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SYFY WIRE Bad Astronomy

A supernova that left chaos in its wake

By Phil Plait
The Vela supernova remnant is the shredded remains of a star that blew up 11,000 years ago, seen against a backdrop of gas clouds in the Milky Way. Credit: Robert Gendler and Roberto Colombari / DSS

There are few events in the Universe more violent than a supernova.

When a star explodes, the energy released is almost unimaginable. In seconds, billons of times the energy of the entire Sun is released; a wave of destruction moves through the doomed star from the inside out, blasting away an octillion tons of gas, sending it raging into space at a significant fraction of the speed of light.

The initial explosion eventually fades, but that gas still moves outward. What does this do over time? What does that look like after a few thousand years?


The Vela supernova remnant is the shredded remains of a star that blew up 11,000 years ago, seen against a backdrop of gas clouds in the Milky Way. Credit: Robert Gendler and Roberto Colombari / DSS

That is the Vela supernova remnant, the aftermath of a massive star reaching its end and exploding. The unnamed star's life ended about 11,000 years ago, but the gas it flung into space is still there, moving away from the blast site at high speed. In this image, you can see it as the thin, filamentary structure in the center, shining on both red and blue, indicating the presence of hydrogen and oxygen; the former the star was born with, the latter created in the nuclear forge in its heart.

From our distance of 800 light years, the supernova still appears huge, spanning 8° from side to side, over 15 times the width of the full Moon on the sky.

And yet, this image is much larger than that, covering twice that angle on the sky. It's a mosaic of 200 individual images taken as part of the Digitized Sky Survey and supplemented using a small telescope in Australia; the image was processed and assembled by Robert Gendler.

So if the supernova remnant is only in the center, what is the rest of all that material you can see.

This part of the sky in the constellation Vela, which itself lies in the plane of the Milky Way galaxy. When we look toward it, we are seeing into our galaxy, towards regions where gas and dust litter space.

The gorgeous Gum 15 nebula, a star-making factory similar in many ways to the Orion Nebula. Credit: Adam Block/ Telescope Live

Most of the red glow you see there is from gas well behind the supernova remnant from our point of view, thousands of light years away. Wherever you see red is where stars are being born, their glow lighting up the gas, exciting it, causing it to glow literally like a neon sign. For example, directly above the supernova and a bit to the left is a small circle of pink glowing brighter than the rest; that is the nebula Gum 15, lit by the fierce light of single star called HD 74804, a massive blue star that emits thousands of times as much light as the Sun.

The others all have similar tales to tell. An annotated version of this image will give you plenty to scour the internet for; this image is literally filled with amazing objects.

But harking back to the supernova, what of the star itself? Did it leave anything behind besides ever expanding besides wisps of gas?

Yes. When the core collapsed, creating the explosion that would tear its outer layers away, it compressed into a ball of neutrons, an object with the mass of a star like the Sun but all contained in a sphere just a few kilometers across. This neutron star is so dense that a cubic centimeter of it would weigh one hundred million tons, and is still fiercely hot from the fires of its creation.

It also spins rapidly and possesses a powerful magnetic field. These combine to power rotating twin beams of radiation, like a lighthouse, sweeping over the sky 12 times per second. This makes it a pulsar, because we see those moving beams as blips in our telescopes, dimmed by the 800 light years of space between us and it.

That pulsar can still be seen in the remnant, a dim star otherwise indistinguishable than thousands of others there.

An annotated section of the larger Vela image, showing the location of the Vela pulsar. Credit: Robert Gendler and Roberto Colombari / DSS

Astronomy asks a lot of us. We see nearly ungraspable violence, but it's reduced to a spark due to the nearly ungraspable distance. One of these huge factors is difficult enough to internalize, but both? And the forces involved, the energies, the interactions, are mostly alien to what we experience in our daily lives, engaging a third way to remove our ability to truly appreciate what we're seeing.

But it also makes up for that in sheer beauty. And, for the scientist, the added pleasure of understanding the mechanisms and engines behind all this.

It may look like chaos, but this is the Universe expressing itself through physics. And even it must obey those rules.