Astronomy

Hubble: Galaxy cluster Abell 370 magnifies ancient objects beyond it

The latest report from the NASA/ESA Hubble collaboration:

BUFFALO charges towards the earliest galaxies
New Hubble project provides wide-field view of the galaxy cluster Abell 370 

The galaxy cluster Abell 370 was the first target of the BUFFALO survey, which aims to search for some of the first galaxies in the Universe. This remarkable cluster in the constellation of Cetus is located approximately four billion light-years away. Its mass, consisting of both hundreds of galaxies and dark matter, bends and distorts the light coming from even more distant objects behind it. This effect is known as strong gravitational lensing. The most stunning demonstration of gravitational lensing can be seen just below the centre of the image. Nicknamed “the Dragon”, this extended feature is made up of a multitude of duplicated images of a spiral galaxy in the background of Abell 370 — all lying five billion light-years away. Credit: NASA, ESA, A. Koekemoer, M. Jauzac, C. Steinhardt, and the BUFFALO team. [Hi-Res images]
The NASA/ESA Hubble Space Telescope has started a new mission to shed light on the evolution of the earliest galaxies in the Universe. The BUFFALO survey will observe six massive galaxy clusters and their surroundings. The first observations show the galaxy cluster Abell 370 and a host of magnified, gravitationally lensed galaxies around it.

Learning about the formation and evolution of the very first galaxies in the Universe is crucial for our understanding of the cosmos. While the NASA/ESA Hubble Space Telescope has already detected some of the most distant galaxies known, their numbers are small, making it hard for astronomers to determine if they represent the Universe at large.

Massive galaxy clusters like Abell 370, which is visible in this new image, can help astronomers find more of these distant objects. The immense masses of galaxy clusters make them act as cosmic magnifying glasses. A cluster’s mass bends and magnifies light from more distant objects behind it, uncovering objects otherwise too faint for even Hubble’s sensitive vision. Using this cosmological trick — known as strong gravitational lensing — Hubble is able to explore some of the earliest and most distant galaxies in the Universe.

With the final observation of the distant galaxy cluster Abell 370 — some five billion light-years away — the Frontier Fields program came to an end. Abell 370 is one of the very first galaxy clusters in which astronomers observed the phenomenon of gravitational lensing, the warping of spacetime by the cluster’s gravitational field that distorts the light from galaxies lying far behind it. This manifests as arcs and streaks in the picture, which are the stretched images of background galaxies. [Hi-Res images]
Numerous galaxies are lensed by the mass of Abell 370. The most stunning demonstration of gravitational lensing can be seen just below the centre of the cluster. Nicknamed “the Dragon”, this extended feature is made up of a multitude of duplicated images of a spiral galaxy which lies beyond the cluster.

This image of Abell 370 and its surroundings was made as part of the new Beyond Ultra-deep Frontier Fields And Legacy Observations (BUFFALO) survey. This project, led by European astronomers from the Niels Bohr Institute (Denmark) and Durham University (UK), was designed to succeed the successful Frontier Fields project [1]. 101 Hubble orbits — corresponding to 160 hours of precious observation time — have been dedicated to exploring the six Frontier Field galaxy clusters. These additional observations focus on the regions surrounding the galaxy clusters, allowing for a larger field of view.

BUFFALO’s main mission, however, is to investigate how and when the most massive and luminous galaxies in the Universe formed and how early galaxy formation is linked to dark matter assembly. This will allow astronomers to determine how rapidly galaxies formed in the first 800 million years after the Big Bang — paving the way for observations with the upcoming NASA/ESA/CSA James Webb Space Telescope.

Driven by the Frontier Fields observations, BUFFALO will be able to detect the most distant galaxies approximately ten times more efficiently than its progenitor. The BUFFALO survey will also take advantage of other space telescopes which have already observed the regions around the clusters. These datasets will be included in the search for the first galaxies.

This image composite shows the new observations of Abell 370 made for the BUFFALO project, as well as the old observation made for the Frontier Fields programme. The composition clearly shows the extended field of view in the new observations. [Hi-res images]
The extended fields of view will also allow better 3-dimensional mapping of the mass distribution — of both ordinary and dark matter — within each galaxy cluster. These maps help astronomers learn more about the evolution of the lensing galaxy clusters and about the nature of dark matter.

Notes

[1] Frontier Fields was a Hubble programme that ran from 2013 to 2017. Hubble spent 630 hours of observation time probing six notable galaxy clusters, all of which showed effects of strong gravitational lensing.