Blustery days for Young Stars?
Astronomers claim to have found the first clear evidence that the gassy and dusty environment around some young stars are actually quite windy.
Many young stars have long intrigued astronomers because the disk of proto-planetary material surrounding them glow unusually with Infrared light. Many suspected this was due to massive wind-like movements that go beyond the usual orbital motion you’d expect from a contracting flattened disk of ancient dust and gas.
These incipient solar systems are hosted by special class of star called a T-Tauri. A T-Tauri star is simply a very young star with a highly variable light output. It is believed that our sun was one of these long ago. When I say young I mean a scant 10 million years at the oldest…a mere baby. They are so young that the star’s retinue of planets whether they be rocky or gaseous or both haven’t even fully coalesced yet.
This phase of a star’s life is a relatively brief adolescent one. It’s often called a pre-main sequence phase which is, for many stars, its adulthood. Main Sequence refers to a band of stars that appears in a diagram when you plot its brightness (luminosity) against its color (temperature). This is called a Hertzsprung-Russell (HR) Diagram and it’s probably as iconic as an image can get in astronomy. If you took Astronomy 101 in high school or college, I would be utterly shocked if you didn’t see this diagram (please send me the name of your teacher if this is the case).
Look at the HR Diagram I have added to the left (yes you). That band of stars across the middle, oriented from the upper left (hot and luminous) stretching down to the lower right (cool and faint) is the main sequence and represents most stars in the universe. As these stars go through their adulthood fusing hydrogen, they will remain on this main sequence. T-Tauris being cooler and fainter would appear above and to the right of the main sequence slowly moving the diagram as they get older and eventually joining their adult brethren. As stars enter old age and stop fusing hydrogen, they grow in size and migrate away from the main sequence to the upper right side as their surface temperature drops and their luminosities increase. At the final stage of their lives, many have become dwarf stars with high termperatures and very low luminosities (the bottom left). The HR Diagram then is essentially a plot of the evolution of stars as they move through their lives.
Back to the T-Tauris.
To resolve this mystery about the weird infrared glow of the disks around some T-Tauri stars, the Atacama Large Millimeter/submillimeter Array (ALMA) looked at a star with a boring name 407 light-years away in the constellation Ophiuchus. As the ALMA website reports:
With ALMA’s exceptional resolution and sensitivity, the researchers were able to study the distribution of carbon monoxide around the star. Carbon monoxide is an excellent tracer for the molecular gas that makes up stars and their planet-forming disks. These studies confirmed that there was indeed gas leaving the disk’s surface, as would be expected if a wind were present.
This was the clearest evidence yet that such winds exist. There was however an anomaly with the wind. It did not behave entirely as expected. A potential explanation is the fact that the star with the boring name is actually part of a multiple-star system with 2 other stars with even more boring names. This raises the possibility that the wind is actually caused by the interactions of these three stars and is not an integral part of many T-Tauri systems. This of course raises the question of why they are even touting this whole wind thing if it could be just an artifact of this triple star system.
Oh well, I hope you enjoyed the pretty pictures anyway.