At the center of our galaxy, and probably all the others, there are objects that are easier to name than to imagine. Supermassive black holes have millions or even billions of times the mass of the Sun, which in turn is equivalent to 330,000 Earths. Ours, that of the Milky Way, is relatively close, at 27,000 light years, and has as much mass as four million suns.
These objects, very different from the black holes that form when large stars run out of fuel and that only reach tens of solar masses, hold the key to the evolution of galaxies and the universe. It is known that there is a correlation between the size of a galaxy and the black hole that inhabits it and also that the stars in the confines of a galaxy move faster the larger the central black hole, despite being outside its “jurisdiction”. ” gravitational.
A decade from now, the European Space Agency (ESA) wants to focus two of its main science missions on these gargantuan objects to unravel their mysteries. The first of them, Athena (from the acronym in English for Advanced Telescope for High Energy Astrophysics), is the largest X-ray telescope built to date and its launch was scheduled for 2031. It is designed to capture the hottest and most energetic phenomena of the cosmos with precision unpublished and collect information to answer two fundamental questions. One has to do with the evolution of black holes at the center of galaxies. The other is how ordinary matter, from which stars or human beings are made, intertwines with much more abundant but invisible dark matter to form the fabric of which the cosmos is made.
ESA’s second major scientific mission for the coming decade is LISA (Laser Interferometer Space Antenna), a constellation of three satellites with an unprecedented disposition to observe gravitational waves, a phenomenon theorized by Einstein more than a century, but it wasn’t first observed until 2016. When two extremely powerful objects collide, like black holes at the center of two merging galaxies, the space-time fabric of the cosmos shakes like a pond. a stone is thrown. Like ripples in water, they fade with distance and when the echo of these phenomena reaches the vicinity of our planet, they are almost imperceptible and on the earth’s surface they are buried in a large number of signals of all kinds.
On Earth, experiments such as Virgo and LIGO have detected the gravitational waves produced by the merger of relatively small black holes, with only tens of times the mass of the Sun. LISA will be able to study very low-frequency gravitational waves, such as those released by black holes supermassive blacks upon meeting. To achieve this, its satellites will be placed in space, far away from disturbances on the earth’s surface, in the formation of an equilateral triangle, separated by 2.5 million kilometers. Like buoys, three free-falling sensors linked by lasers will detect tiny ripples in the fabric of spacetime, smaller than the diameter of an atom.
The launch of LISA was planned for 2034 because, given the complexity of this type of mission, the ESA usually separates them by at least five years. However, the agency’s science leaders saw an opportunity to multiply the value of the observations of Athena and LISA putting them to study the same phenomena with different meanings. As if the first put the sight and the second the touch, the study of the merger of black holes through their X-ray and gravitational wave emissions would offer a much more complete view of the phenomenon.
In order to advance the launch of the gravitational wave observatory, it was necessary to increase the budget dedicated by the ESA member countries to their space science program. That happened at the end of November in Seville, at the meeting of the ministers responsible for space activities of the European countries. For the first time in 25 years there was a significant increase in this item, which reached 1,671 million euros for the next five years. With the new planning, LISA would depart in 2032, just one year after Athena.
The X-ray telescope will carry out measurements on hundreds of thousands of black holes, some close and others further away, but it is precisely the most remote ones, those that formed in the first hundreds of millions of years of the universe, which are of interest to those responsible of the mission. Understanding how these objects, which are a kind of engine of the galaxies, were formed, will also help to understand the evolution of the universe and, ultimately, to better understand the history that one day allowed our appearance on Earth. In combination with LISA, it will also try to understand why some of these galactic monsters become active and begin to engulf the matter around them, shooting intense radiation into space and turning the interiors of their galaxies into active nuclei. The Milky Way, for example, is, at least for now, a sleeping galaxy, but it doesn’t have to be forever.
This joint work between two such different observatories will not be easy. This week in the magazine Nature Astronomy, three researchers from the University of Birmingham (United Kingdom) spoke of the challenges, among others that, as befits a frontier science project, many things are unknown about the physical processes to be analysed. In the collaboration, LISA would first detect a phenomenon such as a merger of two black holes and then arrive Athena to analyze ultra-energetic emissions from the clash of giants. “One of the challenges for Athena will be to identify the true event of gravitational waves [que detectó LISA] among hundreds of candidates in your field of vision”, write the authors of the article. Although they warn about the difficulties of joint observation, they recognize that the opportunity to make new discoveries and observations that transform our vision of the universe is enormous.