Free Astronomy Magazine March-April 2024

MARCH-APRIL 2024 that the companion star appears to have survived the violent death of its partner and the two objects, the compact remnant and the compan- ion, likely kept orbiting each other. The data collected by the Moore team, which included observations with ESO’s NTT in Chile’s Atacama Desert, did not allow them to pin down exactly how the interaction between the two objects caused the highs and lows in the light curve. But the Chen team had additional observations. They found the same regular fluctuations in the system’s visible brightness that the Moore team had detected, and they also spotted periodic movements of hy- drogen gas and bursts of gamma rays in the system. Their observations were made pos- sible thanks to a fleet of instruments on the ground and in space, includ- ing X-shooter on ESO’s VLT, also lo- cated in Chile. Putting all the clues together, the two teams generally agree that when the companion star interacted with the material thrown out during the supernova explosion, its hydrogen-rich atmos- phere became puffier than usual. Then, as the compact object left be- hind after the explosion zipped through the companion’s atmos- phere on its orbit, it would steal hy- drogen gas, forming a hot disc of matter around itself. This periodic stealing of matter, or accretion, re- leased lots of energy that was picked up as regular changes of brightness in the observations. Even though the teams could not observe light coming from the com- pact object itself, they concluded that this energetic stealing can only be due to an unseen neutron star, or possibly a black hole, attracting matter from the companion star’s puffy atmosphere. “Our research is like solving a puzzle by gathering all possible evidence,” Chen says. “All these pieces lining up lead to the truth.” With the presence of a black hole or neutron star confirmed, there is still plenty to unravel about this enig- matic system, including the exact nature of the compact object or what end could await this binary system. Next-generation telescopes such as ESO’s Extremely Large Tele- scope, scheduled to begin opera- tion later this decade, will help with this, allowing astronomers to re- veal unprecedented details of this unique system. !