Major mergers: At first glance, it may seem as though this image was taken through a faulty lens, but the mind-bending distortions visible in this Hubble Wide Field Camera 3 impressive image are actually caused by a cosmic phenomenon. The bright object at the centre of the frame is the galaxy cluster SDSS J1336-0331. The enormous gravitational influence of the cluster warps the very shape and fabric of its environment (the spacetime around it) creating an effect known as strong gravitational lensing. Through this the light from background galaxies in the line of sight to the observer are bent into fantastic arcs. This effect is very useful for studying distant background galaxies. Moreover SDSS J1336-0331 is interesting in itself: the cluster was part of a study of star formation within 42 of the Brightest Cluster Galaxies (BCGs — the brightest galaxies within their host clusters, as the name would suggest). Typically located in the centres of their clusters, BCGs are among the most massive and luminous galaxies in the Universe. They are generally huge elliptical galaxies and are likely to host active galactic nuclei (AGN) in their cores. The study found evidence to suggest that BCGs are fueled by cold gas from the galaxy. It also showed that star formation in older BCGs no longer significantly contributes to the galaxy’s growth; instead, the stellar growth occurs through mergers, the collision of two galaxies. Violent, gas-rich major mergers can trigger intense bursts of star formation in their aftermath.

Name: 6dFGS gJ133600.1-033130, SDSS J1336-0331
Type: Early Universe : Galaxy : Grouping : ClusterEarly Universe : Cosmology : Phenomenon : Lensing
Category: Galaxies
Constellation: Virgo
Distance: z=0.176 (redshift)
Release date: 16 July 2018, 06:00
Credit: ESA/Hubble & NASA

The Milky Way’s big sister: This image taken by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3) shows a beautiful spiral galaxy called NGC 6744. At first glance, it resembles our Milky Way albeit larger, measuring more than 200 000 light-years across compared to 100 000 light-year diameter for our home galaxy. NGC 6744 is similar to our home galaxy in more ways than one. Like the Milky Way, NGC 6744 has a prominent central region packed with old yellow stars. Moving away from the galactic core, one can see parts of the dusty spiral arms painted in shades of pink and blue; while the blue sites are full of young star clusters, the pink ones are regions of active star formation, indicating that the galaxy is still very lively. In 2005, a supernova, named 2005at, was discovered within NGC 6744, adding to the argument of this galaxy’s liveliness (not visible in this image). SN 2005at is a type Ic supernova, formed when a massive star collapses in itself and loses its hydrogen envelope.

Name: NGC 6744
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Pavo
Distance: 35 million light years
Release date: 23 July 2018, 06:00
Credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt

Probing the distant past: Obtained for a research programme on star formation in old and distant galaxies, this NASA/ESA Hubble Space Telescope image obtained with its Wide Field Camera 3 (WFC3) demonstrates the immense effects of gravity; more specifically, it shows the effects of gravitational lensing caused by an object called SDSS J1152+3313. Gravitational lenses — such as this galaxy cluster SDSS J1152+3313 — possess immense masses that warp their surroundings and bend the light from faraway objects into rings, arcs, streaks, blurs, and other odd shapes. This lens, however, is not only warpping the appearance of a distant galaxy — it is also amplifying its light, making it appear much brighter than it would be without the lens. Combined with the high image quality obtainable with Hubble, this gives valuable clues into how stars formed in the early Universe. Star formation is a key process in astronomy. Everything that emits light is somehow connected to stars, so understanding how stars form is key to understanding countless objects lying across the cosmos. Astronomers can probe these early star-forming regions to learn about the sizes, luminosities, formation rates, and generations of different types of stars.

Name: SDSS J1152+3313
Type: Early Universe : Galaxy : Type : Gravitationally Lensed
Category: Cosmology
Constellation: Ursa Major
Release date: 30 July 2018, 06:00
Credit: ESA/Hubble & NASA Acknowledgement: Judy Schmidt (Geckzilla)

A globular cluster’s striking red eye: This Picture of the Week shows the colourful globular cluster NGC 2108. The cluster is nestled within the Large Magellanic Cloud, in the constellation of the Swordfish (Dorado). It was discovered in 1835 by the astronomer, mathematician, chemist and inventor John Herschel, son of the famous William Herschel. The most striking feature of this globular cluster is the gleaming ruby-red spot at the centre left of the cluster. What looks like the cluster’s watchful eye is actually a carbon star. Carbon stars are almost always cool red giants, with atmospheres containing more carbon than oxygen — the opposite to our Sun. Carbon monoxide forms in the outer layer of the star through a combination of these elements, until there is no more oxygen available. Carbon atoms are then free to form a variety of other carbon compounds, such as C2, CH, CN, C3 and SiC2, which scatter blue light within the star, allowing red light to pass through undisturbed. This image was captured by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS), using three different filters.

Name: NGC 2108
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Dorado
Distance: 150000 light years
Release date: 6 August 2018, 06:00
Credit: ESA/Hubble & NASA

Galactic treasure chest: Galaxies abound in this spectacular Hubble image; spiral arms swirl in all colours and orientations, and fuzzy ellipticals can be seen speckled across the frame as softly glowing smudges on the sky. Each visible speck of a galaxy is home to countless stars. A few stars closer to home shine brightly in the foreground, while a massive galaxy cluster nestles at the very centre of the image; an immense collection of maybe thousands of galaxies, all held together by the relentless force of gravity. Galaxy clusters are some of the most interesting objects in the cosmos. They are the nodes of the cosmic web that permeates the entire Universe — to study them is to study the organisation of matter on the grandest of scales. Not only are galaxy clusters ideal subjects for the study of dark matter and dark energy, but they also allow the study of farther-flung galaxies. Their immense gravitational influence means they distort the spacetime around them, causing them to act like giant zoom lenses. The light of background galaxies is warped and magnified as it passes through the galaxy cluster, allowing astronomers insight into the distant — and therefore early — Universe. This image was taken by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 as part of an observing programme called RELICS (Reionization Lensing Cluster Survey). RELICS imaged 41 massive galaxy clusters with the aim of finding the brightest distant galaxies for the forthcoming NASA/ESA/CSA James Webb Space Telescope (JWST) to study.

Name: RXC J0142.9+4438
Type: Early Universe : Galaxy : Type : Gravitationally LensedEarly Universe : Galaxy : Grouping : ClusterEarly Universe : Cosmology : Phenomenon : Lensing
Category: Galaxies
Constellation: Andromeda
Release date: 13 August 2018, 06:00
Credit: ESA/Hubble & NASA, RELICS