To study and encourage popular interest in all branches of Science.

Newsletter Christmas 2001

Dear Member,

May I extend to you on behalf of all the Officers and members of Council our Compliments of the Season.

Hampstead SS Lectures in the Crypt Room at 8.15 pm.

World Pathogen Strategy Disclosed.

Thomas Eisner of Cornell University and Paul R. Ehrlich of Stanford University claim in an editorial in Science of 29th June 2001 to have obtained a leaked copy of a keynote address by President Prion of the World Pathogen Association which portends a threatening shift in policy by our major predators. An abbreviated version of his speech is given below and may offer a salutary dampening of any undue Christmas cheer:

"I must inform the infective community," Prion warns "that most of our natural hosts are disappearing. Never has our future been bleaker, threatened as it is by a reality that was unthinkable a mere 5000 years ago. Our food supplies are being displaced by a single species, Homo sapiens, which has come to reign dominant on Earth. It is dominant by weight of numbers and extent of spread, and has become - for all of us - the great challenge that we can no longer afford to ignore.

"Action is called for. Indeed, in this disaster there is a germ of an opportunity and an opportunity for the germs. In our evolutionary tradition, we must prepare ourselves to change our tastes, shift hosts, and take advantage of the single most appealing and available addition to our menu. Homophagia is the way of the future.

"But first some congratulations are in order. To HIV, for making the big leap most recently and for killing slowly enough to share the host with many of the rest of us. To the tuberculosis bacillus, for its unexpected renewed success. To the viruses - Ebola, Hanta, Lassa and Marburg - for their gallant efforts. To Legionella pneumophila, for its stealth. And to those already at the trough - the great pioneers such as Plasmodium, the dengue virus, and Treponema, and that great debilitator, the common cold virus - for setting splendid examples to ensure that success is within the grasp of all.

"There are many factors that give us hope. Homo is remarkably hospitable to us. In extraordinary numbers they are undernourished and immuno-deficient, and they have a penchant for keeping on the move, thereby spreading us veterans and providing many new opportunities for the novices among us to join in the feast. They expend their medical resources on the few while failing to exclude us from drinking water supplies and foods. They misuse antibiotics, among their best weapons against us, blind to our evolutionary capacity to develop resistance.

"The only dark cloud on our horizon is Homo's propensity for self-injury. They have on occasion threatened to modify some of us for use in intra-specific competition - "germ warfare" they call it. That might cause a food availability problem for us, but they are such prolific breeders that we could wait out a population crash until they once again achieve the biomass necessary for our appetites.

"All in all, my fellow pathogens, Homo is the opportunity that can benefit us all. Although they themselves deny that there is such a thing as a free lunch, we know better. There is a free lunch, and it is them!"


The First Stars

The Big Bang theory is now dominant among cosmologists. They also estimate the age of the universe since then to be 12 to 14 billion years. With the best telescopes available today we can look back in distance and therefore in time to when the Universe was about 1 billion years old, seeing ancient galaxies and quasars. But what had happened before then? The principal evidence for such early times comes from the cosmic microwave background which was emitted about 400,000 years after the big bang and has now been red-shifted by the expansion of the Universe down to a temperature of only a few degrees K. The uniformity of this background shows that matter was then hot and rather uniformly distributed, but with some small-scale density fluctuations. Further expansion allowed the Universe to cool; it would have been dark for some 100 million years.

Today we have a Universe full of brilliant stars and galaxies and know quite a bit about how stars are born by gravitational contraction in gas and dust clouds. Sir James Jeans was an early worker in this field. He showed that a clump of gas must have at least a minimum mass, now called the Jeans mass, to be able to contract into a star; this mass is proportional to the square of the gas temperature and inversely proportional to the square root of the gas pressure. Astrophysicists are now turning their attention to such star formation in the primordial universe between 1 million and 1 billion years after the big bang (see for example "The First stars in the Universe" by Richard B Larson and Volker Bromm in Scientific American, December 2001).

The authors point out two important differences between the environment then and now. The early galactic clouds would have been preponderantly made up of dark matter, that mysterious entity which seems to provide 90% of the mass of the Universe. In today's galaxies the dark matter remains scattered through an enormous outer halo, with the baryonic matter confined to the flattened spiral of the galaxy. Secondly, the ordinary matter would have been made up of the hydrogen and helium formed in the big bang, with no significant amounts of higher elements (inaccurately called "metals" by astrophysicists). These latter are in abundance today, having been formed by thermo-nuclear fusion inside stars or in supernovae explosions.

Several teams have recently been using computers to simulate star formation in the rather simple environment of the primordial universe. They show that gas clouds would have formed and contracted under gravity, the compression heating the gas to temperatures above 1,000 kelvins. Some hydrogen atoms would have combined in the dense gas to form hydrogen molecules and these molecules would emit infra-red radiation after colliding with hydrogen atoms. This would lead to cooling of the densest regions to between 200 and 300 degrees K, reducing the pressure and allowing further contraction into gravitationally bound clumps. This would separate the ordinary matter from the dark matter which, as far as we know, could not radiate and cool.

Star formation would begin in a similar way to that we observe today in molecular gas clouds. However, today's clouds include dust grains and heavier molecules which allow the cloud to cool to temperatures of some 10 degrees K. At this temperature and pressure the Jeans mass is calculated to be about the mass of the Sun, leading to the formation of stars like our sun. But in the primordial gas clouds, with no metals, the temperature is some 20 to 30 times higher and the Jeans mass will be up to 1,000 times larger. The simulations have all shown that the early star forming masses would have been of several hundred solar masses. It is not yet certain what size the resulting stars themselves will be, estimates varying from 100 to 1,000 solar masses.

If these theories are confirmed, these stars would have had a dramatic effect on the primordial universe. Apart from being bigger, their metal-free material results in higher temperatures for thermo-nuclear burning. Calculations suggest that their surface temperatures would have been 100,000 degrees K, 17 times that of the sun, with intense ultraviolet radiation. Their lives would have been short, a few million years. Stars between 100 and 250 times as massive as the sun are predicted to blow up at the end of their lives, discharging large amounts of higher elements (metals). Such a high early supernova rate might explain the observed scarcity of metal-poor stars in galaxies. Stars more massive than 250 solar masses would collapse into black holes. The latter could be the energy source for the quasars and become the immense black holes in galactic nuclei. Perhaps future telescopes will look back far enough in time to confirm these predictions.

Peter R Wallis.

The Next Generation Space Telescope

The Hubble Space Telescope is now more than 10 years old and a successor is being planned by NASA, ESA and the Canadian Space Agency. It is to have a mirror about 6 metres across instead of the 2.4 m of the HST; this will be able to collect 7 times the light. It is also designed to work at longer wavelengths and will be several thousand times as sensitive to infra-red wavelengths as the largest current telescope on Earth. This is important if it is to see back to the primordial universe because the expansion of the universe means that the light from more distant objects has been shifted into infra-red wavelengths. In addition, infra-red can penetrate the dust clouds in both nearby and remote star-forming regions, while visible and ultraviolet cannot.

The detectors will have to be cooled to some 30 deg K and a giant sunshield provided to shade the telescope from the sun. Instead of flying in an earth orbit like the HST, it will be placed in a solar orbit at the second Lagrangian point, a constant 1.5 million kilometers from the Earth. It will not be serviceable by astronauts during its lifetime.

Maybe in 10 years time we shall have confirmation of the ideas in the previous article!



This is a space mission proposed by Professor Ian Roxburgh of Queen Mary College (see the Summer 2001 issue of Frontiers). It has two objectives: the first and most likely to capture the public imagination is the search for habitable planets. From the ground we have already detected some 60 large hot gaseous planets, but only a space mission can detect smaller Earth-like planets which might be able to support life. The technique employed is to observe the minute decrease in the light from the star as the planet transits it. If we looked at our own sun from afar, we would see a reduction by about 1 part in 10,000 lasting 11 hours if we are in the orbital plane, the probability being 1 in 200. One such change is clearly not enough for proof, but if we can see the pattern repeat over several years, we may be confident of the detection. Eddington is designed to study a region of the sky 3 degrees in diameter over 3 years, observing a total of 500,000 stars. It is estimated that it will detect some 20,000 planets, of which there may be 100 Earth-like ones in the 'habitable zone'.

The other objective is to study in minute detail the dynamic behaviour of stars, to improve our understanding of stellar evolution. Eddington is a proposal included in the European Space Agency's Programme Horizon's 2000 +, which sets out the suite of space-science missions from 2008 to 2013.


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Last updated by Julie Atkinson   28-Jan-2018