You can finally see a cosmic supernova explode with your own eyes

A ghostly 'hand' moving across the universe has just shed new light on the death of massive stars. The spectacular structure is the ejecta of a core-collapse supernova, and by taking images of it over more than 14 years, astronomers have been able to watch it blast into space at 4,000 kilometers (2,485 miles) per second.

At the very tip of the "fingertip", a supernova remnant and shock wave called MSH 15-52 blasted into a gas cloud called RCW 89, creating shocks and nodules in the material and causing the expanding supernova to slow down.

Located 17,000 light-years from Earth, MSH 15-52 appears to be one of the youngest known supernova remnants in the Milky Way. About 1,700 years ago, light from a stellar explosion reached Earth as a precursor star ran out of fuel to support fusion, blasting its outer material into space and collapsing its core.

The collapsed core becomes a type of "dead" star called a pulsar, an extremely dense object in which neutrons are tightly packed and have certain properties of an atomic nucleus, emitting pulsing light from its poles as they rotate at high speed .

This rotation also helps shape X-ray nebulae that eject stellar material as they expand into space.

Its expansion rate is detailed in a new study that used images from 2004, 2008 and 2017-2018 to see how RCW 89 changed as supernova remnants fell into it.

By calculating how far these features have traveled over time, we can better understand the velocity of the shock wave, and the nodes that eject stellar material in MSH 15-52. You can see this in the image below.

The shock wave, located near one fingertip of the hand, is characteristic of MSH 15-52 encountering RCW 89 moving at 4,000 kilometers per second, but some nodules of material move faster, up to 5,000 kilometers per second.

The knots are thought to be clumps of magnesium and neon that formed in stars before the supernova exploded, moving at different speeds. Even the slowest seems ridiculously fast, around 1,000 km/s.

Even so, these features are slowing down when interacting with matter in RCW 89. The distance from the pulsar to RCW 89 is about 75 light-years; to make up this distance, the average expansion velocity required for the outer edge of MSH 15-52 is 13,000 km/s.

This means that the researchers have determined that before encountering RCW 89, the material passes through a relatively low-density cavity, or bubble, in the gas surrounding the exploding star, consistent with a core-collapse supernova model.

When the precursor star's main-sequence life comes to an end, a powerful stellar wind blows into the space around it, stripping the star of its hydrogen and creating a massive cavity. Then, when the star's core finally collapses into a supernova, the explosion ejects the remaining stellar material into this relatively empty region of space.

RCW 89 stands for cavity wall. When MSH 15-52 encountered this denser area, the collision caused a rapid deceleration.

Supernova ejecta at higher velocity ranges have also been observed in the supernova remnant Cassiopeia A, 11,000 light-years away. This is also thought to be a core-collapse supernova, but we observed it recently - the light from the explosion reached Earth just 350 years ago.

We don't yet really understand the origin of the fast-moving clumps in these two supernovae, but collecting more data and studying such explosions at different time spans will help astronomers painstakingly piece together the mystery.