Hubble images taken 25 years apart show big changes in the iconic Crab Nebula —‬ Space photo of the week

The Hubble Space Telescope's surprising longevity is giving astronomers a chance to see not only what distant objects look like up close but also how they change over time.

This week, NASA dropped a stunning example: A comparison of two Hubble images from 1999/2000 and 2024 shows how the Crab Nebula — the remains of an exploded star — has expanded and evolved over a quarter century of Hubble images.

There are few more iconic objects in the night sky than the Crab Nebula, a cosmic cloud that links ancient astronomy with modern space telescopes. In the year 1054, a supernova in the constellation Taurus lit up the daytime sky for several weeks — an event recorded by early astronomers in Japan, China and the Middle East. This "guest star" eventually faded from view but it remains one of the best-documented cosmic explosions in human history.

Centuries later, in the mid-18th century, the Crab Nebula was discovered in the constellation Taurus. Astronomers, including Edwin Hubble in the 1950s, linked the Crab Nebula to the 1054 supernova. The smoking gun was the discovery of a pulsar — a rapidly rotating neutron star, the typical leftovers of a supernova — at the center of the Crab Nebula.

That pulsar has been busy powering the nebula's expansion in the 25 years since it was first photographed by the Hubble Space Telescope. The telescope's latest observations of the Crab Nebula, published earlier this year in The Astrophysical Journal, have allowed astronomers to measure the outward movement of the nebula's intricate filaments.

The differences between the two images may seem slight, but the filaments are expanding at about 3.4 million mph (5.5 million km/h). The expansion is driven not by shock waves from the initial explosion — as many supernova remnants are — but by the pulsar, whose powerful magnetic field propels charged particles outward. This energy source drives the nebula's expansion and illuminates its glowing filaments.

The images, which make use of Hubble's high-resolution Wide Field Camera 3 (installed by astronauts in 2009), allow scientists to see 3D structures and details, with blue regions indicating the hottest, lowest-density gas and yellow and red tones revealing energized sulfur and oxygen. (The 1999/2000 photo has also been reprocessed to match the resolution of Wide Field Camera 3.)

"We tend to think of the sky as being unchanging, immutable," William Blair, an astronomer at Johns Hopkins University who led the new observations, said in a NASA statement. "However, with the longevity of the Hubble Space Telescope, even an object like the Crab Nebula is revealed to be in motion, still expanding from the explosion nearly a millennium ago."

Hubble is not the only telescope that has managed to snap this spectacular supernova remnant. In 2023, the James Webb Space Telescope also captured a staggeringly detailed shot of the Crab Nebula, which later helped scientists map out the cosmic dust within its expanding shell, according to NASA.

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