Tag: Andromeda galaxy

Hubble peers in on a galactic snack

By Phil Plait | September 19, 2012 7:00 am

Galaxies come in a lot of shapes and sizes: huge ellipticals, big spirals, weird squishy irregulars. There is a sub-class called "dwarf galaxies" which are smaller than usual. We actually think they dominate the Universe by number, but because they have fewer stars – a few billion or so tops, compared to the hundreds of billions of a big one like our Milky Way – they fade rapidly with distance. Only a handful are close enough to study well.

One of these is DDO 190, a nice little dude something like 9 million light years away. That’s close enough to resolve individual stars in the galaxy, as you can see in this really pretty Hubble image of it:

[Click to galactinate, or grab the cosmic 3700 x 2600 pixel version.]

DDO 190 is small, but not tiny: about 15,000 light years across. That’s about 1/6th the size of our galaxy. It’s also well outside our Local group of nearby galaxies (the Andromeda galaxy is less than 3 million light years distant from us, for comparison) and is thought to be part of the M94 galaxy group. But if true it’s fairly isolated even from the others on its team; the nearest neighbor appears to be another dwarf galaxy several million light years away from it.

This image is pretty nifty. For one thing, you can see lots of far more distant background galaxies, some right through DDO 190, which always gives me a kick. But the dwarf galaxy itself has some surprises. The bluish fuzzy regions are clouds of gas lit by young, hot stars. These stars don’t live long (a few million years or so), meaning there’s still some star birth going on in the little guy. That blue patch at the bottom is the brightest of them – it looks a bit like a more distant galaxy, but don’t be fooled.

Interestingly, it has two different populations of stars in it. The younger ones I mentioned (100 million years or younger) tend to be close in to the center, while older ones (4 billion years or more) are located in the outskirts. This is common in dwarf irregular galaxies. The older stars may be showing us what the primeval galaxy looked like, but now a burst of star birth has occurred near the center, making the galaxy look more condensed.

Since the vast majority of galaxies in the Universe are dwarfs like this, we think bigger ones like ours get to their size by gravitationally colliding with and absorbing dwarfs. In fact, we know the Milky Way is eating several right now!

Galaxies are cool, and pretty, and magnificent, but they’re also cannibals. DDO 190 is isolated enough that it may be safe from that fate for quite some time. But the Universe is young, and galaxies patient. In a trillion years or so, we’ll see who has whom over for dinner.

Related Posts:

- And the cottonball galaxies shall inherit the Universe
- Hubble grills a confused galaxy
- Obese, gluttonous, and cannibalistic is no way to go through life, son
- Lonely galaxy is lonely. But it ate its friends.

CATEGORIZED UNDER: Astronomy, Pretty pictures

Gallery: Cosmic pictures from the AAS

By Phil Plait | January 17, 2012 7:00 am

This is a galaxy?

By Phil Plait | June 27, 2011 10:04 am

I love to post pretty pictures of galaxies and wax lyrical about their magnificent structure, complex history, and complicated internal compositions.

… and then there’s the Carina Dwarf galaxy. It’s so small and faint it wasn’t even discovered until 1977 even though it’s one of the closest galaxies in the sky! How did it avoid detection so long? This’ll make it obvious:

[Click to unendwarfenate.]

See it? Yeah, it’s that faint smattering of stars in the middle of the picture (the bright star near the center is in our Milky Way and coincidentally aligned with Carina). Not much to it, is there? It’s about 300,000 light years away, only 1/10th as far as the much brighter and more famous Andromeda Galaxy, and only about twice as distant as our two satellite galaxies, the Small and Large Magellanic Clouds, both of which are easily visible to the unaided eye.

Like the LMC and SMC, it is apparently a satellite of the Milky Way, but formed long after we did; studies of the stars in the Carina Dwarf indicate it’s only about 7 billion years old at most, while our galaxy is well over 10 billion years old. It probably formed from primordial gas orbiting the Milky Way, taking much longer due to its low mass and relatively quiet environment.

This image is a combination of observations taken with the 2.2 meter MPG/ESO and the Victor M. Blanco 4-meter telescopes in Chile. It shows that the galaxy has very little or no gas at all in it, and so its career in star-formation is long dead. But there’s still much to learn from such objects: they get eaten by bigger galaxies, for example. This cosmic cannibalism is one way galaxies like ours get so big, so studying these smaller bite-sized snacks in situ help us learn about ones we’ve already munched on.

Plus, galaxies like Carina might be the most common in the Universe! We just can’t see them because even at relatively small distances they fade away into the background. They may not be as flashy as spirals or as monstrous as giant elliptical galaxies, but they play an important role in building up such beasts. The more we know about them, the better we’ll understand the Universe itself.

Image credit: ESO/G. Bono & CTIO

Related posts:

- And the cottonball galaxies shall inherit the Universe
- Lonely galaxy is lonely. But it ate its friends.
- Alien clusters invade our galaxy!
- Obese, gluttonous, and cannibalistic is no way to go through life, son

CATEGORIZED UNDER: Astronomy, Pretty pictures

Collision of past and present

By Phil Plait | November 29, 2010 9:40 am

The European Southern Observatory just released this lovely picture of NGC 520, two galaxies in the middle of the long, long process of colliding:


[Click to galactinate.]

NGC 520 is pretty far away, about 100 million light years. Still, even at a glance you can tell something is fishy* about it. Colliding galaxies like NGC 520 are relatively common; hundreds of examples are known. These galactic train wrecks can take billions of years to unfold, and in this case the two galaxies have probably been at it for 300 million years or so. They’re well on their way to merging to become one much bigger galaxy, probably the size of the Milky Way: 100,000 light years across. We think our own galaxy grew over time in this way.

m31_merge_stillAnd if NGC 520 looks familiar to you, that may be because you’ve been reading this blog for more than a week. It was only a few days ago that I posted a stunning video showing a scientifically and mathematically-produced animation of how some scientists think two large galaxies collided and merged, forming the Andromeda Galaxy as we know it today.

Shown here is a still from that animation (flipped horizontally) which looks remarkably like NGC 520, don’t you think? Read More

CATEGORIZED UNDER: Astronomy, Pretty pictures

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

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:


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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