IXPE investigates microquasar jets, finds unexpected magnetic field structure

by Haygen Warren

Creating some of the most powerful gravitational forces and fields in the universe, black holes are known for their extreme nature, including the ways in which they can devour and destroy whole planets and stars in a matter of seconds. When black holes consume planets, stars, and other cosmic objects, the matter from the collision between the two objects gets violently thrown around space — creating streams of particles traveling near the speed of light from black holes. These streams of particles are known as jets, and while scientists know that these jets can accelerate particles, known as cosmic rays, they know very little about the exact process by which the particles are accelerated.

Recently, a team of scientists utilized the X-ray capabilities of NASA’s Imaging X-ray Polarimetry Explorer (IXPE) observatory to investigate how cosmic rays within black hole jets are created. More specifically, the team investigated Stephenson and Sanduleak 433 (SS 433), a microquasar comprised of a black hole pulling in material from a nearby star.

SS 433 is the first microquasar ever discovered and is located in the center of supernova remnant W50, also known as the “Manatee Nebula,” which is located within the constellation Aquila, approximately 18,000 light-years away from Earth. SS 433 contains extremely powerful jets that move at velocities greater than 77,249 kilometers per second — roughly 26% the speed of light. In fact, the jets are responsible for the manatee-shape of W50.

Labeled composite image of supernova remnant W50 showing the location of SS 433’s black hole and jet. (Credit: (IXPE) NASA/MSFC/IXPE; (Chandra) NASA/CXC/SAO; (XMM) ESA/XMM-Newton; (Infrared) NASA/JPL/Caltech/WISE; (Radio) NRAO/AUI/NSF/VLA/B. Saxton; (Infrared/Radio Image) M. Goss et al.; (Image Processing) NASA/CXC/SAO/N. Wolk/K. Arcand)

As mentioned, to investigate the jets of SS 433, the scientists, led by IXPE principal investigator Philip Kaaret of NASA’s Marshall Space Flight Center in Alabama, utilized IXPE and its suite of telescopes. IXPE’s three telescopes measured the polarization — a special property of X-ray light that allows scientists to understand the organization and alignment of electromagnetic waves at X-ray frequencies — of the jets to better understand the physical processes that were occurring in and around SS 433, as well as how particles were being accelerated within the jets.

IXPE observed the eastern lobe of SS 433 for a total of 18 days throughout April and May, 2023. Within this eastern lobe sits one of the particle acceleration sites that Kaaret et al. are interested in investigating, as well as synchrotron radiation, which are emissions comprised of energetic electrons spiraling in a magnetic field.

The results from IXPE showed that the magnetic field around SS 433 is surprisingly intact and organized. For decades, scientists have theorized that when the jets interact with the surrounding interstellar medium, a type of shock would be created, thus creating disordered and messy magnetic fields.

“The IXPE data show that the magnetic field near the acceleration region points in the direction the jets are moving. …The high level of polarization seen with IXPE shows that the magnetic field is well ordered, with at least half of the field aligned in the same direction,” Kaaret said.

Aritst’s impression of SS 433. (Credit: NASA)

Given the new result, Kaaret et al. had to think of new ways to explain the origin of the aligned and organized magnetic fields of SS 433 and other microquasars.

Kaaret explained that the magnetic fields within the powerful jets could be trapped and stretched when the jets come into contact with matter within the interstellar medium — directly impacting the alignment of magnetic fields within regions of particle acceleration like the eastern lobe of SS 433.

SS 433 was discovered in 1977, and, since the 1980s, scientists theorized that the jets of the microquasar accelerate particles and act as a sort of particle accelerator. However, it wasn’t until 2018 that scientists using the High-Altitude Water Cherenkov Observatory in Mexico were able to confirm that the jets indeed act as particle accelerators. Later observations of the jets using NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, and the European Space Agency’s XMM-Newton X-ray observatory pinpointed the exact region of acceleration within SS 433.

Kaaret et al.’s results will not only help future studies into microquasars and jets created by black holes, but also studies into tens of hundreds of different cosmic phenomena. More specifically, the data will allow scientists to determine whether the aligning of magnetic fields in outflows expelled by cosmic phenomena — such as debris ejected from exploded stars, or blazars — occurs in a similar process as it does at SS 433.

“This very delicate measurement was made possible by the imaging capabilities of IXPE’s X-ray polarimeters, making possible the detection of the tenuous signal in a small region of the jet 95 light-years from the central black hole,” said IXPE’s Italian principal investigator Paolo Soffitta.

IXPE launched on Dec. 9, 2021, atop a SpaceX Falcon 9 rocket from Florida. The mission is a collaboration between NASA and the Italian Space Agency and aims to measure the polarization of several cosmic phenomena, including cosmic X-rays ejected from black holes, neutron stars, pulsars, and more. Furthermore, IXPE maps the magnetic fields of black holes, pulsars, neutron stars, supernova remnants, magnetars, quasars, galactic nuclei, and other exotic astronomical objects.

Kaaret et al.’s results were published in the latest edition of The Astrophysical Journal.

(Lead image: Composite image of supernova remnant W50, with the bright blue/purple jet from SS 433 seen in the center of the remnant. Credit: (IXPE) NASA/MSFC/IXPE; (Chandra) NASA/CXC/SAO; (XMM) ESA/XMM-Newton; (Infrared) NASA/JPL/Caltech/WISE; (Radio) NRAO/AUI/NSF/VLA/B. Saxton; (Infrared/Radio Image) M. Goss et al.; (Image Processing) NASA/CXC/SAO/N. Wolk/K. Arcand)

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