Wouldn't it be nice if every one of us were all young and hot, with plenty in common? This kind of homogeneity just doesn't exist on Earth, but in space, scientists have found that between magnetic stars, this is the case.
Astronomers typically segregate stars by their physical characteristics: temperature, size, age, composition. One particular group, young, hot, magnetic stars, that contain low amounts of heavy elements, have interested scientists for some time because they appeared different than their iron-rich magnetic counterparts.
Seeing commonality, finally
The current thinking on how young stars become magnetic is this: There is a magnetic field already in the Universe. When stars collapse during formation, the particles drag a bit of that magnetic field with it. All stars have some magnetic field but it varies widely: Our Sun has a field the strength of 1 Gauss, while the stars that Smith studied have a magnetic field of a couple thousand Gauss. Why different stars have such different magnetic fields is still an unknown.
The magnetic fields of iron-poor stars create invisible cages in which their spewed material stays. Hydrogen, helium and other ionized atoms follow the magnetic fields from the poles and then turn back to the star's equator. These halos glow, but are barely visible, and were thought to be a characteristic special only to magnetic stars low in heavy elements.
That was the case until two scientists, Myron Smith of the Space Telescope Science Institute in Maryland, and Detlef Groote from the University of Hamburg in Germany, discovered all young, magnetic hot stars, regardless of composition, display the dimly glowing rings of ejected materials.
"What's exciting for science is that this may be seen in other types of stars, or maybe even galaxies," said Smith. "We can use this as a model to see if this is going on somewhere else; like gravity that makes an apple fall also makes the Moon travel around Earth. That type of universality is what is nice in science; a few physical laws can explain bewilderingly different phenomenon."
How donuts are made
The signature of stellar magnetic fields is the donut effect on ejected star material. Ionized atoms are shot out at the poles, then pulled along by the magnetic field back toward the center of the star. Because material is ejected from both ends, the material eventually crashes into other particles at the magnetic equator. These intense particle collisions cause the ring of material to glow and radiate at very high temperatures.
This magnetic star commonality might seem obvious in hindsight but it took careful and powerful observations to bring the glowing ring theme to light.
"People just didn't put these things together," said Smith. "When the spectra of the stars look different, this superficial appearance is kind of an obstacle to [seeing] commonality."
"The magnetic fields on stars are very difficult to measure. For stars, the (magnetic band's) light is so faint, you need really big telescopes," said Smith. And also, "These stars rotate rapidly, which blurs out the spectral lines."
Using old data for something new
By studying UV images taken from 1978 to 1996 by the now non-existent International Ultraviolet Explorer (IUE), Groote and Smith were able to discover the commonality by studying UV emission spectra of two magnetic stars with low levels of heavy element emissions, and two with normal heavy element emissions.
Smith's workplace, the Space Telescope Science Institute in Maryland, is home to NASA's visible and UV imaging archives. The astronomer lamented that archived data can be a "real treasure trove of information," but that scientists often have a bias for new data.
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