Astronomy

It Took Five Years and A Million Images to Make this Atlas of Stellar Nurseries

Star formation is an intricate process governed by a swarm of variables, and it all happens behind a thick veil of dust. Astrophysicists understand it to a certain degree. But this is nature, and nature doesn’t give up its intimate secrets without a concentrated effort.

To learn more about the star formation process, astronomers imaged five star-forming regions in the southern hemisphere with the ESO’s VISTA telescope. It took five years and over one million images, and the result is the VISIONS survey.

Massive clouds of hydrogen give birth to stars when the gas collapses into knots. More and more gas and dust join the knot, and eventually, it becomes a protostar. It starts to generate heat, but it’s not a true star yet. Only when it becomes hot and dense enough to trigger fusion is it a star.

That description glosses over a lot of detail, some of which is known, some of which is obscured by the thick veil of dust. The trick to seeing through that dust and spying more detail lies in infrared light. The VISTA telescope has an infrared camera called VIRCAM which allowed a team of astronomers to see through the dust.

The astronomers captured over one million images for their VISIONS survey. They imaged star-forming regions in the constellations Orion, Ophiuchus, Chamaeleon, Corona Australis and Lupus. They presented their results in a new paper in the journal Astronomy and Astrophysics titled “VISIONS: the VISTA Star Formation Atlas.” The lead author is Stefan Meingast, an astronomer at the University of Vienna in Austria.

“In these images, we can detect even the faintest sources of light, like stars far less massive than the Sun, revealing objects that no one has ever seen before,” Meingast said in a press release. “This will allow us to understand the processes that transform gas and dust into stars.”

Alena Rottensteiner is a Ph.D. student at the University of Vienna and a co-author of the study. “The dust obscures these young stars from our view, making them virtually invisible to our eyes. Only at infrared wavelengths can we look deep into these clouds, studying the stars in the making,” Rottensteiner said.

Seeing through all that dust is a recurring theme in astronomy, and infrared telescopes are up to the task. That’s partly what drove the development of the James Webb Space Telescope, which has the power to not only peer through thick veils of obscuring dust, it can actually look back in time.

But ground-based facilities like VISTA and its VIRCAM can also see through the dust, though without the extreme angular resolution of the JWST. But since the five targets in the VISION survey are less than 1500 light-years away, VISTA is a suitable tool.

The images prove it.

This image shows the L1688 star-forming cloud in Ophiuchus. At only 460 light-years away, it’s one of the closest star-forming regions to our Solar System. The image shows several dozen prominent young stellar objects. The young stars are surrounded by a highly structured cloud composed of gas and dust that is largely shaped by young, optically revealed hot stars in the vicinity. Image Credit: ESO/Meingast et al. 2023

The VISTA telescope exemplifies the rapid technological advancements of the last few decades. Thanks to VISTA and the VISION survey—and other similar efforts—astronomers have a wealth of data at their fingertips. New discoveries and understandings lurk in all that data, and the team behind it is emboldened by the survey.

“VISIONS will enable the community to address a variety of research topics from a more informed perspective, including the 3D distribution and motion of embedded stars and the nearby interstellar medium, the identification and characterization of young stellar objects, the formation and evolution of embedded stellar clusters and their initial mass function, as well as the characteristics of interstellar dust and the reddening law,” they explain in their paper.

This image shows the Coronet star cluster in the Corona Australis constellation. The clouds of gas and dust are where new stars are being born. Image Credit: ESO/Meingast et al.

VISIONS contains thousands of young stars from 0.1 to 10 million years old. The survey sensed small objects down to only a few Jupiter masses and has a spatial resolution of 100 to 250 AU. It also measured the motions of young stars that are still buried in their parent cloud and are hidden in optical light. By observing them several times over five years, VISIONS allows astronomers to study how young stars move.

“With VISIONS, we monitor these baby stars over several years, allowing us to measure their motion and learn how they leave their parent clouds,” explained João Alves, an astronomer at the University of Vienna and Principal Investigator of VISIONS. That’s impressive since, from our viewpoint, the stars’ movement can be less than the width of a human hair.

This image compares two views of the star-forming region Lupus 3, about 600 light-years away in the constellation Scorpius. It’s part of a larger complex called the Lupus Clouds. The left panel is an optical light image, and the right panel is an infrared image. Image Credits: (L) ESO/R. Colombari. (R) ESO/Meingast et al.

One of VISIONS particular strengths is detecting young low-mass objects. These objects are hidden in other surveys like Gaia, which is in other ways very complementary to VISIONS. “VISIONS can observe objects with masses of only a few MJup in all cloud complexes included in the survey and, depending on their distance, even at ages above 10 Myr,” the paper explains. That means that VISIONS will contain star formation products across the entire mass spectrum. Maybe most impressively, VISIONS may even contain the locations of free-floating planets or rogue planets.

The VISIONS survey will serve the astronomy and astrophysics community well over the years if other similar surveys are any indication. The Sloan Digital Sky Survey (SDSS,) for example, ended in 2008, and its data is ubiquitous in astrophysics research. There are numerous others, like IRAS, 2MASS, and DES, and data from all of them regularly appears in research. The most impressive survey may be yet to come when the Vera Rubin Observatory gets going sometime in the summer of 2024.

Like VISIONS, those others are public surveys and the data is freely available. “There is tremendous long-lasting value for the astronomical community here, which is why ESO steers Public Surveys like VISIONS,” said Monika Petr-Gotzens, an astronomer at ESO in Garching, Germany, and co-author of this study.

The European Southern Observatory has bigger things on the horizon, and VISIONS will help set the stage for more detailed, follow-up study of individual objects with their future telescopes. When the ESO’s ELT (Extremely Large Telescope) sees its first light sometime around 2028, observing time will be in high demand, and astronomers will be clamouring for access. By pre-identifying targets, VISIONS will make the usage of the ELT and other telescopes more efficient.

The ESO says that the ELT will allow astrophysicists to study star-forming regions in unsurpassed detail at distances ten times larger than is possible today. A bit part of the VISIONS survey is to understand the star formation question in all its complexity, and the ELT will advance it even further.

“The ELT will allow us to zoom into specific regions with unprecedented detail, giving us a never-seen-before close-up view of individual stars that are currently forming there,” concluded Meingast.

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Evan Gough

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