Monday, June 6, 2022

Quasar closest to the Milky Way hides unknown structure in its galaxy

An unknown structure, formed by faint radio emissions in a giant galaxy that harbors a quasar, has been detected by a team of Japanese astronomers. The discovery was made for the first time with a new technique for studying quasars, considered to be some of the brightest in the universe, and could help scientists better understand the relationship between active black holes and the suppression of star formation.

Considered to be the extremely luminous cores of galaxies with supermassive black holes at their centers, quasars emit intense radiation from large amounts of heated gas in the accretion disk around black holes. In the new study, researchers used the Chilean Atacama Large Millimeter/submillimeter Array (ALMA) telescope to examine quasar 3C 273.

Located approximately 2.4 billion light-years from Earth, 3C 273 was the first quasar discovered, and it is also the brightest and most deeply studied. Although it has been known for years, much of our knowledge of it is related to its bright central core, the source of most of the object's radio waves.

The problem is that the quasar's light makes observations of the rest of the galaxy difficult, and this is even more pronounced at the radio wavelengths observed by ALMA . To get around the issue, the team led by Shinya Komugi of Kogakuin University worked with “self-calibration”. This is a technique where 3C 273 is used to reduce its own brightness by correcting for fluctuations in the atmosphere, which can affect detections.

As a result, the method allowed ALMA to carry out observations at the highest dynamic ranges ever achieved, with frequencies of 85,000, 39,000 and 2,500 GHz, and revealed details never seen before: the team managed to observe an unknown structure in the quasar galaxy, formed by a narrow band of radio emissions that spans tens of thousands of light years. The emissions come from the hundreds of billions of solar masses of hydrogen gas ionized by ultraviolet radiation and X-rays released from the quasar .

This is the first time that radio waves from such a mechanism have been found extending thousands of light-years into the galaxy that harbors the quasar, and the discovery could help answer whether the object's energy might be strong enough to affect the galaxy's ability to form new stars . Gaseous hydrogen is an essential ingredient for star formation, but ionization prevents this from happening.

Interestingly, there appears to be a large reserve of molecular hydrogen gas in the quasar galaxy 3C 273, where stars are still forming. This suggests two possibilities: either the relationship between the quasar's emissions and the suspension of star formation is not as concrete as previously thought, or the object and its galaxy were observed in the brief period before the effects of the quasar's emissions became apparent.

Komugi notes that the discovery represents a new avenue for studying problems addressed by visible light observations. "By applying the same technique to other quasars, we hope to understand how the galaxy evolves through interactions with its central core," he said in a statement.

The paper with the results of the study was published in The Astrophysical Journal.

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