The closest star to Earth, Proxima Centauri, is a little over four light years away. That’s the same distance as circling the Earth over 963 million times.
What’s more — it can take one star millions of years to form and, later, die.
So how is it even possible to study stars? The key is careful observation — often under strict viewing conditions and with powerful telescopes — to collect data that can eventually support conclusions, even tell a story.
In Western Kentucky University’s Physics and Astronomy department, two professors — Ting-Hui Lee, Ph.D., and Steven Gibson, Ph.D. — are doing just that.
Gibson’s focus is on stars as they form and, more specifically, the interstellar matter from which stars form. Lee, on the other hand, researches planetary nebulae, which are sun-like stars that are dying but don’t explode as supernovas.
By examining the early stages of star formation and their decline, Gibson and Lee hope to not only learn more about the stars themselves, but also better understand the surrounding galaxy, including its chemical elements, to help tell the story of our galaxy’s evolution.
Planetary nebulae: What dying stars reveal about their origins
You may have seen planetary nebulae and not realized it. As Lee explained, stars approaching death will puff up, and the outer layer of gas and some particles will expand into space. If you’ve ever looked through a telescope and noticed something fuzzy in the sky, that might be a planetary nebula (a misleading name, Lee said, given that the object has nothing to do with planets).
During a star’s life, it emits a large amount of light and heat as hydrogen turns to helium inside the star. Yet as a star approaches its end, those elemental transformations become more complicated.
“The helium starts turning into other, heavier elements — carbon, oxygen, nitrogen — elements that only stars can make, and which are so essential for organic life,” Lee said. “By studying the elements in a planetary nebula, we can figure out where the star came from and how it produced heavy elements inside it.”
Yet factoring in the almost unimaginable distance and time that separates us from planetary nebulae, how can Lee observe what’s happening?
“We observe them by looking at their light,” she said. “I mostly stay in the visible light range (optical astronomy). We use a sophisticated spectrograph that can divide the colors of the light very finely. Then we start seeing structures in the light — maybe a bright line at a certain wavelength, which we call an emission line.”
Lee then measures the wavelengths of those bright lines, which help her determine which elements produced the lines. Think of it as the forensics of astronomy.
“If you look at trace elements inside a bone, you can tell where it’s from,” she said. “Each element produces different sets of lines, kind of like human fingerprints. By analyzing the light from nebulae, we learn how much they have of each element and can tell the environment in which the stars were born. We can use planetary nebulae to tell how our galaxy evolved over time.”
The challenges of observing planetary nebulae include securing access to the right type of (powerful) equipment. Additionally, Lee can only observe planetary nebulae under specific viewing conditions.
“You have to have good weather, clear skies and no light pollution, so you can’t use a telescope in the city,” she said.
In fact, the optimal location is in the mountains, which is why Lee has used observatories in Hawaii and Chile to collect data. Thanks to increasingly sophisticated technology, Lee has been able to work with telescope operators to control the observations remotely from her home — or theoretically anywhere with an internet connection.
Lee has also turned these observing sessions into learning opportunities and has invited students to her home to see how the work is done. Lee often shares updates on her research with her astronomy classes. And although professors know how challenging it can be to juggle research and coursework, Lee said teaching is an important part of her work.
“It’s fun to help students realize how many things are happening in the sky,” she said. “The challenge is finding a balance, but we do what we love to do.”
Interstellar matter: Understanding the storms that help form stars
If you think about space as a vacuum, you’re not alone. To the naked eye, what’s out there looks like a mixture of stars and empty space. But that apparently empty space between the stars actually contains particles that, eventually, form new stars and solar systems. And it’s in those regions that Gibson focuses his research.
Forensics is an apt analogy for Lee’s research. And for Gibson, it’s meteorology.
“The interstellar matter (mostly hydrogen gas but other elements and solid particles we call dust) isn’t just smoothly distributed in space,” he said. “There are areas where it’s more concentrated or less, and temperatures can range from thousands of degrees to 10 degrees above absolute zero.”
Just like clouds gather and form thunderstorms on Earth, similar “storms” erupt throughout space. Yet instead of raindrops and hailstones, these storms form stars.
“I’m interested in finding out the conditions where these star-forming clouds occur and what leads to them,” Gibson said. “How do they become cold and dense enough for the particle motions to be overcome by their mutual gravitational attraction?”
Like Lee, Gibson navigates challenges to collecting data. He uses radio and infrared observations that can be done at any time of day, but here’s the kicker: he must use infrared instrumentation that’s in space. Earth’s atmosphere absorbs most infrared light and won’t let it through.
Instead of splitting his time between WKU and a space shuttle, Gibson taps into a treasure trove of data collected by a variety of space telescopes, including those owned by NASA and the European Space Agency. Much of this data is available on public databases.
“In astronomy, things become more valuable when you share them,” he said. “It’s about getting information out to make it useful, so there’s an incentive to share that data, especially for publicly funded projects.”
Another challenge is that the ground-based radio telescopes Gibson uses need to be large because the amount of radio energy emitted from space is shockingly small.
“If you gathered up all the energy collected from sources outside the solar system by all the radio telescopes in the world over the last 5-6 decades, it wouldn’t be enough to melt a single snowflake,” Gibson said. “The radio noise of human civilization is much louder and requires great care to avoid it contaminating the natural signals we are after.”
With the data, Gibson can make comparisons to physical models. For example, a cloud of interstellar matter of a certain size and brightness in radio or infrared light is expected to have a certain density and temperature. Gibson can then infer how it would change over time and even how much of it may not be directly observable.
The infrared observations, specifically, can help Gibson better understand what’s happening within the gas that makes up most interstellar matter.
“The dust particles glow faintly in infrared light,” he said. “I’ve become more interested in measuring the quantity of the dust that’s out there to try and see if that can tell me what the gas is doing.”
Understanding the bigger picture
For both Lee and Gibson, a better understanding of a small part of a star’s life cycle can help contribute to a more comprehensive view of what’s happening in space.
“Let’s say you’re walking through a forest one afternoon, and you want to understand the lives of trees,” Lee said. “You can’t watch a seed grow into a sapling and then a tree in such a short time, but you could look around and see different stages of trees, then use inference to come up with reasonable conclusions as to how it all works.”
In a larger view, astronomy research of any type offers several primary benefits. First, Gibson said that astronomy is effective in raising general interest in science and the world around us.
“It’s an experience that everybody has,” he said. “Anyone can look up at the sky.”
Secondly, astronomy research helps contribute to a better understanding of how things work, influencing outcomes like instrumentation design. In fact, Gibson is working with WKU physics, astronomy and engineering students and faculty to build a small radio telescope using a discarded 10-foot satellite dish.
“Our goal is to turn this into a working radio telescope that we can actively point around and even control remotely in the long term,” Gibson said. “Research-grade telescopes are much larger, but this one will be a good educational tool so that people can learn how radio telescopes work and study a number of celestial sources like the sun and planets.”
Finally, astronomy research enables a deeper knowledge of topics like basic physics, especially since what happens in space often can’t be replicated here.
“The vacuums in space are better than anything we can make in a lab on Earth,” Gibson said. “We can learn about gravity and matter under extreme conditions — there’s some incredibly wild physics going on in space.”
And when you’re working in a place of infinite size, that means your research is equally infinite.
“When I look out at the universe, there are always new things to explore and do and discover,” Gibson said.