Chris Lintott’s Universe

It’s difficult, as someone who uses telescopes which work in the sub-mm - effectively short-wave radio - it’s difficult not to be jealous of optical astronomers, many of whom are busy in the exhibit hall giving out beautiful posters of their latest hits. Instead, we end up often with spectra, or at best with a picture like this, obtained by the state of the art SCUBA camera on the JCMT.

View from the JCMT's SCUBA camera

I remember SCUBA-guru Rob Ivison’s description of the field on the Sky at Night as ‘blobology’ which hits the nail on the head. When these blobs were first discovered a decade or so ago, no-one knew what they were.

Worse, this simple question turns out to be harder to answer than you might think because the resolution in the sub-mm is so poor. When we look at a sub-mm image, we’re looking at a blurred view of the Universe. If you pointed a big optical telescope at the blob in the image above, the odds are that you’d see many separate galaxies within the one blob. Which of them is responsible for the blob? We wouldn’t know. Rather than jump straight to the optical, therefore, astronomers look deep in longer wavelength radio. Anything we see in the radio is then assumed to correspond to the sub-mm blob, and we’ll have a precise enough position to go chasing the thing with optical telescopes, allowing us to measure the distance.

This technique works for about half the sources, and the orthodox conclusion is that these are rapidly star-forming massive galaxies, the likely precursors of today’s old red and dead ellipticals. What about the other half? My assumption had always been that these were much like the others, but were radio quiet or otherwise difficult to pin down.

In a talk by Kartik Sheth of Caltech here at the American Astronomical Society meeting this morning, I realised I might have to rethink. Sheth’s group used the CARMA array to look directly at one sub-mm galaxy which hadn’t been matched with a counterpart.

The CARMA mm array.

They were able to sidestep the need for radio, and go directly to Hubble data which covered the field.

The Antennae Galaxies

To their surprise, the system was much nearer than other sub-mm galaxies. The best analogue seems to be a merging system, rather like the well-known Antennae which are pictured above. Is this a one-off? Are other nearby galaxies lurking among the distant blobs SCUBA sees? We’ll need, it seems much more data before we can say for sure.

Catchup post from DotAstronomy

One of the most interesting talks on day one of the was by Emily Lakdawalla from the Planetary Society, about armchair space exploration.

The development of this field has been incredible, with rapid release of ‘raw’ data now the rule rather than the exception. Emily made the excellent point that in learning to use their digital cameras and how to share the results people are already learning the skills they need to make use of that data. Similarly, software like powerpoint can be used to produce simple animations - Emily’s example was Encledus passing behind Dione as seen from the Cassini orbiter. This is useful scientific data because it helps refine the moons’ orbits, but it also looks pretty good.

The example that made my jaw drop, though, is this one. Ted Stryk is a biologist an english professor who in his spare time reprocessed the data from Voyager 2’s flyby of Uranus, which took place back in 1986. One of the joys of exploring the outer planets - as more recent missions like Cassini have reminded us - is the way that the moons change from being dots in an image to being worlds in their own right. Uranus was no exception - here’s Ariel as it appeared on January 1st 1986.

The sad thing is that this is essentially the only view Voyager had - the part of Ariel that is in the dark would have to wait for the next mission, which even now, twenty years later, has yet to hit the drawing board let along the launch pad. Except that, thanks for Ted, we don’t have to wait. He reprocessed the data, and suddenly the dark side of Ariel appeared, lit by Uranus-shine just as you sometimes see our Moon lit by Earthshine.

What a stunning project. Go and see the other moons.

<b>Update</b>:Emily emailed to point out I’d posted the wrong before image. It’s correct now.

Here’s my talk from yesterday :

Live streaming video by Ustream

Not the latest Dr Who episode, but the result of playing with Ed Gomez’s Impact Calculator which he’s talking about at the dotastronomy conference.

Here’s the result of a medium sized impact on the centre of London. Go and make your own.

I’m in Cardiff, for the dot astronomy conference organised by Rob Simpson of the Orbiting Frog blog. It should be an interesting few days, and I’ll try and keep you up to date here. I’ve just given the first talk - about Galaxy Zoo and our plans for the future - and you can watch all of the talks live on ustream via the feed here.

(Embedded stream deleted now the talk is over)

All the videos will end up on youtube at the conference’s channel which is here.

Jim Gunn from Princeton - one of the founders of the Sloan - is presenting the final conference summary. A large part of the design was influenced by the impact of people coming into astronomy from other parts of physics, doing things in the x-ray, the radio and the infrared and who were used to working with data, not with the pictures that were the stock in trade of the optical astronomer. Sloan was supposed to fill the gap, taking both images and data in the form of spectra.

The crucial technology were the fibre optic cables that allowed hundreds of spectrographs to be fed at the same time. Without them, the survey would have taken a thousand or so years assuming that everything worked with 100% efficiency. The new technology made much more rapid progress possible, and Sloan has touched every part of astrophysics.

Jim started his run down with the work on large scale structure. Among the surprises were the work on gravitational lenses, which it had never occurred to anyone might be possible. The net result is that our current cosmology is much better than we have any right to expect, and as Jim said ‘there are no obvious cracks - yet’. However, he warned that eventually as data improves it will crack, and said he’d be very surprised if it didn’t.

The study of galaxies themselves has been revolutionized by Sloan. The spectra were of a much greater quality than was necessary just to determine the distance to the galaxies SDSS targeted. Jim’s slide claims that establishing the properties of modern day galaxies was one of the primary purposes of the Sloan. The headline result is probably the discovery that large populations of galaxies can be divided into red and blue sub-populations. One of the current challenges driving research as a result is the need to explain how sufficient galaxies move quickly from the ‘blue cloud’ to the ‘red sequence’, let alone trying to work out what happens to them once they are there. The majority vote is that black holes have something to do with these mysteries, but the details are very sketchy.

Yet we have still made huge progress; as Jim said, when Sloan started we didn’t even know enough about galaxies to ask these questions, let alone to start answering them. Plenty of work has also been done on galaxies’ active cousins, the quasars, and on the Milky Way itself. The most striking thing - which has crept up on my consciousness for starters - is the acceptance of the idea that the Milky Way has grown by the accretion of smaller satellite galaxies.

Jim’s award for the most unsettling talk goes to ‘Pierre Bergeron’ whose talk on white dwarfs - the dense remnant of Sun-sized stars - lead to conclusion that the hydrogen atom, at least in these extreme conditions, is ‘not well understood’! In a more reassuring pocket lie some of the solar system work (the talks on which I missed by being busy elsewhere) where great strides have been made in identifying asteroids, ruling out threats to Earth.

Supernovae - exploding stars - have been the gold standard for cosmology for the last decade, but at current errors we’re getting close to the point where we have to understand the explosions themselves in order to make further progress. A task for the future, probably, but there are a new set of surveys on the horizon. What advice can the Sloan team offer them?

The most important is probably ‘do it right’ rather than take shortcuts. More interestingly, the lesson from Sloan is not to design surveys which are suited only for one task, but can do a whole host of things, most of which you haven’t thought of yet. Finally, one last discovery. It really is possible for hundreds of astronomers to work together across many institutions with very few constraints on who should do what. That’s something that just wasn’t known when Sloan started, and it’s illustrated by the fact that four of Jim’s academic grandchildren gave talks at this conference.

That’s a suitable end to a wide-ranging conference, so I shall leave it there. I hope you enjoyed my coverage.

Another report from the SDSS conference is up on the Discovery blog, but I wanted to write about the penultimate talk, describing the next stage for the survey.

Sloan has been through two phases of operation already, and now SDSS-III is about to start, incorporating four separate surveys, each with a different mission. The first, BOSS, will look once again at very large scale structure in an attempt to measure the acceleration of the expansion of the Universe. While Sloan was able to do this in its previous guise (in fact, this was part of its original raison d’etre) the new observations will, according to David Weinberg ‘turn [this technique] into a precision tool for studying this cosmic acceleration’. Weinberg is wearing a very silly green cap with the roman numeral ‘III’ on it, but we’ll forgive him that because he said the project will include more imaging, particularly of the southern sky. That will gives us 2000 more square degrees to Zoo someday.

The second survey, SEGUE-2 will look hard at 140,000 more stars within the Milky Way that includes many of the exciting weird ones I blogged about the other day. It has first priority for ‘dark time’ (with the Moon out the way) for the next year, and a later program will catch another 100,000 brighter stars.

The third survey, APOGEE is, according to David, ‘a really revolutionary experiment’, looking in detail at 100,000 red giant stars. Less than a thousand of such stars have data of this quality to date, so this is a huge step forward. I’m particularly excited by their plans to map the distribution of 10 chemical elements throughout the Milky Way, which will be very interesting to say the least.

Extra-solar planets is a massive field of research that didn’t exist when the first discussions about what became the Sloan Digital Sky Survey took place. With the fourth and final survey, MARVELS, Sloan is getting in on the planet-hunting action. The plan is to visit each of 11,000 stars 30 times over a period of 18 months. It’ll be looking for the wobble caused by giant planets in orbit around these stars, revealed in the Sloan spectrum. They’ll deliberate target giant planets, in order to get enough data to really test the models of planet formation that have been constructed in response to their presence close to their parent stars (something literally no-one predicted before the observations began to roll in). The forecast is that MARVELS should find 150 planets after 6 years of observations.

The outlook looks good for many more years of Sloan science. To me, as an outsider looking in, there’s a changing of the guard feeling as universities and people join and leave the team. This is a natural part of Sloan’s evolution from the experiment it was to the observatory it is today but the strong commitment to keeping data public will ensure that - wherever people gather for the 25th anniversary in 2013 - there will be plenty more wonders ahead.

If you’d like to know how to rule out intergalactic war on extremely large scales, then you’ll need to wander over to my Discovery blog.

I’m in the Sunday morning session of the Sloan Digital Sky Survey conference (let it never be said that astronomers don’t work hard, even on weekends), and the first talk of the day is by Simon White of the Max Planck Institute in Garching, Germany.

Simon is usually worth listening to, and was introduced by today’s chairman as someone who’d talked at literally every conference he can remember, so in the absence of structured writing I will try and keep you updated here.

He’s started by reminding us that looking at the largest scale structures was the original primary goal of the survey. In the early 90s, as the Sloan was being designed, it was still a relatively new proposition that the structures we see all formed by gravity acting on the tiny fluctuations that we observe in the early Universe, which were themselves detected in our earliest glimpse of the Universe, the cosmic microwave background, by the COBE satellite in 1992.

9.07 : The survey has done this and more - for example, gravitational lensing was considered only to be a curiosity.

9.11 : The world changed rapidly between this point and the survey producing data. For example, astronomers studying distant supernovae realised the Universe’s expansion is speeding up, rather than slowing down. Perhaps more importantly, we were able to measure the geometry of the Universe, and discovered that it is effectively ‘flat’; this is a measure of the energy density in the Universe.

9.13 : The simulation included in the proposal turns out to be not too bad, despite the fact that they had to randomly scatter the galaxies in the absence of other information. By 1996, the resolution of the simulation was good enough to allow us to model the formation of the galaxies themselves - although as with most of these simulations we’re only talking about following the evolution of the dominant dark matter.

9.22 : Simon’s working his way through a list of (fairly technical) observations from the Sloan which compare the distribution of galaxies, and groups of galaxies with the predictions of our standard model of cosmology. Although agreement is currently good, the results are surprisingly sensitive and (at least according to Simon) offer the possibility of distinguishing between the presence of dark matter versus theories which change gravity.

9.24 : Scratch the last bit; a new paper has made him think again about truly testing dark matter.

9.25 : What about looking for the shapes of dark matter halos by fitting profiles to the observed systems? And now we’re on to looking at beautiful simulations. One simulation of the Milky Way’s dark matter has what I think is hundreds of millions of particles whose position and movement are being modelled. This being a science conference, he skipped the movie. Boo!

9.28 : The conclusions from the simulation are many and varied, but include the prediction that the dark matter in our local neighbourhood will essentially be smooth. It will actually be in streams, but there are hundreds of thousands of them and so we won’t be able to distinguish between what the models predict and a truly smooth distribution.

While yesterday morning’s talks focused on the general population of stars in the Milky Way, the last two talks of the day told us a little of what can be learnt by looking at more unusual stars. David Lai of UC Santa Cruz took us through the results of his studies of some of the Milky Way’s most metal-poor stars.

Talking about metals in stars sounds counterintuitive, but when an astronomer talks about ‘metals’ they mean any element heavier than helium. These elements are made in the cores of previous generations of stars (the origin of the wonderful imagery of the phrase ‘we are stardust’), and so the most metal-poor stars must be made of the material in the galaxy which is closest to primordial. In fact, Lai told us that his results were consistent with these stars having formed from gas enriched by only one previous generation of stars, which would have exploded in a supernova a long time ago. What we have, he said, is ‘a window into early environments’, thanks to what are literally ’stellar relics’ of that time. Many such stars have been identified with the SDSS survey, and work is underway to follow up the best candidates in the outer regions of the Galaxy with an instrument attached to the Keck telescopes on Mauna Kea, Hawai’i. One observing night has produced data for nine stars, and their next run is in two weeks; watch this space.

The last talk looked at stars which were unusual in other ways; as the name suggests, high velocity stars are notable thanks to their rapid motion through space. They’d been predicted since astronomer Jack Hills realised in the 1980s that the close approach of a binary star (two stars in orbit around each other) to the supermassive black hole that lurks at the Milky Way’s centre would result in one of the stars being rapidly ejected from the galactic centre at high speed. Identifying them will then allow us to probe the dynamics of and star formation in the Milky Way’s heart. To give just one example, it’s impossible for us to see low mass stars at the distance of the galactic centre, so the only way we’ll know they’re there is to see them once they’ve been thrown out.

They’re therefore of great interest besides being, as speaker Jana Kollmeier of Carnegie Observatory both ’super important’ and ‘awesome’ (it’s always good to have an enthusiastic speaker who realises that we need to be kept awake at the end of the day!). Finding them amongst the rest of the stars in the galaxy has proved a difficult challenge, though – literally like looking for a needle in a haystack. To improve the odds, astronomers have, until now, looked for blue needles in a red haystack. The vast majority of the native stars in the outer part of the Milky Way’s halo are old and therefore red. Young, massive, blue interlopers stand out like, well, still like a blue star amongst many red ones.

The first few were identified as the by-products of studies of blue stars. The first, discovered by Brown et al. was clocked at 710 km per second (more than one and a half million miles per hour – or about 70,000 times faster than the winner of the men’s Olympic 100 metres) heading rapidly away from the centre of the galaxy. In 2005 they were followed by two more. Hirsch et al’s escapee was moving slightly faster (720 km per second), but the star discovered by Edelmann et al. is even stranger. It’s moving at 550 km per second, but not away from the Milky Way’s centre, but apparently from the Large Magellanic Cloud. As the LMC doesn’t contain a supermassive black hole how this could have happened is something of a mystery.

Blue stars aren’t the solution to all of the Milky Way centre’s mysteries. They don’t live long enough for us to see fast moving stars heading on the inward parts of their orbits. Using this technique with the data that the Sloan survey provides has brought the total up considerably.

Dr Kollmeier only shared her preliminary results with the audience on the condition that we all stopped noting things down, so I’ll wait until the paper comes out before writing about it. The next phase of the Sloan survey, the third, is going to include specific follow-up of fast moving stars and it sounds like the fastest moving objects in the Milky Way will have plenty of competition in the years to come.