“We find them smaller and fainter, in constantly increasing numbers, and we know that we are reaching into space, farther and farther, until, with the faintest nebulae that can be detected with the greatest telescopes, we arrive at the frontier of the known Universe.” -Edwin Hubble
While large parts of the internet are blacked out today, in protest of SOPA and PIPA, I could think of no better way to highlight the importance of free exchange of information on the internet than by showcasing one of the most interesting, varied and intricate objects in the entire galaxy: Messier 16, better known as the Eagle Nebula. It’s been imaged by literally thousands of different telescopes and instruments, and it’s only through the free, public exchange of that information that we’ve been able to learn as much about this beautiful object as we have. Let’s get right to it!
A good-sized amateur telescope, looking up at the Eagle Nebula under excellent seeing condition, will see this vast, dusty expanse of glowing red gas amidst a field of hot, blue stars. The red color teaches us about the hydrogen atoms present, while the darker features within the nebula indicate very dense clouds of gas and dust. This is where new stars are suspected to be forming, but we can’t know for sure simply by looking like this.
The very same visible light that allows us to see this intricate structure is the same set of wavelengths that the interstellar dust is very good at absorbing, even with the Hubble Space Telescope!
Very much like the region where our own Sun was born 4.5 billion years ago, these “Pillars of Creation” contain, at the very borders, a large number of evaporating gaseous globules. The light-absorbing dust here is not only where newborn stars are being creating, but these stars are actually in the final stages of growth, as soon the cold gas that can create new stars will be either used up or blasted away.
The false-color showcases the different gaseous compositions of different regions of the cloud (focusing on Oxygen, Hydrogen and Sulfur), but still cannot show us exactly where the vast majority of these ultra-hot, newly formed stars are. But if we can look with a different wavelength of light, sensitive to these stars but insensitive to the intervening dust, we could find out where those stars are.
The Chandra X-ray Observatory, a space-based X-ray telescope, is sensitive to such wavelengths! There are lots of things that emit X-rays: supernova, black holes and neutron stars, as well as hot, ultra-massive newborn stars! It turns out that the evaporating gaseous globules themselves do not contain X-ray emitting stars; in fact most of the X-ray sources are not even in the pillars themselves.
Interesting! But we can learn even more about what is present inside these pillars by looking at still different wavelengths of light. For example, the 8.2 meter Very Large Telescope has taken a look at these pillars in the near-Infrared. What did it find?
Most (but not all) of these evaporating gaseous globules do not contain stars at all, and of the ones that do, pretty much all of the stars in there are less massive (and cooler) than our Sun is!
But looking in the near-infrared can only reveal so much, and leads to even more questions. Are there even less massive stars in there than the VLT can detect? Do each of these globules contain a star (or multiple stars), or are some of them truly sterile? And what came first, these globules or the stars that are inside of them? We tried looking with the ESA’s Infrared Space Observatory,
but it didn’t have sufficient resolution to teach us anything beyond what we already knew. But just yesterday, the Herschel Space Observatory released an image of the Eagle Nebula that probed deep into the far Infrared, where the hottest (blue) regions represent a temperature of just 40 Kelvin, while the coldest (red) regions are merely 10 Kelvin above absolute zero. Take a look for yourself!
This wide-field image of the Eagle Nebula shows that there’s plenty of cool gas still there to form stars even in the hottest regions, but it also shows that the pillars themselves are the hottest regions with the least amount of ultra-cold gas. Yes, the other regions of the nebula are far cooler, and you can clearly see that the interior region looks like a partially carved-out pumpkin, devoid of any cold gas. Know what we think would drive that cold gas away, by heating it up?
A recent supernova. And — if you remember from earlier — supernovae would leave a signature in the X-ray. Let’s take a wide-field look with the best X-ray telescope in space today: XMM-Newton.
In this image, the red colors are the coldest and the blue are the hottest, with temperatures ranging from only a few million Kelvin up to, for the brightest, darkest blues, around 90 million Kelvin. Let’s overlay the XMM-Newton and Herschel images atop one another and see how this stacks up.
Could there have been a recent supernova at the center? To be honest, they don’t know, yet! What you’d look for is faint and diffuse X-ray emission, and you’d see how far it extends around the interior regions of the nebula. If XMM-Newton sees too much of it, it would invalidate this theory, but a small (but non-zero) amount would support it. The work is still being done, but this is the current working theory, and it’s consistent with what Chandra (X-ray) and Spitzer (infrared) have seen in their previous observations.
Still wondering about the pillars themselves, and if there are stars forming at the edges there? Let’s take a look deep inside the pillars themselves, to the maximum resolution that Herschel can achieve.
Those edge regions, where the evaporating gaseous globules are located, are definitely where the hottest portions of the cold gas are, further evidence that this is where the evaporation is occurring. But although there are some stars inside those globules, are they providing the heat that’s causing the evaporation? Or are they simply being formed in regions that are evaporating for entirely unrelated reasons? I wish I had the answer!
It’s clear that the pillars are evaporating, but whether there are necessarily stars, proto-stars or any other interior heat source heating up these globules, or if it was a recent cataclysmic release of energy (i.e., from a supernova) nearby is unclear. Where does that leave us? At the edge of our knowledge, where we’re pushing the limits of what we currently understand; welcome! There’s a wonderful composite image over at Universe Today showcasing all the different data sets, but I prefer this ESA video to illustrate just how remarkable the Eagle Nebula is, looked at with a myriad of different instruments and telescopes.
It’s also important to realize that I, personally, have no claim to any of these images, telescopes, or missions. The only reason I can bring you these images, this video, this story and this information is because the entire community of astronomers, astrophysicists and physicists have decided to make all of this information public, and that it should be public. It’s not only for the people who work on it, who discover it, or who pay for it; it’s for everyone. So share this information — and all the information about the Universe that we learn from here on out — with everyone who wants to know it. It’s your Universe, too, and we all have a right to it.