The Secret Lives of Brown Dwarfs: Hidden Oddballs of the Universe

Caltech Astronomer J. Davy Kirkpatrick to give this year’s Marc Aaronson Memorial Lecture
April 7, 2010
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The lecture is free and open to the public. Media are welcome to cover the event.
Laura Forsyth (520-621-6524;

The 2010 Marc Aaronson Memorial Lecture, “Searching for the Coldest Brown Dwarfs: Breaking the Distinction Between Stars and Planets,” by J. Davy Kirkpatrick, California Institute of Technology
April 9, 2010, 7:30 p.m.
Steward Observatory, Room N210, 933 N. Cherry Ave., Tucson, AZ 85721-0065
J. Davy Kirkpatrick
J. Davy Kirkpatrick

Some of the laws that govern the universe resemble the laws that govern Hollywood. Take stars, for example. Not everyone gets to be one (think planets or moons or asteroids). As a matter of fact, under the laws of the universe, even if you're born as a star still doesn't mean you get to be one. Some start out that way, but never gather enough raw materials to spontaneously ignite and become a full-blown star that will grace the night sky for billions of years to come. Those are the brown dwarfs.

"Brown dwarfs are like stars, but not really," said J. Davy Kirkpatrick, who received his PhD in 1992 at the University of Arizona's Steward Observatory and is now a project scientist at the Infrared Processing and Analysis Center at the California Institute of Technology. "They're also like planets, but not really."

Kirkpatrick, who has invented a classification scheme for low-mass stars and brown dwarfs, is this year's honored lecturer to deliver the 2010 Marc Aaronson Memorial Lecture on April 9 at 7:30 p.m. at Steward Observatory. He is the first former Steward Observatory graduate student to be honored with the Aaronson lectureship.

The public is invited to join Kirkpatrick for an exciting journey of discovery into the strange nature of brown dwarfs during his presentation titled "Searching for the Coldest Brown Dwarfs: Breaking the Distinction Between Stars and Planets."

Brown dwarfs are cosmic oddballs: They defy classification as either a star or a planet.

Just like stars, they form from a collapsing cloud of interstellar gas and dust but stall in the middle of the star formation process and keep puttering along, continuously cooling down for the remainder of their existence.

According to Kirkpatrick, brown dwarfs also have traits in common with planets: "Oddly, all brown dwarfs have roughly the same size, about the size of the planet Jupiter. As brown dwarfs cool, they begin to develop atmospheres, clouds of methane, and, in the coolest cases, water. So in that respect they also resemble planets. However, planets are formed in a disc around a star, quite unlike the birthing process for brown dwarfs."

Because brown dwarfs are so much cooler than stars, they don't emit much light, which has made it tough for astronomers to detect them, even when they're relatively close. However, according to Kirkpatrick, what little light they do emit is concentrated in infrared wavelengths, which can be seen by specialized detectors such as NASA's WISE spacecraft (Wide-field Infrared Survey Explorer), which was launched last December to discover the coolest and closest brown dwarfs yet.

"Quite amazingly, astronomers have detected hundreds of these objects in the neighborhood of the sun," said Kirkpatrick. "We now believe that in our own galaxy, there are twice as many brown dwarfs as there are stars."

Within the WISE project, Kirkpatrick is the leader of the brown dwarf research team, determining the space density of brown dwarfs and hoping to discover the closest brown dwarf to the sun. In his lecture, he will present the history of our knowledge of brown dwarfs and other low-mass objects and explain how the new WISE mission will reach new extremes of discovery: brown dwarfs no warmer than the Earth and perhaps closer than the nearest star.

The Aaronson Memorial Lecture honors the late Marc Aaronson, a Steward Observatory astronomer who died at age 36 in 1987 in an accident while making astronomical observations on Kitt Peak, Ariz. The lectureship and cash prize are awarded every 18 months to an individual or group who, by his or her passion for research and dedication to excellence, has produced a body of work in observational astronomy that has resulted in a significant deepening of our understanding of the universe. The Marc Aaronson Memorial Lectureship Fund is administered by the UA; additional funding comes from Steward Observatory and the National Optical Astronomy Observatory.