2024-02-25 07:00:17
The year 2024 promises to be exciting for the exploration of black holes: putting the satellite into orbit Einstein Probe last January promises to enrich our understanding of these objects thanks to innovative X-ray detection technologies. This summer, it will be joined 600 km above our heads by the satellite ALL (Space-based Multiband Astronomical Variable Objects Monitor). These two missions, the fruit of Sino-European collaborations, will notably devote themselves to the study of “cosmic cataclysms”, often brief events which release large quantities of energy. energy, but which also provide valuable information on black holes.
ATG/ESA, CC BY-SA
Each galaxy harbors at its heart a supermassive black hole concentrating millions of times the mass of the Sun in a region of size comparable to that of the solar system (The solar system is a planetary system composed of a star, the…). How do these black holes form? How do they devour the matter that gravitates in their vicinity? How are they able to eject some of this matter at speeds approaching that of light? These fascinating questions remain enigmas for astrophysicists because the study of black holes is made complex by the simple fact that they do not emit light.
To understand them better, you have to be on the lookout, because the opportunities are rare. The perfect moment comes when they spring into action, engulfing the matter orbiting in their vicinity. The heated gas then emits light, particularly in the field of X-rays, which are absorbed by the earth’s atmosphere and therefore cannot be observed from the ground. This radiation (Radiation, synonymous with radiation in physics, refers to the process of emission or…)sometimes emitted over brief periods of time, is however observable by observatories placed in earth orbit (An Earth orbit is an orbit around the Earth. The Moon, the only satellite…)outside ofatmosphère (The word atmosphere can have several meanings 🙂such as the Einstein Probe and SVOM satellites.
Einstein Probe: lobster eyes in orbit
Led by a collaboration ofAcademy of Sciences (A science academy is a learned society whose role is to promote research…) Chinese, from Max Planck Institute for Extraterrestrial Physics in Germany,European Space Agency (The European Space Agency (ESA) is…) and CNES, thespace agency (A space agency is a state body whose aim is to study Space and develop…) French company, Einstein Probe has two X-ray telescopes on board. One of the two, the Wide Field X-ray Telescope (WXT) is a new generation instrument whose optical design imitates the eyes of the lobster. The latter are in fact made up of small hexagonal structures, the ommatidia, which are responsible for directing light onto the photosensitive cells of the eye.
Microscopic view of lobster eyes. We can see the microscopic pores (ommatidia) arranged on a sphere which reflect the light and direct it towards the retina.
Jordan Camp/Wikimedia Commons
Similarly, the WXT’s optics consist of microscopic channels arranged in a spherical configuration, which focus light onto the detectors while providing a much larger field of view than traditional optical configurations. In this way, the WXT will be able to scan the entire night sky in just under 5 hours, thus allowing the search for new cosmic sources of X-rays.
The ommatidia reflect light rays towards the center of the sphere. Inspired by this mechanism, the WXT optics are equipped with microscopic channels which focus the light on the detectors while offering an unprecedented field of view.
Alexis Coleiro, Provided by the author
One of the main challenges of the Einstein Probe mission will be the observation of supermassive black holes caught in the middle of a feast. The WXT will in fact scan the sky in search of light bursts associated with the passage of a star a little too close to a black hole. By approaching it, it finds itself dislocated, forming an accretion disk, part of the mass of which will then be swallowed by the black hole (The Black Hole is a science fiction film directed by Gary Nelson,…) centrally located. By observing this copious meal and comparing the data obtained to theoretical models, astrophysicists can estimate the mass of the black hole and thus explore the innermost regions of galaxies, theaters of these cosmic tragedies.
Theoretically described in the 1970s, such an event, called a “tidal rupture event”, was first observed in the early 2000s. Since then, around a hundred similar events have been observed, revealing an astonishing variety of characteristics. Einstein Probe will continue this cosmic harvest which will allow us to identify supermassive black holes which are generally so discreet and thus draw up an inventory of their distribution according to their mass, which is still largely unknown.
Under the effect of the intense gravitational pull of a black hole, a star in the surrounding area can be torn apart, releasing large quantities of energy in the process.
NRAO/AUI/NSF/NASA
The end of life of the most massive stars
The Einstein Probe mission will study not only supermassive black holes, but also stellar black holes formed when the most massive stars die. When such a star reaches the end of its life, the nuclear reactions in its core having ceased, the innermost parts of the star collapse on themselves under the effect of their own gravity, creating a déflagration (A deflagration is the set of phenomena resulting from rapid passage…) accompanied by very intense radiation. This is what we call a supernova which leaves behind an extremely dense object: a neutron star or a black hole of stellar mass. The collection of the first photons escaping when thewhere to shock (A shock wave is a type of wave, mechanical or of another nature, associated with…) reaches the surface of the star is essential because their properties provide us with valuable information about the star which has just gone out. The WXT, thanks to its unique field of view, will be an ideal instrument for searching for these signals.
But the story doesn’t end there. Some supernovae are also accompanied by brief bursts of gamma rays so intense that they constitute the most energetic phenomenon observed today in the Universe, delivering a luminosity equivalent to that of hundreds of millions of billions of Suns. These phenomena, called gamma bursts, are produced when a star collapses into a black hole. Jets of matter propagating at speeds close to that of light are then emitted on either side of the star. To detect gamma-ray bursts, perfect alignment with these very narrow jets is therefore necessary, like seeing the light of a lighthouse.
SVOM, in search of gamma bursts
The main objective of the SVOM satellite which will be put into orbit this summer is precisely the detection of gamma-ray bursts. Four instruments will be installed on board including the télescope ECLAIRs designed by French researchers and engineers from the Research Institute in astrophysics (Astrophysics (from the Greek astro = star and physiqui = physics) is a branch…) et planetology (Planetology is the science of the study of the planets. The discipline covers many…) (IRAP), the CEA, the Astroparticle and Cosmology laboratory (APC) and the CNES to detect gamma photons. In this energy range and in order to cover a wide field of view, it is not possible to use mirrors to focus the light because the photons would pass through it without being reflected. The ECLAIRs instrument will therefore use a coded mask imaging technique which uses the principle of the camera’s dark room: a small hole drilled in a box opaque to light makes it possible to form an image on the opposite side of the box. A coded mask telescope works quite similarly.
However, as the hole through which the light rays pass is tiny, the intensity of the image is very low. The small hole is therefore replaced by a mask made of a material opaque to gamma rays and perforated with a multitude of larger holes. As with the pinhole camera, each hole creates an image on the detector, but since there are many holes on the mask, there are as many images superimposed on the detector. Analyzed by appropriate mathematical algorithms, this signal makes it possible to recreate the image of the sky in gamma rays and thus detect our famous gamma bursts.
This technology is not new, but ECLAIRs has the specificity of being able to collect photons of lower energy than its predecessors, which will allow it in particular to search for more distant gamma bursts. and therefore to explore the formation of the first stellar mass black holes.
Thanks to its coded mask, ECLAIRs can observe in the gamma ray domain without the need for a mirror or lens.
CNES/APC/CEA
The research topics discussed here constitute only part of the scientific objectives of the Einstein Probe and SVOM. For example, the search for electromagnetic emission associated with neutron star mergers, like that detected in 2017, is also among the priorities of these two space missions. After their respective launches from the Xichang base in China, what is called a so-called in-flight acceptance phase will begin, marked by the start-up, testing and calibration of the instruments. These preliminary steps are crucial to guarantee the reliability of the data and thus prepare the ground for future scientific exploitation. The first results from these two missions could arrive by the end of the year, thus offering a new perspective on the cataclysmic Universe.
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