But on Friday (12 December), an international group of astronomers claimed analysis of data returned from the European Space Agency's (Esa) XMM-Newton satellite observatory casts doubt on the existence of dark energy.
Now Guido Risaliti of the Harvard-Smithsonian Center for Astrophysics and colleagues have looked at markedly higher energies - less subject to absorption in those gas layers - using Europe's XMM-Newton telescope and the recently launched Nustar telescope.