WISE finds the coolest stars. Literally.

By Phil Plait | November 12, 2010 7:00 am

I have a few pet objects in astronomy that fascinate me endlessly. One of these is brown dwarfs, objects that are bigger than planets, but too small to be bona fide stars. They are much cooler and fainter even than dinky red dwarfs, making them very difficult to find… unless you are WISE:


[Click to embiggen.]

See that pale green dot in the middle? That’s a brown dwarf! I know, it’s not brown, it’s green, but that’s kosher since brown dwarfs are really magenta.

OK, hang on a sec. I’ll explain that in a minute.

The important thing is that this image shows a very nearby brown dwarf, maybe 18 – 30 light years away (the distance is hard to determine, but observations taken over the next year or so should pin it down). That’s really close! The nearest known star, Proxima Centauri (a faint red dwarf) is 4.2 light years away, and only a few hundred stars are within 30 light years. That makes this brown dwarf, named WISEPC J045853.90+643451.9 (after its location in the sky), one of the closest stars known.

You’d think think we’d have a pretty good idea of all the stars near us, since they’d be among the brightest in the sky. But in fact brown dwarfs are so faint that to optical telescopes they can escape detection even if they’re our cosmic neighbors. WISE, however, looks in the infrared, where brown dwarfs glow considerably brighter.

And that brings me to the weird colorful adjectives we use for these objects.
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CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

Three views to a comet

By Phil Plait | October 8, 2010 7:00 am

103P/Hartley 2 is the somewhat prosaic name for a pretty nice comet in our skies right now. It’s still a little bit too faint to see without aid of binoculars or a telescope, but it’s getting brighter: on October 20th it’ll pass by the Earth at a distance of a mere 18 million km (11 million miles)!

Astronomers all over the planet are jumping at a chance to see a comet up close… and the views they’re getting are really, really cool. Behold!


That’s Hartley 2 as seen by WISE, an orbiting NASA mission designed to survey the sky in the infrared, so it’s very sensitive to objects that astronomers consider warm — that is, a few degrees above absolute zero! It’s seen comets before, since they fit the warm-to-astronomers-but-freezing-to-anyone-else category.

Mind you, the actual solid part of the comet is only a few kilometers across, far smaller than a single pixel in this picture. But it’s loaded with frozen ices which turn into gas as the comet nears the Sun, enshrouding the nucleus with fuzz, and streaming behind it as that long, long tail. In this picture, the tail is nearly 2 million kilometers in extent — well over a million miles!

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CATEGORIZED UNDER: Astronomy, Pretty pictures

The Seven WISE Sisters

By Phil Plait | July 19, 2010 7:04 am

If you live in the northern hemisphere and go outside in the winter, hanging not too far from Orion’s left shoulder is a small, tight, configuration of stars. A lot of people mistake them for the Little Dipper — I get asked about it all the time — but really it’s the Pleiades (pronounced PLEE-uh-dees), an actual cluster of stars about 400 light years away. To the eye you can usually spot six of the stars (the seventh, seen in ancient times, may have faded a bit since then), and in binoculars you can see dozens.

But when NASA’s Wide Field Infrared Survey Explorer (WISE) looked at it in February, this is what it saw:


Coooool. Literally! WISE looks in the infrared, and can see cool objects that are invisible to our eyes. The Pleiades stars are bound together in a cluster by their own gravity, and are currently plowing through a dense cloud of dust and gas in the galaxy. The material has been warmed up by the hot stars, and glows in the infrared. Deep images in visible light also show the material, but it looks blue as it reflects the optical light from the stars. In the WISE images, we’re seeing the matter actually glowing on its own, emitting infrared light.
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CATEGORIZED UNDER: Astronomy, Pretty pictures

A WISE flower blooms in space

By Phil Plait | March 22, 2010 8:00 am

I loves me some astronomical nebulae! And the Wide-field Infrared Survey Explorer — WISE — can really deliver:


[Click to emblossom.]

This image shows AFGL 3193 — what looks like a rosebud — a small piece of a very complicated region of gas, dust, and stars in the constellation of Cepheus in the northern sky. This region has star formation, cold and hot dust, and even a supernova remnant (called NGC 7822). This particular part seen by WISE shows a cluster of young stars called Berkeley 59 — the stars colored blue to the right — surrounded by the gas and dust from which they formed. This cluster is less than a million years old, and the massive, hot stars are blasting out radiation that is eating away at the cocoon surrounding them.

In the false-color image from WISE, red shows the coolest dust, blue and cyan warmer material, and green reveals long-chain organic molecules called polycyclic aromatic hydrocarbons, or PAHs. You can see how the PAHs appear to form around the rim of the nebula as the material there is compressed and warmed by the ultraviolet light and solar winds from the young stars. The filaments are testament to the forces tossed around as the stars go through their violent birth process. One of the stars in the cluster is a massive O5 star with dozens of times the mass of the Sun, and blasting out radiation at a rate 100,000 times that of the Sun!

I’m not sure just how big an area this image covers, but it’s roughly a degree across, twice the width of the Moon on the sky. The cluster is located about 3000 light years away, which is good: a lot of those stars will soon (well, in a few million years) explode, and this distance is far enough away that we’ll see a spectacular light show, but won’t wind up hurting us. Phew!

WISE is designed to survey the sky in infrared, literally spinning around and scanning the entire celestial sphere. It doesn’t have a field of view per se; the data come down in a stream and the astronomers on the ground can put them together at any scale they want, a little bit like Google maps. So expect to see lots more images of objects like this one, and you can get the whole list at the WISE gallery.

Image credit: NASA/JPL-Caltech/WISE Team

CATEGORIZED UNDER: Astronomy, Pretty pictures

Two nearby galaxies peek out through the dust

By Phil Plait | March 9, 2010 7:26 am

NASA’s Wide-field Infrared Survey Explorer, or WISE, only launched a couple of months ago, and has already done spectacular work. Gulping down huge tracts of sky every day, it has already discovered over 2000 asteroids — not seen, but actually discovered — including several that pass near the Earth (none on track to hit us, happily). It’s discovered four comets, too, and by the end of the mission in a few months will see far more.

But since it’s a survey instrument, and it sees in the far infrared, the views it gets are nothing short of spectacular! Like this one:


[Click to embiggen, or grab this ginormous 11,000×4000 TIF].

There is a lot to see here! First, the colors: all of this is far infrared, with blue being the IR wavelengths of 3.4 and 4.6 microns combined (5 and 6.5 times the wavelength the human eye sees), green is 12 microns, and red 22. Green is dominated by warm dust and big organic molecules called polycyclic aromatic hydrocarbons.

The glowing gassy stuff is part of the Heart Nebula, which I’ve posted about before (guess what date). But take a look a bit to the left of all that gas, and look much, much farther in distance…


Those are two galaxies, called Maffei 1 and 2. Both are actually quite close to the Milky Way, only about 10 million light years away. They’re big galaxies, and really should be among the brightest galaxies in the sky. Yet chances are you’ve never heard of them! That’s because this area of the sky is loaded with dust in our galaxy, which absorbs visible light. Another incredibly beautiful galaxy, IC 342, is also part of that group, but is hard to see in visible light as well.

Maffei 1 is right and below center, and Maffei 2 is the barred spiral one above it. For comparison, this image here is about twice the diameter of the Moon on the sky. WISE has a huge field of view, so it doesn’t get high-res images of galaxies, but it more than makes up for it in breadth and depth. Observations like this will help astronomers map the dusty content of nearby galaxies, and even get a handle on how much dust is in much more distant galaxies, though the maps won’t be quite as detailed. Still, more information is always good, and getting to study galaxies — and nebulae, and planets, and comets, and asteroids, and and and — in the far infrared will help our understanding of all these objects far better.

As an aside, I learned of this image on my pal Amy Mainzer’s WISE blog. She’s a bigwig with WISE, and when she has time away from doing nonstop firehose science she writes up fun stuff about this new and extremely cool spacecraft. That’s definitely one you want to drop into your RSS feed reader!

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: asteroids, galaxies, WISE

The first spectacular views of the sky from WISE

By Phil Plait | February 17, 2010 10:08 am

NASA’s fledgling Wide-field Infrared Survey Explorer (WISE) opened its eyes a few weeks ago, and astronomers have just released the first of a torrent of spectacular images from it.

Since its launch last December, WISE has been surveying the sky, taking data continuously as it spins on its axis and orbits the Earth. A few images have been released before, but these new ones are fully processed, scientifically-calibrated, and gorgeous.

I have to start with this one, because it’s just so pretty! Behold Comet C/2007 Q3, aka Siding Spring:


Holy dirty snowballs! That’s gorgeous, a classic comet. When this image was taken, on January 10, 2010, the comet was 340 million kilometers (200 million miles) from Earth. That’s a good ways off, so I’m impressed with the detail of this image! It’s actually a four-color image: blue is 3.6 microns (about 5 times the reddest wavelength the human eye can see, so well out into the infrared), green is 4.6, orange is 12, and red is 22 microns.

Since the temperature of an objects determines the kind of light it emits, we can estimate the temperature of the comet just by eyeballing this picture. It’s mostly orange, meaning the comet is pouring out light at 12 microns. A human being radiates infrared from about 7 to 14 microns, so this means the parts of the comet emitting IR (and therefore seen by WISE in this image) are around the same temperature as a person! Well, in physics terms; in human terms it’s pretty cold, about -40 Celsius. And it’ll get even colder now since it’s on its way out of the inner solar system, away from the Sun’s warmth. It’ll dim as it cools, too, returning back to invisibility once again.

WISE is expected to see quite a few comets, and in fact discovered its first just a few days ago. I wonder how many it’ll find, and if they’ll all be this pretty…?

Let’s take a step farther out for the next WISE image:


Recognize that galaxy? I wouldn’t blame you if you didn’t, but it’s Andromeda! That’s the nearest large spiral to our Milky Way. It’s roughly 2.9 million light years away (estimates vary) and can be seen by the naked eye from a dark site. This stunning photo really accentuates how amazing WISE is: the field of view is 5 degrees across, the width of ten full Moons. The Hubble camera I used to work with would barely cover a pixel in this image!

Remember, this image is all infrared. What looks blue here is actually cold stuff compared to what we’re used to: old red stars, for example. The colors are a little different than in the comet image, but red is still the coolest material: dust. These complex molecules are created when massive stars are born and when they die. Since massive stars don’t live long, they tend to die near where they were born, so you see the dust constrained to very narrow areas where star formation occurs. Less hefty stars (like the Sun) live long enough to drift away from their nursery over billions of years, so they fill the galaxy’s disk (in blue). That’s why the dust is so vivid and tightly defined in this image.

If you look closely, you can see the left side of the galaxy is a bit distorted. That’s called a warp, and is probably caused by a nearby pass of another galaxy, or one Andromeda actually absorbed. The fuzzy blob just below the main galaxy is a dwarf elliptical companion to Andromeda, orbiting it like the Moon orbits the Earth. It’s mostly composed of old stars that look red to our eye, so again it’s blue in this false color image.

OK, one more. I like this one a lot: NGC 3603, a star-forming region about 20,000 light years from Earth:

It may not look familiar, but if you’ve been reading my blog for more than a couple of weeks, you’ve seen it: I wrote about a Hubble image of this very nebula. Now, if you’re like me, you’ll click that link, look at the Hubble image, and then try to figure out where it fits in this WISE shot. Pbbbt. Don’t bother. The Hubble image is only a tiny portion of this vast vista, a blip right in the middle of the brightest part of the WISE image. The S in WISE is for "Survey", which means it takes pictures of ginormous swaths of sky, far more than Hubble can do. In fact, Hubble could take picture after picture for weeks and not get a view of the sky as large as WISE does in a few minutes (of course, the Hubble image would be a whole lot more detailed…).

In this image, as before, red is warm dust, and blue is hotter material like stars. The green is what gets me though: at 12 microns, that reveals PAHs, polycyclic aromatic hydrocarbons. These complex organic compounds form in cool conditions in nebulae, which are lousy with them. They’re everywhere where the temperature isn’t too high to disintegrate them. They can form even larger molecules, and some people think they may be important in creating the molecules necessary for life on Earth. That’s not to say those molecules form in nebulae like NGC 3603 and then somehow get here; they most likely form right here as well. The point is, they look like they’re pretty easy to make if conditions are right… on Earth as it is in the heavens.

And the sheer size and breadth of the nebula is simply stunning! I’m so used to narrow fields of view that I forget sometimes just how large these objects are. This nebula is dozens of light years across, forming thousands upon thousands of stars. It’s among the biggest such star factories in our galaxy, and is certainly easily visible from other galaxies as well. Even from 20,000 light years away — 1/5 of the way across our entire galaxy — it’s clearly a formidable object.

And that’s the strength of WISE. It can see large objects, investigate the bigger picture of the sky, and do it in the longest regions of the infrared spectrum, light that we simply cannot explore from the ground — our air absorbs it, and all the warm objects around us glow fiercely at those energies. It would be like trying to find a firefly against the Sun! So we must launch observatories into space to peer at the far infrared light from cosmic objects, and WISE will be our eyes to do just that.

And from these images it looks like it’ll do a fine job. I’m impressed with these images. I’ve seen a few early release observations in my time — I’ve made a few myself! — and these are excellent. The whole mission is only supposed to last a few months; there is coolant on board for the detectors that can only go so far. In that short time it has a whole sky to observe, and that’s a lot of space. But that also means there’s a lot to see: galaxies, asteroids, comets, nebulae… maybe even a gamma-ray burst or two. The next few months will be very exciting for infrared astronomy!

Related posts:
WISE uncovers its first near-Earth asteroid
First light for WISE
The terrible beauty of chaotic starbirth
Spitzer peeks under a cradle’s blanket

Images credit: NASA/JPL-Caltech/UCLA

CATEGORIZED UNDER: Astronomy, Pretty pictures

WISE uncovers its first near-Earth asteroid!

By Phil Plait | January 25, 2010 2:00 pm

The Wide-field Infrared Satellite Explorer has detected its first near-Earth asteroid! Named 2010 AB78, it was discovered in mid-January by the orbiting observatory. Here’s an image of the rock:


AB78 is about a kilometer (0.6 miles) or so across, making it one of the bigger asteroids that can buzz the Earth. The orbital information on it isn’t perfect yet, but we already know its orbit doesn’t actually cross the Earth’s so it can’t hit us. At closest approach it’s still many million of kilometers away from us, and poses no threat.

However, I’ll be honest and say this discovery is mildly alarming (stressing the word mildly). One of the missions of WISE is to find such asteroids; some rocks are dark and therefore hard to detect using telescopes which search in visible light. However, AB78 is warm, so it glows in the infrared, making it an easy target for WISE. That’s why searching for such asteroids is one of WISE’s main goals.

The thing is, statistically speaking we should already know of almost all the kilometer-sized rocks that are in near-Earth orbits; given the rates and methods of finding them, our catalog should be about 90% complete. Finding an asteroid this size that eluded detection up until now is somewhat unsettling. How many more have we missed?

Let me be clear: this could be a statistical fluke; even if we know of 90% of all the NEAs out there, 10% still lurk out in the black. It could simply be that this first one found by WISE is somewhat on the hefty side, and the next 20 will be far smaller. Remember too, this one is bright in the IR (in the above picture, red is actually at a wavelength of 12 microns, 15 times longer what the human eye can see) and so it was easy to spot. Smaller ones are fainter, so they may not be as obvious and will take longer to detect. Also, AB78 is on a weird orbit, tipped substantially (about 33°) to the plane of the solar system, again making it more difficult to spot.

And in a way, this is good news! The more we know about these things, the better. AB78 may be a fluke, or there may be more rocks this size out there hiding, but either way I want as much info as we can get. Just knowing how many asteroids of a given size orbit the Sun and get near the Earth is an important piece of data, so that we can apply some statistics to them and try to figure out, on average, how often we get hit. That’s one of the things WISE will do over its 10-month-long mission, so in a year or so we’ll be in a better position to understand these orbiting worldlets.

Emily Lakdawalla at The Planetary Society has more info as well.

Image credit: NASA/JPL-Caltech/UCLA


First light for WISE!

By Phil Plait | January 6, 2010 2:28 pm

The Wide-field Infrared Survey Explorer (WISE) has seen first light — in other words, taken its first image from space!


[Click to embiggen and get access to a big TIFF version.]

Nice. It may not look as pretty as a Hubble or Spitzer shot at first glance, but to an astronomer it’s the Mona Lisa. The images are sharp (it’s in focus), the stars are not overexposed, diffuse sources are detected, and the diffraction spikes (the crosshairs centered on stars) are clean.

In other words: bingo!

This is an engineering image, not a science one. So it’s not supposed to be gorgeous or ready for publication or anything like that. It’s more like an aliveness test, to make sure the spacecraft is operating as expected. And it is!

This image is an 8-second exposure of a region in the constellation Carina. Normally, WISE will always be on the move, constantly sweeping the sky and taking data. But in this case, they pointed it at one spot to make sure everything was working. WISE works in the infrared, and this picture is actually a composite of three images: blue represents light at 3.4 microns (about 5 times longer than what we can see with our eyes), green is 4.6 microns, and red is 12 microns. This is well into the IR, and shows stars and warm dust in that region.

To give you an idea of the scale, the image covers the same area of the sky as three full Moons, so WISE takes big swaths of the sky when it looks around. That’s why it’s called a survey explorer. It will take millions of images of the sky, which can be stitched together to make mosaics.

WISE launched last December, and we’ve been waiting for news that it’s working. This image shows it is, so we can expect very cool stuff coming from the orbiting observatory in the future. The mission is actually quite short, only 10 months long. In October, it’s expected run out of the frozen hydrogen (!) being used to cool the detectors — warm objects emit infrared light, and you don’t want your telescope glowing in the light you want to see. In this case, the hydrogen keeps WISE’s cameras at a bone-crushing 8 Kelvin, or -445° F.

You can read more about this in my earlier post about WISE. My congrats to the team!

CATEGORIZED UNDER: Astronomy, Pretty pictures
MORE ABOUT: infrared, WISE

WISE to launch Monday morning

By Phil Plait | December 13, 2009 9:36 pm

[UPDATE: As of 8:10 a.m. Mountain time (15:10 GMT) the launch went well, and WISE is now orbiting the Earth. There will be some engineering checkouts over the next few hours, but everything looks good! Congrats to the WISE team!]

wise_rocketIf all goes according to plan, a Delta II rocket will thunder into the California sky at 9:09 a.m. EST (14:09 GMT) Monday, carrying the Wide-Field Infrared Survey Explorer (WISE) into orbit.

WISE is an amazing instrument. It will survey the entire sky in the far mid infrared, with much better resolution than ever before. It is expected to detect hundreds of millions of objects, including galaxies, faint, cool stars, asteroids in our solar system, and much more. Amy Mainzer, Deputy Project Scientist for WISE, is in a video that explains what it’ll do (sorry, the embedding didn’t work, but click through and watch it).

WISE is a precursor mission to the James Webb Space Telescope, a huge infrared observatory that will be to the mid infrared sky what Hubble is to the visible, near IR, and near UV. Surveying the entire sky will enable astronomers to make quite the wish list for JWST once it’s up and running in 2014.

I’m looking forward to seeing what WISE can do; the images alone should be jaw-droppingly beautiful, and of course the science will be great. You can watch the launch live on NASA TV, too.

Image credit: NASA/VAFB


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