BALTIMORE—Warning the disease could prove fatal for the galaxy if left untreated, a team of leading astronomers expressed grave concern Wednesday after their biopsy of a globular cluster from a previously unexplored corner of the Milky Way confirmed a diagnosis of melanoma. “It’s only a small growth right now, about 3,000 light years in diameter, but if we don’t attend to it immediately, our galaxy may have only 5 or 6 billion years left to live,” said Kenneth Sembach, director of the Space Telescope Science Institute, speculating that the Milky Way might have developed the cancer from repeated and prolonged exposure to the intense rays of its estimated 250 billion stars. “We first suspected melanoma after our Hubble telescope sent back images of a tumorous star cluster that was asymmetrical in appearance and had begun to take on a reddish, pinkish hue. Obviously, you can never be too careful with these things. If it were to spread to the galactic halo it could quickly trigger a collapse of the entire cosmos, so we’re glad we caught it when we did.” NASA officials confirmed treatment would begin right away with the launch of a rocket on a multimillion-year mission to target the malignant cluster with its first dose of chemo.