. In this heated state, turbulence within the cloud remains weak.
However, as the cloud cools over time, the kinetic energy from incoming gas increases turbulence, gradually breaking down the filamentary structure and transforming it into a more diffuse, fluffy cloud.
Such differences highlight the importance of heavy elements in stabilizing molecular clouds – elements that play a key role in radiative cooling and help regulate the dynamics within these colossal star-forming factories.
“This study indicates that the environment, such as an adequate supply of heavy elements, is crucial for maintaining a filamentary structure and may play an important role in the formation of planetary systems,” Tokuda added.
Mysteries of star formation
Given that heavy elements were far scarcer in the early universe, these findings hint that many primordial stars might have formed under conditions more akin to the “fluffy” clouds in the SMC. That scenario could alter our perspective on the first generations of stars and the overall evolution of galaxies in the cosmos.
“In the future, it will be important to compare our results with observations of molecular clouds in heavy-element-rich environments, including the Milky Way galaxy. Such studies should provide new insights into the formation and temporal evolution of molecular clouds and the universe,” Tokuda said.
Whether filamentary or fluffy, molecular clouds remain at the heart of one of astronomy’s greatest questions: How, and under what circumstances, do stars emerge?
By studying the SMC and beyond, researchers aim to map out these stellar birthplaces more completely, revealing how different cosmic eras might have shaped the countless stars that fill our skies today.
The study is published in The Astrophysical Journal.
—–
Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.
Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.
—–
