I love all the Hubble images of nebulae and galaxies, but sometimes you need a palate cleanser, an image clean and simple. Like one, say, full of the stars of NGC 288:

[Click to englobularclusternate.]

NGC 288 is a globular cluster, which are usually tightly-packed spheres of stars. NGC 288, though, is looser, with stars dispersed more throughout. This image from Hubble actually resolves the stars even in the core, where they tend to overlap in denser clusters. From 30,000 light years away — half the diameter of our galaxy! — this is a pretty decent feat.

The image is not exactly true color: blue is blue, but orange starlight is shown as green here, red represents near infrared light, and what you see here as orange is actually from the reddish glow of hydrogen. Confused? Yeah, sometimes astronomers color things oddly to make some characteristics clearer. In this case, the colors represent different mass stars. Medium mass red giants look yellow in the picture, and blue stars are more massive. The fainter stars are ones that are still happily fusing hydrogen into helium like the Sun does. However, those stars are much lower mass than the Sun, and have longer life spans.

And there’s more: If you look carefully, you can see fuzzy orange objects poking through the stars. Those are distant background galaxies! They’re probably hundreds of millions of light years away.

We think most globular clusters like NGC 288 form their stars all at once, making them really nice laboratories for studying how stars grow old and die. Since we can be pretty sure the stars are all the same age, it’s one less thing we have to worry about when trying to understand them! Simplification can be nice… in science and in beauty.

I write about spiral galaxies here, and when I do it’s usually because they’re unusual. They’re really big, or small, or violent, or forming lots of stars.

So how about one that’s entirely normal? But don’t let that fool you: it’s still gorgeous. Take a gander at NGC 2841, a perfectly normal spiral galaxy as seen by Hubble:

Breathtaking, isn’t it? Click it to galactinate, or grab the super-dooper 3400 x 3000 pixel high-res version.

NGC 2841 is about 45 million light years way. That kinda sorta close, but not too far, keeping with our theme of averageness. It’s not particularly extraordinary in any way — assuming that any time you see an object tens of thousands of light years across and possessing a hundred billion stars, you’re seeing something ordinary. This type of galaxy is called flocculent: with lots of short arms instead of a two or three long, grand, majestic ones.

It’s forming stars, but not many. Those blue patches are where stars are being born, and they seem small, well-behaved, and scattered evenly across the galaxy’s disk. Everything about this galaxy is, well, polite. It doesn’t have enormous star-birth factories, it isn’t colliding with another galaxy, it doesn’t have weirdly-shaped arms.
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I love stories like this: Hubble spotted a small iceball — only about a kilometer (0.6 miles) across — orbiting the Sun 6.7 billion kilometers (4.2 billion miles) away. And the best part? It was an accident. But it was found on purpose.

The object wasn’t seen directly; it passed in front of a star, momentarily blocking the star’s light. The star is one that Hubble uses to point the telescope itself; it’s one of several thousand guide stars used to keep the telescope aimed at astronomical objects, a bit like stellar benchmarks.

Hubble’s Fine Guidance Sensors are telescopes used to lock onto these guide stars. They don’t take pictures, but instead use a technique called interferometry to (extremely) precisely measure the starlight. If the telescope starts to drift, even a teeny amount, the FGS will sense this and the motion can be corrected.

If a small object passes in front of a guide star it will momentarily block (what we call occult) the starlight, causing a dip in brightness as well as a diffraction pattern, a fluctuation in the starlight caused as the light bends around the object. Knowing this, astronomers dug through 4.5 years of archived data from the FGSs and found the tell-tale sign of such an occultation.

Using this data, the astronomers were able to determine the distance and size of the object. The distance puts it in the Kuiper Belt, the torus of icy comet nuclei orbiting the Sun out past Neptune. The size is remarkable: the smallest known Kuiper Belt Object (or KBO to those in the know) before this was about 20 kilometers across. This is therefore the smallest KBO ever found! Assuming a typical color for the object, it would be about 35th magnitude, or one-trillionth as bright as what you can see with your unaided eye!

Yowza. That’s also far dimmer than anything directly detected by Hubble, by a factor of about 50.

Again, this object was found by going through 4.5 years of archived Hubble FGS data; however, all the FGS data since launch (in 1990) is available, so it’s possible more events like this are waiting to be discovered. There’s real science in this, too: KBOs this small probably come from the collisions and grinding together of bigger objects; getting a handle on the members of this population will let us know more about the history of the Kuiper Belt and the solar system itself.

Also, it’s good to remember that not everything Hubble sees is on purpose! The fact that all the observations are archived means that people will be able to go treasure hunting for years to come. Hubble is the gift that keeps on giving.

Artwork credit: NASA, ESA, and G. Bacon (STScI)

When you poke the Pillsbury dough boy in his bulging tummy, he giggles. When you poke the bulge in NGC 4710, however, you get the history of how galaxies form. Voila!

Awesome. And you really need to embiggen this one to get a sense of the incredible beauty and resolution of the picture. Try the 4000 x 2000 pixel one on for size!

NGC 4710 is an edge-on spiral galaxy located about 60 million light years away in the Virgo Cluster. That puts it in the next town over, cosmically speaking, so it’s a rich target for something like Hubble Space Telescope. This image, newly released (but taken in 2006 before the last servicing mission), reveals spectacular details in the sideways galaxy. Views like this really accentuate the huge sprawling dust complexes littering spiral galaxies.

But it isn’t the dust astronomers are interested in here. Spirals have three main parts: a more-or-less spherical bulge in the center, the disk (which has the spiral arms), and a giant halo of stars surrounding them both. We understand a lot about spirals, but lots of big questions remain, including how and when the bulge forms. A galaxy is born out of a vast, collapsing cloud of gas. It’s possible that the bulge forms straight away, with the infalling gas of the protogalaxy making stars which build up in the galactic center. It’s also possible that the bulge forms later, well after the galaxy itself takes shape, as stars in the inner part of the galactic disk interact gravitationally and fall to the center, building up the bulge.

It turns out there might be a way to distinguish these formation mechanisms, even billions of years after the fact. Globular clusters are small (well, a couple of dozen light years across or so) balls of hundreds of thousands of stars. They orbit bigger galaxies; the Milky Way has well over 100 orbiting it. We know that many globulars formed at the same time as their parent galaxies; the stars in the clusters can be incredibly old. This means that perhaps the formation of the galaxy and its attendant clusters are connected.

In fact, it’s thought that the same process that creates the bulge in the "forms at the same time as the galaxy itself" scenario also creates globular clusters, but the other process (stars from the disk falling inward) does not create globulars.

That’s where NGC 4710 comes in. Being edge-on, we can see the bulge clearly, so it can be studied. But it also presents a good view of its globulars, so scientists can look at pictures like this one and simply count up the number of globular clusters near the galaxy and then figure out if the number is consistent with one of the two formation mechanisms.

In this case, NGC 4710 sports very few globulars, indicating the bulge formed after the galaxy itself. But NGC 4710 is only one of many galaxies being studied this way. Will they all show the same sluggish beginnings to their central bulges?

Time will tell. But I hope that as more of these galaxies are studied more images as lovely as this one become available.

Image credit: NASA & ESA

Ever since the Hubble upgrade a few months ago I’ve been waiting to see the results of it getting back to routine science observations… especially for the new Wide Field Camera 3, which promised to return gorgeous imagery.

Well, the wait’s over. The first image is out, and it’s a nice one: star formation in the spiral arm nurseries of the nearby galaxy M83:

[You know the deal: click it to embiggen, or go here to grab a delicious 15 Mb 3900x3900 pixel version.]

M83 is about 15 million light years away, making it practically a next door neighbor for the Milky Way, as well as a tempting target for telescopes. Proximity = clarity in most cases, and with M83 we have a great view of its lovely spiral arms. This new image from Hubble’s WFC3 shows unprecedented detail, too. There are star clusters everywhere, factories cranking out baby stars by the millions. There are also something like 60 supernova remnants, the expanding gaseous debris from exploded stars, five times the number previously seen in this galaxy.

The colors are interesting. This picture is not quite true color. Sure, blue is blue, green is green, and red is red, but they also added a second version of red coming from the light of warm hydrogen gas (called Hα in astronomical parlance) as well as a fifth color: cyan (turquoise) coming from the light of warm, tenuous oxygen. That light is typically emitted from gas clouds making stars as well as the gas emitted from stars when they die (in fact, my PhD thesis was based on observations of this oxygen-light glowing from a ring of gas around an exploded star). You can see that this teal-like glow pervades the entire image: oxygen is everywhere! But it’s so thin it’s more like a hard laboratory vacuum than anything you could breathe.

Also, if you look closely at the pockets of red clumpy gas, you can some that are edge-brightened, like a soap bubble. These are where stars are being born in vast numbers. Their mighty winds expand outwards, carving huge cavities in the gas. My favorite is the one in the middle left of the image, zoomed in here for your viewing awesomeness. The stars are so closely packed they blur together, and each that you can see here would dwarf the Sun in mass, size, and brightness. You can also see that the rim of the bubble is more pronounced below the star cluster, which means that the surrounding gas in the environment of the cluster is thicker there, and has piled up more as the expanding winds have snowplowed it.

And everywhere in this picture are the dark ribbons and filaments of dust, dust, dust. These are long molecules (usually with lots of carbon) which are created by new stars and dying stars. They litter galaxies like M83 as well as our own. And while they make life difficult for optical astronomers who struggle to penetrate the thick veil and see what lies beneath, the dust is interesting all by itself… and adds a certain depth and grace to images like this one.

And, on the right of the big image, is the white glow of the galaxy’s nucleus. You can see detail of the dust, stars, and gas all the way down to the very center. It’s an amazing image, and I’m sure will keep astronomers busy for a long, long time.

What a great start to the return of the Hubble! And, as always, I can’t wait to see what’s next.

Back in the day when I worked on Hubble, I had an ever-growing mound of paperwork that included FAQs, software instructions, how-to guides for the instruments, and the usual exponentially increasing stack of forms to fill out and process.

How I wish I had this way cool Hubble paperclip to hold those sheaves together!

Now I just need to figure out how to mass produce paperclips bent into a BA shape.

Tip o’ the green-tinted paper-pushing accountant’s visor to Jenny Williams.

What happens when two massive spiral galaxies — each with a hundred billion stars — slam into each other head-on at hundreds of kilometers per second?

Beauty.

[Click to embiggen; or go here to get the massive 15Mb TIF image.]

This is the unusual galaxy NGC 2623, seen in this newly-released and breathtaking Hubble Space Telescope image taken in 2007. We’re seeing this vast smash-up caught in the act, a galactic collision already in progress. It appears frozen in time, but that is an illusion of distance: at a distance of a staggering 250 million light years the tremendous velocities of the collision are reduced to a motionless tableau on the human timescale.

But we see a large number of galactic collisions when we catalog the sky, and together with our knowledge of math and physics we have a good understanding of how these encounters play out.

When two massive galaxies approach each other, the gravity of each starts to affect the other. Call them Galaxy A and B. The side of Galaxy B closer to Galaxy A feels more gravity from it, so stars and gas are drawn toward it more strongly than the stars and gas on the far side of Galaxy B. The same is true in the other galaxy. As they get closer, this force strengthens, teasing out long ribbons of material — called tidal tails — that stretch in the direction of the other galaxy.

If the encounter is off-center, then the tails get curved when the galaxies pass, arcing either gently or severely depending on the speed, encounter distance, and mass of each participant. The Hubble image clearly shows the arcing tails from each galaxy in NGC 2623.

Incredibly, even though hundreds of billions of stars are involved, each individual star is far too small to suffer a physical collision. But gas and dust clouds are much bigger than stars (they can be hundreds of trillions of kilometers across, as opposed to stars which are a trifling million or so kilometers in diameter), so collisions between them are common. When clouds collide they collapse and undergo violent bouts of star formation. This too is clear in the image: the blue clumps in the tidal tails are vast regions of clusters of stars being born; over 100 such clusters have been identified in this image in the tail on the right alone.

Collisions like this blast out energy, not just in visible light, but at other wavelengths as well. In infrared alone, NGC 2623 radiates with the power of 400 billion times the Sun’s energy. This makes NGC 2623 a ULIRG: an ultraluminous infrared galaxy. Although relatively rare locally, they are so common at great distance (and therefore earlier on in the age of the Universe) that they comprise as much as half of all the infrared background glow we see in the Universe. The huge amount of infrared comes from the collision itself; star formation produces prodigious amounts of dust which absorb ultraviolet light from newly-born stars and re-radiate it in the infrared. The collision also dumps gas and dust into the central supermassive black holes in the cores of the two colliding galaxies, which piles up in a flat disk outside the black hole, heats up hugely, and again glows brightly.

Astronomers are making a comprehensive study of such ULIRGs using a fleet of telescopes including Hubble, Spitzer, Chandra, GALEX, 2MASS, VLA, and even the venerable IRAS satellite which surveyed the sky in infrared in the 1980s, and in fact first discovered the ULIRGs.

Why study them? Because galaxies as large as our Milky Way almost certainly started off small and grew to their present size by colliding and merging with other galaxies. Studying ULIRGs is a way of examining how our galaxy came to be… and it’s a glimpse of our future as well. In a billion years or more, we will suffer a massive collision with the Andromeda Galaxy. Our own clouds of gas and dust may smash into those in Andromeda, creating huge waves of star formation and blasting out light at all wavelengths. What will our fate be then? The Earth may survive — the Sun will still be around for this event — and the gravitational repercussions may toss us out of the new galaxy, or drop us down to the core.

It may seem academic, but astronomers thirst for understanding of these events. We want to know how we came to be, and where we are headed. That knowledge may have little or no practical use for our own survival (or at least not for a few million millennia), but for now, for today, we learn more about galaxies in general, more about the physics of cosmic collisions, and more about the interaction of gas and dust on a truly mind-numbing scale.

And of course, we get to gaze on lovely images, illusions of placidity and gentleness to be sure, but lovely nonetheless.

Image credit: NASA, ESA and A. Evans (Stony Brook University, New York & National Radio Astronomy Observatory, Charlottesville, USA)