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A cosmic census

A new census of the Universe will allow scientists to understand more about how galaxies are born, age, and die. The millions of galaxies that have been painstakingly catalogued come in many shapes and sizes and this new work shines a light on every variety that we can see.  

The new measurements, which were published in Monthly Notices of the Royal Astronomical Society, will allow many other people to look for unusual and new types of galaxy hidden within the data. It will also help them to look at whole “populations” to better understand how they evolve. It has already been used to find interesting rare galaxies and to understand how and why they stand out from the crowd. 

The international group of scientists, led by astronomers working with Professor Seb Oliver at the University of Sussex, decided to create the Herschel Extragalactic Legacy Project. This project was set up to understand images from the Herschel Space Observatory; a huge telescope in space which measured the far infrared light that is emitted from the cool dust in galaxies. 

Illustration of the Herschel Space Observatory which is at the center of the work
Credit: Ève Barlier

They brought together observations from across the electromagnetic spectrum; from the bluest light emitted by hot young stars to the reddest which comes from cool dust. The team then used all this information to weigh galaxies, measure how far away they are, and count how many stars are being born within them. 

Usually scientists use a small area of the night sky, but this new work brings together all of the best-studied regions allowing them to search through an unprecedented volume of the Universe. The more sky that we observe, the more rare objects we can find in order to understand all types of galaxies. One unusual object already found in the data was a giant black hole discovered only 1.4 billion years after the Big Bang.

By bringing together public data from many different telescopes and making sure everything is freely available, the team believe it will also open up data to more groups and maximise how many people can get involved. First author Raphael Shirley said: “it will be like a digital library of galaxies where anyone can take out a book on any galaxy that can be seen.” He is keen that this “open science” practice will be more widely adopted as it also means the public can use it. “Maybe there is an intrepid school student who might find an exciting new discovery hidden amongst the millions of galaxies that has been missed by the professionals.”

Featured image: © 2021, Ève Barlier

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