Direct observation of an unprecedented structure in a black hole

November 18 () –

Scientists have achieved the milestone of directly observing the long-sought innermost ring of dust around a supermassive black hole, at right angles to its emerging jet.

Such a structure was thought to exist in the nuclei of galaxies, but it had been difficult to observe directly because intervening material obscured our line of sight.

Now the inner disk is detected using the highest spatial resolution in the infrared wavelengths ever done for an extragalactic object. The new discovery has just been published in The AstrophysicalJournal.

“This is a very exciting step forward to view the inner region of a distant galaxy in such fine detail,” he said. it’s a statement Gail Schaefer, associate director of the Center for High Resolution Angular Astronomy (CHARA) Array.

A supermassive black hole is believed to exist at the center of every large galaxy. As material in the surrounding region is pulled toward the center, the gas forms a hot, glowing disk-like structure. In some cases, a jet emerges from the vicinity of the black hole in a direction at right angles to the disk. However, this flat structure, which is essentially the “engine” of this active system of supermassive black holes, it has never been seen directly because it is too small to be captured by conventional telescopes.

One way to get up close to this key structure is to look directly at an outer “dust ring”: interstellar gas contains dust grains, tiny solid particles made of heavy elements, which can only survive in the outer region where the temperature is low enough. (-about 1500K- otherwise metals evaporate). The heated dust emits thermal infrared radiation and would therefore look like an outer ring around the black hole, if the central system had a planar structure. Detecting its structure would be a key step in delineating how the central engine works.

Attempts to view this structure from the edge are difficult, because the system is obscured by the very dust that acts as a light absorber. Instead, in the new research, the team focused on a front-facing system, the brightest such object in the nearby universe. However, the detection required very high spatial resolution at infrared wavelengths and, at the same time, a great variety of telescopes arranged suitably to observe objects in different orientations.

The CHARA Array interferometer at Georgia State University at Mount Wilson Observatory in California is the only facility that meets both of these requirements. The array consists of 6 telescopes, each of which has a 1 meter diameter mirror, which combine to achieve the spatial resolution of a much larger telescope. While each individual telescope is relatively small, the array design is optimized for observing objects at a variety of angles and with long distances between telescopes. This achieves a very high spatial resolution capability. CHARA Array actually has the sharpest eyes in the world at infrared wavelengths.

With the CHARA Array, the team finally detected the ring of dust, at right angles to the emerging jet at the center of the galaxy called NGC 4151.

“We have expected to see this structure in a bare-core object for a long, long time,” says Makoto Kishimoto, principal investigator of the project at Kyoto Sangyo University.

One big boost was that each telescope has recently added a new system called “adaptive optics.”

Matt Anderson, a postdoctoral researcher at the CHARA Array who played a key role in making the observations, says: “This greatly increased the injection rate of light, compensating for the relatively small collector mirror to observe the extragalactic target, which is much fainter than typically observed stellar targets in our galaxy.”

For the past nearly 40 years, researchers in the field have believed that this dust ring is a key to understanding the different characteristics of accreting supermassive black hole systems. The properties we observe depend on whether we have an obscured edge view or a clear head-on view of the active galaxy nucleus. The detection of this ring-shaped structure validates this model.

Furthermore, the detection is probably not just an indication of a planar structure. Additional studies have shown that the structure seen at slightly longer infrared wavelengths, corresponding to an even larger outer region, appears elongated along the length of the jet rather than at right angles to it. This has been interpreted as an indication that a dusty wind is blowing in the direction of the jet. The current finding that the internal structure appears flat and perpendicular to the jet is an important link to the sucker structure. and its interaction with the rest of the galaxy surrounding the active black hole system.