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 15-m wide James Clerk Maxwell
Telescope (JCMT) on Mauna Kea
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",
The astronomers reported on the following:
SCUBA image of dust
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",
Mystery at Vega, the brightest star in the summer sky
SCUBA image of dust
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 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".
SCUBA image of dust
around Beta Pictoris
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
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
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.