Blogs / Bad Astronomy

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)

Planetary nebulae are too cool.

When a star like the Sun dies, it goes through a series of episodes where it blows off dense winds, vast volumes of gas which expand out from the star in exotic shapes. This is caused by paroxysms in the star’s core; at its advanced age, fusion of one element into another is unstable, and sometimes huge amounts of energy are suddenly dumped into the star’s outer layers. These outer layers respond by swelling and shrinking, and this in turn is reflected in the winds the star blows.

NGC 2371, seen here in a new Hubble Space Telescope picture, is just such a nebula. The winds from the star have slammed into each other, creating the odd puffy shape. As the star sheds its overcoat of material, the hot, dense core is exposed — you can see it as the pinkish-white dot in the center. That color isn’t real; in fact the star, now called a white dwarf, would be bluish or intensely white. But it’s hot, no doubt: it’s over 130,000 degrees Celsius — and that’s not even the hottest one known, which is well over 200,000 degrees!

At that temperature, the star floods the gas with ultraviolet light, which ionizes the material and makes it glow in the same way as a neon sign. In this particular image, sulfur and nitrogen glow red, hydrogen is green, and oxygen is blue. The colors aren’t real; they were just chosen for aesthetics. In general, hydrogen is reddish and oxygen is green.

I was intrigued by the two pink stubs you can in the nebula, on opposite sides of the central star. Those are called FLIERs, for Fast Low-Ionization Emission Regions (I have details on what they are at that link). Their exact formation mechanism isn’t well-understood, but they always appear like that, on opposite sides of the star, so some symmetric shaping force is at work.

I had to laugh when I saw them; they looked like the electrical studs in the neck of the classic Frankenstein’s monster. Too bad I don’t get to name nebulae! I guess, though, after a second look the studs are too high. They look like ears, maybe, or antennae. There was a robot in an old movie or a book cover; I can’t remember, but it had little antennae sticking out of its head just like this. Anyone remember what I’m talking about? Stuff like that makes me crazy when I can’t remember it. Like an itch you can’t scratch.

Anyway, if you like planetary nebulae, then search the blog here for more; I’ve written about them quite bit, since I studied them for both my Masters and PhD. The Hubble website has dozens and dozens of them, too.

The picture above shows a cosmic bulls-eye of epic alignment. But before I can tell you about it, I have to tell you about how the dart got thrown.

One of the more amazing aspects of looking into deep, deep space is that the path there is tortured and twisted. Space itself can be distorted by mass; it gets bent, like a road curves as it goes around a hill. And like a truck that must follow that road and steer around the hill, a photon must follow the curve of space.

Imagine a distant galaxy, billions of light years away. It emits light in all directions. One particular photon happens to be emitted almost — but not quite — in our direction. Left on its own, we’d never see it because it would miss the Earth by thousands or millions of light years.

But on its travels, it passes by another massive galaxy. This galaxy warps space, and the photon does what it must do: it follows that curve in pace, and changes direction… and it just so happens that the curve is just right to send it our way.

The intervening galaxy is essentially acting like a lens, bending the light. If the more distant galaxy is exactly behind the lensing galaxy, we see the light from that more distant galaxy distorted into a perfect ring, a circle of light surrounding the lens. We call this an Einstein Ring. If the farther galaxy is off to the side a bit, we see an arc instead of a complete ring. Gravitationally lensed arcs and rings are seen all over the sky, and they can be used to determine the mass of the intervening galaxy! The more mass, the more distorted the light from the farther galaxy. So the Universe has given us a nice method to let us weigh it.

In a surprising twist, astronomers have found a new type of lensed galaxy: a double ring! In a rare alignment, there are two distant galaxies aligned behind an intervening lensing galaxy. They’re like beads on a wire, lined up just right such that both more distant galaxies are lensed by the nearer one. In this case, the lens is about 3 billion light years away, and the other two are 6 and 11 billion light years away, an incredible distance.

This image is amazing, but it is also a powerful scientific tool. It allows us to measure not just the mass of the lensing galaxy, but also the amount of mysterious dark matter nearby. We cannot see the dark matter, but it too bends light, and contributes to the lensings. By observing lenses like this, we can take a sample of dark matter in the Universe, and that’s a crucial first step in understanding it. Even better, these double rings allows us to measure the amount of total mass not just in the nearest galaxy, as is usual, but also in the middle galaxy as well, since it distorts the light from the galaxy behind it (turns out it’s a rather lightweight one billion solar masses; our own Galaxy has more than 100 times that mass, so the middle galaxy is considered a dwarf).

This is a beautiful happenstance; it gives us a measure of the Universe at two points, with one being for free. In fact, Tommaso Treu, the astronomer at U.C. Santa Barbara who investigated this lens, points out that if we can find as few as 50 of these double rings, we can get a much better idea of the distribution of not just dark matter, but also the even more mysterious dark energy in the Universe. That’s one of the biggest goals of modern astronomy… and we may get a handle on it due to a coincidental ring toss.

M81 and M82 are bright nearby galaxies; you can spot them with binoculars easily in the northern sky, and they are a mere 12 million light years from us (for comparison, the Milky Way Galaxy is 100,000 light years across, so if you think of the Milky Way as a DVD, M81 and M82 would be about 14 meters away). These two galaxies interacted a couple of hundred million years ago, and the gravitational interaction drew out long tendrils of gas (which is very common in colliding galaxies).

Astronomers examined this bridge of material using Hubble, and found clusters of stars in it. That was totally unexpected; the gas was thought to be too thin to form stars! Amazingly, many of the stars are blue, indicating they are young (blue stars burn through their fuel much more quickly than redder stars. This means that the gas is still forming stars, even 200 million years after the collision!

In the image below, almost all the stars you see are young blue stars formed in the aftermath of that titanic collision. The reddish stars are stars in our galaxy, and the bigger objects are distant background galaxies.

Most likely, the stars formed when turbulence in the tendril caused local regions of denser gas, which could collapse to form stars. Before these observations, it wasn’t really thought it was possible to form stars in the regions between galaxies, so this is an interesting new find.