A black hole eating a star again and again
Supermassive black holes lie at the centre of most galaxies, and are the source of some of the most extreme activity in the Universe. Their large masses concentrated in small volumes lead to strong gravitational forces. This artistic impression shows a star pulled into orbit around a black hole, with glowing consequences.
The first panel shows a star (left) on approach to a black hole (right). The black hole attracts the star closer, and panel 2 shows the star beginning to be ripped apart by strong tidal forces. A stream of orange material ripped from the outer layers of the star falls towards the black hole in panel 3. This stream feeds the black hole and forms a disk of bright orange material around it, seen in the fourth panel. Leftover stellar material from the stream is coloured in blue. This process creates outbursts of X-rays, UV and optical light in an event known as a tidal disruption event.
Typically, it takes just one encounter with the black hole to totally swallow the star. However, on rare occasions, the core of the star survives and begins another elliptical orbit of the black hole. This can be seen as the shaded star moves along different positions in the orbit in panel 4.
The disk surrounding the black hole dims, as seen in panel 5. The star approaches the black hole again, and another outburst of light is released when the black hole strips material again from the surviving core of the star. This partial tidal disruption event adds more material to the shining orange accretion disk around the black hole in the sixth panel, and the blue traces of the stellar material stream persist. The lighter colour of the accretion disk, compared to the fourth panel, indicates that the outbursts of light are dimmer after the first encounter with the black hole. Less material is pulled into the disk from the star, leading to dimmer flares.
Two teams of astronomers used ESA’s XMM-Newton to observe two repeated tidal disruption events in 2021 and 2022. Events like these are essential to understand more about black holes, which are usually invisible due to the strong gravitational forces which trap everything including light.
