Archive for March, 2021

LO WOLTJER’S TELESCOPE; THE VLT

March 11, 2021

Francis Bacon, a very wise old bird, wrote; “By far the greatest obstacle to the progress of science and the undertaking of tasks and provinces therein is found in this — that men despair and think things impossible“.[Novum Organon, 1604]. But sometimes a man has the imagination, or effrontery, to see beyond his fellows, and so to build a marvel which they all thought impossible. Such a man was Lo Woltjer who built the VLT, now the most powerful optical telescope on Earth.

In 1976, during a conference in Italy I overheard him say over lunch ‘It’s time for Europe to take back the lead in Astronomy from America’. At the time I thought that idea preposterous but overnight I changed my mind and went to talk to him . I had spent spent several years analysing the Scaling Laws of telescopes, that is to say how their effectiveness and cost scale with their mirror diameter D. Naively I had imagined all would scale with the mirror area, that is to say with D2 , but that turned out to be very far from the truth. Big mirrors also collect unwanted sky light (noise) while some major costs could rise as fast as D4 . Why? Because if they are to focus the light, telescopes cannot afford to bend, and bending moments scale as D4 — that’s why big trees are so much stouter in proportion than saplings. And in engineering, costs tend to rise in proportion to weight. I had thus concluded (1972) that large telescopes were disproportionately expensive and should be replaced by arrays of smaller ones which could add their signals together.

When I went to talk to Lo he was sitting under a tree reading Tacitus’ “The Agricola and the Germania” because he was an historian at heart, son of an eminent Dutch historian. He took the long view, saw the big picture, and realised that America’s huge lead was a temporary consequence of finding better telescope sites in its own back yard. But the coming of the jet airliner Woltjer saw as a chance for Europe to catch up, indeed overtake America in mankind’s race to decipher the Cosmos. He asked me to spend 6 months at his European Southern Observatory (ESO) headquarters, then in Geneva, and help with his visionary plan — which I afterwards did.

In 1977 Woltjer organised a huge conference on Big Telescope Design in Geneva at the end of which he announced his vision of a 16-metre class European telescope at a time when the largest was the 6 metre Russian instrument. 21 years later his his vision bore fruit when the VLT (‘Very Large Telescope’) saw First Light high up in the Chilean Andes. This is now recognised to be the most powerful astronomical facility on Earth, generating even more research papers than the Hubble Space Telescope, which cost ten times as much.

vlt

The VLT up at La Paranal up in the Chilean Andes. It looks nothing like a conventional telescope because the mirror area is equally divided between 4 largely identical 8.2 metre units, each in its own rotating enclosure. The 4 smaller auxiliary telescopes in domes combine with the 4 monsters for the purposes of optical interferometry. Such a single image can convey little of the ingenuity going on inside. For that see later

I played only a minor roll in the VLT’s eventual evolution and confess I’ve never used it because my primary interests turned in other directions, such as Hidden Galaxies for which it wouldn’t be useful. But I would like to celebrate what seems to be a most extraordinary personal , as well as a European-wide, achievement. So many challenges had to be met, so many stubborn minds had to be persuaded, so many co-workers had to be inspired to realize a dream built out of glass, electronics and light. Whereas one can marvel at other great constructions like Stonehenge and Agia Sophia we know almost nothing of how they were built , or even who built them, but the VLT story is still acccessible , not least in Woltjer’s own modest book “Europe’s Quest for the Universe” [2005]. Fascinating episodes include:

Deciding on its fundamental configuration , which had to be a series of tricky trade-offs between performance, politics and cost.

Finding the very best site when cloudlessness and atmospheric steadiness do not necessarily go together.

Building huge mirrors which are very light, yet optically and thermally stable. Eventually the Schott company cast the 8.2 metre monoliths out of its proprietry Zerodur which took months and months to cool as they were spun into shape. Lo Woltjer’s chief optician, Ray Wilson from Brum, devised active support mechanisms which thereafter kept those mirrors in perfect shape as they were tilted to follow the sky. Not least was the challenge of moving such huge but fragile structures via the waterways of the world to their eventual home atop the Andes.

Any telescope’s performance can be ruined by turbulent air bubbling anywhere near it, hence its housing is vital. The VLT housings, while protecting the telescopes from wind and weather, leave them largely out in the pristine night air. This novel design was proof-tested on ESO’s smaller NTT and appears to work remarkably well.

The demands of near-infrared astronomy on a telescope are different from the optical variety. For instance the massive secondary mirrors have to be wobbled at 10 Hertz or more to subtract off the much brighter infra- red sky. At some considerable cost this was achieved by building them out of light but very tricky Beryllium.

Any telescope is only as good as the Instruments fitted to it to analyse and record its light. Here Woltjer took a leaf from Space Astronomy. Such Instrument’s specifications were sent out to tender across Europe, with the winning teams not only paid but rewarded with large grants of telescope time to do their own Science. This not only challenged the best of European brains but built up invaluable infrastructure across the continent.

Last, but not least, Woltjer and his chief lieutenant Maximo Tarenghi had to deal with a Chilean government which was traumatized by the brutal Pinochet coup. They had to sup with some real devilsL

Last but not least , Woltjer and his chief lieutenant Maximo Tarenghi had to deal with a Chilean government rocked by Pinochet’s very violent coup. At times that meant supping with some pretty vile devils.

But in the end, somehow everything came together and worked superbly, so that, in my opinion, the VLT is one of mankind’s greatest achievements, reminding us of what we humans, at our best, can do.

No blog or image can possibly do justice to Lo Woltjer and his great achievement but, as you might expect, ESO runs a quite wonderful website at eso.org and if you look there under ‘Movies’, or on You-Tube, you can find ‘VLT trailer’ , a stirring evocation of this magnificent project, fanfare and all.

THE LOVELL RADIO TELESCOPE

March 8, 2021

is surely the most spectacular telescope on Earth and definitely worth a family visit to the visitor centre at Jodrell Bank near Macclesfield in Cheshire. Remarkably it can tip all the way down to to the horizon and if you can get close to it you can watch its wheels very slowly turn as it follows a radio source across the sky. In other words you can see the Earth actually turn — which fascinated me when I was privileged to observe with it.

Lovell Radio Dish at Jodrell Bank Cheshire

The 250 foot Lovell Radio Telescope completed in 1957 and named after Sir Bernard Lovell of Manchester University who built her largely out of war surplus, is still the only big dish which can tilt all the way down to the horizon. She has numerous scientific discoveries to her credit including gravitational lenses.

The old girl’s getting on a bit but she’s definitely had her moments. The first pictures back from the Moon’s surface, taken by the Russian Luna 2 spacecraft in 1966, were beamed back to Earth using her unique capabilities at the time. The local Manchester University staff decoded them and rushed them down to a Royal Astronomical Society meeting in London where I was lucky enough to be amongst the audience as a student. We all had to pinch ourselves to make sure we weren’t dreaming.

Much later in 2004 my colleague Jon Davies and his team used it to discover a Hydrogen source Virgo HI 21 in the Virgo Cluster, which is, in my opinion, the first Dark Galaxy. It’s massive, it’s spinning and it’s invisible. What else could it be?

The source Virgo HI 21 first discovered by a team from Cardiff University who were searching for Dark Galaxies in the 21-cm Hydrogen Line using a multi-beam receiver specially designed for that purpose. Higher resolution radio observations by the same team with the radio interferometer at Westerbork in Holland are shown above superposed on negative optical images. On the left you can see that the source has interacted with and disturbed the massive Spiral Galaxy NGC 4254, the most luminous in the huge cluster. The velocity map on the right reveals that Virgo HI 21 is spinning at about 200 kilometres a second, about what you would expect of a massive disc. But very deep Hubble Space Telescope images of the mysterious disc revealed no light.

The claim that Virgo HI 21 is a Dark Galaxy gave rise to titanic refereeing battles and vicious arguments which are described in Chapters 12 and 13 of my novel ‘Beyond the Western Stars.’ [ see this site under Category ‘My Books’]. They illustrate that cutting edge astronomy is definitely not for the faint hearted. If you ask me, from a distance of 12 years, much of the opposition was motivated by sour grapes. But why not make up your own mind and look at some of the evidence. Science can be tough, very tough.

THE COSMIC ROSETTA STONE

March 6, 2021

Archaeologists use tree-rings to date events several thousand years ago, climate scientists use ice-cores to decipher the state of the atmosphere as it was several hundred thousand years ago and astronomers bore holes in the Cosmos that potentially tell us of the Universe as it was billions of years in the past. But all these signals need some ingenious deciphering to get at the truth.

Look at the spectrum below, taken with the VLT, the world’s. most powerful optical telescope, sited high in the Chilean Andes. What is so remarkable about the spectrum, which stretches from the violet to the deep red, are all the dark lines imprinted upon it as the light from a very distant quasar has traversed Space on its immense journey to reach us. They probably have a fascinating tale to tell, far more momentous than the Rosetta Stone. But what is that tale? Why not have a go at cracking it?

This image, originally entitled “Fingerprints of the early Universe” can be dowloaded from The European Southern Observatory’s spectacular website eso.org under /images/ ‘Quasars and Black Holes’. It is an extremely deep spectrum of the Quasar (or ‘QSO’ standing for ‘Quasi-Stellar Object’) HE 0945-1050 (at redshift 3) taken with the UVES instrument on their Very Large Telescope (VLT) . What is remarkable about it is the presence of so many dark lines imposed on the spectrum, each the result of an absorbing cloud of gas lying along the line of sight to the quasar, which is several billion light years away from us. ( Acknowledge V. D’Odoricco, Osservatorio Astronomico di Trieste, Italy)

Experts have been staring at such QSO Absorption Line Systems (QSOALS for short, or ‘Spectral Ghosts’ as I prefer to call them) for over 50 years years now, and have come up with some intriguing clues. The lines, which have nothing to do with the quasar itself, are caused by atoms in distant clouds of gas lying at different redshifts ( or distances, because of the expansion of the Universe) along the line of sight. They know that from measuring the ratios of the wavelengths of those lines, ratios which in many cases are identical to to the ratios of spectral lines from ordinary atoms in the laboratory such as Hydrogen, Magnesium, Carbon, Oxygen, and so on. Since most of those atoms can only be made inside stars we infer that the mysterious clouds must also contain stars. But the only gas-clouds we know of containing stars are Galaxies, huge whirlpools of gas and stars , structures like the Andromeda Nebula and our own home The Milky Way ( See our post “Galaxy Gallery” for images). So what we must be seeing are the atoms in galaxies at different redshifts (distances away) intercepting and scattering out discreet wavelengths as the light-beam passes through them. Hence the spectrum is the log of an immense journey, and of all the encounters with galaxies which the light beam has made on its way from the Quasar to the Earth. Right? Well no.

Why not? Because there are about a hundred times too many black absorption lines to be accounted for by ordinary galaxies. A hundred times! That’s going to take some explaining. The experts of course have such an explanation: they say galaxies must simply be a hundred times bigger than we thought; they must have a vast invisible halo of gas around them which intercepts quasar light and etches all those lines we can see.

But don’t you think that explanation sounds just too glib, too ad hoc, rather too much like a child’s lie or the fairy tale about The Emperor’s New Clothes? I do. I think it’s a blatant attempt to brush a fascinating mystery under the carpet. Experts, especially those who make their living out of their expertise, don’t like to admit to mysteries, because they might undermine their claims to expertise. How often have you heard your doctor admit; “To be honest Mr. Jones I have no bloody idea what’s wrong with you.”

Of course the QSOALS experts claim to have at least some evidence in support of their Giant Halo Hypothesis. But if you look at that evidence very carefully, it’s not convincing at all; at least that’s what I think. I’ve got an alternative explanation for the dark lines, even more dramatic than Halos, but I won’t go into that here, because it too has its detractors.

Instead, the purpose of this post, is simply to point out that there is a great mystery out there and to encourage curious outsiders to have a go at solving it. After all The Rosetta Stone itself was solved by a young self-taught outsider, Jean-Francois Champollion who had taught himself Coptic Greek, which turned out to be the key … but that’s another fascinating story.

If it seems ridiculous to suggest that any but a professional astrophysicist (as I am myself) could make a serious contribution to this problem, that ignores how profoundly the Internet has changed Science. Here the germane facts are few. The relevant data is available for all to download from public archives, as are the existing scientific papers on the subject. And just remember that modern academics have become far too busy to really think any more. So you won’t have much serious competition from them.

So why not have a go? Deciphering the Cosmic Rosetta Stone will be far more exciting, and momentous, than cracking Egyptian history. But don’t expect it to come without effort. A couple of thousand hours of focussed reading should get one up to speed however. And here’s a useful tip to start: find out what the ‘ADS’ is ( it’s got something to do with NASA) and start using it.

Good luck. If nothing else you could have a hell of a lot of fun.