Shapley Supercluster

While scanning the sky for the oldest cosmic light, ESA’s Planck satellite has captured snapshots of some of the largest objects populating the Universe today: galaxy clusters and superclusters.

Several hundred galaxies and the huge amounts of gas that permeate them are depicted in this view of the core of the Shapley Supercluster, the largest cosmic structure in the local Universe.

The supercluster was discovered in the 1930s by American astronomer Harlow Shapley, as a remarkable concentration of galaxies in the Centaurus constellation.

Boasting more than 8000 galaxies and with a total mass more than ten million billion times the mass of the Sun, it is the most massive structure within a distance of about a billion light-years from our Milky Way Galaxy.

The hot gas pervading galaxy clusters shines brightly in X-rays, but it is also visible at microwave wavelengths, which Planck sees as a distinctive signature in the Cosmic Microwave Background – the afterglow of the Big Bang.

Looking for this signature – called the Sunyaev–Zel’dovich effect – Planck has already spotted more than 1000 galaxy clusters, including several superclusters and pairs of interacting clusters.

This composite image of the core of the Shapley Supercluster combines the gas detected with Planck at large scales between the members of the supercluster (shown in blue) with that detected in X-rays within the galaxy clusters of Shapley using the Rosat satellite (pink), as well as a view of its rich population of galaxies as observed at visible wavelengths in the Digitised Sky Survey.

The largest pink blobs of X-rays identify the two galaxy clusters Abell 3558 on the right and Abell 3562 on the left, as well as a couple of smaller groups between them.

The image measures 3.2 x 1.8 square degrees and shows the central portion of the Shapley Supercluster. It was produced by reconstructing the Sunyaev–Zel’dovich effect from the Planck frequency maps, and was first published in a Planck Collaboration paper in March 2013.

Image credit: ESA & Planck Collaboration / Rosat/ Digitised Sky Survey

Massive Star Formation in an Intergalactic Filament

The Herschel Space Observatory has discovered a giant, galaxy-packed filament ablaze with billions of new stars. The filament connects two clusters of galaxies that, along with a third cluster, will smash together in several billion years and give rise to one of the largest galaxy superclusters in the universe.

The three galaxy clusters of the emerging supercluster, known as RCS2319, are seen in visible and X-ray light (purple) to the left. Observations by Herschel in infrared light appear to the right, with colored regions indicating greater infrared emissions. A white circle broadly outlines the 8 million light-year-long intergalactic filament in each image.

In visible light, the filament does not stand out because dust obscures the star-formation activity in distant galaxies. Telescopes like Herschel, however, can detect the infrared glow of this dust as it is heated by newborn stars.

The amount of infrared light suggests that the galaxies in the filament are cranking out the equivalent of about 1,000 new Suns in terms of mass per year. For comparison's sake, our Milky Way galaxy is producing about one Sun's mass-worth of new stars per year.

Notably, the third galaxy cluster is off the edge of the image on the right. The reason behind this apparent snub is that the original research proposal called for making a map centered on the top cluster. During the observing run, astronomers did not know the filament existed, so its eventual discovery serves as a nice example of scientific serendipity. The team is now aiming to perform further follow-up observations to examine the filament in more detail.

Photo credit: ESA/NASA/JPL-Caltech/CXC/McGill University

Note: For more information, see Herschel Sees Intergalactic Bridge Aglow With Stars.