Thursday 18 January 2018

Star-Gayzing : Discovering Dwarves

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.

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