Cool star leaves girlfriend cold

May 30, 2007

A great result has come out of UKIDSS, the IR survey of which I am overall PI, led by Steve Warren and Daniel Mortlock at Imperial. This is the discovery of the coldest star found so far – a brown dwarf with the telephone number ULAS J0034-00. We hope this is just the tip of the iceberg with UKIDSS, and are hoping to find a whole new population of super cool/old/small substellar objects. We have already decided what to call them even though we haven’t found them yet – Y dwarfs.

A press release has been put out to coincide with the AAS meeting. I am about umpteenth on the paper. Brown dwarfs are not really my speciality, but I find them fascinating. Not so my partner Deb it seems. I mentioned the result and she mocked. “You mean you are boasting about finding something especially dim and feeble ? How dull is that ? What happened to dark energy and hypernovae ?”

So I tried explaining to the kids but they was too busy revising Chemistry or killing monsters on the Playstation or something.

Well I still think its interesting.

(p.s. I see Fraser Cain picked this one up at Universe Today)


Astro Bloopers

May 28, 2007

Ah, ’tis May time and exams are here ! I hear the distant scratching of a thousand pens in echoing sports halls and I know that all is right with the academic world. The future hangs in the balance; careers are won and lost; the glittering prizes brighten and fade, as inspiration approaches and recedes. But, thanks to Statistics, there are certainties in this contingent world. We just know that most students will do kinda ok; a handful will stun us; and a handful will turn in utter gibberish. Here are some of my favourites, collected from a few years worth of astronomy exams.

Most are from first year Astronomy courses for a wide range of students – what I believe our American chums call “Astronomy for Poets” or “Scopes for Dopes”. But some are from junior and senior honours students .. see if you can tell which..

All real folks.


  • Doppler shift is an effect which doesn’t take place on the poles of the earth, but it does everywhere else.
  • Black bodies do not emit any light, as they are a box with a tiny hole in. Light enters the hole, bounces around the box, and cannot get out again.
  • IR observations tend to be used for trying to find new plants, which at 300K fit neatly in the IR spectrum.
  • Physics is terrestrial whereas astronomy is conducted on an astral plane.
  • IR astronomy is carried out with an instrument called a bola meter, which is made of geranium.
  • Interferometry works because when the dishes are a certain distance apart the radio waves are syncopated.
  • We know there is dark matter in galaxies as they rotate faster than they ought to, so dark matter must be absorbing some of the light…
  • X-ray astronomy must be carried out from space otherwise the radiation would have a damaging effect on Earth, causing cancer and so on.
  • For spiral galaxies, the linewidth technique is known as Tully-Fisher, whereas for elliptical galaxies it is the Fabry Perot method.
  • part of answer to “describe the universe as seen at different wavelengths”….. The infrared universe is a great deal more colourful, although the colour is often false and generated by a computer.
  • Black-body radiation requires dark matter.
  • The spectral shape of the radiation from black-bodies is determined by the allocation of nearby bodies, as the gravitational attraction from these can “stretch” the radiation and make it more elliptical.
  • The rotation curves of galaxies are the wrong shape. This is because dark matter is concentrated towards the centre, absorbing the light and preventing us from obtaining accurate velocities for this part of the galaxy.
  • Astronomy can be seen as applied physics, and indeed most great astronomers have also been great physicians.
  • In astronomy, all experiments conducted are out of our control.
  • We now know of two black holes, Cygnus I and the one at the centre of the Kerr galaxy.
  • A dynamically relaxed system obeys the viral theorem.
  • If it weren’t for Physics, Astronomy would only be the observation of the pretty bright specs we can see in the sky.
  • Answer to “how would Earth’s orbital velocity change if sixteen times closer to the Sun ?”… If the Earth were sixteen times closer to the Sun, it would vaporise and so its orbital velocity would be zero.
  • X-rays from around black holes are produced by accension belts.
  • The radio emission from quasars is not blackbody emission because that is a theoretical concept and does not actually exist in the universe.
  • White dwarfs are white because they are mostly made of carbon and oxygen i.e. CO, which is a white solid.
  • There is no spheroidal component in the Milky Way, as at night we can see that all the stars are in a thin line.
  • When forced closer together, the electrons buss about more violently.
  • A Type II supernova is the death of a star resulting in a big explosion. This only happens once per star.
  • A pulsar is a neutron star that emits ultra-violent radiation.
  • The Sun is a main sequence star. This is the most common type of star in the solar system.
  • The denser the body the less radiation they emit. The most extreme case being “black body” radiation where no detectable radiation is emitted.
  • The mass of the solar system is 10**12 solar masses. When divided by all the stars we estimate, that comes out at 30 solar masses per star.
  • We calculate the distance to the Sun by bouncing radar signals off Venice at six monthly intervals.

Protecting the good citizens of China from the moral cesspit that is WordPress

May 23, 2007

So.. the reason I have not posted for a week and a half is that I have been in Beijing, where WordPress seems to be blocked. I couldn’t even read my own blog. Blogger on the other hand, seems to be fine. I guess this is to do with the deal Google did, but what did WordPress do wrong ? I also got Brit-news withdrawal symptoms, as BBC News was blocked, but CNN wasn’t. (Doesn’t this just make you trust the BBC ??). Even on the CNN site, when I did a search for “China News” I got a list of links which somehow didn’t work….

So I tried other sites. Wikipedia in English – nope. Wikipedia in French – ok. Technorati – nope. Digg – ok. Bad Astronomer and Astronomy Blog – just fine. Guardian – ok. How they decide to ban the BBC but the Guardian is beyond me. I kinda doubt that the Guardian has done a special deal. Maybe they are just too small beer, whereas everybody has heard of the BBC and is out looking for it.

IVOA Exec having dinner in Beijing. Anyhoo. Despite the techno-censorship I had a fine time. The people are great and the food is fantastic.
I was at the twice yearly “interoperability workshop” of the International Virtual Observatory Alliance.

Its all about standards, standards, and standards. And just a smidgeon of politics. Oh and did I mention standards.

This year’s fashion is SOAP bashing. We are all fed up with writing WSDL and want to be a bit more RESTful. Ultra-geeks nod knowingly. Regular astronomers and others, nod patronisingly, as if understanding perfectly well but having better things to do.

St Lawrence about to be martyred on the Grid. Found at So anyway. I am a semi-geek. It was fun but hard and the politics and personality clashes got a bit intense. All I will say is that more than one person has pointed out to that St Lawrence was martyred on the Grid.


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.


Jim Gray : lost but not forgotten

May 1, 2007

Three months ago Jim Gray, database expert, Turing prizewinner, and friend of the Virtual Observatory, disappeared in his yacht off California. The IT world, and some of his astronomy friends, such as Alex Szalay, mounted the most amazing high-tech search, but he has not turned up, so people are assuming the worst. A tribute to Jim has just appeared on The Register. Amongst other things, this article makes the point that people went to such lengths not just because he was clever and important, but because people liked him so much. I only met him a few times, but this is spot on. He was a really really nice guy. And with a quiet but sharp sense of humour. At one very early VO meeting, when people had been burbling on about bandwidth issues for hours, he started his talk by speaking to Alex Szalay, saying “Oh, Alex, I have been meaning to give you these data”. He walked around the bench and handed Alex a hard disk. As he walked back, he said “There you go. Hundred Gigabits per second. Sneakernet.”