accretion: (in astronomy) The growth of any celestial object due to bringing in new building materials, such as gas, plasma, dust and other particles. The object’s gravitational tug brings in these new materials, eventually causing them to coalesce. (v. accrete)
accretion disk: A plane-like disk made from gas, dust and more that grows and orbits around some astronomical object. That gravitational tug of that object, known as the accretor, causes material in the disk to loses energy and angular momentum. This causes the disk to slowly spirals inward. Accretion disks likely play a role in the development of stars and planets and in the powerful spectral emissions that come from quasars, radio galaxies and some supernovas.
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atmosphere: The envelope of gases surrounding Earth, another planet or a moon.
atom: The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.
black hole: A region of space having a gravitational field so intense that no matter or radiation (including light) can escape.
cavity: (in dentistry) a tiny hole in a tooth that develops over time. Dental cavities are more likely to happen when a person eats a lot of sugar or does not brush and floss regularly. Dentists refer to these as caries.
cosmic: An adjective that refers to the cosmos — the universe and everything within it.
cosmos: (adj. cosmic) A term that refers to the universe and everything within it.
density: The measure of how condensed some object is, found by dividing its mass by its volume.
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disk: A round, flat and usually fairly thin object. (in astronomy) A rotating cloudlike collection of gases, dust or both from which planets may form. Or the structure of certain large rotating bodies in the cosmos, including spiral galaxies.
electromagnetic: An adjective referring to light radiation, to magnetism or to both.
electromagnetic radiation: Energy that travels as a wave, including forms of light. Electromagnetic radiation is typically classified by its wavelength. The spectrum of electromagnetic radiation ranges from radio waves to gamma rays. It also includes microwaves and visible light.
fat: A natural oily or greasy substance occurring in plants and in animal bodies, especially when deposited as a layer under the skin or around certain organs. Fat’s primary role is as an energy reserve. Fat also is a vital nutrient, though it can be harmful if consumed in excessive amounts.
infrared: A type of electromagnetic radiation invisible to the human eye. The name incorporates a Latin term and means “below red.” Infrared light has wavelengths longer than those visible to humans. Other invisible wavelengths include X-rays, radio waves and microwaves. Infrared light tends to record the heat signature of an object or environment.
muscle: A type of tissue used to produce movement by contracting its cells, known as muscle fibers. Muscle is rich in protein, which is why predatory species seek prey containing lots of this tissue.
nanometer: A billionth of a meter. It’s such a small unit that researchers use it as a yardstick for measuring wavelengths of light or distances within molecules. For perspective, an average human hair is about 60,000 nanometers wide.
pulsar: The name for a spinning, ultra-dense neutron star. A single teaspoonful, on Earth, would weigh a billion tons. It represents the end of life for stars that had started out having four to eight times the mass of our sun. As the star died in a supernova explosion, its outer layers shot out into space. Its core then collapsed under its intense gravity, causing protons and electrons in the atoms that had made it up to fuse into neutrons (hence the star’s name). When these stars rotate, they emit short, regular pulses of radio waves or X-rays (and occasionally both at alternate intervals).
radiation: (in physics) One of the three major ways that energy is transferred. (The other two are conduction and convection.) In radiation, electromagnetic waves carry energy from one place to another. Unlike conduction and convection, which need material to help transfer the energy, radiation can transfer energy across empty space.
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radio waves: Waves in a part of the electromagnetic spectrum. They are a type that people now use for long-distance communication. Longer than the waves of visible light, radio waves are used to transmit radio and television signals. They also are used in radar.
solid: Firm and stable in shape; not liquid or gaseous.
star: The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become hot enough, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.
telescope: Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.
universe: The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).
visible light: A type of electromagnetic radiation with wavelengths that range between 380 nanometers (violet) and 740 nanometers (red). Visible light has wavelengths that are shorter than infrared light, microwaves, and radio waves but longer than ultraviolet light, X-rays and gamma rays.
wave: A disturbance or variation that travels through space and matter in a regular, oscillating fashion.
wavelength: The distance between one peak and the next in a series of waves, or the distance between one trough and the next. It’s also one of the “yardsticks” used to measure radiation. Visible light — which, like all electromagnetic radiation, travels in waves — includes wavelengths between about 380 nanometers (violet) and about 740 nanometers (red). Radiation with wavelengths shorter than visible light includes gamma rays, X-rays and ultraviolet light. Longer-wavelength radiation includes infrared light, microwaves and radio waves.
X-ray: A type of radiation analogous to gamma rays, but having somewhat lower energy.
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