A black hole is an insatiable cook, and the star beside it is a pot of boiling soup. The cook ladles out the soup, but some spills: similarly, GX 339-4 pulls in gas from its neighboring star, but it doesn't hold onto all of it. The excess matter shoots out from the black hole's poles in two narrow jets, like splashes from an overfilled pot.
For five years, from 2018 to 2023, three telescopes kept an eye on this 'kitchen' every week. MeerKAT caught the radio waves from the jets, Swift-XRT picked up the X-ray glow of the hot gas right near the hole, and MeerLICHT captured the visible light from the star. During this time, GX 339-4 'turned on the stove' four times: twice it flared weakly, and twice at full power. In 2020, after a bright outburst, they managed to spot a blob of plasma detach from the hole and fly away for a whole month.
Such observations are like a frame-by-frame recording of a meal: you can see when the cook starts eating, when he chokes, and when he spits it out. The scientists noticed that the radio waves and X-rays are linked: the brighter the X-rays, the more powerful the jets. They also managed to measure the speed of the ejected blobs: it turned out to be close to the speed of light.
All the radio sky maps from the five years have been made publicly available. Now anyone can dive into the archive and look for themselves to see if anything else has flown past our 'kitchen'.
GX 339-4 lies in the constellation Ara, but you can't see it even with the most powerful optical telescope — only through X-rays and radio waves.
In the movie 'Interstellar,' the black hole Gargantua is shown with a bright accretion disk — exactly the kind of disk observed around GX 339-4, but thousands of times smaller.