Looking up into the night sky, it seems like you can see forever. If you use binoculars or a telescope that feeling is, literally, magnified – you can see thousands, millions of stars.
But what you’re seeing is barely scratching the depths of the Universe. You’re looking out a few thousand light years into a galaxy a hundred thousand light years across, in a Universe where we can see distant galaxies over 10 billion light years away.
We build bigger telescopes so we can see those far-flung objects, and we even put them in space so our bothersome atmosphere doesn’t interfere with the view. The most famous is of course the Hubble Space Telescope. It’s hard to describe just how much of an impact this Grande Dame of astronomy has had on our perception of the Universe… though looking into the Hubble Deep Fields, you get a glimmer of it. In 1995, Hubble stared at one spot in space for over 140 hours, creating the first Deep Field. It revealed thousands of galaxies at tremendous distance, showing us that the sky is filled with galaxies.
The region of the sky for the first Deep Field was chosen because it was nearly devoid of stars and known galaxies, objects that would interfere with their more distant brethren. But what does that field look like from the ground? Astronomer Detlef Hartmann decided to tackle this question, and has done us all a favor by showing us. Using a 44 cm (17") telescope he built himself, he took an incredible 247 five-minute images to create this extraordinary picture with a total of 20 hours of exposure… and then lets it morph into the actual Hubble Deep Field to compare them:
[The image is an animated GIF that weighs in at nearly 6 Mb, so it may take a while to load. I urge patience; it's worth it. Click to edwinenate.]
Let me be clear: Detlef’s image is amazing. It’s a tremendous effort by an "amateur"*, and shows dozens of the galaxies (and the same scattered handful of stars) in the Hubble image. It’s an amazing achievement. A bigger telescope would show more galaxies, of course, and resolve them more clearly, but even the biggest telescope located on the surface of our planet needs to peer through the soup of air above it, which dims the faintest galaxies into obscurity. You need to get above our atmosphere to see the cosmos as clearly as possible.
And when you do, look at what Hubble shows us. That tiny region of the sky – easily blocked by a grain of sand held at arm’s length – contains thousands of galaxies, each a sprawling city of billions of stars. It represents a relatively random part of the sky, so you can expect to see something like it no matter where you point a telescope… and that picture shows just one 24-millionth of the entire sky.
The implication is clear: there are hundreds of billions of galaxies in our Universe. That in turn means there are sextillions of stars, each a Sun, and many, if not most, circled by a retinue of planets.
It’s the most ironic aspect of any science I know: it crushes my sense of scale and ego into dust, but also fills me with wonder and amazement that we can know such things, and be a part of it.
As is so often the case in science, you don’t know what you’ll get when you build a new instrument. You build it for one reason or for many, but later on new applications arise, new ways to use it. And sometimes, years down the road, it’s utilized in a just such a new way which profoundly changes how you see the Universe, how you see yourself and your place in it, and in a way you had may have only had an inkling of when you started out. The Hubble Deep Fields are perfect examples of this.
We knew intellectually the Universe was deep, and our place in it infinitesimal yet rare and beautiful. But Hubble showed that to us.
Image credits: R. Williams (STScI), the Hubble Deep Field Team and NASA; Detlef Hartmann. My deep thanks to Salvatore Iovene (who hosts AstroBin where Detlef’s image is displayed) for letting me know about this amazing work.
* Oh, that word. Detlef built his own ‘scope, took hundreds of these images, then combined them in a painstaking and difficult process that probably took him many, many hours. The word "amateur" has many connotations, but as usual here when I use it, I simply mean someone who is not a career astronomer. Detlef clearly has it going on.
- Revealing the Universe: the Hubble Extreme Deep Field
- BAFact Math: The Sun is mind-crushingly brighter than the faintest object ever seen. Seriously.
- Another record breaker: ultra-deep image reveals ultra-distant galaxy
- What does a half million galaxies look like?
- Hubble digs deep to see baby galaxies
Astronomers using the Hubble Space Telescope have created the deepest multi-color* image of the Universe ever taken: the Hubble Extreme Deep Field, a mind-blowing glimpse into the vast stretches of our cosmos.
Check. This. Out.
Yegads. [Click to cosmosenate, or grab the bigger 2400 x 2100 pixel version.]
This image is the combined total of over 2000 separate images, and the total exposure is a whopping two million seconds, or 23 days! It’s based on the original Hubble Ultra Deep Field, with new observations added in since the originals were done. It shows over 5500 galaxies – nearly everything you see in the picture is a galaxy, an island universe of billions of stars. Only a handful of individual stars in the foreground of our own galaxy can be seen.
Here’s some detail from the image:
The variety of galaxies is amazing. Some look like relatively normal spirals and ellipticals, but you can see some that are clearly distorted due to interactions – collisions on a galactic scale! – and others that look like galaxy fragments. These may very well be baby galaxies caught in the act of forming, growing. The most distant objects here are over 13 billion light years away, and we see them when they were only 500 million years old.
In case your head is not asplodey from all this, I’ll note that the faintest objects in this picture are at 31st magnitude: the faintest star you can see with your naked eye is ten billion times brighter.
I’ll note that the purpose of this and the other deep field images is to look as far away and as far back in time as we can to see what the Universe was like when it was young. The wealth of data and scientific knowledge here cannot be overstated.
But I suspect, in the long run, the importance of this and the other pictures will be their impact on the public consciousness. We humans, our planet, our Sun, our galaxy, are so small as to be impossible to describe on this sort of scale, and that’s a good perspective to have.
But never forget: we figured this out. Our curiosity led us to build bigger and better telescopes, to design computers and mathematics to analyze the images from those devices, and to better understand the Universe we live in.
And it all started with simply looking up. Always look up, every chance you get. There’s a whole Universe out there waiting to be explored.
The folks at Hubble will be holding a public interactive discussion of the HXDF image on Google+ at 13:00 Eastern (US) time on September 27th, where you can ask astronomers questions. Tune in and learn more!
Image credit: NASA, ESA, G. Illingworth, D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens (Leiden University), and the HUDF09 Team
* In 1998 a single-color image was taken with the STIS camera on Hubble, and reached similar depth. It would take some serious analysis to know which image sees fainter objects!
- Astronomers have found when and how the cosmic fog was lifted (a brief history of the young Universe)
- Another record breaker: ultra-deep image reveals ultra-distant galaxy
- Record-breaking galaxy found at the edge of the Universe
- Hubble digs deep to see baby galaxies
The galaxy we live in, the Milky Way, is a large spiral galaxy that lives in a small cluster of other galaxies called the Local Group. The other big member is the Andromeda galaxy, located about 2.5 million light years away. That’s a long way off, but we’ve known for a long time that Andromeda is heading more or less toward us at a speed of roughly 100 km/sec (60 miles/second).
The question is, is it headed directly at us, or does it have some "sideways" motion and will miss us? New results announced today by astronomers using Hubble show that — gulp! — Andromeda is headed right down our throats!
But don’t panic. It won’t happen for nearly 4 billion years.
This is a pretty cool result. They used Hubble to look at stars in Andromeda’s halo, the extended fuzzy region outside the main body of the galaxy. By very carefully measuring the positions of the stars over seven years, they could directly measure the motion of those stars. Extrapolating that into the future has allowed the motion of the Andromeda galaxy itself to be determined for the first time.
So what’s going to happen?
First, watch this awesome video of the collision based on the observations:
So here are the details:
You know why astronomy is cool? Because of things like this:
Galaxy clusters are collections of galaxies held together by their own gravity. We see clusters all over the place, and they’re among the largest structures in the Universe. We can find them at large distances, which means we see them as they (and the Universe) were young — it takes light a long time to travel across the cosmos. Astronomers went looking to find extremely distant clusters of galaxies, and found one at a staggering distance: 12.7 billion light years away!
Here’s an image showing the central part of the cluster:
[Click to bigbangenate.]
Each of those circled red dots is a young galaxy, so distant that the light has been on its way here for more than 90% of the current age of the Universe! And they’re almost lost among all those other stars and galaxies in the image (though their intense red color helps… as to why they’re red, read on).
Finding this cluster was a magnificent achievement. The astronomers used the massive 8.2 meter Subaru telescope to look at large swaths of the sky. They looked at the colors of the galaxies they found (PDF); distant objects would be so far away their light is significantly redshifted by the expansion of the Universe itself (I explain how this works here and here).
Galaxies are distributed throughout space, so you expect to see them scattered across the sky as well as in redshift (distance). When looking at one part of the sky, however, they found an unusually high concentration of galaxies that were very red. Using a different camera on Subaru, they took spectra of those galaxies — breaking the light up into very fine divisions of colors, like a rainbow with hundreds of colors in it — to accurately measure the redshifts of those galaxies. Spectroscopy of objects that faint is no easy task, but Subaru is a big ‘scope, and collect a lot of light even from faint objects at the remote reaches of the Universe,
The astronomers confirmed that many of the galaxies in their sample were at the same redshift (z = 6 for those in the know — which is a mighty big redshift). The odds of these galaxies all being at the same distance happening by chance is extremely small: only about one in a billion! So it’s pretty clear these galaxies really are physically associated with each other.
That is, clustered together.
This makes the cluster the most distant ever found that has been confirmed spectroscopically — one other has been found that might be farther away, but it hasn’t been confirmed yet. At 12.7 billion light years away, that means we see this cluster as it was a mere one billion years after the Universe itself formed! That provides key information about conditions in the early Universe, which are critical to understanding how it formed and changed as it aged.
The cluster itself is vast — it’s something like 50 million light years across. The team of astronomers used various methods to determine its mass, and their best guess is that its total mass is several thousand times the mass of our entire Milky Way galaxy! The estimation methods they used are fairly fuzzy, so it’s not clear how accurate this number really is. Still, the cluster is clearly huge, and massive. If we could see it today, it would probably rank among the largest structures in the Universe.
That’s not terribly surprising, if you think about it: only the biggest monster clusters can be seen at such a mind-crushing distance. The smaller ones will be harder to detect, so we’re likely to find the biggest.
Still, holy cow. I have read and written about extremely distant objects many, many times over the years, and have no doubt: I get chills every single time I think about this stuff. It wasn’t that long ago when the entire human race couldn’t be bothered to look beyond the tip of its collective nose. Now we can look into the fires of the Universe’s birth, into that forge itself, and tease out the secrets of how we came to be.
That’s why astronomy is cool.
- An ultradeep image that’s *full* of galaxies!
- Most distant object ever seen… maybe
- Another record breaker: ultra-deep image reveals ultra-distant galaxy
- Record-breaking galaxy found at the edge of the Universe
What happens when you take a monster 4.1 meter telescope in the southern hemisphere and point it at the same patch of sky for 55 hours?
This. Oh my, this:
[Click to embiggen.]
OK, I know. At first glance it doesn’t look like much, does it? Just a field of stars. However, here’s the important bit: I had to take the somewhat larger original image and reduce it in size to fit my 610-pixel-wide blog. So how much bigger is the original?
It’s 17,000 x 11,000 pixels! If you happen to be sitting on a T1 line, then you can grab this massive 250 Mb file. And I surely suggest you do.
Because yeah, the brightest objects you see in this are stars. Probably a few hundred of them. But you have to look at the bigger image ! Why? Because what’s amazing, truly jaw-dropping and incredible is this:
There are over 200,000 galaxies filling this image!
Here’s a zoom of the image, centered on what looked to me to be one of the biggest galaxies in the frame, a nice edge-on spiral.
With the exception of a handful of blue-looking stars, everything in this zoom is a galaxy, probably billions of light years away. Those tiny red dots are galaxies so far away they crush our minds to dust: we’re seeing them with light that left them shortly after the Universe itself formed.
This light is ancient. And it came a long, long way.
By the way, that picture of the spiral there is not even at full resolution! Just to give you an idea, I cropped out just that galaxy in the full-res image and inset it here. If you want to find it in the full frame, it’s about one-third of the way in from the left, and one-third of the way down from the top. Happy hunting.
[Edited to add: I forgot to add that this galaxy is warped! See how the disk flares up on the left and down on the right, just a bit? This is very common in disk galaxies, and our own Milky Way does it too (see #9 at that link). It's usually caused when a nearby galaxy's gravity torques on the stars in the disk.]
These images were taken with VISTA, the European Southern Observatory’s Visible and Infrared Survey Telescope for Astronomy (VISTA), a 4.1 meter telescope in Chile. This huge image is actually composed of 6000 separate images, and is the single deepest infrared picture of the sky ever taken with this field of view. Hubble can get deeper, for example, but sees a much, much smaller part of the sky.
We live in the Milky Way galaxy, a collection of more than a hundred billion stars forming a flat, spiral disk. Our galaxy is in turn part of a small group called the Local Group, just a few dozen members strong, of which we are among the largest. But galaxies live in larger groups yet, called clusters. Some have hundreds of galaxies, and some thousands. In the direction of the constellation of Hercules is one such smaller cluster, called (duh) the Hercules Cluster, just under 500 million light years from Earth. The VLT Survey Telescope took a look at the cluster and produced this spectacular picture of it:
[Click to galactinate, and you want to; I reduced the size considerably to fit it here.]
The cluster is unusually rich in spiral galaxies, and unlike bigger groups doesn’t have one, massive galaxy sitting at its core (the result of a bigger galaxy falling to the center and eating lots of other galaxies, growing huge in the process). Still, the small size of the cluster means a lot of its members are interacting, and if you look closely you see lots of them tugging at the others:
That edge-on spiral in the lower right is clearly warped, so I expect it’s suffered a near miss from another galaxy in the past few million years (maybe that little spiral above it, or more likely the severely messed-up fuzzball to the left), and other examples aren’t hard to find.
As an aside, when I was poking around the big image I saw lots of red dots aligned next to green ones on the left near the bottom, and realized that must be an asteroid, captured as it moved slowly across the field of view in the multiple exposures and different filters used to make this picture. A long green streak below that may be another asteroid moving much rapidly, or possibly a satellite that streaked across one exposure.
Take a look for yourself. What do you see?
And a thought for you: This small cluster is part of a larger complex called the Hercules supercluster, made up of many smaller groups like the Hercules cluster. Altogether, the supercluster is something like 300 million light years across… and is still not the largest structure. Hercules, together with the Coma Cluster and Leo Cluster, comprise what’s called the Great Wall: a vast structure that is among the largest in the Universe — it’s so big that even at its distance of several hundred million light years away it spreads across more than one-third of the visible sky!
Thinking about these types of things can numb the mind… but remember, the most amazing thing to me about all of this is that we can know them at all. We’re a part of all this, and when we look out at it, when we examine it, we are learning about ourselves. I think peering out into the cosmos so that we can better understand ourselves is one of the noblest things we humans can do, and using science as our tool the best way to do it.
And look what’s it’s given us! The entire Universe! We cannot possibly ask for anything more.
Credit: ESO/INAF-VST/OmegaCAM. Acknowledgement: OmegaCen/Astro-WISE/Kapteyn Institute
Dark matter, to re-interpret Obi Wan Kenobi, surrounds us and penetrates us. It binds the galaxy together.
At least that’s what a new scientific study seems to show. Dark matter appears to stretch well beyond the visible limits of galaxies, flowing through and filling even the vast, previously-thought empty space between galaxies. The researchers, led by Shogo Masaki of Nogoya University, used computer simulations to model how dark matter behaves over time as it helps form galaxies, and found that while it’s concentrated in and around galaxies, it doesn’t fade away into nothing with distance. It does get thinner, but still exists to a measurable degree well outside of galaxies. The model structure they found is actually quite lovely:
Remember, this is a model, and not an actual map. It does show concentrations of dark matter along galaxies and clusters of galaxies, but also shows how even "empty" space well outside of galaxies has pervasive dark matter in it.
OK, so what’s the deal then?
Dark matter was discovered a long time ago, when it was found that galaxies that live in clusters were moving way too fast to be held by the cluster gravity. They should just simply shoot away, and clusters would essentially evaporate. This implied that clusters of galaxies were either very young and hadn’t had time to dissolve — which we knew wasn’t true; they’re clearly old — or there must be a lot more gravity holding them together. We can add up all the light from the stars in the galaxies and estimate their total mass, but what you get is only about 5-10% of the mass needed to hold clusters together. So most of the matter making up the clusters must be dark. Otherwise we’d see it.
A lot of things are dark. Cold gas. Dust. Rogue planets. Burned out stars. Black holes. It’s hard to see how there could be more mass in any of these things then all the stars put together, let alone ten times as much! Still, over time, better observations started eliminating all the possibilities. Basically, everything made of normal matter was eliminated as a candidate. The Sherlockian conclusion is that something extraordinary makes up dark matter. The most likely possibility now is an exotic form of matter like axions, subatomic particles that have mass and gravity, but don’t emit light and don’t interact with normal matter. An axion could pass right through you, and like a ghost it would leave no trace.
But that doesn’t mean we can’t detect it. Read More
Take a look at the image displayed here [click to redshiftenate]. Every object you see there is a galaxy, a collection of billions of stars. See that one smack dab in the middle, the little red dot? The light we see from that galaxy traveled for 12.9 billion years before reaching the ESO’s Very Large Telescope in Chile. And when astronomers analyzed the light from it, and from a handful of other, similarly distant galaxies, they were able to pin down the timing of a pivotal event in the early Universe: when the cosmic fog cleared, and the Universe became transparent.
This event is called reionization, when radiation pouring out of very young galaxies flooded the Universe and stripped electrons off of their parent hydrogen atoms. An atom like this is said to be ionized. Before this time, the hydrogen gas was neutral: every proton had an electron around it. After this: zap. Ionized. This moment for the Universe was important because it changed how light flowed through space, which affects how we see it. The critical finding here is that reionization happened about 13 billion years ago, and took less time than previously thought, about 200 million years. Not only that, the culprit behind reionization may have been found: massive stars.
OK, those are the bullet points. Now let me explain in a little more detail.
Young, hot, dense, and chaotic
Imagine the Universe as it was 13.7 billion years ago. A thick, dense soup of matter permeates space, formed in the first three minutes after the Big Bang. The Universe was expanding, too, and cooling: as it got bigger, it got less dense, so the temperature dropped. During this time, electrons and protons were whizzing around on their own. Any time an electron would try to bond with a proton to form a neutral hydrogen atom, a high-energy photon (a particle of light) would come along and knock it loose again.
During this period, the Universe was opaque. Electrons are really good at absorbing photons, so light wouldn’t get far before being sucked up by an electron. But over time, things changed. All those photons lost energy as things cooled. Eventually, they didn’t have enough energy to prevent electrons combining with protons, so once an electron got together with a proton they stuck together. Neutral hydrogen became stable. This happened all over the Universe pretty much at the same time, and is called recombination. It occurred about 376,000 years after the Big Bang.
450 million light years away are two interacting galaxies. Both spirals, they are caught in each other’s gravitational claws. Already distorted and bound, eventually, to merge into one larger galaxy in a few million years, the view we have of them from Earth is both amazing and lovely… and hey: they’re punctuating their own predicament!
[Click to exclamatenate.]
Looking a lot like an exclamation point, the two galaxies together are called Arp 302 (or VV 340). This image is a combination of pictures from the Chandra X-Ray Observatory (purple) and Hubble (red, green, and blue). The bottom galaxy is a face-on spiral, while the upper one is seen more edge-on, giving the pair their typographical appearance.
The largest structures in the Universe are superclusters: not just clusters of galaxies, but clusters of clusters. They can stretch for millions of light years and be composed of thousands of galaxies.
Abell 2744, at a distance from Earth of about 3.5 billion light years, is one such megastructure (if you want to sound fancy, astronomers call it "large-scale structure"). Astronomers have been studying Abell 2744 with an arsenal of telescopes, and have discovered that it’s actually the result of the ongoing collision of four galaxies clusters. If you’ve ever wondered what 400 trillion solar masses of material slamming into each other looks like, well, it’s more than a bit of a mess:
[Click to enclusternate.]
Yeah, like I said, it’s a mess.
First off, this picture is a combination of observations from Hubble (in visible light, colored blue, green, and red), the Very Large Telescope (also blue, green, and red), and the Chandra X-Ray Observatory (X-rays, colored pinkish). In visible light you can see literally hundreds of galaxies, probably more, dotting the supercluster. The pink glow is from very hot gas between galaxies; it started its life as gas inside of galaxies that got stripped off and heated to millions of degrees as the galaxies plow through the space around them (I like to think of it as opening a car window to let a noxious smell out — the wind from the car’s motion pushes the air inside the car out the windows).
The blue glow is perhaps the most interesting bit here: it’s a map of the location of dark matter. This type of exotic matter neither emits nor reflects light — hence the name — but it has mass, and that means it has gravity. As I described when this method was used to trace dark matter in the Bullet Cluster, gravity bends space, and light follows that curve. Galaxies farther away get their light distorted by the gravity from dark matter, and that distortion can be measured and used to trace the location of dark matter. The blue glow in the image above maps that.
The thing about dark matter is that it doesn’t interact with normal matter (electron, protons, you, me, lip balm, oranges, whatever). But all that gas between galaxies shown in pink is normal matter, so when one galaxy cluster slams into another at a few thousand kilometers per second that gas gets compressed, mixed-up, and heated. But dark matter just blows right on through. So by comparing the location of the galaxies, the dark matter, and the hot gas, a lot of the cluster’s history can be unraveled.