Astronomers discover possible new Solar Systems in formation around the nearby stars Vega and Fomalhaut

21 April 1998

HILO, HAWAII -- Astronomers at the Joint Astronomy Centre (JAC) in Hawaii and at the University of California (UCLA) in Los Angeles today report that they have obtained the first pictures of huge disk-like structures of dust around two of the brightest stars in the sky - Vega and Fomalhaut. These images may reveal planetary systems in formation, and suggest that planets in our galaxy may be more common than scientists previously believed.

The team of British and American astronomers report their findings, based on their observations of three well-known stars in our Milky Way Galaxy - Vega, Fomalhaut and Beta Pictoris - in the April 23rd issue of the journal Nature.

"One of the most striking features we see is a central hole in the disk around Fomalhaut," said Wayne Holland, who led the astronomy team at the JAC. "The lack of bright emission close to the star suggests that dust is largely cleared out, and a probable explanation is that it has formed into rocky planets like the Earth, even though we cannot detect these directly".

"It is generally believed that our own Solar System formed out of such a disk" said Benjamin Zuckerman, UCLA professor of Physics and Astronomy, "but whether the newly discovered disks contain majestic planets like Jupiter and Saturn, or just comets and asteroids, remains to be seen".

What can these stars tell us about our own Solar System?

The ages of Vega, Fomalhaut and Beta Pictoris - from tens to hundreds of millions of years - span a range of great importance in the history of our own Solar System, the astronomers noted. Our Sun's estimated age is around 4.5 billion years, and the giant planets, Jupiter and Saturn, are believed to have formed 10 million years after the Sun, whilst the Earth took something like 100 million years to form.

For about 600 million years, our Solar System was bombarded by comets and asteroids, until, as Zuckerman said, "the gravitation of Jupiter and Saturn, the 'garbage men of the solar system', cleaned out these massive objects that could have decimated life".

These star systems may teach us much about the history of our own Solar System. "What we see is almost exactly what astronomers orbiting nearby stars would have seen if they had pointed a millimetre-wavelength telescope at our own Sun a few billion years ago" said Jane Greaves, one of Holland's colleagues at the JAC.

How were the new images obtained?

The new images - which are not optical pictures, but rather radio images produced through "submillimetre astronomy" - were obtained using the 15-metre James Clerk Maxwell Telescope at the Mauna Kea Observatory in Hawaii. The JCMT is the world's largest telescope dedicated to the study of light at "submillimetre" wavelengths. The team of astronomers used a revolutionary new camera called SCUBA (Submillimetre Common User Bolometer Array), which was built by the Royal Observatory in Edinburgh.

"SCUBA uses detectors cooled to a tenth of a degree above absolute zero (-273 degrees Celsius) to measure the tiny amounts heat emission from small dust particles at a wavelength close to one-millimetre", said Holland.

The astronomers reported on the following:

Fomalhaut, the brightest star in the constellation Piscis Austrinus (the Southern Fish), is believed to be about 200 million years old - very young compared to our Sun. In the new image the brightest emission, and therefore the most dust, is surprisingly far from the star. The star appears to be surrounded by a huge disk of dust aligned roughly in a north-south direction with a hollow central cavity.

Why has the dust disappeared from the star's inner region? The most exciting explanation is that the dust has coalesced and formed into planets. Other possibilities include that the dust was absorbed into Fomalhaut or blown away from the star.

The image appears like a doughnut, with a hole in the center comparable to the size of our own planetary system. The region with the brightest emission is located a distance from Fomalhaut that matches what is called the "Kuiper belt of comets" out beyond Neptune and Pluto in our own system.

"We could be seeing a region around Fomalhaut that is rich with countless comets, although the images cannot reveal comets directly", Holland said.

Mystery at Vega, the brightest star in the summer sky

Vega, in the constellation of Lyra (the Lyre) and the brightest star in our summer sky, is the oldest star of the three at 350 million years old. Viewers of the movie "Contact" will also remember that Vega was the source of radio transmissions received by astronomer Ellie Arrowway (Jodie Foster), who was ultimately transported to Vega to communicate with extraterrestials.

The new SCUBA image of Vega shows it to be enshrouded in faintly glowing dust. As with Fomalhaut, the brightest peak is not centered on the star but at a distance from Vega of about seven thousand million miles - about twice the distance from our own Sun to Pluto. However, this time the emission is concentrated in only one peak which puzzled the astronomers.

The astronomers made a deep search with the 10-metre Keck Telescope (also on Mauna Kea) - the world's largest optical and infrared telescope - for infrared light from possible planets or "brown dwarfs". They detected no such objects, and have no explanation for this bright "blob".

"This bright blob is a real mystery - we simply don't have an explanation yet" Zuckerman confessed. "If it is indeed associated with Vega, it's completely unknown. We can suggest explanations - such as a dust cloud around a giant planet orbiting Vega - but they are complete guesses at this point".

Beta Pictoris, in the southern constellation of Pictor (the Painter's Easel) is the only one of the three stars that had been previously imaged. It is also one of the youngest stars in our Solar neighbourhood - being only about 30 million years old. The emission from dust in this case seems to be mainly concentrated at the position of the star, but as with Vega, there is also an unidentified blob in line with the disk.

This source may be a disconnected fragment of the disk in orbit around an unseen companion planet, the astronomers said. It is far from Beta Pictoris - some 10-20 times the distance from our Sun to Pluto. While the blobs in the Vega and Beta Pictoris images may be dust-enshrouded giant planets, planets are not supposed to be able to form at such great distances from stars, the researchers noted.

"In the Beta Pictoris picture, if this blob is indeed associated with the star," Zuckerman said, "presumably it's a planet-like object surrounded by dust - which is completely unexpected, a total mystery. The blobs in the Vega and Beta Pictoris images seem to be telling us something very surprising, and we have more questions than answers at the moment".

Are planets common?

"These are stars that everyone sees when they look up at the night sky. Fomalhaut looks quite similar to the way we think our own Solar System looked when it was 200 million years old," Zuckerman said, "but the other two stars are very baffling."

Noting that none of the stars has retained a large enough mass of dust to form planets, the astronomers say that if these stars are orbited by planets, they have most likely already formed, or are well on their way to forming.

"If the blobs around Vega and Beta Pictoris surround planets, that could tell us that planets are a common phenomenon", Holland said.

"Even if planets are more common than was believed, these findings do not make intelligent life in the universe more likely", Zuckerman said.

Ian Robson, Director of the JCMT, said "SCUBA really is a fantastic new instrument. This is just one of the exciting new discoveries that SCUBA is making that is revolutionising submillimetre astronomy and our knowledge of the Universe".

Holland's team also included astronomers Jane Greaves, Iain Coulson, Dolores Walther, William Dent, Walter Gear and Ian Robson, and Zuckerman's included UCLA graduate students Richard Webb and Chris McCarthy.

Notes

These are false colour images of the dust emission around Fomalhaut, Vega, and Beta Pictoris, taken with SCUBA at the James Clerk Maxwell Telescope.

The images appear as huge disk-like structures where the brightest emission, and hence the most dust, is represented by the white colours. Since the disks are undoubtedly viewed from different angles from the Earth, some appear flattened (Fomalhaut) and some more circular (Vega) in shape. The dust is most likely composed of silicate grains, although we can't tell that directly from these images.

In each image the position of the star is indicated by the "star" symbol. The bar adjacent to each image shows the apparent diameter of our Solar System, if it were located at the distance of each star.

In the case of Fomalhaut, the image appears like a 'doughnut' with a hole in the centre. It's possible that this hole has been caused by the accumulation of dust into planets like the Earth. Vega is a real mystery, and seems to be enshrouded in a roughly circular envelope of dust. However, the peak dust emission is some seven 7,000 million miles away from the star - maybe a giant planet with a dust cocoon? Beta Pic has a main dust disk that is centered on the star and is inclined in the same direction as the famous Hubble Space Telescope photos. However, like Vega, there is also a surprise blob this time 50,000 million miles away, which could also be a dusty companion planet in orbit about the star.

The JCMT is operated by the Joint Astronomy Centre, on behalf of the UK Particle Physics and Astronomy Research Council, the Netherlands Organisation for Scientific Research, and the Canadian Research Council. This work was also supported, in part, by NSF and NASA grants to UCLA.