The ALMA radio telescope sees a hole in a galaxy cluster

RX J1347.5-1145 galaxy cluster (Image ALMA (ESO/NAOJ/NRAO)/T. Kitayama (Toho University, Japan)/ESA/Hubble & NASA)
RX J1347.5-1145 galaxy cluster (Image ALMA (ESO/NAOJ/NRAO)/T. Kitayama (Toho University, Japan)/ESA/Hubble & NASA)

The ALMA radio telescope was used for the first time to measure the thermal Sunyaev-Zel’dovich Effect aiming it at the RX J1347.5-1145 galaxy cluster, located about 5 billion light years from Earth. This effect is due to the photons from the cosmic microwave background radiation that interact with high-energy electrons because of their temperature. Those measurements are useful to obtain information on the location and distribution of dense galactic clusters such as the one studied in this case.

The cosmic microwave background radiation (CMB or CMBR), is the residue of the earliest stages of the universe and is considered one of the evidence of the Big Bang. Over the decades, various satellites were built to detect it with increasing precision. In May 2009, ESA launched its own satellite, Planck Surveyor, and in March 2013 presented the best map yet of the cosmic microwave background radiation created from its detections.

When the microwaves that constitute the cosmic microwave background radiation pass through galactic clusters its photons interact with high-energy electrons that are on their way with the result that their energy increases slightly. This effect was hypothesized for the first time in 1969 by Rashid Sunyaev and Yakov Zel’dovich, two physicists and astronomers who worked together at the time of the USSR. The effect that took their names was observed for the first time in 1983.

The RX J1347.5-1145 galaxy cluster is one of the most massive and one of the brightest at X-rays among those known. It was studied during the Cluster Lensing And Supernova survey with Hubble (CLASH) survey carried out between 2010 and 2013 using the Hubble Space Telescope. In that case, the researchers were interested in the gravitational lensing effects generated by clusters like this one due to their huge overall gravity, so strong as to deflect light.

The image shows the RX J1347.5-1145 galaxy cluster photographed by the Hubble Space Telescope with the thermal Sunyaev-Zel’dovich Effect shown in blue. The energy distribution of the cosmic microwave background photons appears as a drop in temperature at the wavelengths observed by the ALMA radio telescope, with the result that there’s a dark area at its center.

This study was conducted by bringing together observations made with the Hubble Space Telescope with others taken with the ALMA (Atacama Large Millimeter/submillimeter Array) radio telescope. Inaugurated in March 2013, it’s currently the most powerful radio telescope in the world and researchers are using it for a range of studies increasingly wide.

RX J1347.5-1145 galaxy cluster seen by Hubble only (Image ESA/Hubble, NASA)
RX J1347.5-1145 galaxy cluster seen by Hubble only (Image ESA/Hubble, NASA)

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