How A Star Expanded Our Understanding of the Universe
Humans have stared at the stars throughout history and that makes stargazing one of our oldest sciences. Probably THE oldest, along with the accidental chemical experiments that led our earliest ancestors to create things like soap and tea and other necessities. And, of course, humans have engaged in biological experiments throughout history, and eventually took up engineering and geology and all the other sciences we know of today.
Still, it’s astronomy that piques our interest. I often think about what the first people who stared at the stars thought of what they were seeing.
I’ll give our species the benefit of the doubt and assume that there was intent curiosity about it all, a sense of wondering what they are and if they could be touched or visited. It probably didn’t take long for humans to start woolgathering all kinds of stories about them, and eventually their awe at these sparkly things turned into some kind of reverence. Heck, a sunrise inspires me greatly, and I’m sure it did for those early folks, as well.
I also like to think of those early astronomers getting together and discussing what they saw, debating what the motions meant, how they were made, and what relationship those things had to Earth. The history of astronomy is written by those people who did MORE than just look at the sky. They made careful notes about what they saw, and those observations led to speculation and eventually the application of scientific principles to explain the structure and motions of things in the sky. And, in due time, they shared their knowledge and our societies are richer for it today.
Speaking of meetings, the summer meeting of the American Astronomical Society is taking place this week in Boston. I can’t be at this one, but I’m hearing and seeing lots of fascinating news from the assembled astronomers. They’re sharing what they’ve found — from planetary systems to peeks at the most distant stars and galaxies.
The star that changed our perceptions of distance in the universe. Courtesy STScI.
One story that caught my attention is focused on a star in a distant galaxy. It first caught the attention of an astronomer early in the 20th century. The star is a Cepheid variable star — that is, one that pulsates in brightness in a regular and predictable rhythm. It caught the attention of astronomer Edwin Hubble (for whom the Hubble Space Telescope is named).
He knew that the light pulsations could be used to help measure distances in the universe. So, he did what any self-respecting astronomer would do, he measured the pulsations precisely, kept good records, and when he had enough good data, he calculated the distance to the star.
That calculation (which any student in astronomy can do these days), showed that the galaxy in which the star existed — the Andromeda Galaxy — was not part of the Milky Way Galaxy that we live in. It wasn’t even close. Instead, it and Andromeda were at least 2 million light-years away.
This finding probably excited Hubble very much; enough that he sent a letter to his colleague, Harlow Shapley, describing his finding. Shapley recognized the significance of Hubble’s finding — that is, that the universe was larger than we thought — and commented to another colleague, “Here’s the letter that destroyed my universe.”
It was an important step in understanding how large the universe is, one that astronomers still rely on today to figure out distances to some of the farthest objects in the cosmos. In commemoration of Hubble’s landmark observation, astronomers with the Space Telescope Science Institute’s Hubble Heritage Project partnered with the American Association of Variable Star Observers (AAVSO) to study the star. AAVSO is a group of dedicated observers (both amateur and professional) who focus on the glimmerings of variable stars. Their work has contributed greatly to our understanding of these stars — and hence, to distances in the cosmos.
AAVSO observers followed brightness pulsations of the star in Andromeda — called V1 — for six months. Their observations were combined into what astronomers call a data “plot” (that is, put into an X/Y axis, just like you might remember doing in geometry or calculus). That plot is called a “light curve” and it shows the rhythmic rise and fall of the star’s light. (If you want to see what a light curve looks like, click on the AAVSO link above; they have some on their front page, and explain them in more detail).
Based on this data, the Hubble Heritage team scheduled Hubble telescope time to capture Wide Field Camera 3 images of the star at its dimmest and brightest light levels.
As a reminder of how important these observations are, the combined data and images were presented at the AAS meeting on Monday (you can read the whole story here). Astronomer Max Mutchler commented, “This observation is a reminder that Cepheid variables are still relevant today. Astronomers are using them to measure distances to galaxies much farther away than Andromeda. They are the first rung on what astronomers call the cosmic distance ladder.”
That ladder stretches out to the earliest stars and galaxies, more than 13 billion light-years away. It’s an awesome achievement for a species that only began looking at the stars with the intent to understand them perhaps a few hundred thousand years ago.