on: Tuesday, February 26, 2002
Brown dwarfs are dull, but they
shed light on planets
Advertiser Staff Writer
are not the snappy dressers of the astronomy
|LIU: Studied brown dwarf from Mauna
Other Stars: New Sharp Views From Mauna Kea"a
lecture by Michael C. Liu.
Architecture Auditorium, University of
In a universe
populated by blue stragglers, red supergiants,
ultraviolet catastrophes and black holes, brown dwarfs
are — well ... sooo 2 billion years ago.
exactly what makes them fascinating to astronomers like
Michael Liu, who will make them the subject of "Worlds
Around Other Stars: New Sharp Views from Mauna Kea," a
public lecture tonight at the University of
"A brown dwarf
is an object between a star and a planet," said Liu,
member of a team that recently discovered a brown dwarf
orbiting a nearby star similar to the Sun.
"All stars are
at least 80 times bigger than the planet Jupiter, and
they generate their own energy by nuclear fusion," Liu
explained. "Planets are less than 15 times the size of
Jupiter and have no source of internal
have masses between planets and stars and are sometimes
called 'failed stars,'" he said.
shine may not be a star quality, but in astronomy's
search for earth-like planets, finding brown dwarfs is a
big step toward understanding how stars and planets came
to be formed, Liu said.
Gemini and Keck telescopes at Mauna Kea Observatory, Liu
discovered one particular brown dwarf that is separated
from its parent star by less than the distance between
the Sun and the planet Uranus. That raises interesting
companion is too massive to have formed the way we
believe that planets do, from a disk of gas and dust
when the star was young," Liu said. The parent star is
very similar to our sun, yet it has a brown dwarf
companion whose mass is dozens of times the combined
mass of all the planets in our solar system."
are lots of ideas on how it formed, Liu said, "We don't
yet know for sure."
the brown dwarf and companion star known as HR7672 for
several months, Liu's team concluded they were "moving
through space together, proving they are in orbit around
HR7672 and its brown dwarf — which is about 60 times the
mass of Jupiter — are estimated at 1 to 3 billion years
old. That's slightly younger than the sun.
existence of brown dwarfs has been speculated on for
decades, Liu said. They were not observed directly until
1995. Since then, hundreds of planets and brown dwarfs
have been found far beyond our solar system.
"To find these
objects requires a large telescope, which is why the
largest and most advanced telescopes — Keck, Subaru and
Gemini — are critical for this work," Liu said.
"Observing conditions on Mauna Kea are among the best in
the world in terms of weather, sky darkness and a stable
atmosphere which allows us to make very sharp images,
critical for studying very faint objects like brown
different temperatures have different colors with hotter
stars appearing blue and cooler stars appearing red.
"Without internal energy, brown dwarfs continually fade
and cool over their lifetimes," Liu said. "Before brown
dwarfs were found, their existence was thought of as
objects cooler than the lowest mass stars known as red
And in the
curious minds of astronomers, brown is more exciting
than "dull red."