2023-08-28 10:34:12
MADRID, 28 Ago. (EUROPA PRESS) –
astronomers have made with NOIRLab’s Gemini North telescopethe first observations of the outskirts of the accretion disk of a supermassive black hole.
Specifically, they have obtained the first detection of two near-infrared emission lines in the accretion disk of the galaxy III Zw 002, placing a new limit on the size of these structures.
Emission lines are produced when an atom in an excited state falls to a lower energy level, releasing light in the process. Since each atom has a unique set of energy levels, the emitted light has a discrete wavelength that acts like a fingerprint identifying its origin. Emission lines often appear in spectra as fine, sharp points.
But in the eddy of an accretion disk, where the excited gas is under the gravitational influence of the supermassive black hole and is moving at speeds of thousands of kilometers per second, the emission lines broaden to form shallower peaks. The region of the accretion disk where these lines originate is called the broad line region.
Accretion disks are extremely difficult to image directly, as only two sources have been imaged thanks to the high angular resolution capability of the EHT (Event Horizon Telescope). But the new research reveals that evidence of an accretion disk can be found in a specific pattern of the broad emission lines called a double-peak profile.
Because the disk rotates, the gas on one side is moving away from the observer, while the gas on the other side is moving toward the observer. These relative motions stretch and compress the emission lines at longer and shorter wavelengths, respectively. The result is an enlarged line with two distinct peaks, one originating from each side of the rapidly spinning disk.
These double peak profiles are a rare phenomenon since their occurrence is limited to sources that can be seen almost head-on. In the few sources where it has been observed, the double peak has been found in the H-alpha and H-beta lines, two emission lines from hydrogen atoms that appear in the visible wavelength range.
These lines, which originate in the inner region of the broad line region near the supermassive black hole, do not provide evidence about the size of the accretionary disk as a whole. But recent near-infrared observations have revealed a region of the outer broad line that has never been seen before.
Researchers at the Laboratório Nacional de Astrofísica in Brazil have made the first unequivocal detection of two near-infrared double-peak profiles in the broad line region of III Zw 002, reports NOIRLab.
The Paschen-alpha (hydrogen) line originates from the interior region of the broad line region, and the OI (neutral oxygen) line originates from the outskirts of the broad line region, a region that has never been seen before. observed. These are the first double-peak profiles found in the near-infrared and arose unexpectedly during observations with the Gemini Near-Infrared Spectrograph (GNIRS).
These observations not only confirm the theorized presence of an accretion disk, they also advance astronomers’ understanding of the broad line region.
By comparing these observations with existing disk models, the team was able to extract parameters that provide a clearer picture of the supermassive black hole and the broad line region of III Zw 002.
The model indicates that the Paschen-alpha line originates from a radius of 16.77 light days (the distance light travels in one Earth day as measured from the supermassive black hole), and the line OI originates from a radius of 18.86 light days. It also predicts that the outer radius of the broad line region is 52.43 light-days. The model also indicates that the broad line region of III Zw 002 has an angle of inclination of 18 degrees with respect to Earth observers, and that the supermassive black hole at its center is between 400 and 900 million times the mass of our sun.
The work is published in The Astrophysical Journal Letters.
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