LOFTER-网易轻博

space, the final frontier.

I first heard these words when I was justsix years old, and I was completely inspired.

I wanted to explore strange new worlds. Iwant to seek out new life. I wanted to see everything that the universe had tooffer.

And those dreams, those words, they took meon a journey, a journey of discovery, through school, through university, to doa PhD and finally to become a professional astronomer.

Now, I learned two amazing things, oneslightly unfortunate, when I was doing my PhD. I learned that the reality was Iwouldn't be piloting as starship anytime soon. But I also learned that theuniverse is strange wonderful and vast, actually too vast to be explored byspaceship. And so I turned my attention to astronomy, to using telescopes. Now,I show you before you an image of the night sky. You might see it anywhere inthe world. And all of these stars are part of our local galaxy, the Milky way.

Now, if you were to go to a darker part ofthe sky, a nice dark site, perhaps in the desert, you might see the center ofour Milky way galaxy spread out before you, hundreds of billions of stars. Andit's a very beautiful image. It's colorful. And again, this is just a localcorner of our universe.

You can see there's a sort of strange darkdust across it. Now, that is local dust. that's obscuring the light of thestars. But we can do a pretty good job. Just with our own eyes, we can exploreour little corner of the universe. It's possible to do better. You can usewonderful telescopes like the Hubble Space Telescope.

Now, astronomers have put together thisimage. it's called the Hubble Deep Field, and they’ve spent hundreds of hoursobserving just a tiny patch of the sky, no larger than your thumbnail held atarm's length. and in this image, you can see thousands of galaxies, and we knowthat there must be hundreds of millions, billions of galaxies in the entireuniverse, some like our own and some very different.

So you think, ok, well, I can continue thisJourney. This is easy, I can just use a very powerful telescope and just lookat the sky, no problem. It's actually really missing out if we just do that.Now, that's because everything I've talked about so far is just using thevisible spectrum, just the thing that our eyes can see, and that's a tinyslice, a tiny tiny slice of what the universe has to offer us. Now, there'salso two very important problems with using visible light.

Not only are we missing out on all theother processes that are emitting other kinds of light, but there's two issues.Now, the first is that dust that I mentioned earlier. The dust stops te visiblelight from getting to us. So as we look deeper into the universe, we see lesslight. The dust stops it getting to us. But there's a really strange problemwith using visible light in order to try and explore the universe. Now take abreak for a minute. Say you're standing on a corner, a busy street corner.There's cars going by. An ambulance approaches. It has a high-pitched siren.The siren appeared to change in pitch as it moved towards and away from you.The ambulance driver did not change the siren just to mess with you. That was aproduct of your perception. The sound waves, as the ambulance approached, werecompressed and they changed higher in pitch.

As the ambulance receded, the sound waveswere stretched, and they sounded lower in pitch. The same thing happens withlight. Objects moving towards us, their light waves are compressed and theyappear bluer. Objects moving away from us, their light waves are stretched, andthey appear redder. So we call these effects blueshift and redshift. Now, ouruniverse is expanding, so everything is moving away from everything else, andthat means everything appears to be red. And oddly enough, as you look moredeeply into the universe, more distant objects are moving away further andfaster, so they appear more red. So if I come bac to the Hubble Deep Field andwe were to continue to peer deeply into the universe just using the Hubble, aswe get to a certain distance away, everything becomes red, and that presentssomething of a problem. Eventually, we get so far away everything is shifted intothe infrared and we can't see anything at all. So there must be a way aroundthis. Otherwise, I'm limited in my journey. I wanted to explore the wholeuniverse, not just whatever i can see, you know, before the redshift kicks in.There is a technique. It's called radio astronomy. Astronomers have been usingthis for decades. It's a fantastic technique. I show you the Parkes RadioTelescope, affectionately known as " The Dish." You may have seen themovie. and radio is really brilliant. It allows us to peer much more deeply. itdoesn't get stopped by dust, so you can see everything in the universe, andredshift is less of a problem because we can build receivers that receiveacross a large band. So what does Parkes see when we turn it to the center ofthe Milky way?  We should see somethingfantastic, right? Well, we do see something interesting. All that dust hasgone. As i mentioned, radio goes straight through dust, so not a problem. Butthe view is very different. We can see that the center of the Milky Way isaglow, and this isn't starlight. This is a light called synchrotron radiation,and it's formed from electrons spiraling around cosmic magnetic fields. So theplane is aglow with this light. And we can also see strange tufts coming off ofit, and objects which don't appear to line up with anything that we can seewith our own eyes. But it's hard to really interpret this image, because as youcan see, it's very low resolution. Radio waves have a wavelength that's long,and that makes their resolution poorer. This image is also black and white, sowe don't really know what is the color of everything in here. Well,fast-forward to today. We can build telescopes which can get over theseproblems. I am showing you here an image of the Murchison Radio Observatory, afantastic place to build radio telescopes. It's flat, it's dry, and mostimportantly, it's radio quiet: no mobile phones, no WI-Fi, nothing, just veryvery radio quiet, so a perfect place to build a radio telescope.

Now, the telescope that i've been workingon for a few years is called the Murchison Widefield Array, and I'm going toshow you a little time lapse of it being built. This is  a group of undergraduate and postgraduatestudents located in Perth. We call them the Student Army, and they volunteeredtheir time to build a radio telescope. There's no course credit for this. Andthey're putting together these radio dipoles. They just receive at lowfrequencies, a bit like your FM radio or your TV. And here we are deployingthem across the desert. The final telescope covers 10 square kilometers of theWestern Australian desert. And the interesting thing is, there's no movingparts. We just deploy these little antennas essentially on chicken mesh. It'sfairly cheap. Cables take the signals from the antennas and bring them tocentral processing units. And it's the size of this telescope, the fact whatwe've built it over the entire desert that gives us a better resolution thanParkes. Now, eventually all those cables bring them to a unit which sends itoff to a supercomputer here in Perth, and that's where I come in. Radio date. Ihave spent the last five years working with very difficult, very interestingdata that no one had really looked at before. I've spent a long timecalibrating it, running millions of CPU hours on supercomputers and reallytrying to understand that data. And with this telescope, with this data, we'veperformed a survey of the entire southern sky, the Galactic and ExtragalacticAll-sky MWA Survey, or GLEAM, as I call it. And I'm very excited. This surveyis just about to be published, but it hasn't been shown yet, so you areliterally the first people to see this southern survey of the entire sky. SoI'm delighted to share with you some images from this survey. Now, imagine you wentto the Murchison, you camped out underneath the stars and you looked towardsthe south. You saw the south's celestial pole, the galaxy rising. If I fade inthe radio light, this is what we observe with our survey. You can see that thegalactic plane is no longer dark with dust. It's alight with synchrotronradiation, and thousands of dots are in the sky. Our large Magellanic Cloud,our nearest galactic neighbor, is orange instead of it's more familiarblue-white. So there's a lot going on in this. Let's take a closer look.If  we look back towards the galacticcenter, where we originally saw the Parkes image that I showed you earlier, lowresolution, black and white, and we fade to the GLEAM view, you can see the resolutionhas gone up by a factor of a hundred. We now have a color view of the sky, atechnicolor view. Now, it's not a false color view. These are real radiocolors. What I’ve done is I've colored the lowest frequencies red and thehighest frequencies blue, and the middle ones green. And that gives us thisrainbow view. And this isn't just false color, The colors in this image tell usabout the physical possesses going on in the universe. So for instance, if youlook along the plane of the galaxy, it's alight with synchrotron, which ismostly reddish orange, but if we look very closely, we see little blue dots.Now, if we zoom in, these blue dots are ionized plasma around very brightstars, and what happens is that they block the red light, so they appear blue.And these can tell us about these star-forming regions in our galaxy. And wejust see them immediately. We look at the galaxy, and the color tels us thatthey're there. You can see little soap bubbles, little circular images aroundthe galactic plane, and these are supernova remnants. When a star explodes, itsouter shell is cast off and it travels outward into space gathering upmaterial, and it produces a little shell. It's a long-standing mystery toastronomers where all the supernova remnants are. We know that there must be alot of high-energy electrons in the plane to produce the synchrotron radiationthat we see, and we think they're produced by supernova remnants, but theredon't seem to be enough. Fortunately, GLEAM is really really good at detectingsupernova remnants, so we're hoping to have a new paper out on that soon. Now,that's fine. We've explored out little local universe, but I wanted to godeeper, I wanted to go further. I wanted to go beyond the Milky Way. Well, asit happens, we can see a very interesting object in the top right, and this isa local radio galaxy, Centaurus A. If we zoom in on this, we can see that thereare two huge plumes going out into space. And if you look right in the centerbetween those two plumes, you'll see a galaxy just like our own. It's a spiral.It has a dust lane. It's a normal galaxy. But these jets are only visible inthe radio. If we looked in the visible, we wouldn't even know they were there,and they are thousands of times larger than the host galaxy. what's going on？ What's producing these jets? At the center of every galaxy that weknow about is a supermassive black hole. Now, black holes are invisible. That'swhy they're called that. All you can see is the deflection of the light aroundthem, and occasionally, when a star or a cloud of gas comes into their orbit,it is ripped apart by tidal forces, forming what we call an accretion disk. Theaccretion disk glows rightly in the x-rays, and huge magnetic fields can launchthe material into space at nearly the speed of light. So these jets are visiblein the radio and this is what we pick up in our survey. Well, very well, sowe've seen one radio galaxy. That's nice. But if you just look at the top ofthat image, you'll see another radio galaxy. It's a little bit smaller, andthat's just because it's further away. OK, Two radio galaxies. We can see this,This is fine. Well, what about all the other dots? Presumably those are juststars. They're not. They are all radio galaxies. Every single one of the dotsin this image is a distant galaxy, millions to billions of light-years away with a supermassive black hole at its center pushing material into space atnearly the speed of light. It is mind-blowing. And this survey is even largerthan what I've shown here. If we zoom out to the full extent of the survey, youcan see I found 300 000 of these radio galaxies. So it's truly an epic journey,We've discovered all of these galaxies right back to the very firstsupermassive back holes. I am very proud of this, and it will be published nextweek. Now, that's not all. I've explored the furthest reaches of the galaxywith this survey, but there's something even more in this image. Now, I'll takeyou right back to the dawn of time. When the universe formed, it was a bigbang, which left the universe as a sea of hydrogen, neutral hydrogen. And whenthe very first stars and galaxies switched on, they ionized that hydrogen. Sothe universe went from neutral to ionized. That imprinted a signal all aroundus. Everywhere, it pervades us, like the Force. Now, because that happened solong ago, the signal was redshifted, so now that signal is at very lowfrequencies. It's at the same frequency as my survey, but it's so faint. It's abillionth the size of any of the objects in my survey. So our telescope may notbe quite sensitive enough to pick up this signal. However, there's a new radiotelescope. So I can't have a starship, but I can hopefully have one of thebiggest radio telescopes in the world. We are building the Square KilometreArray, a new radio telescope, and it's going to be a thousand times bigger thanthe MWA, a thousand times more sensitive, and have an even better resolution.So we should find tens of millions of galaxies. And perhaps, deep in thatsignal, I will get to look upon the very first stars and galaxies switching on,the beginning of time itself.