Brazil will participate in largest gamma-ray astronomy observatory

Researchers from USP, UFSCar and other institutions develop film for mirrors and metal structures that will support the 100 telescopes in the Cherenkov Telescope Array.

By Elton Alisson

Agência FAPESP –  A group of some 1,000 researchers from 28 nations, including ten Brazilians, are working to build the world’s largest observatory dedicated to the study of celestial bodies that emit gamma rays—the radiation with the highest energy—by 2015. 

 

Called the Cherenkov Telescope Array (CTA), the observatory will be installed at two different locations—one in the Southern Hemisphere and the other in the Northern Hemisphere. 

 

Chile, Argentina and Namibia are potential sites for the experiment. In the Northern Hemisphere, the United States and Spain have already shown interest. The sites will be chosen by the end of 2013.

 

The observatory will have 100 land-based gamma-ray telescopes equally distributed between the two hemispheres. The instruments will operate together, aimed at observing single bodies, such as supernova remnants, active galactic nuclei and quasars that emit gamma rays. With the observatory, studies on these celestial bodies will become much more precise than they are today. 

 

“The only gamma-ray astronomy observatory functioning today—the Hess [High Energy Stereoscopic System] Observatory in Namibia—has five telescopes working together. The CTA will be able to measure gamma rays produced by astrophysical phenomena with ten times greater sensitivity,” Luiz Vitor de Souza Filho, professor at the Universidade de São Paulo’s São Carlos Physics Institute (IFSC-USP), and one of the Brazilian researchers participating in the project, told Agência FAPESP.

 

According to Souza Filho, the Brazilian researchers are greatly interested in the type of astrophysics the CTA will study, which connects traditional astrophysics with particle (or cosmic ray) astrophysics. 

 

The experiment will make it possible to increase understanding about how this radiation is emitted, how the particles propagate themselves and can be detected and how the celestial bodies that emit gamma rays, with charges between 10 GeV and 100 TeV, are formed, among other questions. Aside from producing knowledge, the Brazilian scientists also intend to contribute to the construction of the CTA instruments. 

 

“It is nearly mandatory that a member nation wanting to have access to the data generated by the experiment along with the other members contribute to its construction. For this reason, we are developing two projects for the instruments at CTA,” said Souza Filho. 

 

Carried out through FAPESP funding, one of the projects is to develop the film for the mirrors that will cover the telescopes. This film will reflect light and at the same time protect the equipment from bad weather. 

 

Because they will be exposed to the atmosphere, the reflective film for the telescopes will have to be highly durable and well made so as not to come loose from the glass and affect the reflective and protective properties of the mirror.

 

To ensure that this does not happen, a group of researchers from the IFSC under the coordination of Souza Filho is investigating aluminizing and application techniques for the reflective and protective surfaces of the CTA telescope mirrors together with the company Opto Eletrônica. 

 

“The mirrors won’t need to be as precise as those in the optical telescopes installed in the observatories in Chile operated by the European Southern Observatory (ESO), but they will have to be much more durable,” explained Souza Filho. 

 

Another CTA equipment project in which the Brazilian researchers are participating is the development of metal structures to support the telescopes. 

 

Approximately 16 meters long, these structures must support a group of electronic instruments weighing 2.5 tons at their extremities, and they cannot flex more than 20 millimeters without harming the images produced by the telescopes. 

 

In a project carried out together with the company Orbital Engenharia in São José dos Campos, located in upstate São Paulo, the researchers designed a structure that was approved by the international collaboration building the CTA. Orbital has received FAPESP Innovative Research in Small Businesses grants (PIPE) for a number of projects. 

 

“We already had the know-how for building this type of equipment because we already developed similar technology for the Pierre Auger Observatory in Argentina,” said Souza Filho. 

 

The IFSC researchers are currently developing the prototypes for the reflective film for the mirrors and the mechanical structure for the telescopes, which should be completed in 2013 so the CTA construction can begin in 2013 for operation in 2015. 

 

Aside from the IFSC group, researchers from the Universidade Federal de São Carlos Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG- UFSCar), the Centro Brasileiro de Pesquisas Físicas (CBPF) [The Brazilian Center for Physics Research] and the Universidade Federal do Rio de Janeiro (UFRJ) are also participating in the construction. 

Broad scope of research

 

According to Souza Filho, the CTA’s scope of research will be quite broad. In the field of astrophysics, topics that may be explored at the new observatory include black holes and star-forming regions. 

 

In the field of particle physics, it will be possible to carry out studies on Lorentz covariance violation—a very specific restricted relativity test. “With this observatory, we will be able to carry out the most restricted relativity test performed to date over long distances and at a long scale,” projected Souza Filho.

 

In addition, the observatory is expected to search regions that are candidates for having concentrations of dark matter and to identify new extraterrestrial sources of high-energy gamma rays. Today, approximately 100 sources are known. This number is expected to multiply with the CTA.

 

“The new observatory has an impressive scientific scope and a double function. While it will be possible to study the most important questions in astrophysics, the experiment will also increase knowledge of elementary particle physics,” evaluated Souza Filho. 

 

For the observatory site selection process, a call for proposals was made defining the minimal conditions needed to host the experiment. These conditions require that the region must have a clean atmosphere, be at least 2,000 meters above sea level, have no light contamination and have minimum cloud and rain formation. There are no regions in Brazil with these characteristics.