When the first five images from the James Webb Space Telescope (JWST) were unveiled, one of them stared at me with two eyes. It was an image of the Southern Ring Nebula, NGC 3132, and smack in the middle were two bright stars.
Now, the fact that NGC 3132 houses a binary star system (two stars orbiting one another) has been known since the days of the Hubble Space Telescope.
But in those early images, the central star that ejected the nebula – a tiny, hot white dwarf – was so dim it was almost invisible next to its bright Sun-like companion. In effect, the nebula had one eye almost closed.
But the JWST reveals more than Hubble did. It can collect “cooler” photons (light particles) in the infrared range of the electromagnetic spectrum. In this cooler light, we saw both stars in the binary system shining as bright as one another: two glaring eyes!
This was surprising to any astronomer who understands this type of nebula; super-hot white dwarfs typically don’t shine brightly in infrared light. It made sense for the cooler star to be shining this way, but observing the same brilliance from its partner was unexpected.
Emails started to bolt coast to coast and across oceans as astronomers pieced the puzzle together. The central white dwarf star of NGC3132, they realised, is enshrouded in dust. The dust is warmed up by the star’s heat and therefore shines in the infrared, producing the light we observed.
It was this that led us on the trail to find out what was really happening in the Southern Ring Nebula. Our findings from a team of nearly 70 astronomers are published Dec. 8 in Nature Astronomy.
At the heart, a hot white dwarf
The Southern Ring Nebula is a planetary nebula. That means it’s a gaseous nebula formed by a Sun-like star shedding most of its gas in the last act before its demise.
Once it shed much of its mass, the star became a hot white dwarf. This central star now sits in the middle of the nebula, cooling like a stellar ember, effectively dying.