8/8/2023 0 Comments A journey into a black hole“Catching the X-ray signal before the black holes become one will be very challenging, but we are pretty confident that we can make a detection during and after the merger,” explains Matteo. Then, just a few hours before the final coalescence of the black holes, LISA can provide a much more precise indication in the sky, roughly the size of the field of view of Athena’s Wide Field Imager (WFI), so the X-ray observatory can directly point towards the source. Simulations indicate that the two spiralling black holes modulate the motion of the surrounding gas, so it is likely that the X-ray signature will have a frequency commensurate to that of the gravitational wave signal. This is still pretty large, but would allow Athena to start scanning the sky to search for an X-ray signal from this titanic clash. This, coupled with the motion of the satellites along their orbits, will allow LISA to gradually improve the localisation of the source in the sky, up until the time when the black holes finally merge.”Ī few days before the final phase of the merger, the gravitational wave data will constrain the position of the source to a patch on the sky measuring about 10 square degrees – roughly 50 times the area of the full Moon. “However, as the black holes inspiral towards each other, the amplitude of their gravitational wave signal increases. Simulations predict that their mergers, unlike those of their stellar-mass counterparts, emit both gravitational waves and radiation – the latter originating in the hot, interstellar gas of the two colliding galaxies stirred by the black holes pair when they fall towards one another. With Athena and LISA together, we would be able to apply multi-messenger astronomy to supermassive black holes for the first time. By combining information from the various types of observations in an approach known as multi-messenger astronomy, scientists could delve into the details of this never-before-observed phenomenon. This time, the gravitational waves were accompanied by radiation across the electromagnetic spectrum, readily observed with a multitude of telescopes on Earth and in space. Then, in August 2017, gravitational waves coming from a different source – the merger of two neutron stars – were discovered. The first few gravitational wave events detected by LIGO and Virgo between 20 all originated from pairs of stellar-mass black holes, which are known to not radiate any light upon coalescence. If two supermassive black holes merge anywhere in the cosmos, LISA will see it.” “This is one of the most energetic phenomena we know of, releasing more energy than all the quiescent Universe does at any time. “LISA will be the first mission of its kind, looking primarily for gravitational waves coming from supermassive black holes smashing into one another,” explains Paul McNamara, LISA study scientist at ESA. LISA will expand these studies by detecting low-frequency gravitational waves, such as the ones released when two supermassive black holes collide during a merger of galaxies. These experiments are sensitive to the mergers of relatively small black holes – a few times to a few tens of times more massive than the Sun. Gravitational-wave astronomy, inaugurated only a few years ago, is currently limited to the high-frequency waves that can be probed by ground-based experiments like LIGO and Virgo. Meanwhile, LISA will be the first space-borne observatory of gravitational waves – fluctuations in the fabric of spacetime produced by the acceleration of cosmic objects with very strong gravity fields, like pairs of merging black holes. “We are in particular interested in the most distant black holes, those that formed in the first few hundred million years of the Universe’s history, and we hope we’ll be able to finally understand how they formed.” “Athena is going to measure several hundreds of thousands of black holes, from relatively nearby to far away, observing the X-ray emission from the million-degree-hot matter in their surroundings,” says Matteo Guainazzi, Athena study scientist at ESA. It is designed to answer two fundamental questions: how supermassive black holes at the centre of galaxies form and evolve, and how ‘ordinary’ matter assembles, along with the invisible dark matter, to form the wispy ‘cosmic web’ that pervades the Universe. Two missions to probe the extreme UniverseĪthena will be the largest X-ray observatory ever built, investigating some of the hottest and most energetic phenomena in the cosmos with unprecedented accuracy and depth.
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