Category Archives: galaxies

Hubble and the Magnificent Spiral Galaxy

Galaxy Beauty
NGC 3370

I like galaxies — especially spirals. They look spectacular and whenever an image like this one comes down from HST, I always wonder about other planets around other stars in distant galaxies. Recently this one crossed my desk. At first glance you can appreciate the spiral structure and the many stars that make up this city of light. But, there’s more to the story. Distant galaxies contain stars that we can use to determine distances. How does it work? Here’s the press release to explain:

Amid a backdrop of far-off galaxies, the majestic dusty spiral, NGC 3370, looms in the foreground in this NASA Hubble Space Telescope image. Recent observations taken with the Advanced Camera for Surveys show intricate spiral arm structure spotted with hot areas of new star formation. But this galaxy is more than just a pretty face. Nearly 10 years earlier NGC 3370, in the constellation Leo, hosted a bright exploding star.

In November 1994, the light of a supernova in nearby NGC 3370 reached Earth. This stellar outburst briefly outshone all of the tens of billions of other stars in its galaxy. Although supernovae are common, with one exploding every few seconds somewhere in the universe, this one was special. Designated SN 1994ae, this supernova was one of the nearest and best observed supernovae since the advent of modern, digital detectors. It resides 98 million light-years (30 megaparsecs) from Earth. The supernova was also a member of a special subclass of supernovae, the type Ia, the best tool astronomers have to chart the growth rate of the expanding universe.

Recently, astronomers have compared nearby type Ia supernovae to more distant ones, determining that the universe is now accelerating in its expansion and is filled with mysterious “dark energy.” Such measurements are akin to measuring the size of your room by stepping it off with your feet. However, a careful measurement of the length of your foot (to convert your measurements into inches or centimeters) is still needed to know the true size of your room. Similarly, astronomers must calibrate the true brightness of type Ia supernovae to measure the true size and expansion rate of the universe.

The very nearest type Ia supernovae, such as SN 1994ae, can be used to calibrate distance measurements in the universe, because other, fainter stars of known brightness can be observed in the same galaxy. These stellar “standard candles” are the Cepheid variable stars, which vary regularly in brightness with periods that are directly related to their intrinsic brightness, and thus allow the distance to the galaxy—and the supernova—to be determined directly. However, only the Hubble Space Telescope, equipped with its new Advanced Camera for Surveys, has the capability to resolve these individual Cepheids.

Adam Riess, an astronomer at Space Telescope Science Institute in Baltimore, Md., observed NGC 3370 a dozen times over the course of a month and has seen many Cepheid variables. Already he and his colleagues can see that these Cepheids are the most distant yet observed with Hubble. Because of their need to observe this galaxy with great frequency to record the variation of the Cepheids, the total exposure time for this galaxy is extremely long (about one full day), and the combined image provides one of the deepest views taken by Hubble. As a result, thousands of distant galaxies in the background are easily discernable.

Dr. Riess imaged NGC 3370 with Hubble in early 2003. His science only required looking at NGC 3370 in two filters that covered the visual and infrared portions of the spectrum. By teaming up with the Hubble Heritage Project, a third blue filter was added to the data to produce the composite three-color image that is shown.

Credit: NASA, The Hubble Heritage Team and A. Riess (STScI)

Whew!

A little more than a year ago I started working on a book about astronomy — actually the sixth one I’ve worked on over the years. It’s due out later this year and I’ll say more about it as time gets closer for it to hit the shelves. Doing a book is a big project. The first book I ever did — about Jupiter — was a commission job for a series. They sent me all the artwork and what I wrote complemented and described a series of paintings by space artist Don Davis.

The next book was called Hubble Vision and it started out as my masters’ thesis in science journalism. But, it quickly grew to be more than a thesis and so I decided to turn it into a book. At the same time I was working with an astronomer named John C. Brandt — we were doing an atlas of Comet Halley images together — and he had been reading my manuscript for Hubble Vision and making some very cogent and useful comments on it. So, I asked him to be my co-author on the book and he accepted. It was published by Cambridge University Press and went through two editions. Between the two editions, I edited a book with Kelly Beatty and Andy Chaikin called The New Solar System, 4th Edition, a year later I did a conference proceedings about HST science with the Goddard High Resolution Spectrograph instrument, and also edited two books for Sky Publishing Corporation when I worked there as an editor.

So, you’d think doing all this book work would get to be old hat, right?

Well, in a way it is and in another way it isn’t. Doing a book requires an incredible amount of mental effort. A writer carries around an amazing amount of stuff in mental inventory, constantly working and reworking it. Every book is new and each has its own challenges. In this latest one — which brought me together with J.C. Brandt again — we wanted to talk about all the great stuff that the world’s observatories are studying. That means showing lots of pretty pictures. And I do mean LOTS of them. There are so many gorgeous cosmic visions out there that picking and choosing which ones to include in the book was really difficult. But our publisher held us to about 180 images in a 225 page book, so we had to be selective.

On a parallel track with the great selection of images we wanted to bring some science to the reader in an approachable way. There’s a lot to write about in astronomy, and nearly all of it requires an explanation. So, one part of doing a really effective book is coming up with approachable, understandable explanations of stuff. It takes a long time. And the writer sorts through an incredible number of details in his/her mind. Keeping track of them almost requires some sort of bookkeeping system on the side so that if you talk about solar physics in chapter 2 for example, you have to make sure it dovetails with the discussion of stellar physics in chapter 4, and so on.

With two of us doing the work it doesn’t exactly halve the amount of effort each of us must put in. I’d say it probably stays at 100 percent for each of us, plus we each have to communicate ideas with the other. That wasn’t too difficult when we saw each other at the lab every day or so, but now that we’re separated by a couple of thousand miles, we rely on email and telephone calls and occasional visits with each other. At those times we lock ourselves away in an office or library and work, stopping only for meals and coffee. And, in the case of our last visit together (at my place), fur fixes — wherein we stop to pet cats. You’d be amazed at how the problems of explaining some difficult concept in stellar physics somehow get solved after a session with a cat.

Galaxy as seen by the VLT
Galaxy as seen by the VLT

Well, we finished our book last week and now I’m slowly getting my brain back to the real world. All the facts and figures, diagrams, queries to researchers, double-checking of late results — all of that is behind us for now. JC is off on a vacation and I’m sitting here writing a blog entry — my first in several weeks!

I’ll leave today’s entry with a pretty picture. It’s one that didn’t make the cut into the book (remember, we couldn’t have everything!). It’s a galaxy that lies about 7 million light-years away in the Sculptor group of galaxies. This image was taken by the European Southern Observatory, using the Very Large Telescope called ANTU.