Credit : Justin Bilicki, the winner of the Union of Concerned Scientist’s Science Idol competition.
Hat Tip : Phil
Credit : Justin Bilicki, the winner of the Union of Concerned Scientist’s Science Idol competition.
Hat Tip : Phil
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.
My first note from the SDSS conference in Chicago is up over on my Discovery blog, reporting on the discovery of a new companion to the Milky Way. There will be more posts there (and possibly) here later today and tomorrow.
Update : Second report is now up too.
Lots to write about from my current trip (Hello from Chicago) but for now let me send you to this week’s all singing all dancing Carnival of Space.
Having been gently prodded by Nereid in the comments to my previous post on the topic, I want to say a lot more about scientific reporting. The reason for the delay in this post, by the way, is probably obvious but the screenshot below – which shows the front page of CNN.com yesterday afternoon says it all.
First off, it’s wonderful that we’re getting a new wave of interest in Galaxy Zoo, which is bringing with it a new flood of people eager to start classifying galaxies. The timing is great; we’re hopefully just a week or so away from the launch of Zoo 2 (don’t hold me to that) when there will be plenty more work to go around. However, I feel very, very uneasy about writing about the Voorwerp now; the paper which describes it has only been submitted to the journal, and it doesn’t yet have the stamp of peer review. For some projects, it makes sense to talk about results at this stage; if you have a beautiful picture of a spiral galaxy then you might as well release the picture and leave the details to the experts. But here at least part of the story lies in what we think the object is, and until that gets accepted by the journal we could all end up with lots of egg on our collective face. If I were our friendly (but thorough – as they should be) referee I’d be more than slightly annoyed that the authors of the paper were talking to the press.
So why are we talking to anyone? Because the steady drip feed of stories from journalists who had read our blog (or – better – who were active members of the zoo) was growing into a torrent, particularly in the Dutch media who recognised a fantastic story in Hanny’s discovery, and that rush of attention meant that if we were ever going to talk about this object we had to do it straight away, or risk losing the media’s attention.
So why did we blog the results as we went along? It’s something we’ve tried to do as we’ve gone through the process of converting clicks on the Galaxy Zoo website into science (current scorecard : 2 papers accepted, 2 under discussion with referees, 1 awaiting a response, many more on the way). The reasons for this are at least threefold. Firstly, I’m serious when I talk about the users of our website as our scientific collaborators. What they do makes the science possible, and it’s a matter of simple courtesy to tell them what we’re doing with it, and to recognise their contributions. Secondly, we were very, very excited about the Voorwerp, and to be honest have probably been talking excitedly about it to everyone we’ve come in contact with.
Thirdly, I strongly believe that something that the media are bad at is showing science in progress. If you read mainstream news coverage of science you’ll see a string of discoveries and eureka moments, but this isn’t how things are in reality. The reality of doing science day to day involves talking and arguing and thinking, and it’s in those arguments that the scientific method lurks. If you can’t defend your idea with data, whether talking to a journal’s referee, to your colleagues in the office down the corridor or even to yourself, then it doesn’t survive.
You wouldn’t get that impression from reading the press, or from the science education that schoolchildren receive. In both, there seems to lurk an assumption that science has a big book of facts which we’re slowly adding to by sitting quietly in ivory towers or in the bath and thinking before announcing The Truth to awestruck colleagues and Nobel prize committees.
Not only is this assumption wrong, but it’s dangerous too. The result of the public never seeing scientific disagreement and debate are horrific. Without any understanding of how to question a scientific statement, is it any surprise that the public are confused when scientist A says ‘Vaccines are safe’ and scientist B says ‘they may cause autism’, or when scientist C says ‘Global warming is man made’ and scientist D blames the Sun. Both are speaking with the Voice of Science (TM), but how to distinguish? To me it’s obvious – ask about their data sets, ask what other studies exist, ask what other explanations they considered and how they ruled them out and so on and so on. The public, confused by the sight of scientific disagreement, tends to throw up its arms and conclude that Science has nothing to say on the subject regardless of what the true weight of evidence is.
That’s why I’m a huge admirer of the way that at least my part of science has been moving – toward having data and papers freely available. Want to do your own project with the data from the Sloan Digital Sky Survey? Here you go. Want to see the images that the Phoenix spacecraft took yesterday on Mars? Their gallery is updated as the images hit the ground, for anyone who cares to take a look.
Mentioning Phoenix, of course, is what opened this can of worms in the first place. There’s a good summary over at the planetary society of what happens if you think you’ve discovered perchlorate on Mars. Scientist Tom Pike weighs in on his blog, too. I don’t have much to add to that specifically, beyond pointing out that for all the references to ‘internet speculation’ the root of this story was a journalist for a print magazine doing good, old-fashioned journalism.
It’s a storm in a teacup which will soon be forgotten by all except those involved, and, no doubt, a bunch of conspiracy theorists who will see this as a leak from NASA’s otherwise excellent smokescreen which excludes all evidence of little green men from the public eye. I, though, am still angry that NASA and the Phoenix team – who were so open and hospitable to us when we filmed there a month or two ago – had to publicly insist they weren’t hiding anything.
If I had my way, it would be possible to have our arguments about what percholorate means for life on Mars, about what Hanny’s Voorwerp is and everything else right in the public eye. To do that, though, we need to help teach people how to argue with scientists and to argue like scientists. I truly believe that in releasing data fast NASA is helping achieve that, and that by blogging Galaxy Zoo’s journey we can too. Even if we end up talking about things before we’re sure about them.
It’s becoming increasingly difficult to know where one stands when writing about – or doing – science. Instead of waiting for the peer review process to take its course and for journals to print the received wisdom, life on the cutting edge is about debating papers released to astro-ph, a slightly policed archive of papers submitted by academics when reviewed, but also sometimes when submitted to the journals or even before. Writers are picking up on that, and that’s fine – I love the fact that you can now read an article on a blog or in New Scientist and with a click be reading the paper.
Some projects have more problems; we’re struggling with Galaxy Zoo to learn what to say when – more on that tomorrow. For now, here’s Emily on what it seems will always be known as the ‘Phoenix flap’.