On February 22, 1971, a sounding rocket with special sensors took off from Wallops Island, Virginia, targeting the Crab Nebula, a bright cosmic object 6,500 light-years away. In those days, before recovering physical tapes from the experiment, scientists first took scientific data on a strip chart recorder, a device that printed signals on paper. Astronomer Martin Weisskopf and his colleagues began their analysis on launch day by measuring the distance between the signals using a ruler and pen.

"What makes science so beautiful and exciting is that for those few moments you're seeing something no one has seen before," said Weisskopf, now an honorary astronomer at NASA's Marshall Space Flight Center in Huntsville, Alabama.

Years later, Weisskopf proposed the development of an Earth-orbiting satellite with powerful instruments capable of collecting much more detailed measurements of the same kind of the Crab Nebula and other mysterious cosmic objects. This satellite became NASA's Imaging X-ray Polarimetry Explorer (IXPE), launched on December 9, 2021.

Now, more than 50 years after the sounding rocket experiment, scientists have used IXPE to create a detailed, nuanced map of the Crab Nebula's magnetic field, revealing its inner workings more than ever before. The new results (preprint available) published in the journal Nature Astronomy help unravel long-standing mysteries about the well-studied Crab Nebula and open new questions for future study.

IXPE data shows that the Crab Nebula's magnetic field is also similar to that of the annular Vela Pulsar Wind Nebula. But in Cancer, scientists were surprised that the fields of magnetic field turbulence were more irregular and asymmetrical than expected.

"This is a clear indication that even more complex models developed in the past using advanced numerical techniques are not able to fully capture the complexity of this object," said Niccolò Bucciantini, lead author of the study and INAF astronomer. Arcetri Observatory, Florence, Italy.

A favorite study object among astronomers, the Crab Nebula originated from a documented supernova in 1054. The explosion left behind an object called the Crab Pulsar, about the diameter of Huntsville, Alabama, or the length of Manhattan, but just as dense. about the mass of two Suns. The chaotic jumble of gases, shock waves, magnetic fields, and high-energy light and particles from the rotating pulsar is collectively called the "pulsar wind nebula." These extreme conditions create a strange environment that is not yet fully understood.

Weisskopf and colleagues hoped to understand this extreme environment in a new way by measuring the polarization of X-rays from the Crab Nebula, which glows brightly in X-rays. X-ray polarization gives scientists clues as to how regular the magnetic field is, as well as the direction the magnetic field is pointing at different parts of a cosmic object. The geometry and turbulence of the magnetic field determines how particles are launched towards the speed of light.

Within five minutes of the 1971 sounding rocket experiment in Earth's atmosphere, he produced the world's first X-ray polarization measurements.

In 1975, scientists tracked down a satellite called OSO-8, which also measured the Crab Nebula's X-ray polarization. The rocket and satellite generally gave the same result: the average polarization of the Crab Nebula was about 20%.

Weisskopf continued to explore the Crab Nebula in new ways as a project scientist for NASA's Chandra X-Ray Observatory, launched in 1999. "We got beautiful images of the nebula and pulsar and were able to see the jets and various structures," he said with Chandra. Chandra's X-ray imaging revealed wispy-like structures moving through the nebula, helping scientists better understand the relationship between the pulsar's energy and X-ray emissions.

Nearly every new major telescope has pointed to the Crab Nebula to better understand this mysterious supernova remnant. But only IXPE can examine X-rays from Cancer for polarization, a measure of the organization of electromagnetic fields.

"The crab is one of the most studied high-energy astrophysical objects in the sky. So it's extremely exciting that we can learn something new about this system by looking through IXPE's 'polarized lenses'," he said.

IXPE found nearly the same average polarization across the entire nebula as Weisskopf and his colleagues did in the 1970s. But with more advanced tools, IXPE was able to improve the polarization angle and examine polarization differences across the entire object. Scientists see areas of multipolarity in the outer regions of the nebula, light-years away from the pulsar, where the polarization is lower.

This allowed scientists to investigate not only X-rays from the Crab Nebula, but also those from the pulsar itself or the sphere of magnetic field around it. The findings suggest that these X-rays originate in a region of the external magnetic field called the "wind" region, although exactly where and how is still unknown. Within the magnetic field, the shocks produced by the pulsar's "wind" push the particles near the speed of light.

"I'm proud of everyone associated with IXPE," said Weisskopf, the mission's first chief inspector. "Everyone worked hard and it works as advertised." "It's like someone said to me, 'Martin, you did a good job,'" says Weisskopf, evaluating his work on the 1971 experiment that formed the basis of the new results.

 

Source: https://www.nasa.gov/