Colours come, colours go

The pops of bright blue and green in this image of the Fireworks galaxy NGC 6946 show the locations of extremely bright sources of x-ray light captured by NASA’s NuSTAR space observatory.

Generated by some of the most energetic processes in the universe, these x-ray sources are rare compared to the many visible light sources in the background image. 

The green blob near the bottom of the galaxy wasn’t visible during the first NuSTAR observation but was burning bright at the start of a second observation 10 days later. 

NASA’s Chandra X-ray Observatory later observed that the source – known as an ultraluminous x-ray source, or ULX – had disappeared just as quickly. 

The object has since been named ULX-4 because it is the fourth ULX identified in this galaxy. 

A new study led by the California Institute of Technology and published in the Astrophysical Journal, explores the possibility that the light came from a black hole consuming another object, such as a star. 

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