2019-07-01_Discover

Spin

axis

Radiation

beam

Beam rotates

around spin axis.

Magnetic

field lines

Neutron star

Magnetic

poles

EVERYTHING

WORTH

KNOWING

46 DISCOVERMAGAZINE.COM

Pulsars

THE UNIVERSE IS FULL OF WEIRD OBJECTS, but pulsars take

the prize as the strangest things scientists can study directly.

The shriveled remains of once-mighty stars, they’re around a

dozen miles across, have approximately the mass of a sun and

can spin hundreds of times per second. They’re also made of

a poorly understood particle soup for which researchers don’t

have the recipe.

Here’s what we do know: Pulsars are a type of neutron star,

the dense core left over after a supernova — a stellar explosion.

Astronomers can see pulsars only because electromagnetic

radiation, especially radio waves, streams from their magnetic

poles. As the pulsars spin, these streams point, once per go-

around, at Earth. They sweep over our planet like transient

lighthouse beams, and telescopes pick up each one as a pulse.

Magnetic Personalities

So how do those telltale pulses get started?

Pulsars have hugely powerful magnetic

fields, some of them a trillion times stronger

than Earth’s. When magnetic fields spin, they

generate electric fields. A pulsar’s spinning

fields then whip up a current of particles —

electrons and positrons — pulled from the

star’s surface. That current travels along

the pulsar’s magnetic field lines, spewing

radiation from the magnetic poles.

“It’s analogous to what produces the

aurora on Earth,” says Slavko Bogdanov, a

pulsar astronomer at Columbia University.

“But this is a much more extreme version.”

Lighthouses of the cosmos.

BY SARAH SCOLES

I told you it was big.

Small and shiny

Big and beautiful.

It’s a youth. Supernova party!

When it dies, your

star blows off its

outer layers, while

its innards collapse

in on themselves.

Is it less than

30 times as

massive as the sun?

Is it at least eight times

as massive as the sun?

Is it nearly dead?

Is that collapsed

star more than 3-4

times the mass of

the sun?

Create Your

Own Pulsar

START with a star, any star.

N

N

N Y

Y

Y

The First Pulsar

As part of her doctoral

work in radio astronomy,

Jocelyn Bell Burnell built

a radio telescope by

hand — pounding posts,

stringing wire, attaching

metal. Once it was ready,

she was in charge of using

it to survey the sky for

what astronomers call

“scintillating sources”

— the radio

equivalent

of twinkling

lights — in

a search

for special galaxies far, far

away. But on Nov. 28, 1967,

she discovered something

unexpected: a recurring

source of radio waves that

appeared and disappeared

like cosmic clockwork. At

first, she called it “scruff.”

Then she and her adviser

jokingly named it LGM-1,

for “little green men.”

Today, we call it a pulsar.