Editor’s note: This article was initially published in The Daily Gazette, Swarthmore’s online, daily newspaper founded in Fall 1996. As of Fall 2018, the DG has merged with The Phoenix. See the about page to read more about the DG.
Today, Richard Townsend — a physicist at the University of Delaware — gave the first colloquium of the semester. Entitled Animating the Glowing Magnetospheres of Massive Stars, the colloquium was a presentation of his recent research into why some massive stars possess large-scale magnetic fields. Although many smaller stars, including the Sun, have such fields, the factors causing those fields are generally not present in massive stars.
The colloquium was in five acts: the Players, the Backstory, the Bridge, the Action Sequence, and the Finale. Said Townsend: “I tried to make it like a play, but it looks more like a Hollywood action flick…which I guess says something about my playwriting abilites.”
Townsend first presented a “tale of two stars,” Sigma Orionis D and E. Both stars are near Orion’s belt in the night sky, though they are slightly too dim to be visible to the naked eye. Although they look nearly identical in the regular light spectrum, Orionis E emits significant amounts of X-rays, while Orionis D emits nearly none. In fact, almost all large stars (“large” meaning from around ten times the mass of our sun on up) do not appear in the X-ray spectrum. Orionis E is even more unusual in that its emissions change regularly and periodically, leading astronomers to think at first that it was actually a system of two separate, but closely bound, stars.
As Townsend explained, the X-ray emission is related to the star’s having a massive magnetic field — unusual in a such a massive star. Orionis E was the first star detected, in the seventies, to have such a field, though about a dozen others have been discovered since. One proposed explanation of the star’s unusual observed properties is that there are two clouds of solar material located close to the star.
The focus of Townsend’s research — on which Swarthmore’s own David Cohen was also one of several contributors — is to determine a computational model with which a good idea of how the system behaves. The “straightforward” magnetohydrodynamic models are far too computationally intensive to be feasible, so Townsend and his colleagues use different simplifying approximations.
These approximations and resulting models were the subject of the Action Sequence, which, although it contained no car chases or shootouts, did contain more pretty animations of superhot plasma than most action flicks. The physics was too in-depth to go into here: suffice to say that the star produces a disk of extremely hot material ejected from the star, which fits the experimental data in most regions very well. The model also predicted that every so often, the star will emit an X-ray flare as the disk becomes too massive to be stable; such a flare was detected in 2004. Additionally, it brought around the interesting aside that conservative forces belong on the right side of the equation. Oh, math jokes….
So what’s next for Dr. Townsend? He, again in collaboration with David Cohen, is beginning to research how well the more advanced model’s predictions fit with the X-ray emission of Sigma Orionis E, as well as searching for other stars to which the model applies. In fact, Swarthmore’s new, soon-to-be-acquired telescope, which will be on the roof of the Science Center, will be ideal for such observations, as the star is too bright in the sky to be safely observed by larger equipment. Such research, it was suggested, would make a great research opportunity for students.
The remaining three physics colloquia of the semester will all take place in November, the first being by Katharina Vollmeyr-Lee of Bucknell University. Check the department webpage for topics as the colloquia near.
