The Universe is getting bigger!
But then, we knew this. We’ve known it for a long time! The reason you know Edwin Hubble’s name at all is because in the 1920s he was critical in figuring out the Universe was expanding. He and many other people did this by looking at a specific kind of star, called Cepheid variables. These stars literally pulsate, getting brighter and dimmer on a regular schedule. As it happens, how much they change in brightness depends on their actual brightness… and that means if you measure how much they change, and how bright they appear in our sky, you can figure out how far away they are. And if they are in other galaxies, then you can tell how far away those galaxies are.
Boom! You can measure the size of the Universe. And more.
Using this method (which I explain in more detail in an earlier post, if you want details), they figured out the Universe was expanding – the farther away a galaxy is, the faster it appears to recede away from us. This is what led to the Big Bang model of the Universe, and essentially all of modern cosmology – the study of the origin, evolution, and properties of the Universe as a whole.
Over the decades, that rate of expansion – called the Hubble Constant – has been measured many different ways. Using Cepheid variables is still a foundation of the work, though, and a new study just released by astronomers using the Spitzer Space Telescope show that the rate of expansion is 74.3 +/- 2.1 kilometers per second per megaparsec. What this means is that a galaxy one megaparsec away (that is, 3.26 million light years) will be moving away from us at 74.3 km/sec. If you double the distance to 2 megaparsecs, a galaxy would be moving away at twice that speed, or 148.6 km/sec.
This study is pretty neat. Spitzer observes in the infrared, which can pass right through interstellar dust. That dust is like a fog, obscuring the visible light from stuff behind it, and it really messes with measuring brightnesses. That has plagued Cepheid studies for years, but Spitzer simply steps around that problem! So this measurement appears to be pretty accurate, more so because they calibrated it using Cepheids in our own galaxy (and one nearby one), and combined it with results from other observatories like WMAP, which can measure other properties of the Universe as well. By doing all this, they’ve produced a very accurate measurement of the Hubble Constant.
I want to be clear here: this new study is more accurate than previous ones, and much more accurate than one done a few years ago using Hubble. However, a study done just last year got the expansion rate to an accuracy of about 3.3%, and that used a combination of Cepheids and Type Ia supernovae – a star that explodes with a measurable and predictable brightness. This new study has an accuracy of just under 3% – an improvement for sure, though not a huge one over last year’s.
Still, this is very cool. That last study got a rate of 73.8 +/- 2.4 km/sec/megaparsec, so they both agree closely within their error margin. In fact, they’re statistically identical (and agree with quite a few other measurements made in the past, too). That’s good! It means we’re really nailing this number down, and that’s further evidence we really do have a pretty good basic understanding of how the Universe is expanding.
There’s still a lot to figure out in cosmology; we don’t know what dark matter is, and about dark energy we know even less. But it’s good that people are looking into other ways to measure basic properties of the Universe. The more we know them, the less we have to worry about them. And it shows that our overall model holds up. The Universe had a beginning, 13.7 billion years ago. It was small then, but it’s been expanding ever since, and in fact is expanding faster every day. We are a small part of it – in fact, our matter is a small part of all the matter (that dark stuff dominates by a lot) and even that is a small part of the stuff that makes up the Universe (dark energy wins that round).
And as amazing as all that is, I am even more astonished by the fact that we can know any of this at all! The Universe obeys rules, and by doing so reveals those rules to us. We just have to be smart enough to investigate them and learn about them.
And we are that smart.
Image credits: Image credit: NASA/JPL-Caltech; CBS
- The Universe is expanding at 73.8 +/- 2.4 km/sec/megaparsec! So there.
- The Universe is expanding at 74.2 km/sec/Mpc
- Wait a sec. How big is the Universe again?
- The Universe is 13.73 +/- .12 billion years old!
One of the most amazing objects in the sky is the Helix Nebula, an expanding cloud of gas and dust surrounding a dying star. This type of object is called a planetary nebula, and it’s formed when a star a bit more massive than the Sun turns into a red giant and blows off its outer layers. These expand away, and eventually the hot core of the star is exposed. This floods the gas with ultraviolet light, causing it to glow pretty much like a neon sign*.
The Spitzer Space Telescope and GALEX combined their forces to observe the Helix Nebula, and what they see is simply stunning:
Oh my. [Click to ennebulenate, or grab a 6000 x 6000 pixel version.]
GALEX sees in the ultraviolet, so it’s sensitive to the light coming from the central star and the hot gas reacting to it (colored blue in the picture). Spitzer sees in the infrared, so it detects warm gas and dust (red, yellow, and green). Where you see pink is where the nebula is emitting both IR and UV. [Note: some of the outskirts of the nebula were beyond Spitzer's field of view, so images from the infrared observatory WISE were used there to match the GALEX field.]
One of the most interesting features of this nebula is the collection of long, comet-like "fingers" you can see throughout the structure. These are where denser clumps of material are boiling away under the intense UV radiation of the central star, blowing out long tails away from the center like spokes in a wheel. Some of those tails are trillions of kilometers long!
Despite being one of the closest planetary nebulae in the sky – a mere 700 light years away – I’ve never seen the Helix through a telescope. Why not? Because it’s so big! The light from the gas is spread out over an area in the sky the size of the full Moon, dimming it considerably. Maybe someday I’ll be at a dark site with a big ‘scope, and I’ll see this fantastic bauble with my own eyes… but it won’t look like this picture. Our eyes see only a small slice of the electromagnetic spectrum. They serve us well in our daily lives, but the Universe itself sends out information in every direction to which we’re blind.
That is, until we used our limited brains to build devices like Spitzer and GALEX that expanded our viewpoint. And that’s what science does: removes the scales from our eyes, allowing us to see what the cosmos itself is showing us.
Image credit: NASA/JPL-Caltech
* I’m simplifying here a bit. If you want more in-depth info on what happens as a star like this dies and glows like some great gaudy celestial Christmas ornament, read this post about the Helix I wrote a while back.
I have no shame in admitting I love face-on spiral galaxies. Scientifically, of course, they’re fascinating; spread out in front of us are all the inner workings of a galaxy. It’s like having an X-ray of human body in front of you, making it easier to understand anatomy.
But their beauty… well. The scope and grandeur of a face-on spiral is unparalleled, I think, in astronomy, or perhaps any field of science. But don’t take my word on it. See for yourself.
[Click to galactinate, or get a 1900 x 1200 desktop image.]
This is the wonderful nearby spiral M101, and is a composite of no fewer than four orbiting observatories! It has images from Hubble, Spitzer, Chandra, and GALEX. These represent (in order) observations in visible light (shown as yellow in the picture), infrared (red), X-ray (purple) and ultraviolet (blue).
Each shows a different aspect of the galaxy. Visible light shows stars and gas, infrared indicates warm dust, X-ray show hot gas and energetic objects like supernovae and black holes, and ultraviolet is where young stars glow and light the gas around them. Each observation is incredibly useful to a scientist, but combining them together makes them even more powerful.
The things to look for are where colors overlap, and where they don’t overlap. For example, in the outer arms you can see dust and gas and young stars all together, showing where stars are born. In the inner regions of the galaxy the infrared and visible images are next to each other, parallel spirals. Dust blocks visible light, so where there’s lots of dust there’s little light we can see, and vice-versa.
You have to be careful interpreting images like this, though. The outer arms, for example, are blue. You might think this means they’re only giving off ultraviolet light. But you have to account for the different telescopes’ field of view, exposure times, and more. Each of those affects what you see no matter what the galaxy itself may be doing. Images like the one above are useful, even important, but it’s also important to remember their scientific limitations.
But artistically? That’s a different matter. All together.
Image credit: X-ray: NASA/CXC/SAO; IR & UV: NASA/JPL-Caltech; Optical: NASA/STScI
Since the first planet was discovered orbiting another Sun-like star in 1995, nearly 800 more have been discovered. Only a handful have been directly detected: most are discovered by their influence on their star, either by tugging it or blocking its light as the planet orbits (at the bottom of this post is a gallery of images of exoplanets detected in these ways). But some have been directly seen: either glowing by their own light, reflecting that of their star, or — ironically — seen when they’re not seen.
Say what? OK, this takes a sec to explain, but it’s cool.
The star 55 Cancri hosts at least 5 planets. Located 40 light years away, it’s one of the closer planetary systems, and has been intensely studied. One of the planets, 55 Cancri e, is bizarre: it’s twice the diameter of the Earth and has 8 times our mass. It’s thought to have a dense core surrounded by water… but Earth-like it ain’t. It orbits its star in a very tight orbit, circling it once every 18 hours. It’s so close to the star that the surface temperature is probably around 1700°C — or 3100°F! That’s hot enough to melt lead.
So yikes. If it does have water, it’s in the form of a weird super-heated steam only held to the planet due to its strong gravity. Even then, the atmosphere may be boiling away like a gigantic comet. So again, this isn’t like Earth at all. Even Venus isn’t this unpleasant, and on Venus it rains sulfuric acid.
Anyway, an object at that temperature will glow in the infrared, quite strongly. If it were sitting all by itself in space, it would be easy to see. However, it’s sitting next to a star which is millions of times brighter, making it a significantly more difficult target.
… but not impossible. Read More
In 2003, NASA’s Spitzer Space Telescope launched into space to begin a mission to observe the heavens in infrared. That kind of light is emitted by warm objects, so its main imaging camera — called IRAC, for Infrared Array Camera — had to be cooled using liquid helium, or else the infrared light it gave off would interfere with its own observations!
This type of coolant leaks away slowly, and after about five and a half years — a much longer period of time than originally hoped, which was a bonus — the liquid helium was finally depleted. However, this didn’t end the mission; instead it marked the beginning of the "warm phase". Observations could still be made, though only with some of the detectors that weren’t so severely affected by the raised temperature.
That was in May 2009. Spitzer has now been running warm for 1000 days, and to celebrate that milestone the folks running the observatory released their favorite 10 Spitzer IRAC images. Over the years I’ve featured half these images on the blog (see the list below), but I have no idea how I missed this amazing shot:
Isn’t that cool? Well, so to speak. Haha. Because of the warm mission, you see. Ha ha.
But what is it? Just off the top of the picture is a young star. It’s a newborn, a mere baby, probably less than a million years old, and like human babies it tends to spew matter out of both ends. In this case, the star’s rapid spin coupled with its intense magnetic field create two powerful jets of material that blast away from its poles at speeds of up to 100 kilometers per second! What you’re seeing here is one of those jets as it plows through a cold cloud of gas and dust. The shape may be due to the material in the jet following the twisted magnetic field lines, or it may be formed as the shock waves emanating from the interaction become unstable, a bit like breaking waves from a ship ramming through the water at high speed. Either way, it looks for all the world — the galaxy! — like a rainbow tornado.
[Over the past few weeks, I've collected a metric ton of cool pictures to post, but somehow have never gotten around to actually posting them. My Desktop Project -- posting one of those pictures every day -- is my way of clearing off my PC's desktop, and also showing you some truly amazing stuff. Enjoy!]
The Orion Nebula is a perennial favorite for astronomers. It’s big (the size of the full Moon on the sky), bright (visible to the naked eye), and gorgeous (even binoculars show some wispy details). It’s also scientifically fascinating, since it’s the closest example of a big star-forming factory in the Milky Way. We get a fantastic view of it and can study it in incredible detail (see Related Posts below for lots more pix).
Because of all that, it amazes me that anything can provide a truly new view of this old friend… but then our eyes don’t see into the deep infrared. When you combine images taken with the Herschel and Spitzer space telescopes, which probe the cosmos in that part of the spectrum, the portrait they make is just stunning:
[Click to ennebulenate.]
As lovely as this picture is, there’s an important science story going on here as well. The stars you see embedded in those filaments and knots of interstellar material are actually very, very young: probably only a few million years old, and on the verge of becoming full-fledged stars like the Sun. They’re still enshrouded in the dust and gas disks in which they formed. Near the embryonic stars, of course, the dust is warmer, and farther out it’s colder. Spitzer and Herschel see in different parts of the infrared, where the different temperatures of dust emit light, so they probe both the inner and outer parts of the clouds.
Astronomers used Herschel to observe this nebula in 2011, taking a series of images over time. What they found is that the stars and their dust changed in brightness by as much as 20% very rapidly — over weeks, when it would be expected to take years! It’s not clear what’s going on behind this variability. I suspect the disks of material around the stars are clumpy, and the inner region has clouds that block the starlight, shadowing the outer region. As that happens, the cooler part of the disk dims, which is what Herschel saw. Other processes may be at work as well, but any ideas as to what they are have to be tested against the observations.
Which is precisely why we observe even familiar objects with telescopes sensitive to different kinds of light. Ultraviolet, infrared, visible, radio, X-ray — these are all parts of the spectrum controlled by different processes, so by observing different flavors of light we see the different engines creating them. It’s the combination of these varying views that gives us insight (literally, in this case, since we’re seeing inside a nebula!) into the physical mechanisms of various astronomical phenomena.
Even though the Orion nebula is one of the best studied objects in the sky, there’s still a lot to learn from it. And as long as we keep our eyes open, especially across the electromagnetic spectrum, then more and more of its secrets will be revealed.
Image credit: ESA/NASA/JPL-Caltech/N. Billot (IRAM)
[Over the next week or two, I'll be posting some of the many, many cool astronomical images I've been collecting and which are cluttering my computer's desktop. These are all really cool pictures, and I'm glad I'm finally getting around to writing about them!]
One of my favorite types of objects are things that look like other things. So how can I resist writing about the Pac-Man Nebula, aka NGC 281? As for why it’s called that, duh. The image inset here (click to powerpelletenate) was taken using a telescope that sees optical light, the kind our eyes see.
The resemblance is obvious, isn’t it? If you’re my age or younger, than Pac-Man is pretty much all you can see there (and it’s not the only cosmic object to look like that, either). Of course, as an astronomer, I also see hydrogen (red), oxygen (yellowish-green), dust (black; it absorbs optical light), and evidence of star formation. Those finger-like things on the left are formed when young stars blast out fierce amounts of ultraviolet light, and eat away at the gas surrounding them. Think of them like sandbars eroding under a current. Still, all-in-all: this is clearly Pac-Man, albeit one over 9000 light years away.
But what happens when you look with telescopes that see other kinds of light? Like, say, infrared and X-ray? Then things look really different. Opposite, even!
What do I mean by that? Well, let me show you:
See! On the left is a combination of infrared and X-ray observations taken with Spitzer and Chandra, and I scaled the images to show the same field of view. Stuff that’s dark in the optical picture on the right glows brightly in infrared on the left — mostly warm dust. And the pink glow is due to X-rays from the very young, massive, and hot stars in the center of the Pac-Man’s mouth (ghosts?).
Looking at nebulae like this at different wavelengths tells us different stories about them. We learn more about how stars form, and what happens to the nebula itself as they do. Eventually, the stars in the center will explode, becoming supernovae, and will tear the nebula apart. And you know what happens to the nebula then, right?
Image Credits: X-ray: NASA/CXC/CfA/S.Wolk; IR: NASA/JPL/CfA/S.Wolk; Optical: NSF/AURA/WIYN/Univ. of Alaska/T.A.Rector
[Over the past few weeks, I've collected a metric ton of cool pictures to post, but somehow have never gotten around to actually posting them. Sometimes I was too busy, sometimes too lazy, sometimes they just fell by the wayside... but I decided my computer's desktop was getting cluttered, and I'll never clean it up without some sort of incentive. I've therefore made a pact with myself to post one of the pictures with an abbreviated description every day until they're gone, thus cleaning up my desktop, showing you neat and/or beautiful pictures, and making me feel better about my work habits. Enjoy.]
I’m fond of saying that the Orion Nebula is one of the biggest, most active star forming regions in the Milky Way galaxy. It has enough gas to form thousands of stars like the Sun, and it’s one of the brightest and closest such gas clouds in the sky.
But, it turns out, Orion is a piker. Or a pike. Because behold: The Dragonfish Nebula!
[Click to ennebulenate, or if you're feeling frisky, grab the huge 7000 x 5500 pixel 26 MB version!]
The Dragonfish nebula — named for its resemblance to a terrifyingly toothy deep-sea fish — is, like its namesake, a monster. It’s something like 450 light years across… compare that to the Orion Nebula’s 12-15 light year width and you start to see how huge this thing is. It’s also incredibly massive: it may have a total mass exceeding 100,000 times the Sun’s mass, and may contain millions of stars!
Incredible. Even from other galaxies, it must be one of the most obvious features in the Milky Way. Yet, ironically, it’s very difficult to see at all from Earth. It’s located over 30,000 light years away, on the other side of the galaxy. There’s a vast amount of interstellar material (like dust) between us and it, absorbing its light, so in optical light it’s essentially invisible. But infrared light can pierce that fog, and the image above was taken using NASA’s Spitzer Space Telescope, designed to look in the infrared.
Astronomers used a different infrared telescope to look at the individual stars in the nebula, and found that it has an incredible 400+ O-type stars, the most massive stars that can exist. These stars are young, hot, massive, and blast out ultraviolet light. That’s what’s making this huge gas cloud glow, and in fact the cloud is expanding under the influence of the terrible flood of radiation. Worse, those stars will eventually explode in the next million years or so, one after another, blasting out radiation and material that will dwarf even what they’re putting out now. That will eventually tear through the nebula, ramming it, causing parts of it to collapse and form new stars, and other parts to dissipate entirely.
We’re safe where we are, tens of thousands of light year away. Too bad! In a million years, that’ll be quite a show.
Image credit: NASA/JPL-Caltech/Univ. of Toronto
Well, this is depressing: Fomalhaut b may not exist.
Fomalhaut is one of the brightest stars in the sky, and is only about 25 light years away — that’s close, on a cosmic scale. It’s young, not more than a few hundred million years old, and surrounded by a vast ring of dust, leftover from the formation of the star itself. The ring is about 20 billion km (12 billion miles) in radius, and has a sharp inner edge.
That last bit is important: the easiest way we know to make the inside edge that well-defined is if a planet is orbiting the star just inside the ring. Its gravity would draw in particles, sculpting what would otherwise be a fuzzy boundary into a clean-cut ring. Not only that, but the ring is off-center; again, that’s likely due to the gravitational influence of a planet.
In 2008, astronomers announced they had found that planet: it appeared in two different Hubble Space Telescope images (shown above; click to embiggen) separated by two years. During that time, it had moved a little bit, by just what you’d expect for a planet at that distance from the star. The news came out the same day as other planets were seen around a different star, and I, along with lots of other folks, made it a headline (see the gallery at the bottom of this post showing all the planets we’ve been able to detect directly in images). This was, after all the first direct detection of a planet orbiting a Sun-like star!
Except, maybe not so much. A new paper has come out (PDF) trying to see Fomalhaut b using the Spitzer Space Telescope. Spitzer is sensitive to infrared, where the planet is far brighter.
And what did they see? Nothing.
This image is pretty damning for the existence of Fomalhaut b. It’s the Spitzer infrared observations of the star, with the star’s light carefully removed. On the left is the actual image, and on the right they artificially added a point of light calculated to be equal to what the planet would emit, in the same position the planet should be — that’s what Arrow 1 is pointing at. It should be one of the brightest things in the image (Arrow 2 points to an unrelated bright spot). And while it’s obvious on the right, nothing can be seen on the left, in the real image. In other words, the planet isn’t seen.
Looking over the paper, it’s clear the astronomers were very careful, and did a number of tests. There’s no known way to make a planet as bright as what was seen in the Hubble images yet invisible in the Spitzer images. If the planet were there, they should’ve seen it. Also, a recent study has shown that if the two images show the planet moving, it would be on an orbit that crosses the ring! That seems extremely unlikely, if not outright impossible. A planet that big and massive — more massive than Jupiter — would disrupt the ring in short order if it physically crossed it. That really does make it very, very likely this is not a planet*.
So what is it? It’s probably a clump of dust orbiting the star, reflecting light from the star enough to show up in the Hubble images but not warm enough to show up in the infrared observations.
That’s too bad. If this is true — and it probably is — then that takes away one of the very few planets directly seen in telescopic observations. However, there are still plenty more, and those have been confirmed (again, see the gallery below). And that number will tend to increase as time goes on, even if every now and again it drops by one or two.
Hmph. I once wrote that destroying a planet is hard. Sometimes, all you need to do is try to observe it a different way, and poof! It’s gone.
And now I have to update that gallery, and all my previous pages about it too. Dang science. Always learning more stuff and changing what we thought we knew.
Image credit: Paul Kalas, U C Berkeley; NASA/Spitzer/Markus Janson et al.
* I chatted with an astronomer friend of mine about this, and he agreed with the authors of this new study. "Overall," he wrote me, "it smells like fish.". I couldn’t help myself. I wrote him back: "Of course it does. Fomalhaut is the brightest star in Pisces!"
[Below is a gallery of exoplanets that have been directly imaged using telescopes on ground and in space. Click the thumbnail picture to get a bigger picture and more information, and scroll through the gallery using the left and right arrows.]