"We might have finally found the cause of a mystery that's lasted over 40 years," said researcher Sandino Estrada-Dorado.

Using ESA's XMM-Newton satellite and NASA's Chandra spacecraft ... which was observed in X-rays by the Chandra and XMM-Newton telescopes during its optically low states, when the source exhibits ...

The space telescope, which NASA has spent years developing ... The space observatory shared a ride with the four small satellites that make up NASA’s PUNCH mission, which will study how ...