Brazilian researchers hope improvements to the Mario Schenberg detector and creative participation by North America’s aLIGO will launch Brazil into the age of gravitational astronomy
A new window on the Universe
March 13, 2013
By José Tadeu Arantes
To open this window, the project, coordinated by Odylio Denys de Aguiar, a full researcher at the National Institute for Space Research (INPE) and collaborative researcher at the Universidade de São Paulo (USP), needs two key components: Brazil’s Mario Schenberg gravitational wave detector and participation of the North American Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO).
The Mario Schenberg detector’s main component is a copper-aluminum sphere that weighs more than a tonne and is cooled by liquid helium to a few hundredths of a degree above absolute zero. At this temperature, nearly all molecular motion ceases, making it possible to observe very weak gravitational waves without unwanted interference from “thermal noise”.
aLIGO (which stands for advanced LIGO project) is basically a laser interferometer that detects gravitational waves through the relative oscillating movement it provokes in mirrors located four kilometers apart.
The advent of radio astronomy in the 1930s allowed the discovery of objects that had escaped conventional optical observation for thousands of years (with the bare eye or through telescopes), and later studies led to extraordinary leaps in data collection by accessing cosmic sources emitting radiation in bands of the electromagnetic spectrum beyond radio and visible light (microwaves, infrared, ultraviolet, x-rays and gamma rays). Today’s study has an even more ambitious goal: to go beyond the electromagnetic standard and study the Universe in a new way, through gravitational interaction.
“In many natural events, some or all of the electromagnetic waves produced can’t pass through layers of matter or overcome intense force fields and reach us. This happens in supernova explosions, in shocks from ultra-dense objects such as black holes and neutron stars and in phenomena related to the primordial universe,” Aguiar told Agência FAPESP.
“In contrast, because gravitational waves have very weak interaction with matter, they can pass through high concentrations of matter (with densities similar to those of atomic nuclei, for example) without being absorbed,” continued the researcher.
This is why gravitational astronomy could radically expand the possibilities for scientific research. Phenomena that have always eluded electromagnetic detection could be observed by means of gravitational detection.
In the investigation of the primordial cosmos, the goal is nothing less than to begin at the point when the Universe was only 300,000 years old and regress to the first infinitesimal fraction of a second after the Big Bang: in other words, to “see” the Universe in the very instant that it was born.
The fundamentals of the experiment
To understand how the window can be opened, we should consider the ABCs of the physics involved in the experiments. Just like electromagnetic interaction, gravitational interaction can be represented by a wave that travels through space at the speed of light. And like any wave, the size of gravitational waves is described in wavelengths (the distance between two consecutive peaks) and amplitude (the distance between the peak and the wave’s median line).
“The peculiarity of a gravitational wave is that it is very long longitudinally and incredibly small transversely,” said Aguiar. It can be said that it has enormous wavelength and minuscule amplitude.
“At a frequency of 100 hertz (100 Hz, or 100 cycles per second), the wavelength reaches 3,000 kilometers. And because the wave travels at the speed of light (300,000 kilometers per second), it covers this distance, completing a cycle, in only one hundredth of a second,” explained the researcher.
“The amplitude, however, is so small that even a ‘tsunami’ of gravitational waves would measure less than the diameter of a proton transversely,” said Aguiar.
The effect that a gravitational wave would produce, however, is exactly in the transverse direction of its movement. The assumption is that, as it passes through a solid body, a gravitational wave causes transverse movements in the atoms that compose the body, and the wave transfers part of its energy to the body.
“As these movements are very small, perceiving the effects of a gravitational wave is a huge challenge. In the resonant mass technique (used at Mario Schenberg), the objective is to detect the oscillation provoked by the wave in the crystalline structure of the sphere. Once the oscillation has been produced, it can be picked up by a very sensitive transducer,” explained Aguiar.
“In the alternative technique, using an interferometry laser like that used in the North American aLIGO project with which we’re collaborating, the assumption is that as the wave passes it produces a relative oscillation in the mirrors, which can be perceived through the interference phenomenon,” he added.
Initiated in 2007 and expected to end this year, the Thematic Project “New Physics from Space: Gravitational Waves” is the continuation of another Thematic Project that lasted from 2000 to 2007 and resulted in the construction of the Mario Schenberg detector. The researchers are now working on improvements to the antenna to achieve a sensitivity similar to that in detectors already operating in other countries.
“The results up to this point were engineering improvements such as ultra-low-phase noise oscillators. At the same time, we are working to develop vibrational isolation subsystems for the Advanced LIGO, one of our contributions to the North American project,” explained Aguiar.
In the words of the researcher, “There is still much ground to cover before the Brazilian detector will be able to detect a gravitational wave.”
The North American detector is already at a much more advanced stage. “The aLIGO is fortunate enough to have a budget 600 times larger than the Mario Schenberg has. And while the Brazilian team has about 30 researchers, many of whom contribute to the project in a purely theoretical manner, the multinational team behind aLIGO has nearly 1,000 researchers,” said Aguiar.
With aLIGO, which will enter commissioned operation in 2014, gravitational astronomy may become as effective a discipline as electromagnetic astronomy, being able not only to detect a signal but also to identify the “signature” printed on it by its source of emission.
With a projected sensitivity to wave amplitude ten times greater than the previous version (LIGO), when aLIGO is operational in “scientific mode” it will be able to observe a volume of the Universe that is approximately 10,000 times larger than the Earth. It will therefore increase the rate of occurrence for astronomical events by the same factor. An event that would take 50 years to be detected by LIGO could be detected in less than a month by aLIGO.
“The contribution the Mario Schenberg detector will be able to make is in determining the wave’s direction (where it comes from) and its polarization (the wave’s orientation in space), which can tell us much about what is happening at the source of emission,” said Aguiar.
“All this will be done using a technique different from interferometry, meaning based on another physical detection principle (absorption of wave energy), which can add to our knowledge of gravitational waves,” he said.
According to Aguiar, there is a lack of students to develop the experimental study. “We need as many students as possible so we can do the work more quickly,” he said—an invitation that calls out to young scientists hoping to play a part in unraveling the great mysteries of the Universe.