“At the last dim horizon, we search among ghostly errors of observations for landmarks that are scarcely more substantial. The search will continue. The urge is older than history. It is not satisfied and it will not be oppressed.” -Edwin Hubble
Given the relative peace of our night skies, combined with the vast distances from our Solar System to the nearest star, we don’t often think about the cosmic catastrophes that took place in our past. But these catastrophes are the very things that gave rise to our Solar System in the first place!
Yes, it’s dense, cold, contracting gas — enriched by previous generations of stars — that gives rise to stars and planets like the ones found right in our own backyard. But the clouds of gas we find strewn throughout are galaxy, for the most part, are far too diffuse to simply contract down under the force of gravity to form all these new stars. It usually takes some sort of catastrophic event to set that off!
On very large scales, two large galaxies colliding together is one of the most spectacular examples of such a catastrophe. The closest galaxy to us in the process of colliding is the magnificent and unusual giant galaxy, Centaurus A, located just 11 million light years away.
Looking at this galaxy even in the above (limited) set of wavelengths shows us something remarkable. It has a diffuse, nearly spherical shape judging by its stars, reminiscent of an elliptical galaxy. But it also has a set of big, central dust lanes, just like we see from spiral galaxies. In fact, Centaurus A is actually two galaxies in the midst of merging: one thought to be a spiral and one thought to be an elliptical. Looking with a full set of visual wavelengths helps make that even clearer.
This is a very impressive image, no doubt, as you can see that the predominant color of the stars around the dust lanes are a bright blue. This contrasts with the rest of the galaxy’s stars, which are yellower, and hence older. These young, blue stars tell us, unequivocally, that these are regions where new stars have just formed.
But, as you might have guessed from the title, even the best ground-based image still can’t hold a candle to the spectacular imaging power of the Hubble Space Telescope. What do you suppose it saw when, last year, it turned its attention towards Centaurus A?
As you might have guessed, not having an atmosphere to contend with greatly amplifies the resolution at which you can take images. And this Hubble image — if you want to see the really high-quality version — can show you not just the bright blue stars, but the red, ionized emission nebulae, the collapsing cold dust, as well as the diffusing, evaporating areas. Here’s just a tiny section from that super high-quality image.
Remember, this galaxy is eleven million light years away, and you can image individual stars in it! This type of interaction — a major merger between two relatively large galaxies — can produce upwards of a thousand stars per year, more than 100 times the rate they’re produced in our own galaxy. Over the duration of just a few million years, literally billions of stars can form from a collision like the one Centaurus A is experiencing. Thanks to the Hubble space telescope, we get an unparalleled view of the formation of these new stars.
But without prior generations of stars that have lived, burned their fuel, and polluted the intragalactic gas with heavier elements, none of those stars could ever have rocky planets orbiting them. Unbelievably, Hubble’s got us covered there, too.
Whether it’s a star like our Sun, that will die in a planetary nebula, like the helix nebula, above, or a much more massive star, that blows off its outer layers in a supernova explosion, these stellar corpses are the sources of all the common heavy elements in the Universe, from Carbon, Nitrogen and Oxygen up through Neon, Silicon, Sulfur, Iron, Nickel, Cobalt and more, all of these elements come from the ejecta from deceased stars. Sun-like stars that die in a planetary nebula can have a roughly spherical end to their life, like the Helix Nebula, above, or a more bipolar structure, like the Butterfly Nebula, below.
The expelled gas from these regions enriches the interstellar medium, but it can also run into these diffuse, massive gas clouds that move through our galaxy. Collisions, under the right circumstances, can trigger the process of star formation in these clouds, leading to a beautiful star-forming region, like Sharpless 2-106, below.
Indeed, in term of resolving power, depth, and clarity, no telescope on Earth can rival the images Hubble produces.
But it gets even better than this!
You see, Hubble isn’t the only telescope that’s looked at these objects, it’s just the best one. By looking at different wavelengths of light, measuring doppler shifts of the outflows, and imaging from multiple locations in space, they were able to infer and construct models of the full, 3-D structure of these objects. Ever wonder what it would be like to fly around a star, not unlike our Sun, as it goes through the final phases of its death? Check out this fly-through of the Helix Nebula. (It takes about 25 seconds to get going, so be patient!)
How about the Butterfly Nebula, where the gas flows outwards from the central region at speeds topping 600,000 miles-per-hour?
Or, as perhaps the best Hubble video ever could show you, take a tour of the star-forming region Sharpless 2-106.
Around four-and-a-half billion years ago, a region of our Milky Way not unlike this one gave birth to the star and planet we call home. When we examine a region like this, we’re examining our own origins — the birth of the Sun and the Earth — as much as anyone possibly can.
Yes, these videos also involve a bit of artistic license; there is only so much we can learn from thousands of light years away, but these are the most scientifically accurate visualizations we can possibly construct. And we can only do it thanks to Hubble: still unbeatable after all these years!
(Thanks to DJ Busby at Astronasty for finding these videos; there’s one more over there to see for the curious!)