Astronomy - USA (2022-06)

Material from

an accretion

disk swirls around the

young star FU Orionis

in this artist’s concept.

NASA/JPL-CALTECH

Accretion creates everything

there is: galaxies, stars, planets,

and eventually, us. It is the reason

the universe is filled with a whole

bunch of somethings instead of a

whole lot of nothing.

The fact that matter tends to

glom together may seem intuitive.

But to scientists, accretion

remains a mysterious topic, filled

with unanswered questions.

For instance: Why do some

stellar nurseries form a few mas-

sive stars instead of lots of smaller

ones? What causes so much

accreting material to ultimately

fall inward onto its central object,

instead of just circling it forever?

And how do space rocks ulti-

mately stick together to form

planets instead of just bouncing

off each other? No one knows the

definitive answers to any of these

questions yet, but there are some

theories gaining traction — and

evidence.

All objects

great and small

Accretion is the inevitable result

of gravitational forces operating

on all scales, and on all types of

material — gas, dust, plasma,

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