A

Some parents tell their children that if a celestial body in the night sky seems to be twinkling, then it must be a star. Actually, it is difficult to differentiate a star from a planet with the naked eye—a powerful telescope or spectroscope is needed to establish whether the light from an object in the sky is being reflected or if it is being produced internally. The former would indicate that the object is a planet, and the latter, a star.

In the early processes of star formation, temperature and mass are crucial. A clump of gas and dust with the potential to produce a star must be massive enough—at least 8 percent of the mass of the Solar System’s Sun—to be able to attain a core temperature capable of initiating the process of nuclear fusion. When the temperature reaches 10 million Kelvin, hydrogen fusion occurs and energy is released, giving the object luminosity.

B

In the 1960s, astronomers theorized the existence of a celestial object that defied classification—not quite planet and not quite star. The American astronomer Jill Tarter classified them as dark sub-stellar objects that did not have enough mass to sustain hydrogen fusion. This raised the question: once the star formation process begins, does a star always result? Astronomers have discovered that the answer is “not always”.

For some reason, some gas and dust clumps that commence star formation do not achieve the requisite mass and temperature needed to support nuclear fusion. Yet, because some energy remains, heat is retained—a heat that is greater than what planets possess. Thus, the object continues to emit radiation. Dr. Tarter originally called them black dwarfs, but they were renamed brown dwarfs to differentiate them from stellar remnants that no longer emit a significant amount of light. In terms of brightness, brown dwarfs are like rooms with a night light, glowing only faintly. This is the reason these objects are also known as failed stars.

C

It isn’t easy to collect information about brown dwarfs because they are hard to detect. Their glow is within the infrared range and can only be detected with sensitive equipment and when the circumstances permit their identification. In fact, it was only in 1994 that the first confirmed brown dwarf, known as Teide 1, was discovered by a team of Spanish astrophysicists. It was located in the Pleiades open cluster through a series of collected images of the constellation as seen through an 80 cm telescope. About 55 times the mass of Jupiter, its size fell within the mass range of brown dwarfs discovered thus far—15 to 75 times the mass of Jupiter.

Astronomers have since learned that brown dwarfs are actually a bright, deep red in color, form part of a binary system—with the distance between the dwarf and its companion star comparable to that of Pluto and the Sun—and has a luminosity about a tenth of the faintest stellar objects. Its mass spectrum contains water vapour and methane, which suggests that its surface temperature does not exceed 1,500 Kelvin. About four-hundred dwarfs have been discovered since 1994, and these have been classified according to size and temperature.

D

Because brown dwarfs are nondescript, scientists were inclined to believe that they merely coexist with their partner star and are insignificant. Some preferred to classify them as planets because of their cool atmosphere, but given that their formation began as stars and that no accretion of spinning dust appeared to be involved in their making, the classification “failed star” endured. Then, on July 11, 2000, a nearby brown dwarf called LP 944-20 emitted what appeared to be a solar flare for two hours. Jupiter emits X-ray flares as well, but the dwarf’s flare was about a billion times greater than those discharged by Jupiter.

In January of 2002, the image of a brown dwarf orbiting a star called 155ge was captured. Its distance from its companion star was only 14 astronomical units, similar to that between Saturn and Uranus. Previously, it was believed that distances between brown dwarfs and their binary companions could only be equivalent to the Sun and outer planets of the Solar System. Moreover, the sheer size of the brown dwarf seemed to confirm that dwarfs do not form as planets do, for it would have been impossible for a planet of that size to be assembled given the abbreviated distance between the two objects.

Three years later, an Irish team of researchers caught a young brown dwarf in a stellar nursery known as Rho Ophiuchi emitting a jet approximately 1.5 billion kilometers long. Since it is known that young massive stars form similar jets, the phenomena seemed to cement the notion that brown dwarfs are not ejected by a companion star, but rather, they form like any other star.

Just as unusual was the discovery of proto-planetary disks around several brown dwarfs in the Chamaeleon constellation. The disks contained dust particles that had crystallized to the point of sticking together, just as planets in the early phases of formation do. The disks also seemed to be flattening, an indication that they were forming into planets. Scientists surmise that this suggests the potential for planets to form around a brown dwarf system. These discoveries have caused excitement as the potential for further research has increased now that the status of the brown dwarf has risen to something closer to objects within the stellar class.