When stars get too close to a supermassive black hole, they are ripped apart in a process astronomers call "spaghettification". As the word suggests, the whole star is stretched into a thin noodle-like filament. The event releases a burst of energy that can be seen hundreds of million light-years away. Many such events have been spotted over the last few decades, however, the filament itself has not been observed before, until now.
An international group of astronomers reports the first direct observations of a spaghettified star in the Monthly Notices of the Royal Astronomical Society. In particular, they were able to spot absorption lines. Some of the molecules from the ex-star absorbed light from its surroundings allowing scientists to see how the material was distributed.
The event, known as AT 2019dsg, took place around a supermassive black hole around 5.4 million times the mass of our Sun, similar in size to the one at the center of the Milky Way. The black hole is not particularly active, which allowed researchers to track the material from just 34 days after the event to 411 days afterward.
The official term for spaghettification is a tidal disruption event (TDE), which is the first thing that happens as the star is pulled apart. This releases a lot of X-rays but this emission tends to get weaker until it is no longer visible 200 days after the TDE. They also looked at the event in visible light and radio waves.
They saw the absorption lines when looking at the black hole's rotational pole. Material appeared to be wrapped multiple times around the equator of the black hole, where its accretion disk is located, but some of it also seemed to be wrapped around and above its pole. The team likened it to a spooling ball of yarn, wrapped around the black hole and disappearing into it. This material is the first observed actual physical filament from a freshly torn apart star.
The teams are confident that the black hole is pole-facing rather than edge-on for two reasons. If the black hole wasn’t facing us showing its pole, we wouldn’t see the X-ray emission from its disk. Also, the light spectrum of the spaghettified material would have crucial clues in it. “Moreover the absorption lines are narrow,” lead author Giacomo Cannizzaro, from SRON/Radboud University said in a statement. “They are not broadened by the Doppler effect, like you'd expect when you would be looking at a rotating disk.”
Our understanding of TDEs has majorly improved in recent years thanks to more discoveries of these types of events, including the closest one to us, which was announced last October by some of the same researchers from this study, and neutrinos detected from another. The mysteries of spaghettification are slowly being uncovered.