A team of European astronomers has discovered an infant solar system on the outskirts of the Milky Way. The dusty, opaque disk appears to be a proto-system much like ours, yet still billion of years younger.
Located 500 light-years from Earth and nicknamed the "Flying Saucer" because of its disc-like shape, the object is providing the astronomers an opportunity to observe what our own Solar System looked like in its early evolution.
The star at the center of the Flying Saucer appears young and stable, leading scientists to believe the dust surrounding it will eventually coalesce into a variety of planets. Just give it a couple billion years.
The Earth and its neighbors formed from a disk similar to that of the Flying Saucer about 5 billion years ago. This is believed to be a complex process of which not all stages are not yet fully understood. It is thought to have begun when small dust particles near our stable star collided and stuck to each other.
No other example of a disc shaped, proto-solar system has been observed so easily as the Flying Saucer as most central stars shine to brightly for astronomers to see the surrounding dust.
Fortunately, the Flying Saucer is "bent" so that it is at an edge-on angle. The thick edge of the disk blocks the star's light which produces a dark line between the top and bottom reflection nebulae formed in the dust above and below the star.
Other such objects have been discovered, but the Flying Saucer is the best such system found for study yet. The Hubble Space telescope first found an object similar to it in 1996 in the Taurus dark cloud, a distance of about 500 light-years from earth. Since then, other objects have been observed using ground-based telescopes. However, most have been inside rather dark regions of the sky, where thick stardust obscures accurate observation.
The Flying Saucer was found quite by accident. A group of astronomers followed up on observations of new X-ray sources found by the ESA XMM-Newton and NASA Chandra X-ray satellites in the periphery of one of the nearest star-forming regions, the Rho Ophiuchi dark cloud. Using the New Technology Telescope at the La Silla Observatory in Chile, the astronomers discovered the resolved edge-on circumstellar disk.
The resolution of the images could barely make out the characteristic nebulae of a disk shaped proto solar system, though. To confirm the discovery, astronomers obtained additional observations with the Very Large Telescope in Chile using it Infrared Spectrometer and Array Camera.
The leader of the group, Nicolas Grosso, recalls the first impression when seeing the true shape of the object: "That is when we looked at each other and, with one voice, immediately decided to nickname it the `Flying Saucer'".
The nature of the new object
Seven young stars in the Rho Ophiuchi region display similar reflection nebulae around a dark lane, but these objects are all still deeply embedded in the dense cores of the dark cloud. They are also thought to be proto-stars with ages of about 100,000 years.
However, the But the Flying Saucer appears to be about one million years old. Our solar system is nearly 5000-times older.
Still it shares some physical characteristics with our home turf. The radius of the Saucer is about 300 Astronomical Units wide, or 5 times the diameter of Neptune's orbit. This would also be the outer limit of our solar system.
From model calculations, the astronomers have found the mass of the disk is at least twice the mass of gas giant Jupiter. Study of the optical to near infrared light indicates the young star is half the temperature, and only 40 percent as luminous as ours is.
A detailed analysis of the both nebulae revealed an unusual excess of infrared radiation in the upper nebula, something that cannot be explained simply. Future high-resolution observations by the Very Large Telescope will help astronomers understand the origin of this phenomenon, and whether it's linked to planet formation.
"The `Flying Saucer' object presents us with a striking portrait of our Solar System in its early infancy," Grosso said. "With this object, Nature has provided us a perfect laboratory for the study of both dust and gas in young circumstellar disks, the raw material of planets."
The astronomers plan to study the object further by looking at its radio waves. These emissions will be easier to study because unrelated background emissions from the surrounding dark cloud material will not interfere. Astronomers will then be able to map the gas and dust material around the young star, and study chemical processes going on there.
Computer simulations predict that any proto-planets will produce measurable structural changes in such a disk. However, such signs of planet formation are far from the sensitivity and resolution available with current instruments. Detection of these features is a goal of member countries supporting the Atacama Large Telescope Array, an international effort to build the world's most sensitive radio telescope.
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