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For centuries, astronomers have scratched their heads and wondered what those strange “spiral nebulae” in the sky are like.
They appeared pretty much everywhere they looked. Some were small, some were large, some were amorphous spots, some showed a clear spiral or other structure. Astronomers knew that some nebulae – Latin for “fog” – were gaseous by the end of the 19th century, but the true nature of their diversity remained elusive. Some astronomers speculated that some of them were separated galaxies like our own Milky Way, while others thought it was gaseous clouds inside our Milky Way, which included the entire Universe.
This changed in the 1920s when, among other things, a team of astronomers (including Edwin Hubble) found variable stars in the “Andromeda Nebula” that gained its distance outside of the Milky Way – thus gaining the galaxy name of Andromeda – around at the same time as Vesto Slipher (such a big name) discovered that more distant galaxies were moving away from us, which made it possible to understand that the Universe is expanding.
This all happened because we improved our technology and could probe these distant objects and understand them better. One of the biggest breakthroughs was that larger telescopes could be fitted with cameras, and we could see that some of these nebulae were made up of stars. Their great distance meant that these stars were all blurring together in a fog (hence nebulae), but with sufficient resolution you could see what they really were.
Today, a century later, to see stars in other galaxies is insignificant. It’s no less magical, but when you take a telescope, place it in space, and give it the name Hubble, stars in other galaxies become easy to choose from. As with the galaxy very close NGC 55:
Wow.
NGC 55 (also called Caldwell 72; click here for a full size image of almost 4000 pixels per side) is a member of the Local Group, our small suburban neighborhood of a few dozen galaxies including Andromeda, the Milky Way and many of tiny galaxies called dwarves. This one is just over 6 million light years away, so twice as far from us as Andromeda, but much smaller. In fact, it’s similar to a dwarf galaxy that orbits the Milky Way called the Large Magellanic Cloud (or LMC), a galaxy that’s generally irregular in shape but appears to be trying to form a spiral structure.
NGC 55 is flattened, and we see it almost on the edge, so it looks like a long smear or a cigar shape. The Hubble image reveals that it is loaded with stars, as well as its own collection of nebulae. The colors in this image are a bit strange; what is displayed in blue is actually red light, and what you see in red is near infrared light, just outside the detection range of the human eye. This is why the gas clouds appear blue here; they are actually quite red, shining with the characteristic light of hot hydrogen.
The images were taken as part of a project to observe spiral galaxies near the edge (NGC 55 counts because it appears to be a spiral, even though it looks like LMC). These galaxies are loaded with opaque dust that can prevent us from seeing their internal structure, so the project took snapshots of many galaxies in these two colors to see how much light is blocked on a very small scale; infrared light passes through dust better than visible light.
This type of work is important because understanding the internal structure of other galaxies helps us understand their behavior, history and evolution. Additionally, the Milky Way is a spiral, so understanding how other people behave helps us understand our own home.
But that’s not the reason I’m writing this, that’s not the point I want to make. Instead, seeing this image reminded me of something I hadn’t thought about in years …
For several years I worked on a camera designed and built to be placed on Hubble called the Space Telescope Imaging Spectrograph, or STIS. I got the job pretty much right after I got my PhD working on older Hubble images, and it was a dream job. Obviously.
One of the improvements that Hubble achieved at the same time that STIS was placed on board by shuttle astronauts in 1997 was a new solid-state data logger, allowing the telescope to store data much faster than the ‘old tape recorder (!!) that he used before. This meant that when a camera was used to observe something in the sky, other cameras could be turned on and also take data. They pointed close to another part of the sky, allowing what is essentially free data to be sent back. It was called the Parallels program.
This data was always immediately made public, so that any astronomer could grab it and take a look. The team I was on would do it automatically when the STIS parallels came in and archive them. As an amateur and asshole astronomer my whole life, I was fascinated by this idea and wrote software that would allow me to easily browse parallels on my monitor. I would come to work every morning and check them early, just to see what we could see.
Most of the time, they were mostly pristine, showing only a handful of stars in the foreground and the occasional blur of a galaxy far away. But sometimes we have found gold. When someone used one of the new cameras to look at a nearby galaxy, we also saw inside, as the galaxy is large and the cameras were all pointing near the same place in the sky.
Whenever we observed the Andromeda galaxy, or the Magellanic clouds (there is also a small one), or the triangle, or Centaur A, we would get an image just loaded with stars, hugging each other. against each other and filling the images edge to edge.
To someone outside of the field, that would seem rather unimpressive, just a black field with a few thousand slightly fuzzy dots spread over it, as if someone had spilled pearls on black velvet.
But for me it was magic. I could sit casually in my office chair, sipping coffee, and look at individual stars in galaxies millions of light years away. Astronomers a century ago would have happily sawed off one of their arms for this privilege.
I got to the point where I could identify galaxies by the stars they contained; the Magellanic Clouds are close in relative terms, less than 200,000 light years away, so the stars were bright. Stars in other galaxies exhibited subtle differences in brightness and distribution that I learned to recognize with unerring accuracy. It was almost a game for me to see who was who.
After a few years though, once the camera was safe on board and working fine, it was time to move on. I quit research and moved on to teaching astronomy, and eventually writing for a living.
I sometimes miss looking at parallels, seeing these amazing and awe-inspiring structures in space that once so baffled the best scientists on our planet, creating consternation, debate and argument until we developed the technology. to resolve these issues.
Seeing NGC 55 in such detail in a press release that appeared in my email reminded me of all this, and for a few minutes I was able to revel in my own personal memories of galactic astronomical discovery.
So, to the thousands of people who made the Hubble Space Telescope a reality, and to the thousands of astronomers who have come before so that today’s astronomers can look a little further and with greater clarity: Thank you.
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