Hickson Compact Galaxy Group 7

The NASA/ESA Hubble Space Telescope has imaged part of the Hickson Compact Group 7, or HCG 7 for short. This grouping is composed of one lenticular (lens-shaped) and three spiral galaxies in close proximity. In this image, one of the spirals dominates the foreground, with many more distant galaxies peppering the background. Observing tightly-knit galaxy groups like HCG 7 is important because they evolve in a different way from their more spaced-out counterparts in less crowded regions of the Universe.

A recent study using Hubble data analysed the star clusters in HCG 7. Three hundred young clusters and 150 globular clusters were charted, and their ages and distributions measured. The results suggest that the rate of star formation has been fairly steady through time, although quite high in the central regions. Additional studies, including searches for material between the galaxies, hint that the stars in the HCG 7 galaxies formed by converting their gas without any gravitational influences caused by merging with other galaxies. This is puzzling, as the galaxies are depleting their supplies of gas at a rate that suggests that they have merged in the past.

This raises the question of whether the group really has evolved serenely, or if there are mysterious processes at work that are yet to be understood. The currently known information is contradictory and an encouragement for further studies to discover the real story behind HCG 7.

This picture was created from images taken with the Wide Field Channel of the Advanced Camera for Surveys. Images through a blue filter (F435W, coloured blue), yellow-orange (F606W, coloured green) and near-infrared (F814W, coloured red) filters were combined. The total exposure times were 1710 s, 1230 s and 1065 s per filter, respectively, and the field of view is 3.3 x 3.0 arcminutes.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1132a/

Wolf-Rayet star WR124

M1-67 is the youngest wind-nebula around a Wolf-Rayet star, called WR124, in our Galaxy. These Wolf-Rayet stars start their lives with dozens of times the mass of our Sun, but loose most of it through a powerful wind, which is ultimately responsible for the formation of the nebula.

Ten years ago, Hubble Space Telescope observations revealed a wealth of small knots and substructures inside the nebula. The same team, led by Cédric Foellmi (ESO), has now used ESO's Very Large Telescope (VLT) to watch how these structures have evolved and what they can teach us about stellar winds, their chemistry, and how they mix with the surrounding interstellar medium, before the star will eventually blow everything away in a fiery supernova explosion.

The image is based on FORS1 data obtained by the Paranal Science team with the VLT through 2 wide (B and V) and 3 narrow-band filters.

Image Credit: ESO
Explanation from: https://www.eso.org/public/images/wr124/

Stellar Explosion in the Orion Molecular Cloud 1

Stellar explosions are most often associated with supernovae, the spectacular deaths of stars. But new ALMA observations provide insights into explosions at the other end of the stellar life cycle, star birth. Astronomers captured these dramatic images as they explored the firework-like debris from the birth of a group of massive stars, demonstrating that star formation can be a violent and explosive process too.

1350 light years away, in the constellation of Orion (the Hunter), lies a dense and active star formation factory called the Orion Molecular Cloud 1 (OMC-1), part of the same complex as the famous Orion Nebula. Stars are born when a cloud of gas hundreds of times more massive than our Sun begins to collapse under its own gravity. In the densest regions, protostars ignite and begin to drift about randomly. Over time, some stars begin to fall toward a common centre of gravity, which is usually dominated by a particularly large protostar — and if the stars have a close encounter before they can escape their stellar nursery, violent interactions can occur.

About 100 000 years ago, several protostars started to form deep within the OMC-1. Gravity began to pull them together with ever-increasing speed, until 500 years ago two of them finally clashed. Astronomers are not sure whether they merely grazed each other or collided head-on, but either way it triggered a powerful eruption that launched other nearby protostars and hundreds of colossal streamers of gas and dust out into interstellar space at over 150 kilometres per second. This cataclysmic interaction released as much energy as our Sun emits in 10 million years.

Fast forward 500 years, and a team of astronomers led by John Bally (University of Colorado, USA) has used the Atacama Large Millimeter/submillimeter Array (ALMA) to peer into the heart of this cloud. There they found the flung-out debris from the explosive birth of this clump of massive stars, looking like a cosmic version of fireworks with giant streamers rocketing off in all directions.

Such explosions are expected to be relatively short-lived, the remnants like those seen by ALMA lasting only centuries. But although they are fleeting, such protostellar explosions may be relatively common. By destroying their parent cloud, these events might also help to regulate the pace of star formation in such giant molecular clouds.

Hints of the explosive nature of the debris in OMC-1 were first revealed by the Submillimeter Array in Hawaii in 2009. Bally and his team also observed this object in the near-infrared with the Gemini South telescope in Chile, revealing the remarkable structure of the streamers, which extend nearly a light-year from end to end.

The new ALMA images, however, showcase the explosive nature in high resolution, unveiling important details about the distribution and high-velocity motion of the carbon monoxide (CO) gas inside the streamers. This will help astronomers understand the underlying force of the blast, and what impact such events could have on star formation across the galaxy.

Image Credit: ALMA (ESO/NAOJ/NRAO), J. Bally/H. Drass et al.
Explanation from: https://www.eso.org/public/news/eso1711/