An article accepted for publication in the journal “Astronomy & Astrophysics” describes a research on the galaxy cluster RCS2 J2327-0204, or simply RCS2 J2327. A team of researchers combined observations carried out with the HAWK-I instrument installed on the VLT (Very Large Telescope) and with the Hubble Space Telescope’s ACS instrument to measure the distortions caused by the gravitational lens effects of the cluster estimating its mass in about 2 quadrillion times the Sun’s.
Galactic clusters can be really huge when they include many galaxies, especially if they contain very massive galaxies. Approximately 6 billion light years from Earth, the RCS2 J2327 cluster is one of the largest known, with such an overall mass that it bends the space around it, with results that can be useful to astronomers when they allow to magnify the images obtained. This phenomenon, known as gravitational lens and predicted by Albert Einstein’s General Theory of Relativity, is well known and exploited in various researches.
In the case of an object as large as the galaxy cluster RCS2 J2327, the phenomenon of gravitational lens can be observed even in three different effects: strong lens, weak lens and microlens. The strong lens effect is the most obvious one, which produces multiple images such as the Einstein cross and the distorted ones of galaxies. The weak lens effect is more localized and is mainly studied in a statistical way but is useful to calculate the mass of cosmic objects such as a galaxy cluster.
The calculations require detailed observations that provide accurate data on the effects of weak gravitational lens in the various areas of the galaxy cluster. To obtain the required data, the researchers combined those obtained from two different instruments: the ground-based HAWK-I (High Acuity Wide-field K-band Imager) on the VLT and ACS (Advanced Camera for Surveys) on the Hubble Space Telescope.
The complex analysis of the data combined allowed to estimate the total mass of the galaxy cluster RCS2 J2327 in just over 2 quadrillion solar masses. It’s one of the most massive clusters known. According to the researchers, the use of the HAWK-I instrument for this type of measurements is valid thanks to its sensitivity.