Caption: Gliese 229B, the small white dot, was the one of the first discovered brown dwarfs (see Wikipedia: Brown dwarf: History). The large astronomical object is star Gliese 229. Gliese 229B is a substellar companion of Gliese 229: i.e., it orbits Gliese 229. The HST image is from 1995 Nov17.

Features:

1. This is a false-color, far red image (see NASA: Hubblesite: Brown Dwarf Discovered Around Star Gliese 229).

2. The astronomical objects are NOT resolved: the image size correlates with its brightness. The spike is an artifact of imaging process.

3. Gliese 229 is an M dwarf with spectral type / luminosity class M1 V. It is 5.75(3) pc (18.8(1) ly) from the Sun in constellation Lepus---which always reminds yours truly of Night of the Lepus (1972 film)---they don't make them like that anymore---or is that they shouldn't ...

4. Gliese 229B has mean orbital radius > 35 AU, orbital period > 1000 days, mass in the range 21--51.4 Jupiter masses (M_J) (i.e., 0.02--0.05 M_☉), and radius 0.468 Jupiter radii (R_J) (see Wikipedia: Gliese 229: Substellar companions). Its surface temperature is ∼ 1000 K (FK-180, CK-306).

5. Brown dwarfs are substellar objects in the mass range 13--80 M_J (i.e., ∼ 0.012--0.076 M_☉). Note 1 M_J = 317.82838 M_⊕ ≅ 318 M_⊕.

   Brown dwarfs too low mass to do nuclear burning of hydrogen (H-1) to helium-4 (He-4) (i.e., hydrogen burning) in their cores which is why they are NOT stars. They can nuclear burn deuterium (D, H-2) for mass > 13 M_J and lithium-7 (Li-7) for mass > 65 M_J.

   The name brown dwarf is a misnomer. Brown dwarfs are NOT brown. They may appear magenta or orange/red. Since they all rotate, they probably have bands like gas giant planets.

   There must be lots of brown dwarfs. But because they are so dim, they are hard to discover and probably only 100s are known, confirmed and unconfirmed (see Wikipedia: List of brown dwarfs). Their observable universal abundance is probably similar to that of stars???, but their net mass is much less and they contribute little to the mass-energy of the observable universe. They do little else. Just form and cool off forever.

   Yours truly thinks brown dwarfs are rather boring astronomical objects. Their interest is probably just in filling gap in the continuum between gas giant planets and small stars.

6. Hey, 229B sounds familiar, but Sherlock Holmes lived at 221B Baker Street, London.