21 July 2022

A glimpse of distant beginnings

Laura Pérez, winner of the 2021 TWAS-CAS Award, is a Chilean astronomer who takes advantage of high altitudes in the Atacama Desert to spot clues about how planets form around distant stars

Chilean astronomer Laura Pérez, a pioneer in highly sophisticated research on the formation of planets around distant stars, is the second-ever winner of the TWAS-CAS Young Scientist Award for Frontier Science

TWAS-CAS Young Scientist Award for Frontier Science is offered by UNESCO-TWAS in partnership with the Chinese Academy of Sciences (CAS) and the Lenovo company, the largest PC company in the world. In 2021, the Award recognized achievements in astronomy and cosmology. The 2022 edition will honour achievements in Earth sciences.

Pérez is an Assistant Professor of Astronomy at the University of Chile and a researcher at the Centro de Astrofísica y Tecnologías Afines in Chile, with a long history working with the Atacama Large Millimeter/submillimeter Array (ALMA). Her work observing and imaging young star systems orbited by thick disks of dust where planets are born has paved the way to how astronomers study planet formation—now a major area of study at ALMA.

Pérez called the award an “incredible honour,” and said it has already led to positive local media coverage in Chile and has boosted her career. “Maybe I can serve as inspiration for younger generations, who can see that we do very exciting science in the South of the world,” she added.

The allure of the stars

Pérez’s interest in astronomy began at a young age. She recalled that, as a child, she and her family would make trips along the northern coast of Chile, and she would be awe-struck by the majestic night sky along the coastline. Years later, as a teenager, she once found a sign taped to a lamp post announcing that visitors were welcome at a local amateur observatory, and eagerly urged her family to take her there. At the observatory, she saw for the first time Saturn, Jupiter and Jupiter’s moons through a telescope, and from that point onward she was determined to be an astronomer. 

She would later study astronomy at the University of Chile, and learned about innovative ways to view distant objects in the sky by detecting light outside of the visible spectrum, such as on radio wavelengths. Once she learned that ALMA was going to be constructed in her home country and conduct this kind of research, she set her mind on working there some day.

ALMA location, five kilometres above sea level in the Atacama Desert in Chile, is critical. Astronomers’ ability to observe objects in the sky is dependent on the light those objects give off, which is distorted by the Earth’s atmosphere. This is, for example, the same reason stars twinkle when viewed with the naked eye—stars don’t actually twinkle, that’s just the atmosphere of Earth distorting their light. 

This is also true outside of the 'visible spectrum' of light. At radio wavelengths, water vapor in the Earth’s atmosphere interferes with how clearly and precisely instruments can detect radio waves. So, astronomers build their telescopes as high up as they can to minimize the amount of atmospheric gas in the way. They also prize dry environments, such as in the Atacama Desert—one of the driest places on Earth.

As a graduate student, Pérez did her PhD work at the California Institute of Technology in the United States, on a technique to correct data from telescopes to account for the distortions from the atmosphere. She also studied planet formation. After she graduated, in 2012, she worked for a few years at the Very Large Array in the United States, and by 2014 was one of a small number of people with the special qualifications needed to research planet formation using ALMA, which, at the time, was just beginning its operations. And so, ALMA quickly invited her to join its staff, and her dream of working at the Chilean telescope array came true.

Distant discoveries

Pérez has now worked with ALMA for about a decade, in addition to serving as an assistant professor at the University of Chile, where she leads a group researching planet formation. 

Fully operational since March 2013, ALMA is the largest-ever international radio telescope project. ALMA has been a key instrument in discoveries on planet formation, because it can create relatively sharp images of distant stars that are still young—billions of years younger than our Sun—and objects in their orbits. Observing young stars is important, because planets don’t form on their own. They co-evolve alongside their young stars through what is known as a 'protoplanetary disk,' a thick plane of space dust that orbits stars.

According to computer simulations, scientists had already anticipated that they would be able to detect baby planets forming by identifying the paths they paved through the protoplanetary disks while orbiting. 

“One of the most common features in simulations is that they leave a ring around the disk,” said Pérez. “The planet is orbiting, growing, being formed and ‘eating away’ at the disk, leaving a path behind it.” 

In 2014, Pérez was part of a select group of scientists at ALMA to use its unique capabilities to attempt to generate detailed images of protoplanetary disks. They found what they were looking for in a star system called HL Tau, a star about 450 light-years from Earth in the constellation Taurus. HL Tau is less than 1 million years old, which is very young for a star, yet the stunning image produced by ALMA already featured numerous ring-like grooves in its protoplanetary disk, signalling the likely presence of several young planets. The findings of the research were published in The Astrophysical Journal Letters.

According to Pérez, the field of research on protoplanetary disks has been accelerating ever since. The sort of work that imaged HL Tau is now a routine practice at ALMA, and a major survey of young stars showed that rings in protoplanetary disks are common and have a variety of features.

“The size of the gap depends on the size of the planet,” she said. “If you have a big planet, it’s going to eat a lot of dust and leave a wide dark ring, and if you have a small planet like Earth forming, it will leave a miniscule gap. So, the field has grown into trying to characterize these features and understand their origins. But it all started with the HL Tau image, which was the first.”

This, however, isn’t the only way planets may form. In 2016, Pérez led a team at ALMA that imaged Elias 2-27, which is also about 450 light-years away from Earth, but in the constellation Ophiuchus. ALMA image revealed a whirling spiral pattern in the disk around the star. 

“I remember opening up the first data sets, and saying ‘Wow, there’s a spiral here,’” she said. “So, here we’re excited again because it means maybe there is a different route for planet formation.”

Pérez said this formation had been theorized before as a possibility in stars with particularly massive disks—massive enough that the gravity from the disk competes with the gravity of its star and accumulates into enormous spiral arms that slowly condense and, eventually, each one forms a planet. But ALMA image was the first through which such a pattern had been directly observed and the measurements obtained with these data suggested the disk was massive, as predicted. She published this finding too, in the prestigious journal Science

Pérez also has a favourite disk, which orbits around a star called HD 143006—about 380 light-years away and located in the southern constellation Scorpius. She led the relevant research, which was published in The Astrophysical Journal Letters in 2018, detailing how scientists found that this disk has rings, but is asymmetrical, as the outermost part of the disk has a thick arc of dense matter. 

Computer simulations can’t emulate this disk, she said, making its origin something of a mystery—though the leading hypothesis is that the gravitational influence of a second star is involved. “There is what we call a warp,” she said, “and the explanations for having warps is very interesting because sometimes it invokes the presence of two stars.” 

This impressive and unique body of discoveries led to Pérez joining the ranks of TWAS awardees, and the kind of high-level research at ALMA is a source of pride for Latin America and Chile. Pérez pointed out that the Chilean people both benefit from and contribute heavily to the operations of ALMA, the most sophisticated telescope of its kind in the world. 

“If you think about it, these machines are on the frontier of technological development for astronomy. So, something on the frontier is sitting here in our country, and the engineers, the people that make the system work, are mostly Chileans,” she said. “It’s beautiful, and it shows there is quality everywhere in the world—maybe we’re missing other opportunities by not considering everyone as we try to push the frontiers of science.”

Sean Treacy

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