At its meeting in Paris on November 28, the Science Programme Committee of the European Space Agency ESA opted for two topics in which the Max Planck Institutes for Extraterrestrial Physics and for Gravitational Physics are closely involved: “The hot and energetic universe” and “The gravitational universe” with the projects Athena and eLISA.
How did ordinary matter transform into the large-scale structures we see today? How do black holes grow and how have they shaped the universe? These questions are some of the most important unresolved issues of modern astrophysics, and the next large ESA mission could provide the necessary answers.
“We are delighted that ESA has selected the hot and energetic universe as one of its main goals for the mission,” says Kirpal Nandra, Director at the Max Planck Institute for Extraterrestrial Physics. Nandra heads an international collaboration which proposed the topic. “But our work is by no means finished. We now have to work on defining an X-ray telescope which can provide us with the answers we are looking for.”
The dominant form of ordinary matter in the universe is hot gas; it gives rise to the galaxy clusters, for example, the largest coherent structures that we know today. At temperatures of more than ten million degrees, the gas emits especially strongly in the X-ray range. An X-ray observatory in space with high sensitivity, good spectral resolution and a wide field of view is thus the key to understanding how these structures form and evolve.
The Advanced Telescope for High-Energy Astrophysics (Athena) was designed especially for this purpose. Such a telescope would enable astronomers to undertake spectroscopic observations of distant galaxies and measure the physical parameters of the largest bound objects. This information would greatly advance our understanding of how the structures formed from hot gas when the universe was in its infancy.
Now that ESA has set the scientific topic, the next step is to look for an X-ray observatory which can achieve these goals. Since the Athena team proposed this topic and already has the requisite technologies, the scientists are confident that their mission will succeed.
As soon as a mission concept has been selected, the technology development should be consolidated over a period of three to four years. It will then probably take another ten years to complete the observatory. From 2028 onwards, Athena could then observe the hot and energetic universe with an accuracy not yet achieved and find an answer to the fundamental question of why our universe looks the way we observe it today.
The European Space Agency has selected “The gravitational universe” as the second mission concept. eLISA was proposed as the mission. This evolved Laser Interferometer Space Antenna is different from any other space observatory, as its mission is to explore space in a new and unique way: eLISA will measure gravitational waves and thus be able to hear high-energy events from all corners of the universe.
The space-based observation of gravitational waves will enable fundamental astrophysical questions to be answered about how the universe evolved directly after the Big Bang, as well as the physics and the evolution during later stages. eLISA is to be launched into space as the third large L-class mission after Juice and Athena.
“We are delighted by this decision. It offers us revolutionary research possibilities,” says Karsten Danzmann, nominated speaker of the eLISA mission, Director at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute / AEI) and professor at Leibniz Universität Hannover. The team will make an immediate start on further optimising the technologies already developed for eLISA. “We will test these key technologies in space as early as 2015 during ESA’s LISA Pathfinder mission,” adds Danzmann.
The observation of gravitational waves will deliver important findings that will give us a better understanding of the General Theory of Relativity. Albert Einstein was the first to predict the existence of gravitational waves back in 1916. With a gravitational wave observatory in space, the scientists will now also observe the early universe, which is inaccessible to other astronomical methods.
In the process, they will hear gravitational waves which originate from early black holes, thousands of binary star systems and maybe even from the Big Bang itself. ELISA could even investigate the mysterious dark energy.
The proposed mission will supplement the existing and planned ground-based gravitational wave observatories. These detectors are searching for tiny undulations in the structure of space-time caused by the most powerful cosmic events in space, such as the merger of black holes. Gravitational waves transport information about their origin and the nature of gravitation, which cannot be detected with other astronomical observation methods.