Aztec Quasar Pilgrimage

March 24, 2009

Twice each year, at the equinox, the feathered serpent Quetzalcoatl returns to his home at the Great Pyramid of Cholula. I was there with my family to welcome him this Saturday, having travelled to INAOE in Mexico to give my UKIDSS/VO colloquium. Quetzalcoatl must be a shy chap. It seems it needs a few thousand people to encourage him home by singing, dancing, eating gorditas, drinking pulque, and jumping over fires wearing absurdly large head-dresses. At twilight, we climbed the ancient pyramid towards the Christian church planted on its top. Halfway we turned and looked back towards Popocatapetl, smoking in the middle distance. It is just so huge and dramatic. How can you not feel stirred ? The church was full of icons of Mary / Diana / Earth Mother, and several images of the Sacred Heart, which seemed gruesomely appropriate. These things are so powerful, I think it is a mistake to think of religion simply as ignorance. Rationality is an insight, a liberation, that battles against some of our wiring.

Back down among the festival tents, there were in fact many astronomers in attendance, showing the locals how to make paper models of the Moon and of Stereo A and B. I am glad to report these stalls were very popular. Almost as popular as the pulque.

This morning I walked into INAOE, in the nearby village of Tonantzintla. I walked past the old Schmidt telescope, part of the original 1940s observatory founded by Guillermo Haro. Like my visit to Byurakan almost two years ago, this was a kind of historical pilgrimage. Haro was I believe the first to use the idea of a Schmidt objective prism to search systematically for blue things. He found all sorts of fascinating things, including discovering the jet-like structures in forming stars now known as Herbig-Haro objects. But his lists of blue things included star forming galaxies, and blue “stars” which later turned out to be quasars. (Ton 202 is a favourite of mine, being one of the quasars where my colleague Makoto Kishimoto uncovered the Balmer edge expected from an accretion disc atmosphere, and the nu**1/3 SED in the infrared – see post here). Today Roberto Terlevich told me that Haro worked with Ambartsumian, and actually convinced Markarian to undertake his historic survey – at first Markarian wasn’t interested. Apparently Haro was eventually awarded the Lenin Prize.

It is so strange to think of those quasars sitting there, in a list in Haro’s office, all those years until somebody knew what they were. What mysteries are hidden today, unrecognised in an anonymous list on somebody’s laptop ?

Thursday Trivia : Astro Pet Hates

November 27, 2008

Tomorrow morning it will be Thanksgiving Day. Of course I have pretty much no idea what this all means, but for sure nobody does any work.  So I have been squeezing in some extra work tonight in a late night drifting kinda way, roaming around the ADS.  I just found a fascinating paper. As I skimmed the abstract however, my teeth began to grind, as I came across the phrase “..we might expect these sources to be heavily extincted quasars..” Aaaggghh !!!! “Extinct” is an adjective. There is no verb “to extinct”, so things can’t be “extincted”. Yeah, I know “extinguished” isn’t quite right either, as it sounds like something wiped out rather than heavily reduced. But you can’t say “extincted”. There is no such word. You just have to find a different way to say it. Seeing it in print is even worse … what was the editor doing ? Of course I know I should relax; language evolves, often by just such incorrect extrapolations; and maybe enough people are using “extincted” now, in both astronomy and evolutionary studies, that it has become de facto a correct useage. Correct grammar (and spelling) is wotever the peepul say. But please … can I have this one just a bit longer ??

Anyhoo. Flame off. Your turn. Astro Pet Hates. Could be scientific, grammatical, or political, as long as there is a Connexion Astronomickal.

Sunglasses, black holes, and unsafe partners

July 25, 2008

Oh Proud Day ! I am on the front page of the STFC web site ! This is the “polarised sunglasses see black hole disks” story. Doesn’t seem to have made the Daily Mirror, but has reasonably spread round the Internut, including Skymania, New Scientist, Universe Today, Astronomy Now and Chris Lintott in his American Manifestation . A week ago I was even more excited, as the first draft of the press release had a quote from Keef, saying how important UKIRT was to UK astronomy, but it got changed into a quote by Chris Davis. Better in some ways and a shame in others.The person who deserves nearly all the credit by the way is Makoto Kishimoto, one of the most careful but insightful astronomers I know.

If you can’t afford a subscription to Nature, you can read it on astro-ph. Here is the story. Quasar phenomenon supposedly caused by accretion onto supermassive black holes. Prediction since 1973 that accretion discs should show nu**1/3 spectrum – very blue. In optical-UV you don’t see this, but, well, there are complications. Should be a safer bet in the IR, coming from the outer bits of disc. But in the IR all you can see is the emission from the damned dust on much larger scales. Thinks. Light scattered from the disc is polarised, so maybe measuring the polarised flux shows pure uncontaminated disc ? Ahh .. but dust emission is often polarised too. Rats. But wait ! Some quasars show no polarisation in the broad emission lines.. in which case any polarisation must be caused interior to the BLR … try these.. Bingo. Nu**1/3. Or actually, about nu**0.4. Thirty year old theory finally vindicated. Phew. Sits down with glass of whisky.

So for half of today, when I wasn’t googling for references to black hole sunglasses, I was at a meeting here at SLAC today celebrating the career of ex-SLAC-Director Jonathan Dorfan. He is the man credited with pulling off PEP-II and BaBar, turning SLAC into the B-factory, focusing on CP violation and the matter-anti-matter asymmetry. But years later, he was also the man who swung the ship round to head towards a future of light sources, lasers, and biology. (But also particle astrophysics … GLAST, SNAP, LSST … thats why I’m here folks..).

One of the key talks was by Albrecht Wagner from DESY, here to remind us that actually there was still a bright future for particle physics, and indeed Linear Colliders are back in fashion. Errrr… just a shame that the US and UK seem to have changed their minds and pulled the funding plug. The only tense moment in a warm and cuddly day was when Wagner said that the US should now be considered “an unsafe partner for international projects”. Think I’ll stop there.

Quasars, Donuts, and the Unified Faith

June 8, 2007

Six a.m. in a Bavarian Monastery. I am woken again by the bloody bells. Worry not, dear readers, I have not become a monk. The ancient Kloster Seeon has been turned into a hotel and conference centre, and I am here with a hundred astronomers arguing about “Obscured AGN across Cosmic Time”. But in some ways this is a gathering of believers – the Church of the Unified Faith – and its an interesting example of science as a sociological process.

Active Galactic Nuclei (AGN) and their big cousins the Quasars come in two flavours, Artists impression of the torus - courtesy of ESO
imaginatively called Type-1 and Type-2. Since the late 1970s various folk including yours truly have suggested that Type-2s are actually the same as Type-1 but seen edge on through obscuring muck. This is known as the Unified Scheme. Grand Title for a kinda simple idea. In 1985 Antonucci and Miller found particularly convincing evidence that the idea was correct, and in 1988 Krolik and Begelman put forward a theoretical explanation involving a dusty torus surrounding the quasar. Since then every observer compares their data to “the torus model”, and every artists impression of a quasar has this nice neat obscuring torus as well as accretion disc, jets, and so on.

The trouble is, there are at least as many Type-2s as Type-1s, so the obscuring torus has to cover a large fraction of sky as seen from inside the quasar. So the torus is not a swirling disc but a great fat rotating donut. Making a fat rotating thing is hard. Cold rotating things are always thin, like Saturns rings. Stars are fat rotating things, but they’re hot. Various forced attempts have been made to fix this problem. The latest one was put forward this week by Julian Krolik, who argued that the torus is kept puffed up by the radiation pressure from the central quasar light. Nice idea, but not yet clear that its stable, or that it fits the facts well enough.

Another option came from me, arguing that there isn’t really a rotating donut at all, but a severely warped disc – fuel coming from large distances is rotating in a different plane to the quasar disc, and as it tilts and precesses on the way down, it ends up blocking much of the sky. People were interested in the idea, but many were perturbed. In torus land, Ski Antonucci is the Founder of the Faith, and Julian Krolik is the Bishop of Rome; I am I guess one of the Cardinals, seen as responsible for the variant known as the “receding torus model”. People love this, as its basically one line of algebra and so dead easy to compare your data to. People kept asking me “so you don’t believe in the torus anymore ? But you’ve been working on this for years.”

This is is unsettling, not just because of the idea of belief in science, but because you are pressured into buying complete packages. Talk after talk at this meeting claimed that their data “supported the torus model”, to which my reaction was “err.. depends what you mean”. Usually the data supported the general idea of unification of Type-1 and Type-2; sometimes it supported the idea that obscuration is axisymmetric, sometimes that it is geometrically thick ..but showed that there is a rotating molecular donut ? Gimme a break. But once a successful model appears, it swallows all the things that made it up, and is very hard to break apart and re-assemble with some new parts.

This is understandable, not because scientists are conservative, but because science is hard work, and because they have careers to make. This is especially true for young scientists. It is very hard work understanding how your instrument works, collecting the data, reducing it carefully, mastering the background theory, and reading the huge literature. You are desperate to make an impact, to tell a story with your work, and need some organising mental framework. If the world is all scepticism and ambiguity you are sunk. So you cling onto the popular model until the facts make it crack, and then you jump ship to the new fashionable model.

So this of course is just what Thomas Kuhn said in his famous book, “The Structure of Scientific Revolutions”. At heart, the scientific process is sceptical and logical – Conjecture and Refutation, as another famous book by Karl Popper has it. But the realities of human debate, the pressures of the sociological process of science, and the need to think within an organising framework, all lead to resistance to change. This is not conservatism – scientists love to be radical in principle – but inertia.

Black Hole Eclipse and the non-existent donut

April 14, 2007

My old chums Guido Risaliti and Martin Elvis have been in the astro-news this week, with a Chandra press release about the disappearing X-ray emission from NGC 1365. They measured it every two days for a fortnight and in just one measurement it wuzzn’t there – eclipsed by an intervening cloud they reckon. This was touted as “measuring the size of the accretion disc” but I know that Martin and Guido have written papers before claiming that rapid variability of absorption shows that the popular obscuring torus or “donut” model for active galaxies must be wrong. I like this because I too am a donut-sceptic, as set out in this recent conference paper.

So I emailed Martin and asked which it was – donut-destruction or disk-size. The answer seems to both, Martin says there is more cool stuff coming. But how can I tell ? Martin ! Write the damn paper !