Two families of exocomets found around nearby star Beta Pictoris

This artist's impression shows exocomets orbiting the star Beta Pictoris.

Astronomers analysing observations of nearly 500 individual comets made with the HARPS instrument at ESO's La Silla Observatory have discovered two families of exocomets around this nearby young star.

The first consists of old exocomets that have made multiple passages near the star.

The second family, shown in this illustration, consists of younger exocomets on the same orbit, which probably came from the recent breakup of one or more larger objects.

Credit: ESO/L. Calçada

Beta Pictoris is a young star located about 63 light-years from the Sun. It is only about 20 million years old and is surrounded by a huge disc of material, a very active young planetary system where gas and dust are produced by the evaporation of comets and the collisions of asteroids.

Flavien Kiefer (IAP/CNRS/UPMC), lead author of the new study sets the scene: "Beta Pictoris is a very exciting target! The detailed observations of its exocomets give us clues to help understand what processes occur in this kind of young planetary system."

For almost 30 years astronomers have seen subtle changes in the light from Beta Pictoris that were thought to be caused by the passage of comets in front of the star itself.

Comets are small bodies of a few kilometres in size, but they are rich in ices, which evaporate when they approach their star, producing gigantic tails of gas and dust that can absorb some of the light passing through them.

The dim light from the exocomets is swamped by the light of the brilliant star so they cannot be imaged directly from Earth.

To study the Beta Pictoris exocomets, the team analysed more than 1000 observations obtained between 2003 and 2011 with the HARPS instrument on the 3.6-metre telescope at the ESO's La Silla Observatory in Chile.

The researchers selected a sample of 493 different exocomets. Some exocomets were observed several times and for a few hours.

Careful analysis provided measurements of the speed and the size of the gas clouds.

Some of the orbital properties of each of these exocomets, such as the shape and the orientation of the orbit and the distance to the star, could also be deduced.

This analysis of several hundreds of exocomets in a single exo-planetary system is unique. It revealed the presence of two distinct families of exocomets: a) one family of old exocomets whose orbits are controlled by a massive planet, and b) another family, probably arising from the recent breakdown of one or a few bigger objects. Different families of comets also exist in the Solar System.

The exocomets of the first family have a variety of orbits and show a rather weak activity with low production rates of gas and dust.

This suggests that these comets have exhausted their supplies of ices during their multiple passages close to Beta Pictoris.

The exocomets of the second family are much more active and are also on nearly identical orbits.

This suggests that the members of the second family all arise from the same origin: probably the breakdown of a larger object whose fragments are on an orbit grazing the star Beta Pictoris.

Flavien Kiefer concludes: "For the first time a statistical study has determined the physics and orbits for a large number of exocomets. This work provides a remarkable look at the mechanisms that were at work in the Solar System just after its formation 4.5 billion years ago."

More information: "Two families of exocomets in the Beta Pictoris system" Nature, 23 October 2014. dx.doi.org/10.1038/nature13849

ESO Image: Lupus 4 - Cosmic Spider Swallows Starlight

A dark, spider-shaped cloud of cosmic gas blocks out light from stars in a new image taken by a telescope in the Southern Hemisphere.

The amazing photo, taken by a telescope at the European Southern Observatory's La Silla Observatory in Chile, is filled with stars glowing brightly in a variety of colours.

Red, blue, yellow and orange stars frame the gas blob called Lupus 4, which blots out light from other, more distant stars in the center of the image. Fly through the image in a new video of the Lupus 4 space cloud from ESO.

Eventually, Lupus 4, which is located about 400 light-years from Earth, could give birth to its own stars.

A dark cloud of gas called Lupus 4 blocks out more-distant stars. Photo released Sept. 3, 2014.

Credit: ESO

"How many stars might eventually start to shine within Lupus 4? It is hard to say, as mass estimates for Lupus 4 vary," ESO representatives said in a statement today (Sept. 3).

"Two studies agree on a figure of around 250 times the mass of the sun, though another, using a different method, arrives at a figure of around 1,600 solar masses."

"Either way, the cloud contains ample material to give rise to plenty of bright new stars."

"Rather as earthly clouds make way for sunshine, so, too, shall this cosmic dark cloud eventually dissipate and give way to brilliant starlight."

Another gas cloud in the same area, called Lupus 3, already hosts about 40 young stars that formed over the course of the last 3 million years, ESO said.

The spidery cloud is part of a loose star cluster named the Scorpius-Centaurus OB association, which is a young, widely dispersed star grouping, according to ESO.

The stars in the cluster also likely come from the same huge cloud of cosmic material, representatives from the astronomy organization added.

ESO La Silla observes Lives and deaths of sibling stars

In this image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at 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 we see here. 

Clusters like this are celestial laboratories that allow astronomers to learn more about how stars evolve. 

Credit: ESO/G. Beccari

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 (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.