Astronomers Detect Evidence of Two Supermassive Black Holes 11.9 Billion Light-Years Away

Astronomers studying the distant system MG B2016+112 have found independent evidence that it contains two active galactic nuclei rather than a single source appearing as multiple images.

The light analysed by researchers has travelled for approximately 11.9 billion years before reaching Earth. A massive foreground galaxy bends and magnifies the light from objects behind it through gravitational lensing, producing three visible spots identified as A, B and C.

Scientists sought to determine whether the three spots represented multiple images of one object or separate astronomical sources.

Spectral Analysis Identifies Different Sources

Earlier radio and X-ray observations from the Chandra observatory had suggested the presence of two active galactic nuclei, but direct spectroscopic evidence had remained elusive.

Researchers revisited archival observations collected in 2018 using the MUSE instrument on the Very Large Telescope (VLT). They examined the spectral signatures of ionised helium and carbon to establish whether the three images originated from the same source.

The analysis found that images A and B had nearly identical chemical signatures, indicating that they were images of the same object. Image C, however, displayed a significantly different ratio of spectral lines.

According to the researchers, the difference could not be explained by the effects of gravitational lensing, providing independent evidence for two distinct active galactic nuclei in MG B2016+112.

Researchers Rely on Reliable Helium and Carbon Signals

Not every spectral measurement could be used to reach the conclusion. Emissions associated with hydrogen, carbon and nitrogen were affected by saturated absorption, which distorted the data and made them unsuitable for reliable quantitative analysis.

The researchers therefore relied on clearer signals from helium and carbon to distinguish between the sources.

The differences in these spectral measurements helped establish that images A and B represented one source, while image C originated from another.

Black Hole Masses Estimated at Millions of Solar Masses

Based on the spectral data, researchers estimated a lower limit of approximately 15 million to 20 million solar masses for the central black holes.

The estimated similarity in their masses, together with a separation of around 570 light-years, suggests that the system may be undergoing a galaxy merger.

The findings indicate that the two supermassive black holes could be moving towards one another as the merger progresses.

Accretion Rates Differ Between the Two Sources

Researchers also estimated the rates at which matter is falling towards the black holes, although these calculations depend on the gravitational lensing models used to interpret the observations.

For the source represented by images A and B, the accretion rate was estimated at approximately 50% of the Eddington limit. This limit describes the theoretical point at which radiation pressure counteracts the gravitational pull drawing matter towards an object.

The estimated rate for source C was considerably lower, at about 4% of the Eddington limit.

However, researchers regard the figure for source C as preliminary because it is particularly sensitive to assumptions about how strongly the foreground galaxy magnifies the distant object.

Near-Infrared Observations Planned to Verify Findings

The next stage of research will involve near-infrared observations to test the existing estimates using different spectral lines.

Scientists also intend to examine the gas surrounding the two active galactic nuclei to obtain further information about their properties and the system’s evolution.

If the interpretation is confirmed, MG B2016+112 could provide a rare opportunity to study two supermassive black holes during the later stages of a merger in an era of active galaxy formation.