Pandora’s Cluster imaged by Spitzer space telescope


In a bid to taker a deeper look into space – as far back as the beginning of the universe nearly 14 billion light years away – the Spitzer space telescope has captured stunning images of the Pandora’s Cluster.

Pandora’s Cluster is a galaxy cluster Abell 2744 that has a strong gravitational lensing effect allowing our powerful telescopes to see what’s lurking behind them far away in space. Through the lensing effect of the Pandora’s cluster astronomers will be able to look back 13 billion light years in time in a bid to spot some of the first galaxies in the Universe.

The images captured by Spitzer were a part of the observations carried out by the telescope under the Frontier Fields project, which is a unique project wherein power of all three of NASA’s Great Observatories — Spitzer, the Hubble Space Telescope and the Chandra X-ray Observatory — are utilised to take the deepest look at space ever.

The fuzzy blobs in this Spitzer image are the massive galaxies at the core of this cluster, but astronomers will be poring over the images in search of the faint streaks of light created where the cluster magnifies a distant background galaxy.

Why is gravitational lensing required and helpful? Our universe is quite old and first galaxies that were formed soon after the Big Bang have now moved far away – as many as 13.8 billion light years – and to spot them even the combined powers of the three most powerful telescopes isn’t enough because the light from these galaxies have either dispersed or have red shifted and this effectively makes them too faint to be captured by any of these telescopes. That’s where gravitational lensing helps.

The gravity exerted by massive, foreground clusters of galaxies bends and magnifies the light of faraway, background objects, in effect creating cosmic zoom lenses. This phenomenon is called gravitational lensing. A recent paper published in the journal Astronomy & Astrophysics presented the full catalog data for two of the six galaxy clusters studied by the Frontier Fields: Abell 2744 — nicknamed Pandora’s Cluster — and MACS J0416, both located about four billion light years away. The other galaxy clusters selected for Frontier Fields are RXC J2248, MACS J1149, MACS J0717 and Abell 370.

Eager astronomers will comb the Frontier Fields catalogs for the tiniest, dimmest-lensed objects, many of which should prove to be the most distant galaxies ever glimpsed.

Astronomers want to understand how these primeval galaxies arose, how their constituent mass developed into stars, and how these stars have enriched the galaxies with chemical elements fused in their thermonuclear furnaces. To learn about the origin and evolution of the earliest galaxies, which are quite faint, astronomers need to collect as much light as possible across a range of frequencies. With sufficient light from these galaxies, astronomers can perform spectroscopy, pulling out details about stars’ compositions, temperatures and their environments by examining the signatures of chemical elements imprinted in the light.

Because the universe has expanded over its 13.8-billion-year history, light from extremely distant objects has been stretched out, or redshifted, on its long journey to Earth. Optical light emitted by stars in the gravitational-lensed, background galaxies viewed in the Frontier Fields has therefore redshifted into infrared. Spitzer can use this infrared light to gauge the population sizes of stars in a galaxy, which in turn gives clues to the galaxy’s mass. Combining the light seen by Spitzer and Hubble allows astronomers to identify galaxies at the edge of the observable universe.

Hubble, meanwhile, scans the Frontier Fields galaxy clusters in optical and near-infrared light, which has redshifted from ultraviolet light on its journey to Earth. Chandra, for its part, observes the foreground galaxy clusters in high-energy X-rays emitted by black holes and ambient hot gas. Along with Spitzer, the space telescopes size up the masses of the galaxy clusters, including their unseen but substantial dark matter content. Nailing down the clusters’ total mass is a critical step in quantifying the magnification and distortion they produce on background galaxies of interest. Recent multi-wavelength results in this vein from the Frontier Fields project regarding the MACS J0416 and MACS J0717 clusters were published in October 2015 and February 2016. These results also brought in radio wave observations from the Karl G. Jansky Very Large Array to see star-forming regions otherwise hidden by gas and dust.

The Frontier Fields collaboration has inspired scientists involved in the effort as they look ahead to delving even deeper into the universe with the James Webb Space Telescope, which is planned for launch in 2018.

Credits: NASA/JPL-Caltech
Credits: NASA/JPL-Caltech