On paper, the two most spectacular astronomical discoveries of the last few weeks couldn't possibly have less in common. One is an image captured by the James Webb Space Telescope of a newborn star in our Galaxy, the Milky Way, about 450 light-years away. It's an amazing picture of the birth of a solar system in a thin disc of dust in which planets are, as we speak, slowly starting to form.
The other is a combination of optical and radio data showing us a giant astrophysical system, larger than the Milky Way, and so far away that its light has taken more than 12 billion years to reach us. It gives us a glimpse of the incredible, intergalactic violence wrought by a supermassive black hole actively devouring its surroundings.
Still, a glance at the images shows a striking similarity, challenging any sense of scale. Both objects seem to be shooting light or material out into space in long, straight jets, stretching far out into the distance, like double-sided lightsabers.
Astrophysical jets are extremely common in the Universe and while the details vary, the physics that drive them are all based on the same basic features: gravity, rotation and magnetic fields.
The first thing you have to know is why so many things in space make discs. There are the spiral-armed, disc-shaped galaxies (like the Milky Way we live in); there are the proto-planetary discs that coalesce into planets orbiting more or less in a flat plane; and there are accretion discs, where gas and dust swirl into black holes and other massive objects with disc-y whirlpools around them.
In all these cases, the formation of a disc happens in a few simple steps. First, gravity attracts material toward an object from all directions. You might think that would be the end of the story and it would just fall right in, but since everything in space is moving all the time, the chance that the path is an absolute straight shot is very small. Generally, the material has some momentum to one side or another and falls in an arc, possibly settling into an orbit around the object.
But when there's a lot of falling material – bits of gas and dust, all on different trajectories – it tends to get knocked around en route. If two specks of dust are coming from the same direction, they'll start to orbit together, but if they're coming from opposite sides, they'll crash into each other, lose Once momentum and fall toward the centre. Over time, this means that whatever the average rotation of the collapsing cloud was in the beginning, the whole thing will flatten out to a rotating disc in the same direction.
image [https://cdn.magzter.com/1422872401/1742287718/articles/l8UhR3epi1742363546755/9992299934.jpg]
So gravity and rotation can account for all the discs. But how do jets happen? This is where magnetic fields come into the picture.
Magnetic fields are pretty much everywhere in the cosmos. They show up inside stars and planets due to the movement of the stuff inside them (like the fluid meta...
The other is a combination of optical and radio data showing us a giant astrophysical system, larger than the Milky Way, and so far away that its light has taken more than 12 billion years to reach us. It gives us a glimpse of the incredible, intergalactic violence wrought by a supermassive black hole actively devouring its surroundings.
Still, a glance at the images shows a striking similarity, challenging any sense of scale. Both objects seem to be shooting light or material out into space in long, straight jets, stretching far out into the distance, like double-sided lightsabers.
Astrophysical jets are extremely common in the Universe and while the details vary, the physics that drive them are all based on the same basic features: gravity, rotation and magnetic fields.
The first thing you have to know is why so many things in space make discs. There are the spiral-armed, disc-shaped galaxies (like the Milky Way we live in); there are the proto-planetary discs that coalesce into planets orbiting more or less in a flat plane; and there are accretion discs, where gas and dust swirl into black holes and other massive objects with disc-y whirlpools around them.
In all these cases, the formation of a disc happens in a few simple steps. First, gravity attracts material toward an object from all directions. You might think that would be the end of the story and it would just fall right in, but since everything in space is moving all the time, the chance that the path is an absolute straight shot is very small. Generally, the material has some momentum to one side or another and falls in an arc, possibly settling into an orbit around the object.
But when there's a lot of falling material – bits of gas and dust, all on different trajectories – it tends to get knocked around en route. If two specks of dust are coming from the same direction, they'll start to orbit together, but if they're coming from opposite sides, they'll crash into each other, lose Once momentum and fall toward the centre. Over time, this means that whatever the average rotation of the collapsing cloud was in the beginning, the whole thing will flatten out to a rotating disc in the same direction.
image [https://cdn.magzter.com/1422872401/1742287718/articles/l8UhR3epi1742363546755/9992299934.jpg]
So gravity and rotation can account for all the discs. But how do jets happen? This is where magnetic fields come into the picture.
Magnetic fields are pretty much everywhere in the cosmos. They show up inside stars and planets due to the movement of the stuff inside them (like the fluid meta...
You're reading a preview of
BBC Science Focus (Digital) - 1 Issue, March 2025