NASA’s Hubble Revisits Crab Nebula to Track 25 Years of Expansion - UNIVERSE

A quarter-century after its first observations of the full Crab Nebula, NASA’s Hubble Space Telescope has taken a fresh look at the supernova remnant. The result is an unparalleled, detailed look at the aftermath of a supernova and how it has evolved over Hubble’s long lifetime. A paper detailing the new Hubble observation is published in The Astrophysical Journal.

This new Hubble observation continues a legacy that stretches back nearly 1,000 years, when astronomers in 1054 recorded the supernova as an impressively bright new star that, for weeks, was visible even during the day. The Crab Nebula is the aftermath of SN 1054, located 6,500 light-years from Earth in the constellation Taurus.

“We tend to think of the sky as being unchanging, immutable,” said astronomer William Blair of Johns Hopkins University, who led the new observations. “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."

The supernova remnant was discovered in the mid-18th century, and in the 1950s Edwin Hubble was among several astronomers who noted the close correlation between Chinese astronomical records of a supernova and the position of the Crab Nebula. The discovery that the heart of the Crab contained a pulsar — a rapidly rotating neutron star — that was powering the nebula’s expansion finally aligned modern observations and ancient records.

In its new image, Hubble captured the nebula’s intricate filamentary structure, as well as the considerable outward movement of those filaments over 25 years, at a pace of 3.4 million miles per hour. Hubble is the only telescope with the combination of longevity and resolution capable of capturing these detailed changes.

For better comparison with the new image, Hubble’s 1999 image of the Crab was re-processed. The variation of colors in both of the Hubble images shows a combination of changes in local temperature and density of the gas as well as its chemical composition.

This 2024 image that NASA’s Hubble Space Telescope captured of the Crab Nebula, paired with its past observations and those of other telescopes, allows astronomers to study how the supernova remnant is expanding and evolving over time. 

Image: NASA, ESA, STScI, William Blair (JHU); Image Processing: Joseph DePasquale (STScI)

“Even though I’ve worked with Hubble quite a bit, I was still struck by the amount of detailed structure we can see and the increased resolution with the Wide Field Camera 3, as compared to 25 years ago,” Blair said. Wide Field Camera 3 was installed in 2009, the last time Hubble instruments were updated by astronauts.

Blair noted that filaments around the periphery of the nebula appear to have moved more compared to those in the center, and that rather than stretching out over time, they appear to have simply moved outward. This is due to the nature of the Crab as a pulsar wind nebula powered by synchrotron radiation, which is created by the interaction between the pulsar’s magnetic field and the nebula’s material. In other well-known supernova remnants, the expansion is instead driven by shockwaves from the initial explosion, eroding surrounding shells of gas that the dying star previously cast off.

The new, higher-resolution Hubble observations are also providing additional insights into the 3D structure of the Crab Nebula, which can be difficult to determine from a 2D image, Blair said. Shadows of some of the filaments can be seen cast onto the haze of synchrotron radiation in the nebula’s interior.  Counterintuitively, some of the brighter filaments in the latest Hubble images show no shadows, indicating they must be located on the far side of the nebula.

According to Blair, the real value of Hubble’s Crab Nebula observations is still to come. The Hubble data can be paired with recent data from other telescopes that are observing the Crab in different wavelengths of light. NASA’s James Webb Space Telescope released its infrared-light observations of the Crab Nebula in 2024. Comparison of the Hubble image with other contemporary multiwavelength observations will help scientists put together a more complete picture of the supernova’s continuing aftermath, centuries after astronomers first wondered at a new little star twinkling in the sky. 

Source: NASA’s Hubble Revisits Crab Nebula to Track 25 Years of Expansion - NASA Science