- How stars are born
- What is ALMAGAL, the largest census of stellar nurseries to date
- What are the mechanisms behind star formation
Stars are large spheres of plasma –– nuclear reactors that bring light to the Universe. But where do they come from? Stars are born in giant clouds of gas and dust which collapse and break down into smaller fragments. How this actually happens isn’t fully understood, but a new survey of 1000 stellar nurseries is helping to answer this question.
Take a look at the night sky and observe our galaxy, the Milky Way. Among the countless stars that make up this faint patch of light, there are also clouds of gas and dust –– industrial powerhouses that work tirelessly to create new stars.
Much like some of the factories we have on Earth, these clouds use simple building blocks –– hydrogen, helium and small amounts of heavier elements –– to make more complex pieces like stars. But the inner workings of each "factory" and the output results may be very different from place to place. Each factory may be working at very different rates and with very different structures. Their products, stars, end up having different masses, temperatures and compositions. These variations have left astronomers wondering: what is happening behind closed doors?
We know that star-formation is an extremely intricate process. Astronomers have already studied many stellar nurseries in detail, but what if the lessons we learn from one of these nebulae don’t apply to the rest? Do different stellar factories follow different recipes to form stars? To tackle the many open questions still to be answered, we need to see the bigger picture.
This is the goal of ALMAGAL, a survey that has been analysing as many stellar factories as possible to explore the mechanisms behind star formation. The numbers of ALMAGAL are impressive. Alone, it has observed around 1000 star-forming regions, three to four times more than all previous censuses put together, all with an impressive level of detail.
With the first results of the survey now available, we can start figuring out the differences and similarities in the way stars are born in different regions.
Journey to the centre of a star factory
Deep within these nebulae, dust and gas intertwine to create loose bundles called “clumps”. These clumps are further broken down into smaller objects called “cores” –– dense cocoons out of which stars form. Different processes like turbulence in the gas or magnetic fields are thought to control how nebulae fragment into clumps and cores, and ALMAGAL is designed to better understand how this happens.
As its name implies, ALMAGAL uses observations from ALMA, the Atacama Large Millimeter/Submillimeter Array, high up in Chajnantor, in Chile’s Atacama Desert. ALMA doesn’t observe visible light; instead, it studies light at much longer millimeter and submillimeter wavelengths. This makes it perfect to observe cold cosmic objects like the dust and gas of stellar factories, which only glow at those long wavelengths. Moreover, because ALMA combines the light of different antennas a few kilometers apart from each other, it can discern very fine details. ALMAGAL has looked at a large number of clumps, of different sizes, ages and star populations, all across different areas within our galaxy, presenting us with the common features shared across all stellar factories.
Unveiling a star’s production line
After examining 800 clumps and 6000 cores, ALMAGAL has made one thing very clear: not all star-forming regions are the same.
Like any factory, the more material, the higher the production yield. Cores need the material of their parent clumps to grow, so massive clumps are able to produce not only more cores but also more massive ones.
By observing regions of different ages, ALMAGAL has found that these factories evolve over time. Clumps tend to start with roughly circular shapes, but as they break into cores, they develop more intricate geometries. On the other hand, some massive clumps have not broken down into cores yet, probably because they are very young –– like factories that are still ramping up production and are not yet operating at full capacity.
By this point, the processes governing star formation already look quite complex, and it’s becoming clear that there isn’t a unique recipe to form stars. One of the next steps for the ALMAGAL team will be to study in more detail how gas flows from clumps into cores, and how the energy released by newly formed stars affects this inflow of gas.
Overall, thanks to the large and diverse dataset produced by ALMAGAL, we are in a better position to understand the mechanisms regulating the birth of stars and even the formation of their planetary systems.
Links
ALMAGAL is an international collaboration led by Sergio Molinari (Italian National Institute for Astrophysics - IAPS, Rome, Italy), Peter Schilke (University of Cologne, Germany), Cara Battersby (University of Connecticut, USA) and Paul T.P. Ho (Institute for Astronomy and Astrophysics, Academia Sinica, Taiwan). The description of the ALMAGAL survey and the first results are described in the following papers accepted for publication in Astronomy & Astrophysics:
- ALMAGAL I. The ALMA evolutionary study of high-mass protocluster formation in the Galaxy. Presentation of the survey and early results
- ALMAGAL II. The ALMA evolutionary study of high-mass protocluster formation in the Galaxy. ALMA data processing and pipeline
- ALMAGAL III. Compact source catalog: Fragmentation statistics and physical evolution of the core population
Biography Alejandro Izquierdo López
Alejandro is an evolutionary biologist from Spain who has been researching the ancestors of shrimps, centipedes and insects, trying to understand how evolution worked 500 million years ago. He has discovered several strange-looking extinct animals such as the “Pac-man crab” Pakucaris or the “Cambrian-beagle” Balhuticaris. He also loves communicating any type of science, including (of course), astronomy. At ESO, he aims to strengthen his communication skills while re-igniting his childhood passion for the cosmos.