The XRISM mission has revealed important data about the supermassive black hole at the center of galaxy NGC 4151 and improved our understanding of how the black hole interacts with its environment. Since starting scientific operations in February this year, the Japanese-led XRISM (X-ray Imaging and Spectroscopy Mission) has been investigating the massive black hole at the center of the galaxy NGC 4151.

“XRISM’s Resolve instrument captured a detailed spectrum of the region around the black hole,” said Brian Williams, project scientist for the mission at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Peaks and troughs are like chemical fingerprints that can tell us what elements are present and provide clues about the fate of matter as it approaches a black hole.”

XRISM (pronounced “crisis”) is managed by JAXA (Japan Aerospace Exploration Agency) in collaboration with NASA, with input from ESA (European Space Agency). It was released on September 6, 2023. NASA and JAXA developed Resolve, the mission’s microcalorimetric spectrometer.

NGC 4151: A spiral galaxy with a supermassive black hole

NGC 4151 is a spiral galaxy located about 43 million light-years away in the northern constellation Canis Venata. The supermassive black hole at its center has a mass 20 million times the mass of the Sun.

The galaxy is also active, which means its center is extremely bright and variable. Gas and dust swirling toward the black hole forms an accretion disk around the black hole and is heated by gravity and friction, creating variability. Some of the matter at the edge of the black hole forms twin jets of particles that fly from either side of the disk at nearly the speed of light. Surrounding the accretion disk is a puffy, doughnut-shaped cloud of material called a torus.

Unique aspects of NGC 4151

In fact, NGC 4151 is one of the closest known active galaxies. Other missions, including NASA’s Chandra X-ray Observatory and the Hubble Space Telescope, have studied it to learn more about the interactions between black holes and their environments; This could tell scientists how supermassive black holes in galactic centers grow over cosmic time.

The galaxy is extremely bright in X-rays, making it an ideal early target for XRISM.

Insights from XRISM spectral analysis

Stability spectrum of NGC 4151 shows a sharp peak at energies just below 6.5 keV (kiloelectron volts), the iron emission line. Astronomers believe that most of the power in active galaxies comes from X-rays from hot explosions near the black hole. X-rays reflected from the coolant gas in the disk cause the iron to fluoresce, producing a specific X-ray peak. This allows astronomers to paint a better picture of both the disk and the explosion zones much closer to the black hole.

The spectrum also shows a few dips around 7 keV. Iron found in the torus also caused these declines; but through absorption of X-rays rather than radiation, because the material there was much colder than in the disk. All this radiation is approximately 2,500 times more energy than the energy of light that we can see with our eyes.

Iron is just one of the elements that XRISM can detect. The telescope can also detect sulfur, calcium, argon and others, depending on the source. Each tells astrophysicists different things about cosmic events scattered across the X-ray sky.