At the limits of the Universe

Brazilians see the oldest and most distant explosion of a star

At 3 hours, 7 minutes and 21 seconds of September 4, the Swift satellite from NASA, the American space agency, sent out an alert to the astrophysicists on duty: apparatuses on board the spaceship had just captured traces of what could be an explosion of gamma rays at the limits of the Pisces constellation. It could be an important star event or one more occurrence without any greater predicates. Land-based telescopes, located in the most diverse latitudes, gave a pause to their routine observations and rapidly turned their mirrors to the coordinates broadcast by Swift (professional equipment has mirrors, not lenses). Eighty-six seconds after the advice, Tarot, an observatory on the Côte d’Azur, was already recording the region indicated by the satellite. An effort in vain. Its images did not show any explosion and, at 7:23, the French astronomers sent out a bulletin on what they had seen. Nothing out of the ordinary. Thirty five minutes later, another negative response, this time from the small Palomar telescope, in California.

The scenario began to change at 10 o’clock, always following Greenwich time. Operated by a young astrophysicist from São Paulo, Eduardo Cypriano, the Southern Observatory for Astrophysical Research, or simply Soar, a telescope located at the beginning of the Atacama desert, more precisely on Cerro Pachon, a mountain at an altitude of 2,700 meters in the Chilean Andes, released a bulletin of good tiding: it had captured the first images of the possible stellar blast. It was still not possible to say how long ago the mysterious phenomenon had happen, nor to define exactly what it was about. And the event was only to be sighted in the wavelengths equivalent to infrared, but not in the optical frequencies of visible light. For this reason, there were doubts about its nature. “It could be cosmic dust, or an explosion with high redshift, jargon to designate very distant sidereal events”, says Cypriano, who could count on the help of another astrophysicist from São Paulo, Elysandra Figueredo, his wife, in the work of processing the images. At the request of Daniel Reichart, from the University of North Carolina, a hunter of gamma ray explosions, the Brazilian couple redirected the mirrors of the telescope, which has Brazil as one of its major partners, to the Pisces constellation, in the hope of achieving some record. As was to be seen soon afterwards, this move yielded dividends.

On September 12, after a series of measurements and observations made in a pioneering way by Soar and subsequently ratified by other telescopes, there was the formal announcement: the gamma ray explosion GRB 050904, so called by the researchers, had occurred at 12.7 billion light-years from the Earth (one light-year is equivalent to about 9.5 trillion kilometers), “a mere” 1 billion years after the Big Bang, the primordial event that probably gave origin to the Universe. It was the most distant and ancient cosmic bang ever detected by man, which signaled the death of a star with a mass tens of times greater than the Sun, and the birth of a black hole from its leftovers. “We are entering into unmapped territory”, said Reichart, in the collective interview that made the discovery public. “We are finally seeing the remains of some of the oldest objects of the Universe.” The previous record belonged to an explosion 500 million years more recent than GRB 050904.

The death of a massive star causes an extremely fleeting explosion of gamma rays, which usually lasts no more than ten seconds. GRB 050904 was an exception to the rule: it took 200 seconds. Some astrophysicists estimate that, in a little over three minutes, the explosion confirmed by Soar generated 300 times more energy than the Sun will release over the probable 10 billion years of its life. Strictly speaking, it was not this rapid and uncommon event that the mirrors of the telescopes from all over the world pursued, but rather the remnants of the explosion. Its residual brilliance, which, in its long cosmic journey, lasted those 12.7 billion years to reach us. Throughout three nights running, from September 4 to 6, Cypriano, one of the members of the international team resident in Chile that operates Soar, observed the residual brilliance of the explosion vanishing. “I was in the right place at the right time”, says this 34-year old citizen of São Paulo.

The original images of the phenomenon, made in several wavelengths, are not as sharp as those published in this article. Before the public announcement of the discovery of the oldest cosmic explosion, Elysandra spent a week removing instrumental noises from information that made it difficult to analyze the records obtained from the remote stellar collapse, in a joint effort with the researchers from the University of North Carolina. “For being very bright in the infrared, the sky is the most difficult part to treat in the images”, comments Lys, as this 32-year old from the state of São Paulo, born in São Vicente, likes to be called. At the end of the work, it all worked out right. The snapshot of the oldest cosmic explosion is a light in a period marked by the darkness. There is less information about the stars that arose in the infancy of the Universe than about the Big Bang itself. Even without being fully operational, the images of GRB 050904 produced by Soar, a heavy bet by national astrophysics, have made history.

Opened in April 2004, after over a decade of design and construction, the observatory has a main mirror of 4.1 meters in diameter, 6.6 times more powerful than the largest of the telescopes installed in Brazil. Although it is located in a desert zone, it is not alone on the mountain. It shares Cerro Pachon with an illustrious neighbor, the South unit of the Gemini Observatory, located 400 meters away, and which was also used in the observations of GRB 050904. Soar cost US$ 28 million, an amount apportioned amongst the four partners in the enterprise. Three partners are from the United States – the University of North Carolina, the University of Michigan and the National Optical Astronomy Observatories (Noao) – and the other is Brazil, which invested US$ 12 million in the venture. The National Council for Scientific and Technological Development (CNPq) went in with US$ 10 million and FAPESP with US$ 2 million.

Privileged access
The amount allocated to Soar afforded the Brazilians scientific access to 30% of the telescope’s schedule of use, the largest slice amongst those participating in the enterprise. Something like 127 nights of observation a year. In no other first class astrophysical enterprise does Brazil have so much time. Along with six nations, Brazil, for example, is part of the Gemini consortium, which boasts two 8.1 meter telescopes, larger than Soar’s, one in Chile and the other in Hawaii. But Brazil only has Gemini’s equipment at its disposal for less than 3% of its time in use. “Amongst the major infrastructures recently created for Brazilian science, Soar and the National Synchrotron Light Laboratory (in Campinas) are those of the greatest importance”, explains astrophysicist João Evangelista Steiner, from the University of São Paulo (USP), who is the president of the consortium and of Soar’s board of directors. “This telescope will be the most valuable tool for Brazilian astronomy”, comments Albert Bruch, the director of the National Astrophysics Laboratory (LNA), in Itajubá, Minas Gerais.

Strictly speaking, the use of the verb in the future tense is justified. In spite of already being capable of producing spectacular results, such as the first-hand detection of the oldest explosion of gamma rays, outwitting telescopes from all over the world, Soar is currently working at half-mast. Its largest contribution to (Brazilian) science is still to come. Today, the greater part of the operating time of its equipment is taken up by engineering adjustments. A fraction of the hours of work is dedicated to getting data for scientific projects. After being inaugurated, every telescope passes through this stage of tests and refinement, in which the time aimed at scientific research increases gradually, as the engineering problems are resolved. If there are not delays in its timetable, the Brazilian-American telescope will be fully operational in the second half of 2006.

The observations made by Soar’s mirrors serve varied line of astronomic research pursued by Brazilians. For the time being, the findings are not so spectacular as the snapshot of a gamma ray explosion because of the collapse of a supermassive star. Nonetheless, they are not uninteresting. At the beginning of July, for example, at the request of Enos Picazzio, of the Astronomy, Geophysics and Atmospheric Sciences Institute of the University of São Paulo (IAG-USP), the telescope captured images of the Tempel 1 comet, a mass of ice, rock and dust, with an estimated age of 4.6 billion years, which passed by at a distance of 133 million kilometers from the Earth. The records were made before and after this celestial body being hit by a projectile launched by the American spacecraft Deep Impact. “We were able to see that before the collision the comet had a structure with four active zones (jets of gases), and after the crash it showed only three”, comments Picazzio, who also sighted Tempel 1 from the Pico dos Dias Observatory, where there is the largest telescope at work on Brazilian soil. Located at an altitude of 1,860 meters in Brasópolis, Minas Gerais, where the sky is not as limpid and cloudless as in the Andes, Pico dos Dias has a main telescope of 1.6 meters in diameter, modest if compared with Soar.

The apex of a mission that cost NASA U$ 333 million, the moment of the crash between Tempel 1 and the projectile fired by the Deep Impact probe, occurred, as had been programmed, on the night of July 4, not by chance the national date of the United States. The collision, though, could not be seen by telescopes located outside North America. Even so, the passing of the comet, which travels through space at 37 thousand kilometers an hour, was a good chance for testing Soar in the work of observing an object moving at a speed apparently far higher than stars and galaxies (sidereal movement). It was the first time that the telescope was used to pursue a target with non-sidereal movement. “With Soar, we can also see comets of a high apparent magnitude and with little brilliance”, says Picazzio. “We have many more opportunities for observation.” To the naked eye, an observer from the Earth, on a day with excellent conditions for observation, manages to see at the most stars or planets that have a brilliance equivalent to magnitude 6. With Soar, it is possible to produce images of celestial objects of magnitude 26. The larger the magnitude of a star, the smaller the quantity of light that reaches our planet, emanating from this body.

Pulsating white dwarfs
Another line of research in which Soar is already proving to be very useful is the study of a rare kind of astronomic object, the ZZ Cetis, also called variable or pulsating white dwarfs, which can be looked on as fossils of stars that, in the remote past, were exuberant. In an article to be printed in the December issue of the Astronomy&Astrophysics scientific magazine, the team of researcher Kepler de Souza Oliveira Filho, from the Federal University of Rio Grande do Sul (UFRGS), reports the discovery of 14 new pulsating white dwarfs with the assistance of the Brazilian-American telescope located in the Chilean Andes. In another work, not yet published, Barbara Castanheira, a pupil of Kepler who is studying for a doctorate, identified, with Soar’s mirrors, another three ZZ Cetis (and seven more with the Pico dos Dias telescope, in Brasópolis). They are considerable figures, even more so when one takes into account that up until now about a hundred pulsating white dwarfs are known.

But exactly what is this kind of sidereal object? In the twilight of their existence, when they cease to produce the thermonuclear reaction that supply them with energy, small or median stars, with little mass, more or less like the Sun, shrink in size and become dense and colder bodies. They become white dwarfs. The final destination of 98% of the stars is, one day, to be transformed into a senile star with this stunted profile. If, during the process of contracting and losing heat, a white dwarf shows periodic instabilities – in other words, emits pulsations at fixed intervals, which alter its brilliance -, it is classified as a ZZ Cetis. To capture these tenuous changes in luminosity, astrophysicists take a series of photos of stars that are candidates for being pulsating white dwarfs. “These variations are the only clues we have about the internal composition of the stars”, explains Kepler, who this year is living in Chile, where he is one of the astronomers responsible for the operation of Soar. “In the same way that waves from earthquakes are analyzed to study the interior of the Earth, we can use the variations of the white dwarfs to measure their interior.”

Ancient and remote gamma ray explosions, swift comets that cross the orbit of the Earth, the changeable and weak pulses from variable white dwarfs – these and other phenomena of the Cosmos are now more in the reach of Brazilian researchers with the privileged access that the country has to Soar, a telescope of the first water. Albeit small, the participation in other major international projects is also important, without a doubt, as well as the maintenance of more modest equipment installed in the national territory. But nothing compares with being a partner in Soar. “We can, in fact, play in the first division of the astrophysics championship”, says Steiner. “And score goals, showing that we can do frontier science.” As Eduardo Cypriano and Elysandra Figueredo did.