University of Minnesota
School of Physics & Astronomy


The Biggest and Brightest

Roberta Humphreys
Roberta Humphreys
courtesy Inventing Tomorrow

CSE Distinguished Professor Roberta Humphreys likes them big – stars, that is. For many years her research has focused on the evolved, most massive stars and the unstable final stages before they explode as supernovae. These very massive and very large stars have relatively short lifetimes of a few million years. Near the ends of their lives, due to still poorly understood physics, they shed a lot of mass, and in many cases producing visible circumstellar nebulae as a record of their instabilities.

The mass loss may be driven by radiation pressure exceeding gravity, surface activity, and possible interior instabilities. There is increasing observational evidence that many of the most massive and luminous stars experience episodic high mass giant eruptions and even explosions.

In recent years a number of non-terminal explosions have been identified in the numerous surveys for supernovae, and are often called “supernova impostors”. Since these giant eruptions are in other galaxies, very little is known about their progenitors other than that they are most likely evolved massive stars.

Humphreys has begun an observational program, that expands on her previous work, to better characterize the progenitor population of the giant eruptions. The observations include spectroscopy of Luminous Blue Variables and candidates like eta Car, hot emission line stars, and warm and cool hypergiants like VY CMa in nearby resolved galaxies. The observations take advantage of the University of Minnesota’s membership in the Large Binocular Telescope Consortium.

"There is always the chance that we might catch one of these stars in the act of a giant eruption or even shortly prior to its terminal explosion as a supernova," Humphreys says.

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