The Korea Astronomy and Space Science Institute announced on the 25th that it has found a new observation method that can detect more quasars, which are supermassive black hole objects.
Quasars that emit strong light play an important role in early cosmic astronomical studies, but they are too far from Earth to be easily observed.
An international joint research team led by Dr. Arman Shapilu and Dr. Satadru Park from the Theoretical Astronomy Center of the Korea Astronomy and Space Science Institute proposed a method for finding quasars that have undergone gravitational lensing by reconstructing the luminosity curves of quasars.
Gravitational lensing is a phenomenon in which a celestial object with mass warps nearby space-time and acts like a lens. It refers to a phenomenon in which light is refracted by the gravity of the celestial body acting as a lens, so that the celestial body, which is the light source, appears multiple or deformed, and becomes brighter or darker. A typical example is the appearance of multiple quasars that are point sources of light.
When gravitational lensing occurs on a quasar, the image of the quasar appears in multiple shapes at different locations. In this case, if a large telescope is not used, it is difficult to distinguish the images, so it is impossible to clearly determine whether gravitational lensing has occurred.
On the other hand, by using the luminosity curve of a quasar, it is possible to determine whether gravitational lensing has occurred without the need for long-term observation with a large telescope. A luminosity curve is a diagram showing the change in luminosity of a celestial body over time. However, there is a disadvantage in that it is difficult to understand the luminosity curve of the original quasar because it is difficult to standardize the pattern in which the brightness of the quasar changes.
To solve this problem, an international research team has proposed an observation method to discover gravitational lens quasars without knowing the shape of the luminosity curve of the original quasar. First, it was assumed that the quasar had undergone gravitational lensing, and the time taken between the two signals separated by gravitational lensing was adjusted. If the time taken between the two signals is different from the actual time, severe distortion occurs in the light curve of the randomly reconstructed quasar. Using this method, he discovered the gravitational lens quasar by finding the time at which distortion occurs the least in the light curve.
The researchers expect that this will at least double the chance of discovering gravitational lensed quasars. The chance of finding a normal quasar incorrectly as a gravitational lens quasar is significantly reduced.
It is also expected to contribute to a more accurate measurement of the Hubble constant, which indicates how quickly space expands. Although the Hubble constant is an important value for understanding the properties of the universe, the problem of ‘Hubble constant mismatch’ has appeared in the last 10 years, in which the values of the Hubble constant measured by various methods do not match each other.
In order to solve the Hubble constant mismatch problem, it is necessary to accurately measure the distances of numerous distant objects in various ways. The gravitational lens quasar has various information such as the brightness between images and the time difference of the luminosity curve, and by combining them, it is possible to measure the exact distance.
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“This study suggests an effective way to discover gravitational lensed quasars without using a giant telescope for a long time,” said Dr. Arman Shapilu.
This research paper was recently published in The Astrophysical Journal.
