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Astronomy Terms - B



The common center of mass about which any two or more bodies of a gravitationally bound system orbit. The barycenter is one of the foci of the elliptical orbit of each body participating in the system; its location is strongly influenced by the mass of each body and the distances between them. For example, in a planetary system where the mass of the central star is significantly larger than the mass of an orbiting planet, the barycenter may actually be located within the radius of the star, such that the planet appears to orbit the star itself, though both bodies actually orbit the shared barycenter.


The process by which the class of subatomic particles known as baryons were generated in the early Universe, including the means by which baryons outnumber antibaryons.

Big Bang

The prevailing cosmological model for the origin of the observable universe. It depicts a starting condition of extremely high density and temperature, followed by an ongoing expansion that led to the current conditions.

binary star

star system consisting of exactly two stars orbiting around their common barycenter. The term is often used interchangeably with double star, though the latter can also refer to an optical double star, a type of optical illusion which is entirely distinct from true binary star systems.

black hole

A concentration of mass so compact that it creates a region of space from which not even light can escape. The outer boundary of this region is called the event horizon.


blazar is an active galactic nucleus (AGN) with a relativistic jet (a jet composed of ionized matter traveling at nearly the speed of light) directed very nearly towards an observer. Relativistic beaming of electromagnetic radiation from the jet makes blazars appear much brighter than they would be if the jet were pointed in a direction away from Earth.[1] Blazars are powerful sources of emission across the electromagnetic spectrum and are observed to be sources of high-energy gamma ray photons. Blazars are highly variable sources, often undergoing rapid and dramatic fluctuations in brightness on short timescales (hours to days). Some blazar jets appear to exhibit superluminal motion, another consequence of material in the jet traveling toward the observer at nearly the speed of light.

break-up velocity

Also critical velocity or critical rotation.

The surface velocity at which the centrifugal force generated by a rapidly spinning star matches the force of Newtonian gravity. At rotational velocities beyond this point, the star begins to eject matter from its surface.[2]

brown dwarf

substellar object that is too low in mass to sustain the nuclear fusion of hydrogen-1 in its core, with the latter being a characteristic of stars on the main sequence. Brown dwarfs can still generate energy from gravitational contraction and by the fusion of deuterium.


In astronomy, a galactic bulge (or simply bulge) is a tightly packed group of stars within a larger star formation. The term almost exclusively refers to the central group of stars found in most spiral galaxies (see galactic spheroid). Bulges were historically thought to be elliptical galaxies that happened to have a disk of stars around them, but high-resolution images using the Hubble Space Telescope have revealed that many bulges lie at the heart of a spiral galaxy. It is now thought that there are at least two types of bulges: bulges that are like ellipticals and bulges that are like spiral galaxies.


  1. Barycenter: Picture a "Barry Center," a fitness center named "Barry's Gym." Inside, a large star (like a celebrity) and a smaller planet (a regular gym-goer) are both on treadmills. They're not running in place but orbiting a point between them, which is glowing and marked "Barycenter." This symbolizes how both bodies orbit a common center of mass.
  2. Baryogenesis: Imagine "Barry's Genesis," a scene where a person named Barry is sculpting subatomic particles from clay. He's making more baryons than antibaryons, showing the process of baryogenesis, where more baryons were created in the early universe.
  3. Big Bang: Visualize a huge, colorful "Big Band" concert. The band is playing explosively loud music, symbolizing the extreme conditions of the Big Bang, and the audience is moving away from the stage, representing the ongoing expansion of the universe.
  4. Binary Star: Picture two celebrity stars, "Bin and Ary," dancing around each other on a dance floor. Their dance pattern forms a figure-eight, symbolizing the orbit around their common barycenter, and helps you remember the concept of a binary star system.
  5. Black Hole: Imagine a "Black Whole" donut shop, where the donuts are so dense and dark, light can't escape them. The boundary of the shop is marked "Event Horizon," representing the outer boundary of a black hole from which not even light can escape.
  6. Blazar: Envision a "Blazing Laser," a super-bright laser light show directed straight at you. The intense brightness and beams moving at nearly the speed of light represent the relativistic jet of a blazar pointed towards Earth.
  7. Break-up Velocity: Picture a "Break-up Anniversary" party at a spinning venue. The venue spins faster and faster until it breaks apart, symbolizing the point where a star's rotational velocity is so high that it starts to eject matter.
  8. Brown Dwarf: Imagine "Brownie the Dwarf," a small, stout fantasy character who's too weak to light a large campfire (representing the nuclear fusion of hydrogen-1) but can still warm himself with smaller fires (symbolizing the fusion of deuterium).
  9. Bulge: Think of a "Bulging Bag" filled with glowing stars, located at the central section of a larger, spiral-shaped handbag. This represents the densely packed stars in the central bulge of a spiral galaxy.