Flashes of bright blue and green in the recent image of the Fireworks galaxy display the locations of significantly bright sources of X-ray light captured by NASA’s NuSTAR space observatory.
Created by some of the most energetic procedures in the universe, these X-ray sources are a rarity compared to the various visible light sources in the background picture.
The latest study, published in the Astrophysical Journal, gives some possible reasons for the surprise display of the green source near the center of the galaxy, which came into eyesight and disappeared in a matter of weeks.
The main objective of the NuSTAR observations was to know the supernova – the explosion of a star much larger than our Sun – that comes out as a bright blue-green spot at upper right.
These violent incidents can temporarily produce sufficient visible light to outshine entire galaxies consisting of billions of stars. They also create a lot of the chemical elements in our universe that are much heavier than iron.
The green blob next to the bottom of the galaxy wasn’t clear during the first NuSTAR observation but was burning bright at the beginning of a second observation a few 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 immediately. The object has since been called ULX-4 as it is the fourth ULX discovered in this galaxy. No visible light was seen with the X-ray source, a fact that most likely rules out the possibility that it is also a supernova.
“Ten days is too short an amount of period for such a bright thing to appear,” told Hannah Earnshaw, a postdoctoral researcher at Caltech in Pasadena, California, and the lead author on the new study. “Usually with NuSTAR, we see more gradual changes over time, and we don’t often get to see a source multiple times in quick succession.
In this event, we were fortunate to see a source changing extremely quickly, which is very exciting.
