For no other reason than we are coming to the end of the British pantomime season I thought I’d write about one of the dwarves today. Not one of Snow White’s seven dwarves but an interstellar brown dwarf star and an lgbt astrophysicist who discovered the very first one.
As with the dwarves of
Snow White there are seven different types of dwarf star. They are named after
the colours which indicate their temperature and mass – red, yellow, orange,
blue, white, black and brown. All of them are relatively small in size compared
to our Sun (obviously, that’s why they’re called dwarf stars!).
The Sun, like the majority
of stars, fuses hydrogen atoms to produce its light, heat and radiation. Early
on in their life-cycle stars also fuse lithium atoms. Once a young star has
burnt up all its lithium and uses hydrogen it has become what you might call an
“adult” star. However, a brown dwarf star is too small to produce enough energy
to fuse hydrogen and still has lots of lithium left to carry on fusing for the
rest of its life cycle. Brown dwarves can be only slightly bigger than the
planet Jupiter but have more mass (heavier, for want of a better word). The
illustration below shows you the relative sizes of our Sun, Earth, Jupiter and the
Gliese 229 star system of which Gliese 229B is a brown dwarf star.
In size brown dwarves come
between the smallest red dwarf stars and the largest gas planets. The
difference is that a gas planet, like Jupiter and Saturn, aren’t quite massive
or active enough for nuclear fusion to take place within them when they form.
Another difference is that a brown dwarf forms from the same cloud as other
stars, whereas planets are formed from the dust discs that surround stars that
have already been formed. There are varying other criteria and definitions
still being debated and discussed about brown dwarf stars.
Their existence was first
theorised back in 1962 and were given the name brown dwarf in 1975. Because
these brown dwarves are only just bigger than Jupiter and emit very little
light they have been difficult to find. As telescopes and technology has
developed the hunt became easier. Searches using infrared found several
possible candidates in the 1980s.
Now we come to the Gliese
229 star system and Gliese 229B in particular. This was the first brown dwarf
star to be confirmed and photographed. It is also the first methane-rich brown
dwarf and the first in a new category called T Dwarf star. A leading member of
the team of astronomers who discovered Gliese 229B was transgender astrophysicist Dr.
Rebecca Oppenheimer of the California Institute of Technology (Caltech).
Gliese 229B is located in
the constellation of Lepus and is the companion to the larger red dwarf star
Gliese 229 (the stars are not visible to the naked eye, even though I have
shown them on the star map above). The distance between them is roughly the
same as the average distance between out Sun and Pluto. Both Gliese stars are
quite close to us, almost 19 light years, meaning that what telescopes see
today is how they looked just before the millennium. At the time of its
discovery Gliese 229B was the faintest object ever seen.
Gliese 229B was discovered
during the systematic survey of near-by stars by Caltech. Rebecca Oppenheimer,
a graduate Research Fellow, led the Caltech team. Using the 60-inch diameter
reflecting telescope at Mount Palomar Observatory in California an image of the
larger red Gliese 229 was taken on 27th October 1994. The image was enhanced by
using adaptive optics, an image-sharpening system. Adaptive optics was used by
another lgbt astronomer, Franck Marchis, which he helped to developed and led
to his discovery of satellites around asteroids. Infrared images and follow-up
observations and images from the Hubble Space Telescope confirmed the new brown
dwarf star’s existence.
The discovery was
important in another area of research, the hunt for exoplanets, planets
orbiting other stars. Because it is hard to tell if an object is a brown dwarf
star or a giant gas planet the information gathered by Rebecca Oppenheimer and
her team has helped to clarify the distinctions between the two.
In fact, it was the
discovery of Gliese 229B that led Rebecca to switch to searching for
exoplanets. She has led several planet-hunting projects and developed better
adaptive optic systems. In July I’ll return to Dr. Rebecca Oppenheimer and
planet hunting and look at her and other lgbt astronomers involved in searching
for worlds beyond our own solar system.