After having recently posted an interesting picture of the results of star formation in a nearby galaxy, here’s another example, but far closer: an incredibly detailed image of the heart of the Omega Nebula, where stars are being born from huge clouds of gas and dust:
[Click to ennebulenate, or grab an even bigger version.]
This image was taken using the 8.2 meter Antu telescope, one of four making up the European Southern Observatory’s Very Large Telescope in Chile. What you’re seeing here is the central region of a much larger complex of gas and dust located about 6500 light years away toward the center of our galaxy. The whole thing is about 20 light years across, and perhaps as many as 1000 stars are in the process of being born or were recently formed there.
The red color is due to the presence of warm hydrogen gas, the basic building material of stars. It’s being lit up and is glowing due to very young, massive and hot stars — the alpha dogs, if you will — flooding the nebula with ultraviolet light. The dark material is actually dust, which is opaque in visible light, so it blocks the glow from material behind it.
That dust really caught my eye: some of it is not shapeless and random, but has been sculpted into very long, very thin wisps and tendrils. Most of these are parallel, which is a big clue to what causes them. They are most likely being shaped this way by shock waves; supersonic material blasted out from those same young, hot stars. These powerful stellar winds of subatomic material race out and slam into the surrounding material, compressing it. Waves from various stars can also collide, creating very thin streamers like this. Some are so narrow they’re barely resolved in the picture at all.
Take a look at the image displayed here [click to redshiftenate]. Every object you see there is a galaxy, a collection of billions of stars. See that one smack dab in the middle, the little red dot? The light we see from that galaxy traveled for 12.9 billion years before reaching the ESO’s Very Large Telescope in Chile. And when astronomers analyzed the light from it, and from a handful of other, similarly distant galaxies, they were able to pin down the timing of a pivotal event in the early Universe: when the cosmic fog cleared, and the Universe became transparent.
This event is called reionization, when radiation pouring out of very young galaxies flooded the Universe and stripped electrons off of their parent hydrogen atoms. An atom like this is said to be ionized. Before this time, the hydrogen gas was neutral: every proton had an electron around it. After this: zap. Ionized. This moment for the Universe was important because it changed how light flowed through space, which affects how we see it. The critical finding here is that reionization happened about 13 billion years ago, and took less time than previously thought, about 200 million years. Not only that, the culprit behind reionization may have been found: massive stars.
OK, those are the bullet points. Now let me explain in a little more detail.
Young, hot, dense, and chaotic
Imagine the Universe as it was 13.7 billion years ago. A thick, dense soup of matter permeates space, formed in the first three minutes after the Big Bang. The Universe was expanding, too, and cooling: as it got bigger, it got less dense, so the temperature dropped. During this time, electrons and protons were whizzing around on their own. Any time an electron would try to bond with a proton to form a neutral hydrogen atom, a high-energy photon (a particle of light) would come along and knock it loose again.
During this period, the Universe was opaque. Electrons are really good at absorbing photons, so light wouldn’t get far before being sucked up by an electron. But over time, things changed. All those photons lost energy as things cooled. Eventually, they didn’t have enough energy to prevent electrons combining with protons, so once an electron got together with a proton they stuck together. Neutral hydrogen became stable. This happened all over the Universe pretty much at the same time, and is called recombination. It occurred about 376,000 years after the Big Bang.
I’ve been accused of having a big head (which is literally true; finding hats that fit properly can be difficult), but even I wouldn’t have any trouble squeezing the 13 trillion kilometer (8 trillion mile) wide Necklace Nebula around my noggin:
[Click to enlarynxate.]
This Hubble image shows the so-called planetary nebula, which is the product of a dying star. Deep in the center of the ring are actually two stars circling each other. As one started to die, it puffed up, literally engulfing the other star. This spun up the larger star, and the centripetal force flung off material in a huge disk well over a light years across. As the star lost its outer layers, the much hotter inner core was exposed, flooding the gas with ultraviolet light, causing it to glow like a neon sign.
Or, more accurately, a hydrogen/oxygen/nitrogen sign, the gases highlighted in this image (shown as green, blue, and red, respectively). See the knots of pink emission in the ring? As the gas was expelled, the speed of the wind increased with time while the density decreased. This faster wind caught up with and slammed into the slower wind, creating clumps and other features. You can see how the gas appears to be streaking away from the center of the ring; that’s real, as the fast wind carves away the slower one.
You can also see faint red blobs at the upper right and lower left, well away from the ring itself; those are probably the caps of a very faint (in this image, invisible) hourglass shaped nebula. The disk prevents the wind from expanding along the equator of the system, so it blows up and down, out, creating two lobes of material. Those caps are all you can see, where the gas gets mildly compressed at it expands into the gas surrounding the star system.
If this whole thing looks a bit familiar, well, it should: it’s very similar to Supernova 1987A, which I’ve written about a bazillion times (seeing as how I studied it for six years for my PhD). In this case, the central star(s) is lower mass, so not as hot as the explosion that flash-ionized the gas around the supernova. That’s why it’s fainter, even though at 15,000 light years away it’s actually ten times closer than 87a!
I love planetary nebulae. They’re weird, and pretty, and tell us a lot about how stars similar to the Sun die. In our daily lives death is rarely beautiful, but in astronomy it almost always is.
Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Spiral galaxies are inherently interesting. Something about their beauty is so enticing… but when you look at them more carefully, the science and physics behind them is terrifically compelling. And when you use different eyes — say, radio telescopes — then you see something different entirely:
This shows two views of the lovely face-on spiral galaxy NGC 6946. On the left is a visible light image, and on the right is the radio view, taken by the Westerbork Synthesis Radio Telescope (taken over the course of 192 hours). Amazingly, these two images are to the same scale!
Spiral galaxies emit light across the entire electromagnetic spectrum, including visible and radio light, but what emits that light is different. Stars and warm gas emit visible light, but cold hydrogen glows at radio wavelengths. At a wavelength of 21 centimeters (about 8.5 inches, much, much longer wavelength than visible light, by a factor of tens of millions!) cold hydrogen can actually be quite bright, making it a perfect target for big radio telescopes.
In this image on the right I superposed both shots so you can see just how much more there is to NGC 6946 than the eye sees. What this image immediately tells us is that cold hydrogen extends well beyond the region where hydrogen is warmer, toward the center of the galaxy. It also shows the gas still takes on a spiral shape well past the visible boundaries of the galaxy.
A more detailed analysis indicates there are over 100 holes in the cold hydrogen gas as well, and these correspond to areas where stars are actively forming. That’s hardly a surprise! Stars use up hydrogen gas when forming, and then heat up what remains around them in the neighborhood. Once warmed up, the gas doesn’t emit as much 21cm radio waves.
The astronomers also found a lot of this gas is moving at high speeds, up to 100 km/sec (60 miles/second, fast enough to go from the Earth to the Moon in a little over an hour!). This is probably gas that’s been blown up and out of the galaxy by stars and supernovae, only to fall back down due to the gravity of the galaxy. That’s not known for sure, but we do see such fountains in other galaxies, including our own.
I’ll be honest: I’m more of a medium-to-high energy guy than radio guy. That’s why I tend to talk more about X-rays and gamma rays from astronomical objects, but every part of the spectrum tells a story. Radio astronomy has been around for almost a century now, and it is still and always will provide insight into the mechanisms behind the Universe.
Image credit: Rense Boomsma/Digitized Sky Survey/WSRT; ASTRON/JIVE Archive
I’m such a sucker for emission nebulae, the sites of intense star formation. Part of that is because I spent years researching other types of gaseous clouds, but also because they’re just so darn pretty, like this shot of NGC 371:
[Click to ennebulanate, or get the 2000 x 2000 pixel version).]
NGC 371 is in the Small Magellanic Cloud, a companion galaxy to our Milky Way. That puts it at a distance of about 200,000 light years, or 2 quintillion (2,000,000,000,000,000,000) kilometers.