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

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

The Hubble eXtreme Deep Field – Credit: NASAESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team

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:

Nearby galaxies in the XDF resemble modern-day spiral and elliptical-shaped 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:

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:

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!

A sky full of awesome

I love looking up at the night sky. Whenever I’m outside at night, the first thing I do is look up. How can I not? But there’s always something marring my view – light pollution, clouds, the moon, treetops, and, oh yeah, the Earth itself! I’ve often thought how great it would be if the Earth, Moon, and Sun were to vanish and to be able to see the entire night sky at the same time*. How cool would that be? This cool:

Nick Risinger’s 37,440-image portrait of the entire night sky. The entire sky.

That’s the whole night sky. The entire. Night. Sky! This work of awesome comes to us courtesy of astrophotographer Nick Risinger’s Photomic Sky Survey. And wow, what a sky it is!

The first thing that jumps out is the Milky Way. Here, we see it just as it really is – a great spiral galaxy seen edge-on, or in this case, within the disk of the galaxy itself. In fact, it’s really no different than other spiral galaxies seen edge-on as well. At center is a well-defined bulge partially obstructed by dust silhouetted by the bright stars beyond. Toward the edges are the telltale populations of younger stars. In other words, your typical spiral galaxy!

To the lower right are the Large and Small Magellanic Clouds – two irregular-shaped satellite galaxies that orbit the Milky Way.

And there is so much more detail in this image. To experience it, you really want to check out the zoomable version. Seriously, click the link. Click it now!

If that wasn’t cool enough, check out the 360-degree version; you’ll feel like you’re floating in space! Make sure you are in full-screen mode. And maybe dim the lights – it’s that awesome.

How he do that?

To pull this off, Nick travelled more than 60,000 miles around the globe for the better part of a year taking no less than 37,440 exposures of the sky at night. But it wasn’t just a matter of simply picking a destination, going there and wait for the Sun to go down and shoot. Nick had to plan his destinations well in advance to find clear, dark skies and to be there when there during New Moon.

After a year, Nick then worked to stich together all 37.440 exposures to make this beautiful all-sky masterpiece. Nick has a really cool writeup of the project. His story is as fascinating as the image itself.

An app for that

If you’d like to appreciate Nick’s gorgeous work on the go, he has an app for iPhone and iPad available. If you prefer to just hang it on your wall, there are some rather nice prints available as well (my birthday is coming up…).

I really have to hand it to Nick Risinger for a tremendous effort and a spectacular result!

* Allowing, of course, for the ability to actually survive under those conditions

The Milky Way’s hot halo

It’s easy to think about our Milky Way galaxy all by itself out in space, surrounded by a halo of globular star clusters, some small satellite galaxies, and that nothing else except for its neighbors millions of light-years away.

But the reality is likely quite different. Our home galaxy may be surrounded by an extended halo more than three times he diameter of our Milky Way, like this:

Artist’s impression of the extended halo surrounding our galaxy. Click to enhalonate!

That’s our home galaxy at the center, and those two puffs to the lower left are the Large and Small Magellanic Clouds, which are two irregular-shaped satellite galaxies that orbit the Milky Way. But surrounding all three is a halo of hot gas that extends for hundreds of thousands of light years, and as hot as 1-2 million kelvin!

How they do that?

A team of astronomers used NASA’s Chandra X-Ray Observatory to observe eight bright X-Ray sources hundreds of millions of light-years away; much farther away than the extent of our own Local Group of galaxies. It turns out that the some of the X-Rays from these distant sources were absorbed by by ionized oxygen gas surrounding our galaxy.

The fact that the oxygen is ionized means that the gas itself must be very hot – between 1 million and 2.5 million kelvin. And the fact that this absorption is the same no matter which distant X-Ray source we look at means there is quite a lot of this gas surrounding the Milky Way. How much? Perhaps as much as 10 billion to 60 billion suns worth. That’s a lot of hot gas!

The hot halo (not to be confused with the warm halo)

Astronomers already understand there is a halo of cooler (anywhere from 100,000 to 1 million kelvin) gas surrounding the Milky Way. But these observations seem to imply there is a lot more hot gas making up a much larger halo, indeed.

Missing baryons?

Now to be clear, these results are not yet unconfirmed. It could be that no such halo exists, and the observations can be explained by some other phenomenon. That’s ok, that’s how science works. But if it turns out that the halo is real, it could help explain the Milky Way’s “missing baryon” problem.

Baryons are ordinary matter – things like protons, neutrons, elections – in other words, ordinary everyday matter. When we look at very distant galaxies, we’re looking back in time to see how they looked when the universe was one-sixth its current age. But when we look around in our own Milky Way and nearby galaxies, it turns out there is only about half as much of this baryonic matter visible.

This halo, if its real, would contain about enough mass to account for the “missing baryons.” They wouldn’t be missing at all, they’d just be in a very extended and diffuse cloud surrounding the galaxy!

And that’s a good thing, because the universe is mostly filled with weird and mysterious stuff like Dark Matter and Dark Energy as it is. Its nice to be able to account for some of it once in a while.

An award-winning Whirlpool

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!

A slightly warped edge-on spiral galaxy

NGC 4634 as seen by the Hubble Space Telescope – click for 1280×1093 version, or for full-on warpage, get the 23796×2388 version

Hot on the heels of another beautiful Hubble image of an edge-on spiral galaxy is a Hubble image of NGC 4634. What makes this image so interesting is the slight warp in the disk. If you look closely, you’ll see that the  disk is tilted upright on the right hand side of the image and slightly downward on the left hand side. This is because NG 4634 is not alone in the cosmos, but has a nearby companion tugging on it, just outside of Hubble’s field of view. The companion – NGC 4633 is clearly visible in this wide-field image from the Digital Sky Survey:

Digital Sky Survey image of NGC 4634 & NGC 4633, rotated to match the Hubble image. Get the full field of view or the full resolution version

Even though they’re not interacting yet the Hubble image clearly shows that NGC 4634 is already feeling the gravitational effects of it’s neighbor, NGC 4633. As the two galaxies tug on each other, their shapes begin to distort, as clearly seen by the warp in NGC 4634’s disk. But something else is going on as well – as gas clouds are tugged about the disk of NGC 4634, they collide with slower-moving material. When clouds collide, gravity takes over and stars eventually form within them.

But don’t take my word for it, just look at the Hubble image and you’ll see pink cloud formations that are billowing from the radiation of hot, newly formed stars within. And then there’s all of these jewel-like clusters of very hot, massive stars that have formed all along the length of the galaxy’s disk!

Over the next billion years (or so), these two galaxies will merge, first by passing through one another, and eventually coalesce to form one large elliptical-shaped galaxy. All of the while, new stars will be bursting into life as more and more of the clouds come together and gravity starts working its magic. Should be a very cool show indeed!