Galaxies are fascinating places to explore. They have been around since nearly the beginning of the universe, are home to stars, planets, and other objects. When astronomers look at galaxies, with observatories such as Hubble Space Telescope, they might see star formation regions. They can also observe areas of star death. Many galaxies have black holes, particularly at their cores. And, of course, many stars in galaxies have planets or disks of material in which planets can form. In short, they present fascinating collections of telescope targets to study.
One famous galaxy has even changed our perception of the universe. Another one showed us how much a telescope could be improved. The first happened when astronomer Edwin P. Hubble began studying the Andromeda Galaxy in the 1920s. In 1924, as he observed it, he saw a variable star in one of its spiral arms and took images. Then, he calculated the distance to the galaxy using the period of the star’s brightening and dimming. It was a simple thing to do, but the results reverberated through the astronomy community like a shock wave. And, it forced astronomers to expand their understanding of the size of the universe.
Eventually, astronomy came to grips with the idea of an expanding universe. Astronomers found that galaxies were, indeed, stellar cities of their own. Up until Hubble’s work, they strongly suggested that these fluffy-looking spiral “nebulae” were probably part of our own Milky Way. Hubble’s work changed that forever. In addition, it altered our understanding of the age and extent of the universe.
So, of course, the telescope named after Edwin P. Hubble, the Hubble Space Telescope, has done some of its finest work when looking at galaxies. Whether it’s one galaxy, such as Andromeda, or millions of them (as in the various Deep Field studies it has done), HST regularly cranks out highly detailed views of them.
Hubble Space Telescope’s Grand View of a Grand Design Galaxy
Galaxy M100 has also taught us some lessons. Yesterday, I showed a pic of M100 as the telescope saw it with spherical aberration. Next to it was another one after one of the cameras was outfitted with corrective optics to sharpen the view. Each image of M100 that we’ve seen shows how the venerable and still-flying Hubble Space Telescope has improved.
Hubble turned to look at M100 again after it had an even better camera installed, the Wide Field Camera 3. It was put into the telescope during the last servicing mission in 2009, and almost immediately astronomers turned to M100 to get a better view.
Astronomers have long referred to the shape of M100 as a “grand design” galaxy. That’s because it has very obvious spiral arms (two of them!). In the outer regions of the two arms, we can see massive clouds of blue stars. Their presence also makes M100 a starburst galaxy. The region around the core is also blazing with newborn stars. The brownish dust lanes mark regions where stars could form in the future. The core of the galaxy is packed with older stars.
Hubble’s view of M100 resolves individual stars throughout most of this galaxy. Over the years, it has identified Cepheid variables within its arms. Cepheids are stars that vary in a predictable period of time. They have been used to establish cosmic distances since Henrietta Swan Leavitt discovered the period-luminosity relation (in 1908). She came up with that relation by charting their brightening and dimming cycles.
Edwin Hubble used her work to deduce the distance of the Andromeda Galaxy using the Cepheid variable he observed. As I mentioned above, his work showed astronomers that the universe is much larger than they thought at the time. It also gave them a way to more accurately measure distances between galaxies. Other fundamental discoveries about distance and the expansion rate of the universe have flowed from Hubble’s work.
Hubble Views Hubble’s Cepheid: Var!
In May 2011, Hubble Space Telescope turned its gaze toward the galaxy that had so fascinated its namesake. The Andromeda Galaxy is another grand design spiral, and the closest one to our own Milky Way. It lies some 2.5 million light-years away, and it’s moving toward us on a collision course. The 2011 view of Andromeda showed the Cepheid variable star that Hubble measured. It also revealed incredibly sharp images of individual stars. HST’s image gives remarkable insight into Andromeda, which is the only spiral galaxy we can see with the naked eye.
I especially like the comparison view below. It shows a remarkable ground-based view of Andromeda Galaxy, coupled with an inset made by HST (upper right). Edwin P. Hubble’s marked-up plate (lower right) shows the 1924 observation that led to his remarkable discovery. It really shows us how far astronomy has come since Hubble’s day. And, it’s all thanks to his namesake on orbit around Earth.
