Galaxies Are Like People

They Come in All Shapes and Sizes

Artist's concept of the Milky Way Galaxy. Credit: NASA JPL

You grew up in this galaxy.  It’s what astronomers call a “barred spiral” and if you were an alien living on a planet a galaxy with a “top down” view of the Milky Way, this is what the view would be.  The central area, called the “bulge” is filled with stars and, of course, our own supermassive black hole.  The bar of light extending out from the center is a sort of “transport” mechanism for gas and other materials toward the core. The spiral arms are where a lot of the latest star-forming (and star death) action is taking place.  Our planet is about 2/3 of the way out from the center, between a pair of spiral arms. We don’t live in the center of this stellar city, but more like in the outskirts where the action is a bit quieter. That’s good for us, since being too close to the center might not be good for our solar system’s health.

Astronomers are well aware that not all galaxies look like this. In fact, the Milky Way didn’t always look as it does now. It has evolved, just as all other galaxies have throughout the cosmos. To study the changes that galaxies go through, astronomers have categorized them by shape (their “morphology”) and their sizes, as well as other characteristics like the ages of their stars and the metal content they have.

A new, colorful collection of galaxy specimens has been released by NASA's Wide-field Infrared Survey Explorer, or WISE, mission. Image credit: NASA/JPL-Caltech/UCLA

NASA’s WISE mission (the Wide-field Infrared Survey Explorer), is studying distant galaxies and today has released images of an assort mix of colorful and shapely galaxies. Just as people come in all sizes and variations on the two-arms, two-legs, height and weight arrangements of our bodies, galaxies also exhibit a wide array of variations on the standard theme.

The new collection of nine galaxies shows off this diversity, with members of different sizes, colors and shapes. Infrared light from the galaxies, which we can’t see with our eyes, has been translated into visible-light colors that we can see. Blue colors show older populations of stars, while yellow indicates dusty areas where stars are forming.

This collage of WISE images shows everything from “grand design spirals,” with their elegant swirling arms, to so-called “flocculent” galaxies, which look more patchy and nebulous.  All these galaxies are close enough to us that WISE can see details of their structures. Some show sinuous arms and central bulges filled with packed-together stellar populations and possibly even central supermassive black holes.

Some of the galaxies are oriented toward us nearly face-on, such as Messier 83, and others are partly angled away from us, for example Messier 81. One galaxy, NGC 5907, is oriented completely edge-on, so that all we can see is its profile. The edge of its main galaxy disk appears pencil-thin, and its halo of surrounding stars is barely visible as a green glow above and below the disk.

The arms of the galaxies come in different shapes too. Messier 51 has arms that look like a spiral lollipop, while the arms of the flocculent galaxy NGC 2403 look choppy, perhaps more like layered frosting. Astronomers think that gravitational interactions with companion galaxies may lead to more well-defined spiral arms. One such companion can be seen near Messier 51 in blue. Some of the galaxies also have spokes, or spurs, that join the arms together, such as those in IC 342.

As astronomers scan the universe, they’ll be able to dig more deeply into the different galaxy shapes they see. Just as images of different people at different ages tell us about how humans are born, age, and die, images such as these give important clues about a galaxy’s evolutionary history and the stars it contains. Not only will this work help us understand the life stories of all galaxies, it contributes to a greater appreciation of our own Milky Way and the changes it went through that led to the creation of our own Sun and planets.

Good Night, Spirit

NASA Says Spirit Isn’t Phoning Home

Mars Exploration Rover Spirit. Courtesy NASA.

The Mars Exploration Rover Spirit, a mission designed to last three months but instead lasted more than six years, has not responded to NASA’s attempts to contact it for the past 10 months. The last transmission to the plucky little rover, which got mired in a sand trap on Mars but continued to send information until the onset of Martian winter last year, will be tomorrow.  NASA engineers say that the rover has endured a pretty stressful winter, what with the lack of sunlight to keep its batteries charged to run its survival heaters. Without those warmers, the internal temperatures on the rover likely got cold enough to damage or destroy critical components and connections. If that has indeed happened, then Spirit has gone to sleep and won’t be waking up again.

Spirit landed on Mars on Jan. 3, 2004. After accomplishing its prime-mission goals, the rover’s controllers programmed it to accomplish additional objectives, including further exploration of the region where it landed, and ongoing imaging of the surface and atmospheric measurements. Its twin, Opportunity, continues active exploration of Mars on the other side of the planet.

With the loss of Spirit, NASA is redeploying teams to work with the Mars rover, Curiosity, which launches in November of this year. Mars exploration goes on — building on Spirit’s successes and accomplishments. For those of us who are interested in Mars and its continued exploration, it’s a sad passing, but we know that Spirit has advanced our understanding of the planet.  If you haven’t kept up with the latest in Mars exploration, check it out at NASA’s MER pages.

Hubble’s Star

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.