W28 is a supernova remnant in Sagittarius, an old shell of shocked gas ploughing into the dense molecular clouds around it, where it lights up in gamma rays.
At a glance
| type | supernova remnant |
|---|---|
| distance from the Sun | 6,200 light-years (1.9 kpc) |
| its light left it | 6,200 years ago |
| size in the piece | about 85 light-years acrossmodel |
Read off the piece’s own catalogue, the same values it draws with. Model marks a property of the piece’s galaxy model rather than a measurement.
About W28
W28 is what is left of a massive star that exploded long ago, in the crowded direction of the inner Milky Way, near the Lagoon and Trifid nebulae on the sky. Its blast wave has slowed and cooled. In radio it shows a broken shell; in X-rays the hot gas fills the centre instead, which places it among the so-called mixed-morphology remnants.
What makes W28 a reference object is where it sits. Part of its shock is running into dense molecular clouds, and the collision betrays itself through masers, natural microwave lasers produced in shocked hydroxyl gas, and through gamma rays coming from the clouds themselves. That pattern is read as particles accelerated by the shock striking the cloud gas, which makes W28 one of the places used to test the idea that supernova remnants are the source of the Galaxy’s cosmic rays.
What you see in the piece
In visible light W28 is nearly lost behind the dust of the inner Galaxy; switch the band row to radio, X-ray or gamma to see the remnant and the clouds it is striking.
Measured or modelled
A pulsar lies close to W28 on the sky, but whether it was born in the same explosion is debated. The extent shown in the piece is modelled.
Questions
How far away is W28?
W28 is about 6,200 light-years (1.9 kpc) from the Sun, in the direction of Sagittarius.
Why does W28 shine in gamma rays?
Its shock wave is hitting dense molecular clouds; particles accelerated by the shock collide with the cloud gas and produce gamma rays.