Massive object discovered hiding behind the Milky Way

The discovery of one of largest known structures in the Universe has recently been announced by a multi-national team of astronomers. Led by Renée Kraan-Korteweg from the University of Cape Town, the team discovered the presence of an unknown major supercluster roughly 800 million light-years away from Earth.

Superclusters are some of the biggest structures in our Universe. They are essentially clusters of thousands of galaxies, reaching up to 200 million light years in size. The most well-known of these is the Shapely supercluster. It is the largest concentration of galaxies in our nearby universe, and one of the most massive objects which form a gravitationally interacting unit. The newly discovered Vela supercluster, however, appears to challenge Shapely’s rankings in size and mass. But how could such a huge object have gone unnoticed?

The key to the supercluster’s concealment lies in its strategic position as it is located behind the disk of our very own galaxy, in what is termed the Galactic Plane. This plane is the lighter, dense band of stars you see when you look up into the night sky. The Milky Way contains over 100 billion stars, trillions of planets, and ubiquitous clouds of gas and dust. Although this richness in material is great for astronomers studying our galactic neighbourhood, it’s actually a huge optical hurdle for observing more distant structures outside of our galaxy. Dense star and dust layers block our view, meaning this region has sparse observations.

The team’s solution to this was to fuse a combination of observations of thousands of partly obscured galaxies from different sources. Telescopes used include the South African Large Telescope (SALT), the Anglo-Australian Telescope (AAT), and X-ray surveys of the galactic plane. They calculated how fast the galaxies above and below were moving away from the Earth. Their results showed the galaxies all moving together, indicating the presence of numerous galaxies that couldn’t be observed.

Kraan-Korteweg expressed her surprise by stating she “could not believe such a major structure would pop up so prominently” when her team analysed the results in the new survey’s spectra. According to the team’s predictions, Vela supercluster could host somewhere between 1,000 and 10,000 trillion stars. Further follow-up observations are however required to understand the supercluster’s full extent, mass, and influence. The team’s next step is to proceed with additional observations, such as the multi-wavelength programme. Ultimately they hope to unearth the full influence of the supercluster not only on our galaxy, but on our entire understanding of cosmography and cosmology of the Universe.”

Gaia Stucky de Quay is studying for a PhD in Earth and Planetary Sciences

Banner image: Star field, Anatolii Vasilev

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