Tag: ultraviolet

The Helix has pink eye

By Phil Plait | October 4, 2012 7:00 am

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.


Related Posts:

Down the throat of a dying star
The Helix screams in the infrared
A warm anniversary for Spitzer
The Helix’s dusty heart

Andromeda's majestic spray of billions of hot stars

By Phil Plait | May 18, 2012 11:33 am

Well, what can I say about this devastating and jaw-dropping picture of our nearest spiral neighbor, the Andromeda Galaxy?

[Click to massive chainedmaidenate. Do it!]

Well, I could start with HOLY HALEAKALA!

This image is a collection of 11 separate observations of Andromeda taken by NASA’s GALEX satellite. Launched in 2003, GALEX (which stands for Galaxy Evolution Explorer) scans the sky in ultraviolet light, specifically targeting galaxies. Hot stars produce UV light, and so does the gas it illuminates, so by looking in the ultraviolet astronomers can learn about how galaxies are constructed. In the decade since its launch, GALEX has been phenomenally successful, cataloging hundreds of millions of galaxies, some as far as ten billion light years away!

This image of Andromeda is simply stunning. It’s comprised of two colors: what you see here as blue is higher-energy ultraviolet light, and red is lower energy (closer to the kind of light we see). Right away you can see that objects emitting the higher-energy UV are confined to the spiral arms, and lower-energy emitters are spread out across the galaxy. That’s exactly what I would expect: massive stars, the kind that really blast out UV, don’t live very long. They’re born, live out their short lives, and die (as supernovae) pretty much near the spot where they formed, which is in spiral arms. Lower mass stars live long enough to gradually move away from their nurseries, populating the rest of the galaxy.

Also, star formation at the very center of the galaxy probably occurred long ago and shut down, so we don’t see many or any massive stars there.

One thing I didn’t know is that the arms of Andromeda are more like rings! The galaxy is at such a narrow angle that it’s hard to tell, but if you trace the blue emission, the pattern does look more like a ring than a spiral. This jibes with earlier images in infrared taken by Spitzer Space Telescope (which I’ve inset here) and a huge and incredibly beautiful newer one taken with ESA’s Herschel far-infrared telescope (and OMFSM you want to click that link).

From what I’ve read, it’s not clear why the spiral arms appear to be more ring-like. Which I love. Why? Because Andromeda is the nearest big spiral galaxy in the sky, a mere 2.5 or so million light years away. It’s easily visible to the naked eye from a dark site, and I’ve seen it myself countless times using my own eyes, binoculars, and telescopes ranging from small ones up to Hubble. Yet there it is, in all its huge and obvious splendor and beauty, still able to surprise me. That rocks.

And a note about GALEX: NASA recently handed off its operations to Caltech, a very unusual move. The satellite was put into standby mode in February, and I was worried it would be shut down permanently. However, Caltech signed a three-year agreement with NASA — while NASA still owns the satellite, Caltech will now be in control of GALEX’s science mission, managing and operating it. At the end of the agreement it can be renegotiated if GALEX is still in good operating condition. This is an interesting idea, and I’m not sure how I feel about it. I love that GALEX gets to continue operations, but handing off science missions to private groups makes me a little uneasy. In this particular case I think it’s fine — Caltech is a research institute after all — but the precedent may have unforeseen consequences. We’ll see.

Still and all, it’s good to see new life breathed into an important and wonderful instrument like GALEX. I certainly hope it will continue to produce cutting-edge science for years to come… as well as amazingly beautiful images like this one.

Image credit: NASA/JPL-Caltech


Related Posts:

The cold arms and hot, hot heart of the fuzzy maiden
The first spectacular views of the sky from WISE
A Swift view of Andromeda
Andromeda’s warm glow
Andromeda: born out of a massive collision?

An ultradeep image that's *full* of galaxies!

By Phil Plait | March 23, 2012 6:00 am

What happens when you take a monster 4.1 meter telescope in the southern hemisphere and point it at the same patch of sky for 55 hours?

This. Oh my, this:

[Click to embiggen.]

OK, I know. At first glance it doesn’t look like much, does it? Just a field of stars. However, here’s the important bit: I had to take the somewhat larger original image and reduce it in size to fit my 610-pixel-wide blog. So how much bigger is the original?

It’s 17,000 x 11,000 pixels! If you happen to be sitting on a T1 line, then you can grab this massive 250 Mb file. And I surely suggest you do.

Because yeah, the brightest objects you see in this are stars. Probably a few hundred of them. But you have to look at the bigger image ! Why? Because what’s amazing, truly jaw-dropping and incredible is this:

There are over 200,000 galaxies filling this image!

Ye. Gads.

Here’s a zoom of the image, centered on what looked to me to be one of the biggest galaxies in the frame, a nice edge-on spiral.

With the exception of a handful of blue-looking stars, everything in this zoom is a galaxy, probably billions of light years away. Those tiny red dots are galaxies so far away they crush our minds to dust: we’re seeing them with light that left them shortly after the Universe itself formed.

This light is ancient. And it came a long, long way.

By the way, that picture of the spiral there is not even at full resolution! Just to give you an idea, I cropped out just that galaxy in the full-res image and inset it here. If you want to find it in the full frame, it’s about one-third of the way in from the left, and one-third of the way down from the top. Happy hunting.

[Edited to add: I forgot to add that this galaxy is warped! See how the disk flares up on the left and down on the right, just a bit? This is very common in disk galaxies, and our own Milky Way does it too (see #9 at that link). It’s usually caused when a nearby galaxy’s gravity torques on the stars in the disk.]

These images were taken with VISTA, the European Southern Observatory’s Visible and Infrared Survey Telescope for Astronomy (VISTA), a 4.1 meter telescope in Chile. This huge image is actually composed of 6000 separate images, and is the single deepest infrared picture of the sky ever taken with this field of view. Hubble can get deeper, for example, but sees a much, much smaller part of the sky.

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CATEGORIZED UNDER: Astronomy, Pretty pictures

The Sun blows some gas to Venus

By Phil Plait | November 25, 2011 7:02 am

On November 15, the Sun had a minor eruption on its surface that launched a prominence — a towering arc of ionized gas — into space. Sometimes these prominences collapse back down to the surface, and sometimes they wind up ejecting that material into space. This one did a little of both:

The animation was made from images taken over the course of 13 hours by the Solar Dynamics Observatory. The images are false-color; what you see as orange is really ultraviolet light, where the energized gas glows brilliantly. This particular event sent some gas more or less toward Venus, where probably not much will happen. This isn’t like a major flare or coronal mass ejection… but it’s still cool.

Prominences occur all the time (click the picture here to see a gorgeous one from last year), and generally don’t wind up affecting us here on Earth. Still, it’s fascinating to watch the gas — which is hot enough to have its electrons stripped off its atoms, so it follows the Sun’s magnetic field as strongly or even more strongly than it does the Sun’s gravitational field — writhe and seethe under these tremendous forces.

Credit: NASA/GSFC/SDO

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: prominence, SDO, Sun, ultraviolet

Astronomers have found when and how the cosmic fog was lifted

By Phil Plait | October 13, 2011 10:13 am

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.

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CATEGORIZED UNDER: Astronomy, Cool stuff

Bang!

By Phil Plait | August 11, 2011 11:30 am

450 million light years away are two interacting galaxies. Both spirals, they are caught in each other’s gravitational claws. Already distorted and bound, eventually, to merge into one larger galaxy in a few million years, the view we have of them from Earth is both amazing and lovely… and hey: they’re punctuating their own predicament!

[Click to exclamatenate.]

Looking a lot like an exclamation point, the two galaxies together are called Arp 302 (or VV 340). This image is a combination of pictures from the Chandra X-Ray Observatory (purple) and Hubble (red, green, and blue). The bottom galaxy is a face-on spiral, while the upper one is seen more edge-on, giving the pair their typographical appearance.

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CATEGORIZED UNDER: Astronomy, Pretty pictures

Two videos of the Sun: a blast and a blast-off

By Phil Plait | July 19, 2011 10:34 am

Scott Wiessinger produces video for NASA’s Goddard Space Flight Center — my old stomping ground, and I did some work with the video folks while I was there, too — and he sent me links to two very cool videos he put together recently.

In early June the Sun erupted, letting loose a huge plume of plasma from its surface which then fell back down along magnetic field lines in a display the likes of which I had never seen before. I created a video (at the link above) which was far and away the most popular I’ve ever done, garnering nearly 1.5 million views as I write this.

But Scott’s video of the event is much, much cooler:

[Don’t forget to set the resolution as high as possible!]

Breathtaking, isn’t it? The video is greatly sped up; the whole event took many hours to complete. All the different animations were taken in the ultraviolet, where the highly-energetic plasma erupting from the Sun emits strongly. You can really see that the plasma does not fall along ballistic trajectories (the usual arcs due to gravity) but instead moves along the magnetic field lines, sometimes twisting around in non-intuitive ways. Beautiful, graceful, and stunning.

And I love the music*.

The second video is from a camera mounted on a sounding rocket, a rocket that goes essentially straight up and back down. At its highest point it goes up nearly 300 km (180 miles), well into space. It was carrying an instrument to observe the Sun in the ultraviolet.

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CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Followup on the star torn apart by a black hole: Hubble picture

By Phil Plait | April 7, 2011 8:31 am

I recently wrote about a mind-boggling event: astronomers capturing what are apparently the final moments in a star’s life as it was literally torn apart by a black hole.

Today, NASA has released some new pictures of the event, including this Hubble Space Telescope shot:

[Click to embiggen.]

I know, it may not look like much at first. But remember what you’re seeing: the violent death of a star ripped apart by the gravity of a black hole… and it’s happening 3.8 billion light years away! That’s about 40,000,000,000,000,000,000,000 kilometers, so the fact that we can see it at all is pretty amazing. And terrifying.

In this false-color Hubble image, the galaxy and explosion are marked. Pretty much everything you see in the picture is a distant galaxy, a billion of more light years away. Normally, the host galaxy itself would appear as a dot, at best with some small amount of fuzz around it, the glow of billions of stars reduced by the incredible distance. But the dying light of the star increased the galaxy’s brightness by a lot. A whole lot.

This image (click to greatly embiggen!) is a combination of visible light (white), ultraviolet (purple), and X-rays (yellow and red) from NASA’s Swift observatory, the satellite that first detected the explosion. While the spikes are not real — they’re just an optical effect from the telescope itself — it still speaks to the drama of what we’re seeing.

And so just what are we seeing?
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CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Solar storms coming our way this week?

By Phil Plait | October 11, 2010 5:45 pm

The Sun is getting back into the swing of things: a big active region on its limb erupted yesterday (October 10), sending out a small storm of subatomic particles into space. We weren’t in the line of fire, but over the next few days the rotation of the Sun will bring Active Region 11112 closer to the center of the Sun’s disk, and if that region erupts it may send a storm our way.

Here’s a recent image of the Sun from the Solar Dynamics Observatory:

sdo_0193_oct112010

This shows the Sun in ultraviolet (where activity can manifest itself) from around 23:00 UT (19:00 Eastern US time) on October 11. The active region is pretty obvious there to the lower left.

sdo_magnetogram_oct112010A magnetogram, which shows magnetic activity, makes the region obvious as well. A recent one (shown here on the left) from around the same time as the image above again shows the active region has a lot of magnetic activity going on.

The Sun’s magnetic field lines can contain a huge amount of energy. As the gas in the Sun roils and swirls, the field lines get tangled together. If they connect, bang! They can explode, sending that energy out into space. Read More

A Swift view of Andromeda

By Phil Plait | October 5, 2009 7:59 am

NASA’s Swift satellite is a modern success story: designed to peer at the Universe in ultraviolet, X-rays, and gamma rays, it is on constant lookout for gamma-ray bursts, explosions so vast they are second only to the Big Bang itself.

Swift scans the skies, constantly observing, always on its toes for that fleeting blast of high-energy light. But it also does other science as well; an orbiting camera like that has many uses. For three months in 2008, astronomers used Swift to target the nearest major spiral galaxy like our own: M31, the Andromeda Galaxy. And what they got was this gorgeous picture:

Swift_uv_m31

Wow. You absolutely want to click that to embiggen it most cromulently — you’ll get a whopping 4400 x 200 pixel version.

This image is incredible, both scientifically and logistically. It is the combination of 330 images, totaling 24 hours of solid observations, and amounted to a hefty 85 gigabytes of data. It covers three UV wavelengths: 192.8, 224.6, and 260 nanometers, which are just outside the range the human eye can see.

The image is huge; the full Moon would just fit over the apparent size of the central bulge of the galaxy. Over 20,000 individual sources of ultraviolet light can be found. Some science can be seen just with just a glance: for example, the light coming from the spiral arms is clumpy, and from the bulge it’s smooth. The arms are where you find patches of giant gas clouds forming newly born stars; the most massive of these blast out UV light and fierce winds which make the clouds themselves glow in UV.

But the bulge at the core is smooth, because stars there are old; star formation long ago ceased in the galactic center. The UV glow is mostly from tightly packed stars, not from gas. There are so many stars that the individual sources blend together into what looks like a continuous glow (not unlike a digital image itself, where individual pixels blend together to make what looks like a smooth picture).

This image is the most detailed ever taken of our big neighbor in the ultraviolet, and I have no doubt it will be used as an atlas for higher-resolution cameras aboard Hubble and future spacecraft. Pictures like this are scientifically incredibly useful; they are roadmaps we can use to plan out our travels ahead.

And they are also just very, very cool.

Image credit: NASA/Swift/Stefan Immler (GSFC) and Erin Grand (UMCP)

CATEGORIZED UNDER: Astronomy, NASA, Pretty pictures
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