The image is the first high-resolution picture taken from a ground-based telescope of the protostar known as L1551. The Hubble Space Telescope previously captured images of the object in the visible wavelengths, but the Subaru gazer is the first to show the protostar's features in the infrared. The high quality of the image attests to the value of the new class of 8-meter telescopes, some astronomers say.
Perched at the summit of the 14,000-foot Mauna Kea peak on the big island of Hawaii, the Subaru Telescope is operated by the National Astronomical Observatory of Japan. Astronomers began observations with the telescope's 8.3-meter (27-foot) primary mirror in January.
About 450 light years from Earth, L1551 interests scientists because it is one of only a few hundred observed protostars -- infant stars so young that scientists use them as textbooks to learn about the formation of stars and galaxies.
The protostar in the Subaru image has just started along its path to becoming a binary star system. It is beginning to condense enough that the center of the swirling cloud is becoming recognizable as two distinct bodies. Astronomers estimate it has been only about 100,000 years since the growing star nuclei were a single undifferentiated cloud of gas and dust.
The system is now old enough that it is beginning to radiate its own energy, caused by the heat of its collapse and by the burning of the lightest gasses such as deuterium -- a form of hydrogen. The binary protostar system is about half the mass of the sun, said Yoichi Ito, a scientist working at the Subaru telescope. Because the star won't begin thermonuclear fusion for about another million years, it shines only very faintly in visible light, and is brighter in infrared wavelengths.
Thermonuclear fusion is the process that fuels solar-type stars, what astronomers call main-sequence stars.
The vast majority of a star's energy is released when two hydrogen atoms fuse together to become one helium atom, releasing energy in the process.
The L1551 protostar surprised the astronomical community about 20 years ago when astronomers recognized a peculiar signature, showing the star was ejecting material at high speeds, said Klaus Hodapp, an astronomer at the University of Hawaii, and an expert in protostar formation.
It was one of the first protostars to be recognized with an outflowing jet. Although scientists now know jets to be a feature typical of newly-forming stars, the shooting material was perplexing two decades ago because astronomers expected to see signs of material falling into the star at high speeds, not shooting out.
That mystery took a few years to clear up, but scientists soon found that protostars commonly have jets of ejecting material. It is a natural part of the star-formation process, Hodepp said.
The early clouds from which stars form always rotate with some energy. As they collapse, their rotation accelerates as more and more mass becomes concentrated in the compact center of the clouds. The increasing rotational speed is the same phenomenon a spinning figure skater takes advantage of when he brings his outstretched arms into his body to speed up a spin. This is the conservation of angular momentum.
It turns out that the shooting jets are a natural reaction to a swiftly rotating and collapsing cloud, a sort of natural mechanism for shedding much of the angular momentum, Hodepp said. If protostars did not have such a mechanism, they would never slow their rotation enough to become stars. They would be spinning too fast and be too unstable and chaotic to become stars, he said.
While any observation of early stars provides useful information about the evolution of stars and planetary systems, one of the most impressive facts about the images is its high quality, Hodepp said.
"It's a very impressive image for an uncorrected ground-based telescope," he said. "Also, for us here in Hawaii, it is really rewarding to see how good the atmosphere on Mauna Kea really is, allowing these type of images to be taken even without compensation."
The Subaru telescope has a complicated adaptive optics system that will compensate for much of the distortion that Earth's turbulent atmosphere creates in an image, but that system is not installed yet, according to the telescope's director, Noiro Kaifu.
"Within months the Japanese telescope will also have their adaptive optics system up and running and then we can expect even more spectacular images," Hodepp said.
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