Chris Lintott’s Universe

Imagine being in our solar system, standing just where the Earth is now, roughly four and a half billion years ago. Around you would be the detritus of star formation, left over material forming a protoplanetary disk from which the planets are coalescing. Understanding just how this disk of dust and gas became the eight planets of the Solar System is one of the fundamental questions of astronomy, and in the penultimate plenary talk today David Wilner from the Harvard-Smithsonian Centre for Astronomy took us through the latest results from this fast moving field.

There are just two major problems with looking for these disks. The first is that most of the disk is cold, dark and not shining, and the second is that they are very small and thus difficult to image. For a nearby example, you’d be lucky if your disk appeared to have a size of a 1/4000th of a degree.

Battling manfully against these challenges, astronomers have had extraordinary success to understand these systems. To get around the first, we can look for comparatively rare chemicals such as hydrogen cyanide (HCN) or Carbon Monoxide (CO) and use these to trace the structure of the disk.

Through these and other methods, we can now measure the mass of a typical disk, and find that 1/100th of the mass of the Sun is typical; that’s a good number because you have enough stuff to form a Jupiter and a few other planets besides, but it does illustrate how small a proportion of the whole we’re talking about. We can also work out a lifetime for the disk. About half of the material disappears in the first 3 million years, and most of the rest in another 2 million; the blink of an eye in astronomical terms.

The next stage is to try and see these things; to do that, we string together light from many separate telescopes, producing images which are as good as telescopes many times larger than we could possibly produce. Unfortunately, perhaps, the disks tend to look just like blobs, but at least we are seeing the places where planets are forming for the first time.

So how do these disks form stars? Well, we have to first get dust grains to stick together. As the clumps get larger, then their gravity can attract further material to keep them growing all the time. If there’s enough material, then gas will be attracted too and you can form a nice new Jupiter. Remarkably, we can actually see evidence for each of these processes in the details of our observations of protoplanetary disks.

One nightmare researchers like the speaker have is their inability to prove that the disks they’re seeing are the same as those which go on to produce planets. The best evidence that they’re getting it right is the presence of large gaps in some of the studied disks; just as small moons of Saturn can create gaps in the rings, so small, newly formed planets still embedded in a protoplanetary disk might produce the gaps we see.

In some cases it’s even possible to make this connection directly. TW Hyd is a star which is known to have a disk, with an observed hole. Earlier this year, a large planet (about 10 times Jupiter’s mass) was detected orbiting the star, and while this planet isn’t the one creating the observed hole at least there’s a system with both a disrupted disk and a planet.

Our early Solar System, then, will have gaps in the disk where Earth and the rest are forming. For now, we can only see such things in detail in our mind’s eye, or in the distorted world of computer simulations. That might chance soon though, with the advent of the ALMA array high up in the Chilean Atacama desert. ALMA’s high resolution images might reveal not only the gaps in the disks, but also material streaming into those gaps to form smaller dust disks around the nascent planets. In viewing these secondary disks, we will be seeing not the birth of planets, but the birth of systems of moons like those around Jupiter. Now that’s a view worth waiting four and half billion years to get.

The Great Observatories Origins Deep Survey (GOODS) : An Observational Legacy for Studying Galaxy Evolution
Prof Marc Dickinson

The following was written during the final plenary talk of the first day at the American Astronomical Society Meeting in St Louis. I was going to post as we went along, but the wireless connection in the meeting room was very flaky (probably just as well – it means the audience are paying attention to the speaker!) I’m posting it in a lump near the end of the talk. Images to follow.

In the introduction to this talk, we were told that the hallmark of modern astronomical research is the survey, and it’s certainly true that astronomers have learnt to make use of projects which carefully chart sections of the sky. The speaker began by reminding us that it’s more than a decade since the Hubble Deep Field – as he said, every time you get a new telescope the temptation is to push it to its limits. After 150 orbits staring at the same field, it turned out Hubble was excellent at seeing the distant Universe.

The data were released, and then most other major observatories all observed the same field, producing hundreds of papers to understand this region of the sky. Not bad for a patch just 2.5 arcminutes square (an arcminute is a sixtieth of a degree). But the question is, with such a small area how can we be sure that we have a fair census? What if that patch turned out to be unusual in some way? Even if we’ve got lucky and picked the right region, then rare objects will be missed entirely.

GOODS is the solution to this problem; using Chandra in the x-ray, Spitzer in the infrared and Hubble’s ACS camera (not available at the time of the original HDF), they set out to cover two regions, each thirty times larger than the original Hubble Deep Field. The aim was to disentangle the evolution of normal galaxies in the first third of the Universe’s evolution, taking a census of black hole growth and activity, understanding how and when star formation takes place and so on.

Each telescope had a different role to play; Spitzer, for example, in the mid Infrared allowed the team to weight the galaxies. The total stellar mass in a galaxy turns out to be very sensitive to the brightness in this band (although you have to worry about the evolution of the stars, we’ve got pretty good at doing that). As before, other observatories have chipped in, with GALEX providing the Ultraviolet, for example, and the SCUBA camera on the JCMT providing a view of the cold early Universe in the sub-mm region of the spectrum.

Astronomers are greedy, though, and as well as imaging we demand data. The first step in understanding an object is to work out how far away it is, and for objects as far as those in GOODS that means measuring their redshift. Lines in their spectrum will be shifted due to the expansion of the Universe; in all more than 5000 GOODS objects have had their distance measured. That’s not a huge number compared to something like the Sloan Digital Sky Survey, but the objects are much further away (so more telescope time is required per object to get a decent spectrum).

The results were far too numerous to go into here, but there are some nice highlights. For example, we can show that galaxies were, on average, smaller in the past, just as you’d expect if the systems we see around us today were assembled by mergers of smaller galaxies. Arguments are raging about the star formation history of the Universe; we know our Universe is past its peak, forming ten times as many stars about 6 billion years ago as it does today, but the GOODS data suggest that looking further back the rate drops once more.

One of the reasons this is controversial is that most of the energy emitted by the newly formed stars is absorbed and then reradiated by dust. This process makes the galaxies bright in the infrared, and so Spitzer can help here. Prof Dickinson went so far as to call the early Universe (before z=0.7 if you understand and care about redshifts) ‘the age of obscurity’.

As well as changing sizes and star formation rates, the population of galaxies has changed too. In the first third of the Universe’s evolution, the average massive galaxy was what is called a ULIRG – an Ultra-Luminous InfraRed Galaxy. Spin forward to today and you’ll find that in the present day the typical massive galaxy is an elliptical – old, red and dead, devoid of star formation and about as far from a ULIRG as it’s possible to be while still being a massive galaxy.

Disentangling everything that might contribute to the light we receive from a galaxy is hard work, to say the least. The team looked at a set of galaxies which had an excess of light in the mid-infrared – the massive galaxies described in the previous paragraph. It’s tempting to assume that the infrared is due entirely to star formation, but by looking with Chandra they detected x-rays from hidden Active Galactic Nuclei. In other words, these galaxies are not just forming stars, but half of all galaxies had black holes at their centre which were in the act of consuming large amounts of material. As Prof Dickinson said, it seems that around 4 billion years after the Big Bang was an important time in a galaxy’s life.

Perhaps one of the most surprising results is the presence of another population of galaxies at this time. There seem to be a set of galaxies which aren’t doing very much at all – they’ve already formed their stars and are already quietly and passively enjoying the galactic equivalent of late middle age. One mystery is that there are smaller for their weights than we’d expect – and it’s hard to imagine how they might ‘puff up’ to see the galaxies that we see today.

Looking further back, the team managed to detected light emitted from galaxies when the Universe was not much more than a billion years old. Even at this time, there’s evidence for a fairly mature stellar population, so substantial numbers of stars must have been formed before the epoch of the earliest galaxies astronomers have seen to date. They have some candidates from this early epoch, but it’ll have to wait for the next generation space telescopes to confirm these detections, so don’t hold your breath.

As if all of that wasn’t enough, the team realised that by going back to the same parts of the sky every 40 or so days, they stood a great chance of discovering distant supernovae. Of those they discovered, almost 50 are a particular type of exploding star – supernovae type 1a. These explosions seem to contain a clue to their true luminosity, and so by comparing how bright they appear with how bright they actually are we can try and measure the acceleration of the Universe.

At this stage I’m being to feel a bit breathless after all the work the GOODS team have done. Prof Dickinson is finishing his talk by asking ‘are we done yet’? The answer, perhaps not surprisingly, is an emphatic no. One of the major problems is tht the measured star formation rate should tie up with the measurements of the total number and mass of stars –and they don’t. They also know there must be more black holes hiding, because they see energetic x-rays with no obvious source. Black holes hiding behind dust are the obvious candidates.

What we really need is a new telescope, working in the far infrared. ESA’s Herschel space telescope – larger than any other telescope ever to fly into space - is due for launch early next year is designed to solve this problem, and will take a long early look at the GOODS fields. I’m planning to head straight from AAS to go and visit Herschel which is undergoing final tests, so it’s great to hear that people are already anticipating the data it will provide.

As you probably realised, my trip to Hawaii was more or less a complete washout. Of the four nights we had on the telescope, we made it to the summit for one and a half of them. The last night was the most depressing, when we sat there for hours waiting for fog to clear only for it to start snowing heavily. Once that happens, you need a team with shovels to be able to open up and it’s time to head down. We did manage to get about an hour’s data on the third night, for a program which didn’t need as good conditions as mine did, providing data on targets which will be viewed by the new Herschel telescope.

Herschel doesn’t need to worry about snowstorms, as it’s ESA’s new space telescope. With a 3.5m mirror, it will be the largest telescope ever to fly. Designed to work in the far-IR – a region of the spectrum that hasn’t been covered by recent missions – it should produce spectacular views of the coolest bits of the Universe, from nearby star formation to the most distant galaxies. In order to make sense of the results expected when it launches later this year, scientists are currently carrying out large surveys with existing ground based telescopes. These will be used to calibrate and to help interpret Herschel’s results – which will no doubt send scientists scurrying back to Mauna Kea. If it isn’t snowing, that is.

No telescopes open and more snow on the way. We could do some laundry for excitement, but are saving that for tomorrow in case we need more excitement then. Chris needs cheering up - please help!

And in a rash moment, he gave posting access to his fellow observers, heheh… so
Chris Quote of the day: (we were walking past the visitor centre where someone was grappling with a shiny metal thermos) “Look, that man has a telescope!” Um… yeah, that’s why they pay you the big bucks, Chris…
Survival Tactic of the day: not eating the Prawns of Death, which re-appeared again on the salad buffet. They’re kinda brown now.

The above image is from the latest release from the context camera on Mars Reconnaissance Orbiter which, Emily reports, has now covered 20% of Mars at a resolution of 6m per pixel. Ironic that this should come out just after I’d written about faces on Mars for the BBC, but it does fit with my being told to be more cheerful about the observing run. So, reasons to be cheerful :

1. I’ve made it up the mountain; not to the summit just yet, but close enough to get there if a miracle happens and we get a clear night tonight (it’s currently 6.15am on Wednesday, local time).

2. I have no excuse for getting a large percentage of the things on my ‘to-do’ list done. Have internet connection, will travel.

3. The new instruments on both JCMT and UKIRT are performing brilliantly. HARP - essentially a 3d camera for the sub-mm - is a joy to use, and I’ve already written this year about the survey that UKIRT’s new camera has produced.

4. Cloudy observing runs mean an excuse to come back.

5. The residence up here, Hale Pohaku, has ice cream available 24 hours a day. With proper cones and everything.

At about five am this morning, two thirds of the way through my second shift on the telescope, I went outside to watch the dawn. The peak immediately behind the JCMT is called Pu’u Poliahu and I decided that would be the perfect spot to watch the Sun come up. Poliahu is the Hawai’ian snow goddess, who was constantly at war with her sister, the volcano god Pele. Pele’s home is the still active Mauna Loa, whereas Poliahu lived on the summit of Mauna Kea which is frequently snow covered. Pu’u Poliahu is therefore a sacred site, but as the place where the first astronomical site testing on the mountain was done, I suppose it might be considered sacred to astronomers too!

The sky was already bright when I stepped out of the door, with a crescent moon hanging about the summit ridge which is home to Gemini, UKIRT and several other telescopes. I walked through one of the JCMT’s neighbours down here in ’sub-mm valley’, the SMA which consists of eight small dishes, and began climbing the mountain. I could see Jupiter extremely low on the horizon, and off to the right I could see the neighbouring island of Maui sticking above the clouds.

As I climbed higher, I began to feel the effects of the altitude. Climbing even a small hill at more than 14,000 feet above sea level is not easy, and I found myself becoming short of breath. I was also being blown about a bit by an extremely strong wind cutting across the summit, gusts of which blew me from one side of the track to the other. I had my back to the West, and between concentrating on breathing and resisting the wind I didn’t turn round to look at the dawn until I reached the top.

My pictures - taken while crouching down trying to shelter the camera from the wind - don’t do the sight justice. With the crescent moon above the greatest collection of professional telescopes anywhere in the world, the colour of the dawn was a deep red, purple low on the horizon rising to a golden yellow higher up. There were still stars visible in the sky as well as the Moon, and most of the telescopes were still open, most of them pointing toward me, away from the rising Sun.

I know it may be hard to believe, but sitting up there I was thinking of all the times when doing research feels like a hard slog, a prison sentence in front of a computer which won’t cooperate. Combined with the excellent data we got last night, it’s trips like this that remind me why I’m doing any of this in the first place. All I could think about (apart from the need to avoid being literally blown away) was how incredibly, incredibly lucky I am. I think I stayed up there for about twenty minutes, not able to tear my eyes away from the colours laid out in front of me (and realising that clouds are useful for something!).

And walking back down, frozen but ecstatic, I thought about how unique this wonderful island is. On the way up to the telescope, we’d looked over and seen the glow of the vents from one of the world’s most active volcanoes. Where else in the world could you find such an amazing variety within an area not much bigger than greater London? I also think I found the perfect spot to capture almost all of Mauna Kea’s telescopes on pixels.

From left to right: Subaru, Keck, IRTF (NASA), Canada-France-Hawaii Telescope, Gemini North, Uni. Hawaii, UKIRT, small Uni. Hawaii dome and in valley JCMT and CSO.

I love my job.

It’s 7.20am. I started my shift when we left the astronomer’s residence at 8pm. It’ll be at least another three, probably more like four hours until I’m back in bed. And then we’ll do it all again tomorrow.

And yet getting fantastic data with Harp, the new instrument on the JCMT, can make react like this (spontaneous movement captured by the webcam). It’s not even my data as the weather’s still preventing us from doing what we came here for.

I went out and watched the dawn earlier, but I’ll save that story for when I’ve got the pictures off the digital camera.

Morning. Or evening. I’m not sure, you see. Living in three different time zones does that to you. There’s UK time, which my body is still just clinging to. Local Hawaiian time, too, and nocturnal time which means that it’s 7pm at night and time to get up.

We drove halfway up to mountain to the astronomer’s residence yesterday, spending a night here to get acclimatized before heading on up to the summit. Needless to say, last night was absolutely stunningly clear, one of the darkest skies I’ve ever seen. I was reminded of something someone in Chile said to be - ‘really good skies are grey’ with all the starlight, and last night definitely was. Seeing the Milky Way overhead stretching down into Scorpius was just stunning, especially with Jupiter high in the sky instead of hugging the horizon as it does at home.

So my hopes were high for tonight’s observing. However, I woke up this evening to find that we were sitting in the middle of a cloud. This isn’t necessarily bad news - the summit’s clear conditions rely on the inversion layer, a band of cloud which sits almost permanently around the island. So cloud here might mean that the summit is perfectly clear - but we should head on up and see. Keep an eye on us here (scroll down for the webcams).

Update 20.27 HST : Doors opening. Sky’s beautiful up here to the naked eye - Jupiter and Venus in the same sky, Crux just visible above the horizon.

Update 22:02 HST : Currently observing the molecule CS in the Antennae galaxies. The idea is that such molecules will help us understand the massive rates of star formation associated with such galactic collisions. Unfortunately we’ve got a computer problem so we’re stuck on this source for a while, and it’s setting…

Update 22:69 HST : Computer’s fixed, and we’re off to our next target, which is Sakurai’s object. Which targets we observe are determined by where they are in the sky, and also by the quality of the sky. As we’re observing in the sub-mm, nothing matters is the amount of water vapour in the air above us (which is also the reason to be so high up). That means that it’s possible to walk outside and see a perfect sky, and come back in and see terrible conditions - which is what we have tonight. So we do other people’s observations, and they’ll do ours, and in the meantime we’re working on data taken for our project on previous nights.

Update 1:23am HST : We’re still looking at Sakurai’s object, looking for hydrogen cyanide. This is usually used as a tracer of high density gas, but I’m not sure what it signifies in this object. I’ll look it up when we get a second. We’ve finished the rough analysis of our data on the Antennae, and are fairly confident we have a detection of CS, which is pleasing. Almost half way through the shift, and I’m going to take a walk outside shortly.

Update 3am HST : It’s cold and clear outside,but the weather from the sub-mm point of view is worse than ever. There must be some wet air up above us. As a result, we took the only decision we could in the circumstances and have switched to rock music to stay awake. Look out for air guitar on the webcam.

Update 4:09 HST : Finished our integration on Sakurai’s object (finally) and have moved to the variable V605 Aql. About which I know nothing, but if I get a second, I’ll find out for you. Feeling reasonably awake, and I haven’t attack the coffee yet either.

Update 4:55 HST : Found the science proposal (the things we spend hours writing to be allowed to get here in the first place) for the project we’ve been observing. It turns out that the objects we’ve been looking for are ‘born-again’ giant stars which were once quietly heading toward being white dwarfs. In about 20% of cases, for reasons that aren’t clear, the stars suddenly flare up again. This normally takes a couple of centuries, still pretty fast for astronomical objects but Sakurai’s object managed it in just a couple of months about a decade ago. Why look for HCN? If I’m reading this right, the stars throw off a shell of dusty material, and HCN should be contained there. Right, off to see the sunrise…

Update 6:06 HST : And it’s daylight out there. Subaru were still open when I went out, but there was a stream of other cars heading down the mountain as everyone else went home. The advantage of the sub-mm is that we can observe in daylight, so we’ve got almost three more hours on sky to go. We’re onto our third born again giant - tentative detections of the molecule we were looking for in both the others so far.

Update 7.32 HST : Feeling pretty tired now, but the view out the window is showing the beautiful red colour that I’ve only ever seen here and in bits of the South Devon I grew up in. And which I imagine covers lots of Mars. The Atacama desert was sandier, not quite so vividly red. In the meantime, we’re pointing (just) at our last science target, a high mass protostar. We’re looking for molecules that shouldn’t be there - the PhD student who wrote the proposal is trying to establish where molecules are still frozen onto the surface of dust grains despite heating from the central star.

Update 8:55 HST : The last science is done - the weather is the best we’ve had all night, and if this trend continues we’ll be observing the sources we came to see when we do it all again in about 11 hours time. The telescope is pointed at Mars to get an observation which will allow us to callibrate all of tonight’s data, and then we’re off down the hill. More tonight - probably picture based.

It’s not always easy being an astronomer whose work is based on observations in the sub-mm, even though this part of the electromagnetic spectrum (think of it as very short wave radio) is perfect for spotting the signatures of the more than 100 molecules which have been detected in space. The problems start when we have to deal with molecules closer to home, however; microwave ovens operate at these frequencies because they can excite the water molecules in food and that also means that it’s especially important for sub-mm telescopes to be high above sea level, away from most of the atmosphere. In one of my early observing runs I managed to make a completely independent detection of ozone in the Earth’s atmosphere which, suffice it to say, was not what I was looking for!

Even after we’ve got over that problem, though, applied for and got our fabulous data of huge scientific importance, when it comes to presenting results it’s hard not to be jealous of everyone else. My office neighbours produce incredible images from optical, infrared, ultraviolet and X-ray telescopes, but the largest sub-mm camera in the world until recently, SCUBA has a few tens of pixels. Not megapixels, but pixels. So when it comes to giving research talks we’ve been rather left behind as far as flashy pictures go.

However, things are changing. When the Sky at Night was last in Hawaii, we featured the new instruments being prepared for the JCMT. SCUBA’s successor, SCUBA2, is moving slowly in the right direction, but the spectral line receiver, HARP, is up and running. Instead of taking a spectrum at each point in a field, HARP makes maps which can be quickly converted into visual representations. I’ve already got my first data, and the first press release came out last week.

This is the centre of the Orion nebula, as seen in emission from Carbon Monoxide (the most common molecule in the Universe behind molecular hydrogen). The real beauty of this data, though, is that we can tune to different frequencies as this schematic shows

When you do that, as in this movie, you get a sense of the motion of the gas. The movie starts with a frequency corresponding to material moving rapidly toward us, at about 200 km/s (half a million miles an hour), and tunes through the different frequencies to end up with material rapidly receeding from us. This is a beautiful illustration of a ‘champagne flow’, as gas is forced away from the central part of the nebula, where star formation is most vigorous.

There will be a lot more from HARP, and from the JCMT in the next few years, and the ability to actually see in the sub-mm will certainly help us get a grip on the surprisingly complicated story of star formation.