Northwest astrophysics professor directs first Webb telescope project


An artist’s conception shows the James Webb Space Telescope orbiting the Sun, one million miles from Earth. Credit: NASA-GSFC, Adriana M. Gutierrez (CI Lab)

Since early July, the James Webb Space Telescope has been providing Earthlings with stunning images of nebulae (star-forming regions), a cluster of galaxies that appeared in It’s a wonderful life and thousands of galaxies in deep field images, all with clarity and detail never before possible. More recently, NASA touted the telescope’s first images of Mars.

But the Webb Telescope – JWST for short – is more than just an expensive camera that took 25 years to build. Positioned in orbit around the Sun, one million kilometers from Earth, JWST helps scientists look farther out into space and billions of years back to more clearly observe the universe in its earliest stages of formation.

Professor of physics and astronomy Allison Strom. Credit: Northwestern University

Closer to home, Allison Strom, a professor of physics and astronomy at Northwestern University, is leading one of the first science projects to use JWST: the CECILIA Survey, which took 40 hours of research on the new telescope from celebrities in early July.

The survey used an instrument called NIRSpec (for Near-InfraRed Spectrograph), which took images of about 30 galaxies that were forming 10 billion years ago, during a period called “cosmic noon”, several billion years after the Big Bang.

“These are like teenage galaxies going through a period of rapid change and rapid growth, and what happens to them during this period of their lives will essentially determine what happens for the rest of their lives,” explained Strom, whose research focus on how galaxies grow and change. Studying relatively young galaxies during this 10 billion year “look back time” provides a basis for understanding how older galaxies developed and why some are different from others. (When a telescope looks at objects that are, say, 10 billion light-years away, it actually sees them as they were 10 billion years ago.)

The CECILIA Survey team will use the JWST data to determine the chemical composition of each galaxy – the presence and amount of oxygen, sulfur, silicon and other elements emitted during the evolution and death of stars. The amount of these elements helps reveal the rate and speed of star formation in a galaxy, which in turn sheds light on how the galaxy formed and grew. Strom compares the chemistry of galaxies to DNA, which provides information about the origins of living things and can also predict certain aspects of their development.

Follow the galaxies in a rainbow

CECILIA – an acronym for Chemical Evolution Constrained using Ionized Lines in Interstellar Aurorae – detects specific elements using spectroscopy, a method of viewing the amount of light coming from an object such as a planet, star or a galaxy in different colors. “Light” in this sense means wavelengths of varying frequencies on the electromagnetic (EM) spectrum, only a small portion of which can be seen by the human eye.

Electromagnetic radiation includes radio waves, microwaves, infrared radiation, visible light (what we see), ultraviolet light, X-rays and gamma rays. JWST examines near-infrared and mid-infrared radiation in the universe.

Credit: NASA and the Space Telescope Science Institute (STScI)

Each element of the periodic table has a unique spectrum that is expressed through a rainbow-colored band of light marked with dark absorption lines. A spectrum can also be viewed upside down: a black band with colored emission lines (the “ionised lines” named after CECILIA).

JWST’s distance from the moon and Earth, as well as its exclusive focus on infrared light, make it a more sensitive tool than ground-based telescopes for capturing the spectra of distant galaxies, according to Strom.

Credit: NASA and the Space Telescope Science Institute (STScI)

“Because they are very distant, they are also rapidly moving away from us due to the expansion of the universe, so all of their features are red-shifted, they stretch into longer wavelengths , and then you have to look in the infrared,” she said.

The NIRSpec instrument used by CECILIA is similar to a camera, but with 250,000 tiny “microshutters”, each measuring about the width of a human hair. NIRSpec can collect spectra of up to 100 objects at once, so it’s much faster than observing a single object at a time through a more traditional telescope.

Gwen Rudie, co-principal investigator with Strom on the CECILIA survey, spent around 100 hours selecting galaxies with a wide range of properties for NIRSpec to visualize. These galaxies will serve as a benchmark for building a new tool to help astronomers measure the chemistry of other galaxies during the same 10 billion year retrospective period and even earlier.

“The goal of CECILIA is to build this tool that we can apply to thousands of galaxies at cosmic noon and many other galaxies up to the time of reionization, the very first galaxies,” said Rudie, an astronomer at the Carnegie. Institution for Science in Pasadena, California. “By doing so, we hope we can trace the accumulation of heavy elements in the universe that signal this growth of galaxies and how they change over time to resemble all the diversity of galaxies we see today. “

Tribute to a Stellar Pioneer

The name of the CECILIA survey honors Cecilia Payne (later Payne-Gaposchkin), the astrophysicist who first determined that the sun and the earth had a different chemical composition. Payne, born in England, studied science at Cambridge University, completing her studies in the early 1920s, although she was refused a degree because she was a woman. She accepted a postgraduate fellowship at the Harvard College Observatory, undertook her doctoral dissertation, and in 1925 became the first woman to earn a doctorate. in Astronomy from Radcliffe, Women’s College, Harvard.

Cecilia Helena Payne-Gaposchkin (1900-1979), an astrophysicist at Harvard College Observatory, determined that stars and planets had different chemical “DNA”. Credit: Smithsonian Institution Archives, Accession 90-105, Science Service Records, Image No. SIA2009-1326

Supported by his extensive analysis of stellar spectra, Payne’s doctoral thesis proposed that helium and especially hydrogen – the lightest and most abundant elements in the universe – were the main components of stars, contradicting the long-held beliefs that planets (which are largely composed of heavier elements) and stars were the same.

A prominent Princeton astronomer, Henry Norris Russell, disputed his discovery, but four years later realized that Payne was right. More than three decades later, Payne had not only become Harvard’s first female faculty member, but she also became the first woman to be named chair of Harvard’s astronomy department, after spending years teaching and to conduct research – much of it on variable stars with her husband, astronomer Sergei Gaposchkin – without the status or salary of a full professor.

“I think she’s definitely one of those really big giants of the field that a lot of women look up to,” Strom said, “and given the connection to learning how to make things up, we were really excited to pay homage to her.”

In 1977, Payne was rewarded when she became the first woman to receive a prestigious award named in honor of her former critic: the Henry Norris Russell Lectureship, an award for lifetime achievement in astronomical research given by the American Astronomical Society. (Russell had died 20 years earlier.)

Rudie adds that the project’s name not only honors women like Payne – pioneers of astronomy and astrophysics who received little or no credit for their work – but also symbolizes her and Strom’s desire to make astronomy a more inclusive environment for all.

“A hundred years ago, women weren’t allowed to have innovative ideas and participate in science,” Rudie said. “Women are allowed now, but there are still barriers and a lot of progress to be made. We are doing our best to open doors more widely to other communities that have been excluded and still are today.

Galactic DNA: what is it for?

In a world that seems to be wasting away from rising temperatures and collapsing under the weight of inflation, some might wonder what galaxy formation has to do with them and why anyone but the most dedicated science nerd would be interested.

Strom emphasizes that science can be an expression of human creativity, and she thinks more children might be interested in science if they were exposed to the creative aspects of it. Additionally, many scientific instruments have evolved for everyday use, including digital cameras and medical scanners whose roots began in astronomical imaging. More importantly, she said, scientific research like the CECILIA survey contributes to our knowledge of who we are and how we got here, from the Big Bang to the formation of our galaxy, our solar system and our home planet.

“If you want to know where we came from, knowing where the Milky Way came from is really a big part of this story,” Strom said, “so understanding galaxies is really one of the central questions about our own origin. and our own place in the universe.”

Related: The James Webb Space Telescope has sparked some controversy over its namesake, and some astronomers – including two from the Chicago area – are demanding that NASA change the name of the device.

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