A Stellar Birthplace Shaped and Destroyed by Energetic Offspring

The little-known cloud of cosmic gas and dust called Gum 15 is the birthplace and home of hot young stars. Beautiful and deadly, these stars mould the appearance of the nebula from which they formed and, as they progress into adulthood, will eventually also destroy it.

This image was taken as part of the ESO Cosmic Gems programme using the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile. It shows Gum 15, located in the constellation of Vela (The Sails), some 3000 light-years from Earth. This glowing cloud is a striking example of an HII region. Such clouds form some of the most spectacular astronomical objects we can see; for example the Eagle Nebula (which includes the feature nicknamed “The Pillars of Creation”), the great Orion Nebula, and this less famous example, Gum 15.

Hydrogen (H) is the most common element in the Universe, and can be found in virtually every environment investigated by astronomers. HII regions are different because they contain substantial amounts of ionised hydrogen — hydrogen atoms that have been stripped of their electrons through high energy interactions with ultraviolet photons — particles of light. As the ionised hydrogen nuclei recapture electrons they release light at different characteristic wavelengths. It is one of these that gives nebulae such as Gum 15 their reddish glow — a glow which astronomers call hydrogen alpha (Hα).

In HII regions the ionising photons come from the young hot stars within the region, and Gum 15 is no exception. At the centre of this image you can see one of the culprits: the star HD 74804, the brightest member of a cluster of stars known as Collinder 197.

The clumpy, irregular appearance that enhances this nebula’s beauty is not unusual for a HII region and is again a result of the stars within. HII regions have diverse shapes because the distribution of stars and gas inside them is so irregular. Adding to Gum 15’s interesting shape are the forked dark patch of obscuring dust visible in the centre of this image and some dim blue reflection structures crossing it. This dust feature makes the nebula resemble a larger and fainter version of the better known Trifid Nebula (Messier 20), although in this case the name Bifid Nebula might be more apposite.

An HII region like this one might give birth to thousands of stars over a period of several million years. Some of these stars cause it to glow and sculpt its shape, and it is these stars that will eventually destroy it. Once the newly minted stars have passed through their infant stages, strong winds of particles will stream away from these large stars, sculpting and dispersing the gases around them, and when the most massive of these stars begin to die, Gum 15 will die with them. Some stars are so large that they will go out with a bang, exploding as supernovae and dispersing the regions last traces of HII, leaving behind just a cluster of infant stars.

Image Credit: ESO
Explanation from: http://www.eso.org/public/news/eso1420/

Lives and Deaths of Sibling Stars

In this striking new image from ESO’s La Silla Observatory in Chile young stars huddle together against a backdrop of clouds of glowing gas and lanes of dust. The star cluster, known as NGC 3293, would have been just a cloud of gas and dust itself about ten million years ago, but as stars began to form it became the bright group of stars we see here. Clusters like this are celestial laboratories that allow astronomers to learn more about how stars evolve.

This beautiful star cluster, NGC 3293, is found 8000 light-years from Earth in the constellation of Carina (The Keel). This cluster was first spotted by the French astronomer Nicolas-Louis de Lacaille in 1751, during his stay in what is now South Africa, using a tiny telescope with an aperture of just 12 millimetres. It is one of the brightest clusters in the southern sky and can be easily seen with the naked eye on a dark clear night.

Star clusters like NGC 3293 contain stars that all formed at the same time, at the same distance from Earth and out of the same cloud of gas and dust, giving them the same chemical composition. As a result clusters like this are ideal objects for testing stellar evolution theory.

Most of the stars seen here are very young, and the cluster itself is less than 10 million years old. Just babies on cosmic scales if you consider that the Sun is 4.6 billion years old and still only middle-aged. An abundance of these bright, blue, youthful stars is common in open clusters like NGC 3293, and, for example, in the better known Kappa Crucis cluster, otherwise known as the Jewel Box or NGC 4755.

These open clusters each formed from a giant cloud of molecular gas and their stars are held together by their mutual gravitational attraction. But these forces are not enough to hold a cluster together against close encounters with other clusters and clouds of gas as the cluster’s own gas and dust dissipates. So, open clusters will only last a few hundred million years, unlike their big cousins, the globular clusters, which can survive for billions of years, and hold on to far more stars.

Despite some evidence suggesting that there is still some ongoing star formation in NGC 3293, it is thought that most, if not all, of the nearly fifty stars in this cluster were born in one single event. But even though these stars are all the same age, they do not all have the dazzling appearance of a star in its infancy; some of them look positively elderly, giving astronomers the chance to explore how and why stars evolve at different speeds.

Take the bright orange star at the bottom right of the cluster. This huge star, a red giant, would have been born as one of the biggest and most luminous of its litter, but bright stars burn out fast. As the star used up the fuel at its core its internal dynamics changed and it began to swell and cool, becoming the red giant we now observe. Red giants are reaching the end of their life cycle, but this red giant’s sister stars are still in what is known as the pre-main-sequence — the period before the long, stable, middle period in a star’s life. We see these stars in the prime of their life as hot, bright and white against the red and dusty background.

Image Credit: ESO/G. Beccari
Explanation from: http://www.eso.org/public/news/eso1422/

In Search of Space

At 5000 metres above sea level, high upon the Chajnantor Plateau in Chile, the antennas of the ALMA Observatory peer skywards, scanning the Universe for clues to our cosmic origins. This plateau is one of the highest observatory sites on Earth.

Visible amongst the thousands of stars on the right side of this image are the Small and Large Magellanic Clouds, appearing as luminous smudges in the sky. These cloud-like objects are both galaxies — two of the closest galactic neighbours to our galaxy, the Milky Way.

ALMA's main aim is to observe the coldest and most ancient objects in the cosmos — known as the "cold Universe". The array measures radiation emitted in the millimetre and submillimetre wavelengths, which lie in between infrared and radio waves in the electromagnetic spectrum. It features 66 mobile antennas which can be moved and configured over the ALMA site to meet the scientists' requirements, making it the biggest astronomical experiment in existence.

This amazing picture of the ALMA landscape was taken by ESO Photo Ambassador Stéphane Guisard, an optics engineer at the European Southern Observatory's Very Large Telescope in the Atacama Desert, Chile.

Image Credit: ESO/S. Guisard
Explanation from: http://www.eso.org/public/images/potw1431a/