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An optical image of the galaxy Centaurus A, with radio data overlaid showing the jets coming from the galaxy’s active black hole, not seen in optical wavelengths. The different colours show the luminosity in radio light of the jets, with red being the brightest. Credits: ESO (optical); NRAO (radio)
Let’s talk about... multi-wavelength astronomy BY MICHELLE WHEELER AND CASSANDRA CAVALLARO (SKAO)
In November, ESA’s optical/near-infrared Euclid telescope released its first full-colour images of the cosmos. Launched in July 2023, it’s part of a new generation of telescopes which will be highly complementary, enabling astronomers to observe the same regions, objects and phenomena in great detail at different wavelengths, to create the most complete picture ever of our Universe. At the heart of the most turbulent galaxies in the Universe lies a supermassive black hole that’s actively swallowing up anything that gets a bit too close to its extreme gravitational pull. Some of the material, though, is saved from the brink, instead being ejected in powerful jets that can travel millions of miles an hour, close to the speed of light. “This is a violent process,” says SKAO Senior Scientist Dr Anna Bonaldi. “It releases a lot of energy and this leads to jets of emission that can be, in some cases, much bigger and much more luminous than the galaxy itself.”
HOW MASSIVE IS SUPERMASSIVE?
Supermassive black holes are a million to over a billion times as massive as our Sun.
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C O N TA C T
Radio telescopes can observe these jets in detail. But look with an optical telescope – one that observes the light that can be seen with the human eye – and the galaxy might just look like a very bright star. This is just one example of “multi-wavelength astronomy” – using telescopes that observe at different wavelengths to look at the same object in space to create a more complete picture of the processes at work. “All the objects in the sky – the stars, the galaxies, everything – they emit light on a broad spectrum of wavelengths,” she says. “If you look at something in just one wavelength, you might see that there is an object there. But you might not be able to really identify what it is, where it is, what kind of physical and chemical processes are taking place, or how the object is interacting with its surroundings.”
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