A baby star has been spotted blowing bubbles, confounding researchers who say young stars are not supposed to know how to do this. If the finding holds up after further observations, it could alter theories about how stars form and evolve, and even how planets like ours develop.
Infant stars grow like weeds and are known to behave much like young children, spitting out a good portion of what they take in. And like a child, a star gets rid of stuff at both ends, expelling jets of gas in two opposite directions along its axis of rotation.
The process behind these gas jets is a form of stellar indigestion. Getting rid of some stuff makes room for more stuff.
In scientific terms, the expulsion of excess gas dissipates angular momentum and allows material with less angular momentum to drift inward from the flat, rotating disk of gas and dust that forms around all developing stars. If a star were to spin too fast, it would fly apart.
In the new study, the researchers have not seen an entire bubble. Instead, they spotted an arc of water vapor near a star in a stellar nursery called Cepheus A, about 2,400 light-years away. This arc is thought to represent a portion of the bubble's surface.
And it's a big bubble, roughly half again as big as our entire solar system, or about 60 AU across (1 AU, or astronomical unit, is the distance from Earth to the Sun).
The bubble is expanding as it races outward at 20,000 miles per hour (9 kilometers per second). By watching it move over several months, the researchers calculate that it is being observed as it was just 33 years after leaving the star.
The finding, reported in the May 17 issue of the journal Nature, comes as a big surprise to people who thought they knew how stars formed.
"Where we expected to find a water hose, we found an exploding, perfectly spherical water balloon," said Kevin B. Marvel of the American Astronomical Society. Marvel, who was not involved in the research, told SPACE.com the findings "will help expand our understanding of the early stages of star formation."
But in an accompanying analysis in Nature Marvel cautions that there is a chance the source could be a mature star. More study will be required to pin things down with certainty.
Seeing the invisible
The space bubble is made of gas that is compressed compared to the surrounding space into which it is expanding. It is thought to be made of the same substances found throughout the cosmos -- mostly hydrogen, but also some water and other chemicals.
It is the water that was detected. Researchers used the National Science Foundation's Very Long Baseline Array -- 10 radio telescopes around the United States that combine to effectively form one giant telescope. But even with this power, a signal boost was needed to reveal the distant object.
Nature, it turns out, provides a nifty amplifier, which scientists call a maser (microwave amplification by stimulated emission of radiation). Masers are regions of space where high concentrations of molecular gas, including water, amplify radio waves. The result is a bright spot in telescope data.
Previous observations have found masers that revealed the jets of young stars. But these masers are different. They don't represent a jet.
"The arc we see, we believe is part of a circle," said Paul Ho of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. "This circle is the limb-brightened part of a 3-D sphere."
A series of masers forming the arc can be thought of as a part of a giant ball made of material so clear as to render it virtually invisible. You would look right through its midsection without noticing it, just as a super clean window can go unnoticed. Now step closer and peer along the ball's edges; you're looking through more material and the curvature becomes apparent. You see an arc, and only a little high school math is needed to figure out that the arc is, or could be, part of a circle.
"In that sense, the circle is the 2-D projection of the 3-D sphere," Ho explained.
And this is the key to the finding. If the arc were truly two dimensional, then it would have to be perfectly edge-on to be detected. But a sphere seen from any direction would reveal an arc using this technique.
This fact makes it highly unlikely that the arc represents anything but a sphere, Ho and his colleagues argue. And, they say, a sphere would not likely form as it zoomed through space. Instead, it is most likely that it was expelled as a sphere.
The study also indicates that more than one bubble was ejected.
"We now have at least one case, we believe, in which a young star has repeatedly ejected mass spherically in short bursts," said Guillem Anglada of the Institute of Astrophysics of Andalucia in Granada, Spain. "In light of our current understanding of star formation, we don't yet understand how this can happen, so we have an exciting new scientific challenge.
The international effort also included researchers from the Institute for Space Studies of Catalonia, Spain, the National Institute for Aerospace Technology in Madrid, Mexico's National Autonomous University and the University of Chile.
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