Donuts
of dust: An artist's impression of the PDS 70 system with protoplanets, each
surrounded by dust rings illuminated by starlight. The planets themselves (not
to scale) have thin rings of plasma heated to around 14,000 degrees Fahrenheit,
which glow at the red emission line of H-alpha light. Credit: Emmeline Close
and Laird Close
With
a sun more than 4.5 billion years old, our solar system is considered
"middle-aged," and the pictures of what it might have looked like in
its infancy are lost to time. Taking advantage of a sophisticated adaptive
optics instrument, a team of astronomers at the University of Arizona made
observations that reveal unprecedented details of planets when they are very
young.
The instrument, dubbed Magellan Adaptive
Optics Xtreme, or MagAO-X, observed two young planets orbiting PDS 70, a very
young 5 million-year-old star in the constellation Centaurus, 370 light-years
from Earth.
Published in The
Astronomical Journal, the observations show
for the first time compact rings of dust surrounding the "baby
planets," which will likely give rise to moons. The team also observed
startling changes in planet brightness, telltale signs of the system's
turbulent youth.
With a deformable mirror that changes its shape quickly, MagAO-X corrects
for atmospheric distortion in a way that is reminiscent of how noise-cancelling
headphones filter out noise.
"This is a really great breakthrough in technology," said Laird Close, a professor of astronomy at Steward Observatory, in the U of A College of Science, adding that the images surpass the resolution of space telescopes, including the 2.4-meter Hubble Space Telescope and the James Webb Space Telescope.
This video animation shows an artist's view of
the PDS 70 system transition to real images of the two planets and
theircircumplanetary "dust donuts." The movie ends with the planets
changing in brightness in H-alpha light over the last three years as they orbit
PDS 70. Credit: Emmeline Close and Laird Close
Paired with the 6.5-meter Magellan
Telescope at Las Campanas Observatory in Chile, the instrument works as an
"adaptive optics system," meaning it corrects for turbulence in the
atmosphere that hampers astronomical observations. Effectively, the system
eliminates the "twinkle" of stars, enabling the telescope to make
images rivaling those from an optical space telescope.
"The mirror shape-shifts at a
rate comparable to adjusting an eyeglasses prescription 2,000 times per
second," Close said. "Because our technology removes disturbances
from the atmosphere, it's a bit like taking a 6.5-meter telescope mirror and putting it in outer space by clicking
a computer mouse button.
"This level of resolution
revealed features around these planets in incredible detail," he added.
"To give you an idea of the resolution, picture me standing in Phoenix,
and you standing in Tucson. With MagAO-X, you'd be able to see whether I'm
holding up one quarter-dollar coin or two from 125 miles away."
Astronomers believe that during its
infancy, our solar system might have resembled a smaller version of the PSD 70
planetary system. The star is surrounded by a giant, pancake-shaped disk of gas
and dust. Intriguingly, the disk is marked by a large dust-free gap, hinting at
planets.
"Multiple massive planets act
kind of like brooms or vacuum cleaners," Close said. "They basically
scatter the dust away and clear the large gap that we observe in this great big
disk of gas and dust that surrounds the star."
Infant planets, known as
protoplanets, are very rare, and the PDS 70 planets b and c are the only such
planets well known to astronomers out of 5,000 confirmed exoplanets. Developing
sharper images of protoplanets and the dust around them is key to understanding
how planets and their moons form, according to the research team.
Although
the planets in PSD 70 already contain several times the mass of Jupiter, they
are only about 5 million years old—which means that they are still growing. As
the planets gain mass from their "birth cloud,"
"waterfalls" of hydrogen gas fall onto them, Close explained.
When that happens, the planets glow in
what astronomers call H-alpha, a wavelength of light emitted by hydrogen gas
when in a certain excited state from the shock heating of the gas hitting the
planet's surface.
"Targeting that special wavelength
of light allows MagAO-X to effectively limit noise and distinguish between
protoplanets and their surrounding features or imaging artifacts," Close
explained.
"We can see, for the first time,
rings of dust surrounding protoplanets made visible by the bright starlight
reflecting off of them," added Jialin Li, a doctoral student in astronomy
and co-author of the paper.
Over the next few million years, the
dust will likely collapse to form moons around each of these young planets.
MagAO-X's sharp images revealed the
first observation of young planets dramatically changing in brightness. The
researchers saw one of the planets (PDS 70 b) fade to one-fifth its original
brightness over just three years while the other (PDS 70 c) doubled in
brightness, Close said, explaining that the rapid change in brightness at
H-alpha could be due to changes in the amount of hydrogen gas that is flowing
onto the planets.
"Essentially, one of the planets
abruptly went on a diet while the other was feasting on hydrogen," he
said.
Still, scientists are not yet sure what
exactly causes such dramatic changes.
"Our team will continue to utilize
MagAO-X to search for more protoplanets around other young stars," Close
said. "While discovering these protoplanets is right at the edge of what
is technically possible today, as technology improves we should discover more
such systems in the near future."
"One of our main goals is to
demonstrate just how well these observations can be done with telescopes on the
ground," said MagAO-X Principal Investigator Jared Males, an associate
astronomer at Steward Observatory.
"We can always build larger telescopes on the ground than in space, and this result shows how important it is to build the next generation of even larger telescopes and equip them with instruments like MagAO-X."
by Penny Duran, University of Arizona
Source: Sharper image: Optics instrument reveals pictures of 'baby planets'
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