2019-07-01_Discover

JULY/AUGUST 2019. DISCOVER 47

NICER Neutron Stars

Astronomers are currently arguing

(nicely) about what might be deep inside

neutron stars and pulsars. They don’t

actually know, because the pressures

and temperatures inside these objects

are among the most extreme of any

in the universe, and they can’t be re-

created in a lab.

But NASA hopes to learn more

through its Neutron star Interior

Composition Explorer (NICER) mission,

an X-ray telescope that literally snapped

onto the International Space Station in

2017. Scientists have already discovered

that a pulsar and a white dwarf can orbit

each other more tightly than the moon

orbits Earth. They’re also testing how our

descendants might one day use pulsars

like GPS beacons to navigate the cosmos

without satellites.

Astronomers still want to figure out

how massive and how wide pulsars

actually are so they can determine the

exact density of their interiors — and

finally learn what exotic stew must be

brewing inside. They’ll also watch for

“starquakes” (the stellar equivalent of

earthquakes, possibly due to varying

rotation rates) and learn how magnetic

fields and extreme gravity whip the

radiation around.

Meanwhile, other teams are using

superfast pulsars to search for

gravitational waves, the ripples in

space-time that result when massive

objects accelerate or collide. By

watching for pulses that arrive at Earth

not quite on schedule, astronomers

hope to learn about the weird curves

and bends in space-time that can

stretch or squeeze the signals, delaying

or hastening their travels.

SLOWEST: PSR J0250+5854

This pulsar moseys around just once every 23.5 seconds. It’s so

slow that astronomers could actually watch it clap on and clap off,

a normally impossible feat. Currently, no one knows how it could

turn this languidly and still produce radio waves.

FASTEST: PSR J1748-2446ad

Faster than a kitchen blender, this guy zings

around 716 times per second. Despite its above-

average mass, it must still be less than 20 miles

across, or else it would spin itself apart.

OLDEST: PSR J0108-1431

The Methuselah of pulsars, this one has been

around solo for some 200 million years. And it’s

still pumping out X-rays. Astronomers wonder:

Where does it get the energy?

YOUNGEST: PSR J1846-0258

About 500 years ago, light from the supernova Kes 75 reached

Earth. But the dust and dinginess between here and there — an

expanse of 19,000 light-years — meant human eyes couldn’t see

the explosion. The baby pulsar gestating at its center escaped

attention until 2000.

Know Your Pulsars

Sorry, no pulsar.

You made a black hole!

Not bad for your first try.

But...

If they stay stubbornly pointed at

open space and other planets, you

discovered a plain-Jane neutron star!

You’ve got a neutron star on your

hands. It’s spinning super-fast, and it’s

squashed itself down to something as

dense as an atomic nucleus but the size

of Washington, D.C.

Everything lines up!

Because its business ends

face our planet, scientists

can see its blip-blip-blips.

It’s a PULSAR!

Do either of its

magnetic poles point

at Earth during its

N merry-go-round?

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NICER on the ISS