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astrophysics

The new sun flashes

A telescope captures signals that seem to precede large explosions

The solar telescope for sub millimeter waves (SST), which has been working for almost two years at the astronomy complex “El Leoncito” (Casleo), in the Argentinean Andes seems to have captured “the light” which justifies its existence. The telescope is an international project conceived and coordinated by Brazilians its the antennae of 1.5 meters in diameter, which operates in the high frequencies of 212 and 405 GHz (gigahertz, a unit that is equivalent to a billion Hertz or cycles per second), in the upper end of the infra-red waveband, has collected evidence of the existence of a form of emission never before verified. They are extremely fast pulses or flashes, coming from a region with solar sunspots and perceivable only by radio telescopes that work on this band of the electromagnetic spectrum. With a duration of milliseconds, this new impulse seems to provide a good clue about the production of energy during solar activity, a process that still little understood.

The emission at these frequencies could be associated with micro brilliances – waves or seismic disturbances in the active regions of the sun. “It is as if these flashes were a type of forewarning of the explosions that are about to occur on the sunspots. These discrete emissions do not have a periodicity, but their occurrence increases dramatically moments before an eruption happens.” says Dr. Pierre Kaufmann, Director of the Center of Radio Astronomy and Space Applications (Craae), of the consortium which operates the SST – formed by researchers from the Presbyterian University of Mackenzie (UPM), of the National Space Research Institute (Inpe) and of the universities of São Paulo (USP) and of Campinas (Unicamp).

The discovery of these emissions, first identified on 22nd of March 2000 during a large solar explosion, was described in the issue of last February the 10th of the North American magazine The Astrophysical Journal. Signed by Dr. Kaufmann, a professor with the UPM, and other Brazilian scientists, the paper had as its coauthors researchers at Casleo, of the Institute of Astronomy and Space Physics of Buenos Aires and of the Max Planck Institute for Extraterrestrial Physics, in Germany.

Pulses from an active area
The six channels of SST, four operate at 212 GHz and two at 405 GHz, registered on that day 1,300 pulses coming from an active region, a system of sun spots, and therefore an area that is subject to explosions and catalogued by the NOAA (American National Oceanic e Atmospheric Administration) as 8910. The channels that had focused on the areas closest to the sun spots, captured more clearly the pulses. Those set towards more distant points had registered discretely the emissions.

To demonstrate that there had not been any error in the interpretation, Dr. Kaufmann’s team compared the emissions originating from the active area with measurements taken on a central and calm point of the sun, without sun spots, and in a limbo zone, which is a less brilliant and further away area from the center of the star. The two comparisons made it clear that the antennae of the SST radio telescope had captured pulses coming from the sun spots, and not simply interference.

Convinced that they had discovered a new type of solar emission, Dr. Kaufmann began to investigate if there had been a further register of explosions in the active areas associated with region 8910 on that day. There had been. Data from two satellites, Sotho (maintained by the space agencies of Europe and the United States) and Trace (North American), showed traces of large movements of energy in that area starting at 17:00 GMT (2 PM in Brasilia). Everything fitted together. The images on the ultraviolet frequency of Trace showed the formation of a large alteration in the magnetic structure of the sunspots in that region. The magnetic structure was shaped like an arc above the region. The image from Soho, obtained in white light, corroborated the ejection of material on the solar corona, the most external part of the star, an event involving a large amount of energy caused by an explosion in the active area 8910. “The sub millimetric pulses could be of great value for us in investigating the instability of plasmas (very hot ionized gases) close to the surface of the sun, that in some manner are linked to the launching of mass from the corona into interplanetary space.” explains Dr. Kaufmann.

The distance
The sun gives off varied electromagnetic radiation, from radio waves to gamma and x-rays, passing through microwaves, visible light and ultraviolet radiation. On some frequencies there is no proof of the existence of solar pulses. This was the case of the region of the distant infrared in which the SST is working. As it happens with almost all of the celestial bodies, the exploration of this immense source of cosmic energy is carried out from a distance, through satellites, unmanned space flights, and space and earth telescopes. A gap in the solar activity observation was filled in May 1999, with the kickoff of operation of SST, the first and only radio telescope of the world projected to work at the high frequencies of 212 and 405 GHz. Its construction took seven years and cost US$ 1 million, a little more than two thirds of it funded by FAPESP, which also finances close to half of the current project of US$ 300,00.00.

Two reasons explain the character of the vanguard of the project, evaluated and accompanied by international advisors. The first is the conception, using the most modern artifacts for observation, some custom-made. The antennae and its protective dome cover came from the United States, the receptors from Germany and the precision direction finder from Israel. The telescope was tested in Switzerland by the Institute of Applied Physics of the Bern University, one of the partners of the project, and, after installation, by the team from Casleo. This cutting edge technology has permitted SST to pick up extremely fast pulses with duration of up to 1 millisecond.

Another peculiarity is the privileged location. In El Leoncito, there is a clear sky for close to 300 days per year and the humidity of the air is very low, close to 5%, two conditions that favor the observations of pulses in the far infra-red. “The SST is on a frontier area of science, where there are chances and risks. However, its potential for discoveries, expected and unexpected, is stimulating.” evaluates Dr. Kaufmann.

Close to 30 years ago, using adapted equipment, British and North American researchers believed that they had captured sub millimetric emissions. However, at that time, without the precision of today’s instruments, they were not able to prove the existence of the emissions that the equipment of Dr. Kaufmann is examining in more detail. After all, the moment for the observations of the pulses related to solar explosions is excellent.

Weak and intense
Since the nineteenth century, it has been known that solar activity obeys a fixed pattern, which changes its intensity every 11 years. It alternates between periods of relative calm (the minimum of the solar cycle, without spots or explosions) to periods of intense activity (the maximum of the solar cycle, with spots and frequent explosions). At this moment, the star which shines on us is at the peak of an intense cycle, marked by large formations of sun spots that create dark points on the surface, and constant eruptions and explosions, with the liberation of enormous quantities of energy. The researchers know that the present cycle has just entered its most acute point (solar maximum). That means that the next few years will be, in theory, excellent for observing events related to solar explosions and for proving once and for all the new form of emission detected by the SST.

With modern equipment, well located and years of strong solar intensity to look forward to, the radio telescope will however, have to tackle an administrative problem. There is a lack of personnel to constantly operate it at El Leoncito, a location of difficult access in the Andes, which means that the equipment remains shut down for the greater part of the time. Since it began operating two years ago, it has only been in operation for about 80 days, as a result of missions of short duration, one to two weeks every two months.

Star mysteries
A gaseous sphere with a much more dense nucleus, formed 5 billion years ago, almost all of what you say about the Sun, is huge. Owner of 99.8% of the mass of the solar system, weighing 330,000 times more than the Earth, along its diameter of 1.3 million kilometers we could hang somewhat like 110 planets the size of ours. Why study the activity of the Sun? Besides its importance as the star that provides heat and light to the Earth and provided the first conditions for life to flourish on the planet, there are other reasons. The activity of this incandescent body – a series of sporadic events such as explosions, and everlasting events, such as solar wind which is a permanent river of particles electronically charging, leaving the star towards space – could effect our system of telecommunications and the energy networks on Earth and also knock down satellites.

The conquest of the Sun is clearly impossible. Its distance of 150 million kilometers, is 400 times greater than to the Moon. The solar corona, the most external layer of its atmosphere, a type of gaseous mantle that wraps the star, has an average temperature of 1.1 million degrees Celsius (°C). This external layer, and not yet known why, is hotter than the surface itself, which has temperatures of the order of 5000°C. At the center the mystery is even greater. Here there are nuclear fusion reactions of hydrogen, which correspond to 75% of the composition of the star, and the temperature rises up to 14 million degrees. Also, like most of the universe, the sun is not a solid body. It is a mass of plasma, gases heated to such a point that their particles turn themselves electrically charged, in the form of protons (positive charge) and electrons (negative charge).

The Project
Application of a Solar Telescope for Sub Millimetric Waves (SST) (nº 99/06126-7); Modality Thematic project; Coordinator Dr. Pierre Kaufmann – Presbyterian University of Mackenzie; Investment R$ 137,496.00 and US$ 83,061.06

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