Galaxies – Christian Ready

3 December, 2012

A galaxy in perspective

One of the things that’s very difficult to appreciate is the relative sizes and distances of celestial objects. After all, their sizes and distances aren’t remotely small enough for us to appreciate. As a result, everything we see looks in some way compressed – one object in an image may just as easily be twice as distant, or ten times as near, as another with little way of knowing the difference.

But if we apply a little knowledge to these images, the relative distances seem to jump out at us, like this:

ESO 318-13 as imaged by the Hubble Space Telescope using its Advanced Camera for Surveys. Image credit: NASA/ESA & Hubble

This is a Hubble Space Telescope image of ESO 318-13 taken with Hubble’s Advanced Camera for Surveys. ESO 318-13 is an irregular-shaped galaxy. That is, a galaxy that has no formal structure such as spiral arms or even a well-defined central nuclear region.

It’s a beautiful image, but what I really love about it is that in one shot we can discern a tremendous amount of perspective and depth. Let’s start with the nearby stuff and work our way outward.

The brightest objects are foreground stars in our own Milky Galaxy. Coincidentally the foreground star in the middle right of the image happens to line up with the middle of ESO 318-13, but keep in mind that the galaxy is itself a collection of stars millions of light years beyond.

If you look at the full-resolution version of the image, you’ll see individual stars within ESO 318-13. And if you look toward the right-edge of the galaxy you’ll spot a beautiful face-on spiral tens of millions of light-years in the distance behind the galaxy. For all of their grandeur, galaxies are mostly empty space, and can be transparent enough to allow background galaxies to easily be seen through them.

Pan around the image and you’ll see a lot more galaxies in the background, including a giant elliptical galaxy in the upper right-hand corner of the image. ESO 318-13 is a dwarf galaxy and may contain a few tens of millions of stars. But the elliptical galaxy in the background is a cosmic titan containing several hundred billion suns!

The distances to objects in this image are all relative – there isn’t anything that tells us exactly how far away they are just by looking at them. To get those measurements we need to use indirect methods such as spectroscopy. But in one image we can begin to get an idea of the sheer scale of the cosmos – keeping in mind that this is still a fairly local region of the universe!

16 October, 201216 October, 2012

NGC3344 – a mini-me Galaxy in a spin

I can’t say I ever tire of looking at galaxies – the great islands of the universe home to billions of Suns. but the Hubble Space Telescope’s image of NGC 3344 shows a galaxy that in some ways is a lot like our own. Behold:

The bright stars with the diffraction spikes are nearby stars in our own Milky Way, so let’s get them (figuratively) out of the way and admire the beautiful galaxy beyond. NGC 3344 is 25 million light-years away, making it a cosmic neighbor to our own Milky Way, though it contains about half as many stars.

NGC 3344 is a spiral, like our Milky Way. It even has a subtle central bar, oriented vertically in the image. Our own galaxy has a similar bar at the center, though it is believed to be better defined NGC 3344’s. Because it’s relatively nearby, the galaxy covers a wider region of the sky than Hubble’s camera sees, so we only see about 1/3 of it here.

However, a wider field of view shows that the NGC 3344 has an extended, faint ring of stars surrounding it. It turns out this outer ring of stars is orbiting galactic central point in an opposite direction than the inner spiral arms. It’s not clear why this is the case, but it could be due to the cannibalization of a smaller passing galaxy some time ago.

If you haven’t already, check out the giant 3845×3049 version and admire this galaxy in all of Hubble’s glorious detail!

2 October, 20122 October, 2012

NGC 1672, a galaxy a-bursting with stars

Galaxies are the great islands in the universe where stars live out their lives. But over the course of a galaxy’s evolution, there are times when it is active with more star formation than others, like this gorgeous example of NGC 1672 courtesy of the Hubble Space Telescope:

You really want to click that image to see the large version or, if you’re keen to experience the finer details, get the amazing 5302×3805 version.

You’re welcome 🙂

As I was saying, galaxies evolve over time and go through periods where there is a lot more star formation going on than others. NGC 1672 is one of those active galaxies, with star formation taking place not only in the spiral arms, but also in its nucleus as well:

Stellar Nursery in the arms of NGC 1672 — Dude! Star formation in the nucleus of NGC 1672!

NGC 1672 is a type of galaxy known as a Seyfert galaxy. Galaxies typically have quiet nuclear regions – that is, they are dominated by older stars and have very little activity going on in those parts. Seyfert galaxies are quite different from typical spiral galaxies in that their nuclei are are very bright and are typically active with star formation, which you can easily see in the close-up.

So what’s going on here? The answer may lie in the fact that NGC 1672 is also a barred spiral galaxy. The Hubble image shows the central region of the galaxy but this ground-based image shows NGC 1672 in all of its barred-spiral glory:

NGC1672-DSS — Portion of a wide field ground-based image of NGC 1672’s taken by the Digitized Sky Survey 2 (DSS2). The image was rotated to match the Hubble Space Telescope image. Note the bar!

As you can see, the bar is chocka-block of stars, gas, and dust that orbit the core in a highly inclined orbit. In other words, the gas is largely “aimed” toward the supermassive black hole at the very center. This in turn creates an accretion disk around the black hole which makes for a very bright nucleus.

But it also means that there is a lot of moving material in the outer region of the nucleus as well, and that means star formation around the nucleus!

There’s still a lot about barred spirals that we don’t yet know. Our own home galaxy contains a bar as well and barred spirals are not uncommon. Astronomers believe that bars are temporary but many questions remain. How do bars form? How long do they last? When do they form – do the form early in the galaxy’s evolution or late? And perhaps most interesting, why do they form in the first place?

There are lots of other little amazing details in the image, and I invite you to grab the 5302×3805 version and start digging around. The brightest stars are foreground stars that live right here in the Milky Way, but there are lots galaxies deep in the background, some of which can be seen through NGC 1672, like this one:

NGC1672-backgroung-galaxy — Dude! A galaxy in the background of of NGC 1672!

Notice the color of this galaxy – that’s not because the background galaxy is really that color, but because it’s blue light is scattered by the dust in NGC 1672 itself, letting the yellow, orange, and red light through, giving the background galaxy a caramel color. Pretty cool!

There’s lots of beautiful gems in this image so dig away!

26 September, 201226 September, 2012

The deepest view of the universe: the Hubble eXtreme Deep Field

How deep into the universe have we looked? As of today, this deep:

This is the Hubble eXtreme Deep Field, (XDF), and it’s a masterwork ten years in the making*. What you’re seeing is what you get when you take a very long exposure with two of Hubble’s best cameras of a region of the sky that contains no known stars – an ocean of 5,000 galaxies! And it’s a very deep ocean, indeed. More than 5,500 galaxies are crammed into a field of view just a fraction of the size of the full moon.

The galaxies are arranged at varying distances from us. Some are relatively bright and even have spiral arms as seen in nearby spiral and elliptical galaxies:

But others, way, way, waaaay in the background, don’t appear to have any structure at all. Instead, they just look like little blobs of stars and gas:

Portion of the HUDF — A portion of the HUDF. The tiny points of light are primordial clumps of newly formed stars, gas, and dust that would combine to form modern-day galaxies.

So what’s going on here? It turns out that these fainter galaxies are so far away, their light took billions of years to reach us. In other words, we’re seeing these galaxies as they were several billion years ago when the universe was only a few hundred million years old!

To put that into perspective, it helps to think of the XDF as a kind of “core sample” of the cosmos; the deeper into the field we look, the farther back into the universe’s past we can probe:

heic1214c — The XDF, separated by the distances of objects within it. The most distant objects within the XDF are more than 95% of the way back to the Big Bang.

Our universe is 13.7 billion years old. Thanks to Hubble, we can see what galaxies looked like in the current era, what they looked like in its earlier years, and what they looked like a relatively short time after the Big Bang.

And so, in just one image, we can trace the evolution of galaxies over time – from small embryonic building blocks of fluff to beautiful spirals, to giant ellipticals that are the relic of collisions of multiple galaxies. It’s the story of the universe, writ in a single image.

I’ll never tire of looking at this image, and marveling at just how far we’ve come in our understanding of the universe in so short a time.

But what really gives me goosebumps is what’s left to discover.

* I realize in retrospect I didn’t explain this elsewhere in the post. XDF is actually part of the Hubble Ultra Deep Field, which was made with Hubble’s Advanced Camera for Surveys (ACS) from September 2003 through January 2004. But this new image was made with additional ACS images taken since then, as well as Hubble’s new Wide Field Camera 3 (WFC3) which was installed in 2009. WFC3 is sensitive to near-infrared, allowing even fainter, more distant proto galaxies to be imaged. Hence my comments about this image being ten years in the making, as well as the deepest view ever!

21 September, 201220 September, 2012

An award-winning Whirlpool

M51-the Whirlpool Galaxy — Martin Pugh’s award-winning image of M51. If you *really* want to be blown away, check out the full resolution image. Wow!

M51, aka the Whirlpool Galaxy, is a favorite target for professional and amateur astronomers alike. It’s a relatively nearby pair of galaxies that are interacting with one another. M51 is the large spiral, seen nearly face-on to us, and its arms are bursting with new star formation. This of course is due to the tidal interaction with its companion NGC 5195, which is a dwarf galaxy passing “underneath” one of the Whirlpool’s spiral arms.

Of course, the Whirlpool has been imaged in exquisite detail by the Hubble Space Telescope and others, but this image is a winner in more ways than one. Martin Pugh’s image was voted the overall winner in the Royal Observatory’s 2012 Astronomy Photographer of the Year competition. And yeah, click that link because even the “als0-rans” images are breathtaking. Seriously, you won’t believe that these images were made by amateur astronomers with backyard telescopes!

What amazes me about Martin’s image is the combination of subtle details and wide range of features. The wisps of scattered gas and dust from the smaller companion are rarely imaged, and yet there they are in the same image as the fine, tightly wound spiral arms near the nucleus of the Whirlpool itself. Then there are of course the fine dust lanes etched into the spiral arms, dotted with the sapphire blue that is the telltale sign of hot new stars recently born in the arms. The colors, the hues, the saturation, and the balance of capturing all of that stunning detail make this one of the best images of the Whirlpool I’ve ever seen – and yes, I’m willing to rank it up there with Hubble’s image.

Not bad at all for a guy with a 17-inch telescope! I can’t imagine the hard work, patience, and skill it must have taken to produce this image. Fortunately, Martin has a few more knockouts on his Flickr stream for our viewing and mind-blowing pleasure. Take some time to check them out, as well as browse through the contest’s photo pool which is chock-a-block of amazing astro-image awesomeness!