ESA Releases The X-Ray Survey of 365 Galaxy Clusters and 26,000 Active Galactic Nuclei

  • ESA’s XMM-Newton spent more than 2,000 hours working on XXL Survey. 
  • In this survey, the X-ray space observatory observed numerous galaxy clusters and active galactic nuclei. 
  • The data obtained from this survey will help astronomers understand how galaxies and black holes evolve. 

European Space Agency’s (ESA) X-ray observatory, XMM-Newton is built to analyze interstellar X-ray sources, perform broad- and narrow-band spectroscopy, and carry out the simultaneous imaging of objects in both optical (ultraviolet and visible) and X-ray wavelengths.

Recently, ESA released the second batch of data of XXL Survey revealing the details of 365 galaxy clusters that trace a huge structure of the universe and its evolution, along with the information on 26,000 active galactic nuclei.

This the first X-ray survey that investigates 2 massive areas of the sky at higher sensitivity. It will enable astronomers to accurately map the distribution of AGN and galaxy clusters in the distant universe.

The XXL Survey

Over the last 8 years, XMM Netwon (also known as the X-ray Multi-Mirror Mission) has spent more than 2,000 hours working on XXL Survey. During this period it looked for several AGN and galaxy clusters by scanning 2 large regions of the void sky, each measuring 25 square degrees. To put this into context, the full moon measures across 1/2 degree.

The first batch of survey data was published in 2015. It was comprised of 100 bright galaxy clusters and 1,000 AGN. Overall, the survey has mapped X-ray of far distant galaxy clusters and AGN, so far that the light (or photons) left them when the universe was nearly 7 billion years old.

The XLSSC006 galaxy cluster | Multi-wavelength view | Credit: XMM-Newton/ESA

Some powerful events in the Universe generate X-rays, but since these rays cannot penetrate Earth’s atmosphere, astronomers use space-based telescopes to record them. When such telescopes detect the extragalactic universe, they usually observe 2 sources:

  1. The hot gas representing different galaxy clusters
  2. Small, bright regions at the center of a few galaxies where a supermassive black hole is engulfing nearby materials. These regions are called active galactic nuclei.

The matter isn’t uniformly distributed over the universe. Instead, it is present in the form of clusters that are shaped by gravity. For instance, galaxy clusters have the highest density peaks. The evolution and shape of the universe can be characterized by certain parameters that involve density of several cosmological components and the rate at which they are expanding.

Reference: arXiv:1810.03849 | ESA

The values of some parameters are well-known, but in order to precisely define the universe structure, astronomers have to trace numerous cosmic samples that are far away from our galaxy. That’s what XXL Survey is trying to provide here: a well-defined catalog of clusters for constraining cosmological parameters.

An optical view of 365 galaxy clusters | Credit: CFHT Legacy Survey/XXL Survey/ESA

Data obtained from XXL survey help astronomers measure the 3D cluster effect of distant galaxies and AGN on massive scales. The survey has made it possible to locate where the AGN are situated in the universe, and to understand how black holes evolve with time.

What’s Next?

The third version of XXL survey results will be released in 2021. It will contain more X-ray sources (probably thousands of more galaxy clusters and AGN) and a comprehensive analysis of cosmological parameters.

ESA is also working on a mission named Euclid. It will analyze the evolution of cosmic objects by measuring redshifts and structures of galaxy clusters. The satellite will detect light (photons) emitted up to 10 billion years ago, in infrared and optical wavelengths.

Read: The Richest Star Catalogue Of 1.7 Billion Stars | Details Of Milky Way

Moreover, the questions raised by analyzing data obtained from the XXL survey will be examined in details by ESA’s next mission, Athena. It’s Advanced Telescope for High-ENergy Astrophysics set to launch in 2031. It will be far more sensitive than XMM-Newton and will tell us more about these massive structures: how they form, take shape and evolve.

Written by
Varun Kumar

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