Star sheds light for astronomers
By Jan TenBruggencate
Advertiser Science Writer
Astronomers have taken detailed images of a lumpy disk orbiting a nearby red star, and believe it may represent a blueprint for how our own solar system formed.
University of Hawai'i Institute for Astronomy professor Michael Liu used the Keck II telescope atop Mauna Kea to take pictures of the disk around AU Microscopii, which astronomers have nicknamed AU Mic, pronounced mick or mike.
The star, about half the mass of our own sun, is the closest star known to have such a disk. It is 33 light years away, well within our galaxy and for astronomical purposes, "right within our neighborhood," Liu said.
While our own sun is about 4.6 billion years old, AU Mic is a youngster, just about 12 million years old and still in its planet-formation period.
"By studying very young stars like AU Mic, we gain insight into the planet formation process as it is occurring. As a result, we learn about the birth of our own solar system and its planets," Liu said.
The images show a dust disk that extends outward from the sun, but does so in an irregular way, with fat places on the disk and thin ones. Since the star is so close to us and the telescope so powerful — it is the largest infrared telescope in the world — the images are the sharpest ever taken of such a stellar disk.
"We can see features there that are intriguing to say the least," said Eugene Chiang, an astronomer at the University of California at Berkeley, who has reviewed Liu's work. The lumps "represent planets forming. That's my view," he said.
Liu said the gravity of rocky planets within the dust disk would cause irregularities in the dust that show up in the telescope images.
"We cannot yet directly image young planets around AU Mic, but they cannot completely hide from us either. They reveal themselves through their gravitational influence, forming patterns in the sea of dust grains orbiting the star," he said.
Chiang said it's also interesting that the lumps appear the same distance from AU Mic as some of our solar system's planets are from the Sun. They are found in the region where Neptune and Pluto are in our system—between 2 billion and 4 billion miles from the star.
It is a phenomenon in astronomy that telescopes are sometimes able to pick out smaller particles and not bigger ones. In this case, AU Mic's reflected light off its dusk is visible, but the individual planets are not. In a way, it's similar to your being blinded by your headlights reflecting off the fog, but unable to see solid objects in the fog.
Liu said other scientists are working with the images to try to calculate the size of AU Mic's planets from the effects of their gravity on the dust disk.
"We are entering a new age of high resolution imaging in astronomy. Dr. Liu's breathtaking images of possible planets in formation around AU Mic would have been unimaginable from any telescope — space-based or on Earth — a few short years ago," said Dr. Frederic H. Chaffee, director of the W. M. Keck Observatory.
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808) 245-3074.
Correction: The distance from Earth to the star AU Microscopii was incorrect in a previous version of this story.
