The night the universe got bigger
In 1923, Edwin Hubble used the 100-inch Hooker telescope on Mount Wilson in California to identify a Cepheid variable star in the Andromeda "nebula". Cepheids pulse with a rhythm tied to their true brightness, a relationship worked out by Henrietta Swan Leavitt at Harvard in 1912. Hubble's measurement placed Andromeda far outside the Milky Way. It was a galaxy in its own right. By 1929 he had shown that more distant galaxies recede faster, the first observational evidence that the universe is expanding.
Everything in this bulletin descends from those two steps: galaxies are separate islands, and space between them is stretching.
Objects in the log
Hubble Deep Field
In December 1995, Hubble observed a tiny patch near the Big Dipper for about ten days, revealing roughly 3,000 galaxies. The Hubble Ultra Deep Field (2004) and JWST's first deep field (July 2022, galaxy cluster SMACS 0723) pushed further back in time.
Pillars of Creation
Columns of gas and dust in the Eagle Nebula, about 6,500 light-years away, photographed by Hubble in 1995 and again by JWST in 2022. Inside them, new stars are forming.
M87* and Sagittarius A*
The Event Horizon Telescope linked radio dishes across the planet into an Earth-sized instrument. It published the shadow of M87* on 10 April 2019 and of Sagittarius A*, our galaxy's central black hole, in May 2022.
GW150914
On 14 September 2015, LIGO detected ripples in spacetime from two merging black holes about 1.3 billion light-years away, confirming a century-old prediction of Einstein's general relativity.
Worlds around other stars
Michel Mayor and Didier Queloz found 51 Pegasi b in 1995. NASA's Kepler mission (2009–2018) found thousands more. The confirmed count now exceeds 5,000.
JWST's first galaxies
Webb has confirmed galaxies that existed only a few hundred million years after the Big Bang, some brighter and more mature than models predicted.
Black holes: from theory to photograph
Karl Schwarzschild found the first black hole solution to Einstein's equations in 1916, while serving on the Russian front. For decades, many physicists treated it as a mathematical curiosity. Then came Cygnus X-1, an X-ray source identified in the 1960s and 70s as a compact object too heavy to be a neutron star.
In 2020, Reinhard Genzel and Andrea Ghez shared the Nobel Prize in Physics with Roger Penrose for showing that stars at the Milky Way's centre orbit an invisible mass of about four million Suns. The Event Horizon Telescope image of 2022 put a face to that mass.
Open question: what happens to information that falls in? Stephen Hawking showed in 1974 that black holes should slowly emit radiation. Reconciling that with quantum theory, the "information paradox", remains unresolved.
Reading light as a time machine
Light travels at about 300,000 kilometres per second, so every look outward is a look backward. Sunlight is about eight minutes old. Light from Andromeda left it some 2.5 million years ago. When JWST records a galaxy whose light has been stretched deep into the infrared by cosmic expansion, it is seeing that galaxy as it was more than 13 billion years ago.
The oldest light of all is the cosmic microwave background, discovered by accident in 1965 by Arno Penzias and Robert Wilson at Bell Labs in New Jersey. It is the afterglow released when the universe was roughly 380,000 years old. ESA's Planck satellite mapped it in extraordinary detail between 2009 and 2013, and those maps underpin the 13.8-billion-year age of the cosmos.
Open question: how did galaxies grow so large so early? JWST's early results have prompted astronomers to revisit star formation models, dust estimates and the nature of the first black holes. Explanations are being tested, and none has won yet.
Continue to the machines behind these discoveries: Missions.