According to my software, this blog post you are reading is the 7000th article I have published on the Bad Astronomy Blog.
That’s a lot of words. It’s also a lot of astronomy, geekery, science, antiscience, web comics, puns, embiggenates, and "Holy Haleakala!"s (61, to be exact, plus this one to make 62).
I am generally not one to wade into maudlin celebrations of arbitrary numbers, so instead I’ll celebrate this milestone by showing you something appropriate: the North America Nebula, taken by Mexican astronomer César Cantú.
[Click to encontinentenate.]
Why is this appropriate? Because the New General Catalog of astronomical objects – familiar to and used by astronomers across the planet – lists it as entry number 7000.
And it should be obvious why it’s named as it is.
Of course, I can’t leave you with just a pretty picture. This nebula is something of a mystery; we don’t know how big it is or how far away it lies. In the sky, it’s very near the star Deneb – which marks the tail of the swan constellation Cygnus – and Deneb is a massive, hot, and luminous star. It’s possible the gas in the nebula is glowing due to the light from Deneb; if so NGC 7000 is about 1800 light years away and over 100 light years across.
It’s the site of furious star formation, too, with stars being born all along the bright sharp region which look like Mexico and Central America. The "Gulf of Mexico" region – the darker area with fewer stars – is actually the location of thick interstellar dust that blocks the light from the stars behind it. Visible light, that is; the dust glow in the infrared, so if you look at it with a telescope that sees IR like the Spitzer Space Telescope, what is invisible becomes ethereally visible:
This mosaic shows the North America Nebula in different wavelengths of light: in the upper left is visible light; the upper right is visible plus infrared, so you can see the two together; the lower left shows infrared light from 3.6 to 8 microns (roughly 5 – 11 times the longest wavelength the human eye can detect), and the lower right is similar but going out to 24 microns, over 30 times the wavelength we can see. The visible light images show the gas, while the infrared show not only the dust, but the warm spots where stars are being born, their new light penetrating the surrounding cocoons of material, reaching across space, and finally ending its journey here on Earth where we can detect it and learn from it.
I’ve struck upon many ideas for this blog over the past seven years, six months, and one week I’ve been writing it, but one of the most important is this: not everything is as it seems. Whether it’s someone’s opinion, a "fact", a picture, an argument, or even a vast sprawling cloud of gas and baby stars a thousand trillion kilometers across, this much is what astronomy and critical thinking has taught me: What you see depends very much on how you see it. And if you want a more complete picture, something that ever-approaches reality, you must view the Universe with different eyes and with an open, but trained mind. Only then will you not get fooled, and not fool yourself.
Thank you honestly and sincerely to everyone who’s been along with me this far into the ride, here on my 7000th milestone. There’s still a long way to go, of course, but it’s the journey itself that’s so much fun!
Image credits: César Cantú; NASA/JPL-Caltech/L. Rebull (SSC/Caltech)/D. De Martin
We live in the outskirts of our disk-shaped galaxy, our Sun and planets located about halfway from the center to the edge. This is a bit like living a few kilometers away from a city, in the suburbs. From that distance, when you look toward the city, you see more buildings, more activity, just more stuff going on.
The same thing is true for us on Earth: the center of the galaxy (downtown) is located toward the constellations of Sagittarius and Scorpius, so when we look in that direction there’s lots of fun things to see: more stars, more gas and dust, more clusters, more stellar nurseries.
And when you point the monster Very Large Telescopes ginormous 8 meter mirror in that direction you can see amazing details in that buzzing hubbub, like this lovely shot of the nebula NGC 6357:
[Click to ennebulanate, or grab the 3760 x 1560 pixel version. note: I rotated the image to make it fit the blog better and so you can see it more properly embiggened here.]
This piece is actually part of a much larger complex of gas and dust, but shows some nice features. The whole place is lousy with hydrogen gas, glowing rosy red due to energy pumped into it from young, massive, hot stars. Those stars are forming from that very gas, so they’re lighting up their own nursery. Running right through the middle is a river of interstellar dust – not like the dust bunnies under your bed, this is actually more like soot, and made up of complex clumps of organic molecules. This dust absorbs and blocks light behind it, so it looks like it’s splitting the gas cloud in half.
You can also see some structures in the dust, like the "fingers" of material at the top pointing to the center of the gas. Those are actually dense clumps of material being slowly blasted away by the fierce, intense ultraviolet light from newborn stars. Think of them like sandbars in a river getting eaten away by the current. They point right at the stars doing the deed, a cosmic "j’accuse!"
Nebulae like this are among my favorite objects in the sky. They’re beautiful, they’re fascinating, and it’s more than a little mind-blowing to know that there are dozens, hundreds, maybe thousands of stars being born in these objects even as we watch. And it also gives me a bit of a shiver to know that these objects are ephemeral, too: the stars being born really are slowly eating away at the material… and many of these stars will explode as supernovae someday, and that destruction won’t be slow anymore! The onslaught of high-energy radiation and material moving outwards from those stellar blasts at thousands of kilometers per second will make short work of this nebula. So take a look while you can. In a million years or four, this whole thing will be gone.
[This is another in a series of posts I’m doing to help me clear off the zillions of cool astronomy pictures I have sitting on my computer desktop. I’ve been posting one of these every day and will continue until my desktop is cleared!]
One important aspect of science is its ability to question its own tenets. Some people think that’s a weakness, but it’s a strength! A stiff tree breaks in the wind, but a flexible one survives.
There are, of course, a lot of basic things we do know pretty well. Evolution is real, the Universe is expanding and billions of years old, and so on. As we observe nature more, we learn more, and we can add to these ideas, fill in the details. Sometimes, of course, we learn something that means our models may be wrong, or need to be modified. Again, this is a strength of science: it improves our understanding. We don’t want to think something wrong is true! We need to be flexible.
Which brings us to the weird little galaxy I Zwicky 18, which is so odd-looking I thought at first this Hubble image of it was a drawing!
But no, this is real! [Click to galactinate.]
It’s an amazing shot: it’s the sum of nearly 200 separate Hubble observations of the galaxy, giving a total exposure time of 243,000 seconds: nearly three solid days!
Wow. When I worked on Hubble, many of the images I analyzed had exposure time of only a few minutes. So yeah. This is a deep image.
Astronomical imagery is a tricky business. Different objects behave differently, emitting light in different ways. So, for example, a cool dinky star might give off very little blue light — through a blue filter it virtually disappears — while a hot, massive star blasts out blue light. Your choice of filter can drastically change the way an object looks.
Having said that, I recognized right away that this image is the core of the nearby galaxy M82… but it still looks funny to me:
[Click to galactinate, or grab the huge 12.5 Mb image.]
One reason this new image from Hubble looks funny to me is that there aren’t as many stars in it as I expect. M82, also called the Cigar Galaxy due to its elongated shape, is pretty close as galaxies go, about 12 million light years away. It’s one of the closest large galaxies in the Universe, and a Hubble image usually shows it littered with stars, so closely packed they form a bluish background glow in most pictures.
And while that background of stars is there, it’s more diminished than usual because in this image astronomers used a series of filters that accentuate the light emitted by gas. While stars put out this kind of light as well, these filters downplay starlight and crank up the volume on, um, gaslight. Specifically, blue and green are from oxygen, red is from sulfur, and teal is hydrogen. The dark material is dust: long-chain molecules that absorb starlight. They also tend to redden light coming from behind them, similar to the way haze in the air makes sunsets look red.
Clearly, M82 is lousy with gas and dust in its core. Read More
When Galileo first turned his telescope to the sky, almost exactly 400 years ago, he could not possibly have known what he was starting.
Today, four centuries later, we’ve come a long, long way. To celebrate the anniversary of Galileo’s telescopic revolution, NASA’s Great Observatories — Hubble, Spitzer, and Chandra — have released a jaw-dropping mosaic of the very heart of the Milky Way galaxy. Behold!
This image is nothing less than a heroic effort of astronomical artistry. It’s a chunk of the sky 38 x 14 arcminutes across, or about half the size of the full Moon, and it’s aimed right into the core of our galaxy. See the bright spot just to the right of the center? Buried in there behind light years of dust and gas is the monster of the Milky Way, a black hole with four million times the mass of the Sun. But even that is dwarfed by the 400 billion solar mass heft of the entire galaxy.
There is so much going on in this image it’s hard to know where to start. But first… the Hubble images are in the near-infrared, with a wavelength a little more than twice what the eye can see (1.87 microns for those playing at home). That’s represented in the image as yellow. Spitzer contributed observations in four infrared wavelengths (3.6, 4.5, 5.8, and 8.0 microns), and those are depicted in red. Chandra sees X-rays which are normally written as units of energy, but to remain consistent with the other two images, they were at wavelengths of 0.0005, 0.00025, and 0.00016 microns, and are shown in blue.
What does all this mean? Different objects emit light at different characteristic wavelengths. Warm dust, for example, emits strongly in the infrared. Stars and warm gas emit visible and near-infrared light. Violently heated gas, affected by huge magnetic fields or shocked by colossal collisions glows in X-rays. So this image is a polychromatic view of the crowded downtown region of a bustling city: our galaxy.
You might want to look at an annotated version of this image so you can get your bearings. It’s worth it!
The huge arches of gas on the left are actually the edges of gigantic molecular clouds (dense nebulae where stars are born), lit up by the torrential blast of light from a clutch of massive stars nearby. This clot of stars, called the Arches Cluster due to the arcs it excites, can be seen as a small spot glowing blue just to the left of center in the picture. Don’t be deceived by its diminutive appearance: the Arches cluster has thousands of superstars in it, each dwarfing our Sun, and each capable of sleeting out vast amounts of radiation that lights up the gas surrounding it. Were this cluster much closer than its 25,000+ light year distance, it would blaze in our sky like a beacon. Replace the Sun in our solar system with just one of those stars, and the Earth would be fried beyond the capability of any life to survive. You might as well try living in the flame of an arc-welder.
Below and just to the left of the Arches is a clumpier, more twisted arc of gas called the Sickle. That’s a giant cavity being carved out of dense gas by the Quintuplet cluster, the pinkish glow in its center. It’s another nursery of stars like the Arches cluster, which is also blasting out light and stellar winds which eat away at the gas enveloping it. The Pistol Star resides there, perhaps one of the most massive stars in the Milky Way.
And there’s more! The blue glow on the left is from an X-ray binary called 1E1743.1-2834, what is probably a massive star being orbited by either a neutron star or a black hole. Matter is being stripped from the star and piling up outside the collapsed companion, where it gets heated up to millions of degrees and emits X-rays.
Supernovae remnants dot the image, as do stars, filaments of gas, clouds of dust, and more. This picture is an astronomer’s dream, a map of everything someone might want to visit with a starship — as long as the shields are at full strength. This image is also a map of violence, turbulence, and unrest… a typical scene, so we think, of any normal spiral galaxy like ours. And our Galaxy’s center is considered quiet by astronomers! Some are far worse.
But this is home for us. It’s a place of unimaginable fury but also astonishing beauty… and we see it now as we do because we have dared to examine the world around us, to use tools we invent to peer closer, to magnify the tiny, to extend our eyes into realms we once didn’t even know existed. And every time we do — every single time — we find more questions, more puzzles, more things to examine.
And we find art. Galileo wasn’t the first to turn his telescope to the sky, nor was he the first to record what he saw. But he was the one who made everyone see what he did, and for that, all these years later, he is owed a debt of gratitude.