Astronomy

Look up.

I've always wondered about the night sky. As a kid I could never work out why the moon kept following me whenever I walked, and I still look up every chance I get. The sky has a way of shrinking our problems back to their real size, and I genuinely think that if everyone looked at it once a night, we'd live differently.

Tonight's moon

While you're reading this

Earth has carried you 0.0 km around the Sun since you opened this page.

Voyager 1 is about … km from home and still going. A message to it would take … hours to arrive.

A lighthouse made of a dead star

When a big star dies, its core can collapse into a neutron star: more mass than the Sun, packed into a ball about 20 km across, spinning absurdly fast. Its magnetic poles fire beams of radio waves, and because they're tilted off the spin axis they sweep around like a lighthouse. Every time one crosses Earth, a telescope sees a pulse. The Crab Pulsar does this 30 times a second, more regularly than most clocks.

Things that still get me

2015 · LIGO

Spacetime, measured

Two black holes merged 1.3 billion light-years away, and the ripple in spacetime stretched LIGO's 4 km arms by less than a hundredth of a proton's width. We noticed.

2017 · GW170817

Where gold comes from

Two neutron stars collided 130 million light-years away. We caught it in gravitational waves and in light at the same time, and watched the blast forge heavy elements. Some of the gold on Earth was probably made like this.

2023 · Pulsar timing arrays

The galaxy as a detector

By timing dozens of pulsars to within a millionth of a second for years, astronomers found evidence of a slow background hum in spacetime, most likely from pairs of supermassive black holes all across the universe.

2019 · Event Horizon Telescope

A photo of a shadow

Linking radio dishes across the planet into one Earth-sized telescope, we photographed the shadow of the black hole in M87. In 2022 we did it again for Sagittarius A*, the one at the centre of our own galaxy.

2020 · SGR 1935+2154

Fast radio bursts, traced

Fast radio bursts are millisecond flashes from other galaxies. For years nobody knew what made them, until one went off inside the Milky Way and pointed straight at a magnetar.

Magnetars

10¹⁵ × Earth's magnetic field

Magnetars are neutron stars with magnetic fields about a thousand trillion times stronger than Earth's. From a thousand kilometres away, one would pull apart the atoms in your body.

Neutron star crusts

Nuclear pasta

Just under a neutron star's surface, nuclei may get squeezed into sheets and tubes physicists call nuclear pasta. Simulations suggest it could be the strongest material in the universe, billions of times stronger than steel.

Right now · Hubble tension

73 vs 67

Measure how fast the universe is expanding using nearby stars and you get about 73 km/s per megaparsec. Work it out from the Big Bang's afterglow and you get about 67. Better data hasn't made the gap go away, and nobody knows why yet.

Numbers are rounded, and the moon is worked out from the average lunar cycle, so it can be off by a few hours.