Make yourself feel good

December 10, 2008

I am at least fourth off the blocks here … but I recommend you go visit http://www.physics.ox.ac.uk/skyphoto , get a piece of history, help a very sick child, and give yourself a nice warm christmassy glow. The basic idea is selling framed prints from old Palomar Sky Survey plates, to raise money for Alexander Thatte, the son of two Oxford astronomers, who is battling leukaemia, and whose last chance may be a new anti-body treatment. I haven’t met Alexander, but his parents are lovely people and they all deserve a break.  Apparently there are even copies signed by Jocelyn Bell Burnell … oooohhh

Old plates really are beautiful …  like a few other locals, I rescued a few glass positives from the non-survey part of the UK Schmidt collection, and a lot more went to the local art school .. but framed prints for charity is a great idea.

Visit the web site and do something.


UKIDSS world release

January 10, 2008

UKIDSS logo

As I warned just before Xmas in this post, the first world release of UKIDSS has now gone public, with a press release at the AAS. The blogosphere is picking it up, here, here and here. You have no idea how nice it feels after a couple of weeks of STFC-cuts politics.. This has been my baby since 1998 … but others have done much more work than me. Thanks especially Steve Warren, Nige Hambly, and Mike Irwin. Steve doesn’t seem to have a home page. This isn’t him.

Key links : explanations at the UKIDSS web site; data access at the WFCAM Science Archive; and Mike Read’s groovy pannable Milky Way.


Explore the infrared sky

December 21, 2007

UKIDSS logo

Most of this week I was actually doing some science for a change, at a workshop in ESO with all my UKIDSS chums. We just issued our third data release, which with exquisite taste we have called DR3. UKIDSS is now the biggest Infrared Sky Survey ever made, in terms of database size, number of objects, and effective volume (but not sky area). DR3 is announced on the UKIDSS web site, and you can get the data at the WFCAM Science Archive (WSA). Or at least you can if you are European.. but also DR1 is about to go world public, so all the Americans can get at it. This will be announced at the upcoming AAS meeting.

Mostly the WSA is for serious pro work, not for public consumption of pretty pix. However, our secret weapon Mike Read has knocked up a lovely pannable zoomable mosaic of the Galactic Plane Survey. Its still kinda patchy, but full of gorgeous things. Try it out.


Cows, Quasars, and Cosmic Rays

August 23, 2007

Day-4 at the Joint European National Astronomy Meeting. Much stuff today about Very High Energy Astronomy. This was hot stuff some decades ago, but is now undergoing a revival. Felix Ahoronian showed how TeV astronomy is finally taking off, with HESS, MAGIC, and VERITAS detecting real sources at high S/N. John Carr reviewed neutrino astronomy – under the sea (ANTARES), under lakes (BAIKAL), and under the Antarctic Ice (AMANDA) – which seems just on the brink of becoming real astronomy (roll on ICECUBE). These are maybe the last new windows on the Universe. Meanwhile Vahe Petrosian reviewed particle acceleration in the Universe, and argued that shock acceleration is not the solution to everything as most people have assumed for thre decades ; the answer is stochastic (second order Fermi) acceleration, and the snag is we need to understand turbulence …

Last night we had our excursion to Byurakan Observatory. As ICows and 2.6m at Byurukan explained a few days ago, this is something of a pilgrimage for Active Galaxy and Quasar fans, especially because this is where Markarian and Arakelian undertook their historic objective prism surveys, searching the cosmos for the blue and emission line objects – especially starburst galaxies and active galactic nuclei.

Its a beautiful observatory, spread out over a rural setting on the slopes of Mount Aragatz, and with a stunning view of the enormous Mount Ararat (of Noah’s Ark fame..). There are cows all the over the place (see pic-1). This is is nearly as good as the AAO being overrun with kangaroos. In the dalek-like 2.6M dome, there isYours truly on the BAO 2.6m controls a control system that seems to come from the Ark. As well as analogue dials, there are two computers, but they are Pentium IIIs… Pic-2, taken by Jonathan Tedds, shows yours truly pretending to control the telescope but actually coming out a bit Phantom of the Opera-ish.

Following this there was a lovely outdoor dinner on the longest table I have EVER seen. I tried hard to be rude to various French astronomers but they are just too ready with the timed riposte and le bon mot. Dammn.

Yes Yes I know Google Sky got released today but the network here is so crap I can’t really try it out yet.


Exploring the Cosmos Part III : The End of Astronomy ?

May 10, 2007

OK folks, here is Andy’s entry for the possibly overcrowded “end of science” market. I am not really making a case that Astronomy as a whole is finished – just that the Golden Age of Surveys is closing. This is not for any profound reason, but just because we have already ticked off the easy wins, and there is only so much money in the world.

This material is recycled from my long overdue article for “Astronomy and Geophysics” – its the written version of a review talk at last year’s National Astronomy 2006 meeting. (Sorry Sue). The astro-ph version is here. Off we go:

In 1950, the universe seemed to consist of stars, and a sprinkling of dust. Over the last fifty years, the actual diverse and bizarre contents of the universe have been successively revealed as we surveyed the sky at a series of new wavelengths. Radio astronomy has shown us radio galaxies and pulsars; microwave observations have given us molecular clouds and the Big Bang fossil background; IR astronomy has shown us ultraluminous starburst galaxies and brown dwarfs; X-ray astronomy has given us collapsed object binaries and the intra-cluster medium; and submm astronomy has shown us debris disks and the epoch of galaxy formation. As well as revealing strange new objects, these surveys revealed new states of matter (relativistic plasma, degenerate matter, black holes) and new physical processes (bipolar ejection, matter-antimatter annihilation). Having opened up gamma-rays and the submm with GRO and SCUBA, there are no new wavelength windows left. Has this amazing journey of discovery now finished ?

Well… wavelength is not the only possible axis of survey discovery space. Lets try some others.

Photon Flux. We could just go deeper. Historically, this has been as productive as opening new wavelength windows. The classic example is the discovery of the entire extragalactic universe, which did not become apparent until reaching ten thousand times fainter than naked eye observations, requiring both large telescopes and the ability to integrate. We can now see things ten billion times fainter than the naked eye stars. However, we have reached the era of diminishing returns. The flux reached by a telescope is inversely proportional to diameter D but its cost is proportional to D**3. Significant improvements can now only be achieved with world-scale facilities, and orders of magnitude improvements are unthinkable. The easy wins have been covered already – our detectors now achieve close to 100% quantum efficiency; we have gone into space and reduced sky background to a minimum; and multi-night integrations have been used many times. We will keep building bigger telescopes, but it no longer seems the fast track to discovery.

Spectral resolution. Detailed spectroscopy of individual objects is of course the key technique of modern astrophysics, but what about spectroscopic surveys ? This has been a big winner over the last few decades, because the spectrum of a galaxy gives you the redshift, and so the distance. This way we mapped out the Universe in 3D. We were not expecting the voids, bubbles and walls that were found in the galaxy distribution in the 1980s. This industry will continue, but there is no obvious new barrier to break. Narrow band imaging surveys centred on specific atomic or molecular features (21cm HI, CO, H-alpha) have been fruitful, but again its not obvious there is anywhere new to go. Some of my X-ray chums have suggested that deep X-ray surveys are the next-big-thing. I can see they will be v.good, but I can’t see it really cracks open a new part of parameter space.

Polarization. Polarisation measurements of individual objects are a very important physical diagnostic, but are polarisation surveys plausible ? Surveys of samples of known objects to the 0.1% level have been done, with interesting results but no big surprises. Perhaps blank field imaging surveys in four Stokes parameters would turn up unexpected highly polarised objects ? This has essentially been done in radio astronomy but not at other wavelengths.

Spatial resolution. If we can just resolve tiny tiny detail, perhaps we will see something really new ? This is the dominant big-project target of the next few decades, and of course is the real point of Extremely Large Telescopes. Put together with multi-conjugate Adaptive Optics, we hope to achieve both depth and milli-arcsec resolution at the same time. However, the royal road to high spatial resolution is through interferometry. Surveys with radio interferometers in the twentieth century showed the existence of masers in space, and bulk relativistic outflow. In the twenty first century we will be doing microwave interferometry on the ground (ALMA) and IR interferometry in space (DARWIN/TPF), hoping to directly detect Earth-like planets around nearby stars. So there is excitement for at least some time to come; however, as with photon flux, we are hitting an economic brick wall. Significantly bigger and better experiments will be a very long time coming.

Time. The observation of temporal changes has repeatedly brought about revolutionary changes in astronomy. Classic example number one is Tycho’s supernova, which cracked open the crystal spheres. Classic example number two is the measurement of stellar parallax, which showed how unspeakably vast the Universe is. The last two decades has seen a renaissance in this area, with an impressive number of important discoveries from relatively cheap monitoring experiments – the discovery of extrasolar planets from velocity wobbles and transits; the discovery of the accelerating universe and dark energy from supernova campaigns; the location of substellar objects from survey proper motions; the existence of Trans-Neptunian Objects, and Near Earth Objects (killer rocks in space !); the final pinning down of gamma-ray burst counterparts; and the limits on dark matter candidates from micro-lensing events. The next decade or two will see more ambitious photometric monitoring experiments, such as PanSTARRS and LSST, and a series of astrometric missions, culminating in GAIA, which will see external galaxies rotating. Overall, the “time window” is well and truly opened up. However, the temporal frequency axis is far from fully explored. My instinct is that this technique will continue to produce surprises for some time.

Non-light channels : particles. The origin of Cosmic Rays was one of the key puzzles of the twentieth century, and still can’t be considered solved. But you can’t really do surveys – indeed the central mystery has alway been where cosmic rays come from. Today, the underground experiments trying to directly detect Dark Matter particles are confronting what is arguably the most important problem in physics, let alone astrophysics. But again no survey is plausible. The big hope is neutrino astrophysics. Neutrinos should emerge from deep in the most fascinating places that we could otherwise never see – supernova cores, the centres of stars, the interior of quasar accretion discs. Measurement of solar neutrinos has solved a long standing problem, and set a challenge for particle physics – but what about the rest of the Universe ? New experiments such as ANTARES (under the sea) and AMANDA (under the ice) seem to be clearly detecting cosmic neutrinos, but no distinct sources have yet emerged. Possibly the next generation (ICECUBE and KM3NET) will get there. This looks like the best bet for genuinely unexpected discoveries in the twenty first century.

Non-light channels : gravitational waves. Like neutrinos, we know that gravitational waves have to be there somewhere, and their existence has been indirectly proved by the famous binary pulsar timing experiment. However after many years of exquisite technical development, we still have no direct detection of a gravitational wave. The space interferometer mission LISA should finally detect gravitational waves, unless current predictions are badly wrong. However even LISA will not produce a genuine survey. We will detect many events and understand more astrophysics, but will have essentially no idea where they came from, except that hopefully some will correlate with Gamma-ray bursts. If we see totally unexpected signals, it will be very hard to know what to do next.

Hyper-space planes : the Virtual Observatory. As we explore the various possible axes one by one, many if not most of them are running out of steam, or are too expensive to pursue. But we are a long way short of exploring the whole space – for example narrow line imaging in all Stokes parameters versus time. This exploration does not necessarily need complex new experiments. More survey-quality datasets come on line every year. As formats, access and query protocols, and analysis tool interaction protocols all get standardised, the virtual universe becomes easier for the e-astronomer to explore, and unexpected results will emerge. This, of course, is the agenda of the worldwide Virtual Observatory initiative.

So there we have it. The fify-something Prof’s recommendation for the eager young survey astronomer : time, neutrinos, and the internet.


The man who measured the size of the Universe

April 14, 2007

Last night I was faced with a mixture of achievement and failure, wonder and decay, drinking tea in the room where Thomas Henderson calculated the distance to the stars.

I was giving a talk to the Astronomical Society of Edinburgh, a long established amateur society. My talk was about mapping the Universe, first stepping through the history, and ending up with modern results from SDSS, 2dFGRS, and UKIDSS. I mentioned Thomas Henderson, my predecessor as Regius Professor; a great hero, as in 1833 he was the first man to measure parallax and so determine the distance to a star (Alpha Centauri). He made the measurements in South Africa and finished the calculations in Edinburgh. Alpha Centauri is the very nearest star system; but it is almost seven thousand times further away than Pluto… The universe of stars is unimaginably vast.

I showed a picture of a memorial to Henderson Thomas Henderson Memorial on Calton Hill Edinburghwhich I had found on the web, and mentioned that I wasn’t sure where it was – maybe in the same cemetery as David Hume ? Oh no, they piped up – its on the side of this building ! (And the image came from their website… oops.) The ASE are lucky enough to use as their HQ the old City Observatory on Calton Hill, where the Astronomers Royal worked until 1894 when the new Royal Observatory was built on Blackford Hill on the outskirts of Edinburgh. (This is where I work now of course..). Well…I say lucky, but the state of the buildings is a scandal. They are owned by the City, but gradually decaying. The toilets don’t work, and the ASE guys warned me to go before I turned up.

After the talk they fed me tea and biscuits in a room where they reckon Henderson did his calculations after returning from the Cape. But its also where he lost his nerve. In the 1830s measuring parallax was the big prize, and some people had had egg on their faces -Henderson was nervous about whether he had got it right, and didn’t publish. Finally in 1838 Friedrich Bessel beat him to it and published the parallax of 61 Cygni. Henderson finally published the next year. His distance was right within about 30%.

So on the way out I walked around the side of the beautiful Playfair building. Fog was swirling around the walls (no observing last night !). ASE scretary Graham Rule shone his torch for me, and there it was – a modest monument to the man who showed just how big the Universe really is.


UKIDSS marches on

March 2, 2007

Yesterday saw the second data release (DR2) of the UKIRT Infrared Deep Sky Survey (UKIDSS), the biggest infrared sky survey so far. The UKIDSS home page is here, but you get the data from the WFCAM Science Archive (WSA).

I am the PI of the survey, but lots of other people do more work than me – especially Survey Scientist Steve Warren, who is the lynchpin of the whole thing, and Nigel Hambly, who masterminds the WSA. Nige is the one who has been losing sleep getting ready for the release..

This event put me in mind of a strange day a year back when I went out to Hawaii to do a UKIDSS observing run, and got stuck into a five hour conversation about science and religion. I would have expected this to irk me, but in fact it was fascinating .. I will try to write this up over the weekend…


Exploring the Cosmos Part II

February 3, 2007

So.. some days back in an earlier post I waxed lyrical on how mapping the sky has been of profound cultural importance – setting our lives in context, and satisfying a deep desire to discover whats out there. But are surveys the right thing to do scientifically ? When we map the sky, do we not spend many nights of expensive telescope time collecting data “just in case its handy” ? Would it not be more cost effective to do much more targeted experiments ? Au contraire …(Pretentious ? Moi ?)

Surveys are cheap

We do the science in two steps. Surveys are a kind of summarised digest of the sky. Once we have this digest as a database we can do multiple experiments from the same database, without having to go back to the telescope. This could be anything from “I have an X-ray source – does it have an IR counterpart ?” to “I want to test my model by calculating the correlation function of a special subset of galaxies chosen to have parameters XYZ”. This multiple use is hugely productive and very cost effective. In modern times the prime example is the Sloan Digital Sky Survey (SDSS). The team themselves have written plenty of papers, but astronomers all over the world suck data out of the SDSS archive every day, and the net effect has been almost a thousand scientific papers using the survey.

Put another way, online survey maps and catalogues can be seen as a kind of virtual sky. It is no coincidence that people like me who like surveys are also pushing on the Virtual Observatory front… more of this another time.

You need big surveys

Often the science we do just needs big swathes of sky. There can be three typical reasons for this. First, the thing we are studying covers a large fraction of the sky – like the Milky Way for example, or the Local Supercluster. Sometimes it is because we are looking for needles in a haystack – very rare objects such as quasars at z=6 or the very nearest and coldest brown dwarfs – we expect a handful over the sky, but don’t know where they are .. Finally, it can be because we need a very large sample – millions of objects – to beat down the statistical errors. The classic example is measuring the power spectrum of galaxy clustering, where we want a few percent accuracy in every spatial frequency bin. Another good example is mapping out the dark matter by measuring the distortions in galaxy images caused by weak gravitational lensing. (As in the recent result from the COSMOS survey). To do this, we need to average over hundreds of galaxies in each spatial bin in our map.

Surveys are the engine of discovery

Since the 1950s, every time we survey the sky at a new wavelength, we have been taken by surprise – radio galaxies, X-ray binaries, gamma ray bursts, huge starbursts. (More examples in the earlier post).

Many people would take this aspect of surveys as the best value for money for the last fifty years. We have been through a Golden Age of discovery. But has it now ended ? SCUBA, the submillimetre camera, plugged the last wavelength gap. It was very successful, discovering debris disks round nearby stars, and so many high redshift starbursts, that this seems to be the way that half the stars were formed. SCUBA2 will be bigger and better .. but not rdaically different. So is that it ? Have all the windows have been opened…. ? I will take a look at this in part III.


Exploring the Cosmos Part I

January 20, 2007

I seem to have spent my life mapping the sky. Jemima Public might find this strange. As a scientist paid by her taxes, surely I should be doing something useful, like curing cancer or teaching her son how to integrate ? As a human being, surely there are more enjoyable or profound things – reading King Lear, or throwing darts at a picture of Donald Rumsfeld ? Even some of my professional colleagues are a bit snooty about it – sounds a bit of a dull slog, Lawrence … shouldn’t you get back to quasar variability studies ? Well, my colleagues, my fellow humans, I find that I must disagree.

Maps of the sky are of considerable cultural significance; they have been hugely productive scientifically; and they have been the engine of discovery, revealing an unknown universe step by step. Lets take each of these in turn, starting with the human impact of exploring the cosmos.

So.. the Cosmic Explorer boards his ship and sails forth into the dark unknown, observing, sketching, and writing as he goes, a modest supply of the King’s gold jingling in his pockets. He does this for the Advancement of Learning, but when he returns from the tropical glare to the grey skies of home, weary and bearded, the people want to hear his story. Draw us a map, they say, with the coastlines, cities and mountains you have found, that we may know the true extent and form of our world. Tell us of the other nations and peoples, how rich, how powerful they are, that we may know our place. Tell us of the wonders that you found – what strange beasts, what customs – that we may appreciate the true variety and beauty of the world.

Where do I live ?

Schoolboy answer : 33 Ironside Villas, Edinburgh, Midlothian, Scotland, UK, Europe, Earth, Solar System, Western Arm, Milky Way, Local Group, Virgo Supercluster, Universe..

Turn left just after Barnard’s star, you can’t miss it. Yes its silly and its whimsical; but it springs from a true need to know.

There is a long tradition of trying to produce a map of everything. This is now very hard in astronomy as the universe is soooo big. One needs to show a series of expanding views : the solar system, the solar neighbourhood of stars, the Milky Way, the Local Group, the Virgo Supercluster… There are some interesting web sites trying to do this. Probably the best is the Atlas of the Universe. This has lots of other good links. Another nice one is Tour the Universe, part of the online presence of the PBS Nova TV programme. There is a web version of the famous Powers of Ten There are also several downloadable programmes for roaming round the Universe on your PC – one from the Hayden Planetarium, a big open source project called Celestia, and a more home grown one just called Universe. One of the most interesting recent professional attempts to get the whole Universe across has been led by Gott and Juric who try to put everything on a single logarithmic strip.

One of my favourite pictures, shown here, is a whole sky map made in the infra-red by the 2MASS project. The Infrared sky by 2MASS. It is cleverly done to show both the Milky Way and the sea of other galaxies that it is lost within, colour coded by distance. Regular visible-wavelength light is extinguished by the obscuring muck in the interstellar medium, so that we can’t even see the centre of our own Galaxy. (Note : if another astronomer uses the word “extincted” I shall scream). In the infrared, you can see clean through, and we can finally see that yes, the Milky Way really is like two fried eggs back to back.

My own project, UKIDSS, is the successor to 2MASS – an infrared survey that doesn’t cover the whole sky but is much deeper. In fact The Ultra Deep Survey from UKIDSSone piece of it, the Ultra Deep Survey (UDS), led by my old chum Omar Almaini, is intended to build up over several years to map out a volume at redshift three that is big as the map of the local Universe that 2MASS has made. The UDS isn’t finished yet, but here is a picture showing the map so far – the faint red blob by the arrow is an object pinned down by Ross McLure, that he believes is a luminous “Lyman break” galaxy at redshift 6.

What is our place in things ?

We all know that Copernicus knocked us off our self-important pedestal. But the obsessive star mappers of the 18th and 19th centuries made an arguably bigger change : we live in a vast sea of stars at huge distances – we are insignificant. Temporarily we reverted to believing we were at the centre of a structured Universe, as star maps seemed to show that we live at the centre of a flattened swirling disc. But this was an illusion caused by the obscuring muck; now we know we live in an unfashionable suburb of the Milky Way. Next came two great twentieth century revolutions. The Milky Way is only one of many island universes; the Universe was again unimaginably vast and formless. For decades now we have been mapping the realm of the galaxies, but we have not uncovered another layer of structure – no Metagalaxy – the galaxies just go on and on and on and on. They are clumped and clustered, and measuring this clumpiness has filled many careers (including mine) as it is a diagnostic of rival cosmological theories … but no new landmass is emerging through the mist. We are just a dot within a dot within a dot.

However .. Slipher and Hubble and friends found all those galaxies rushing away from us. The Universe is expanding; running the movie backwards, the Universe had a beginning, in a violent explosion : what Hoyle scornfully termed the Big Bang. (Here is a free plug for Simon Singh’s book about the Big Bang.) This is philosophically unsettling, and Hoyle wriggled bravely, but every year the facts pile up. The Universe was different in the past and began 14 billion years ago. Much of our mapmaking now, like the UKIDSS-UDS, is aimed at mapping very very faint galaxies, to directly study the past, and we are struggling towards an understanding of the era of galaxy formation. But the philosophical discomfort remains. The Big Bang universe is one of the central features of our time.

What’s out there?

Astronomical surveys are not just about structure. They are about content. It is surveys that have gradually revealed the true variety of the cosmic bestiary. With the naked eye we see only stars and planets. Telescopic surveys revealed fuzzy patches that are either clouds of gas, or separate island universes. The patchiness in star counts revealed that the space between stars is not empty, but filled with smoke. But the real action started from the middle of the twentieth century, as technology allowed us to map the sky at different wavelengths. Radio surveys revealed the existence of pulsars, and radio galaxies squirting out jets millions of light years across. X-ray astronomy revealed collapsed objects – neutron stars and black holes – swallowing material from companion stars. Infra-red astronomy revealed new stars in the process of forming, and far-infrared astronomy showed us ultraluminous starburst galaxies. Not only did we find new objects that we didn’t know existed, but even new states of matter – relativistic plasma, degenerate matter, gas at ten million degrees between the galaxies.

Because of multi-wavelength surveys, twentieth century astronomy was a story of never ending surprises. But could it be that no windows remain to open .. Are there any surprises left ? Back soon ..


Follow

Get every new post delivered to your Inbox.

Join 130 other followers