Page 30 - GALIET PHYSICS BLOSSOMS III

• “Object x is compact and very massive.
• We don’t know of anything that is that small and massive.
• Therefore, object x is a black hole.”31
BLACK HOLE EVIDENCEàQUASARS
Some galaxies emit from their centers or active galactic nuclei enormous amounts of radiation and powerful jets of matter. Quasars are the brightest and most luminous active galactic nuclei, so bright indeed, that some of them can emit more brilliant light than 1000 Milky Ways.32
Quasars were discovered in the 1960s as strong sources of radio emission that looked like stars. As a result, the name quasars originate from “quasi-stellar radio sources.” They emit energy across a wide swath of the electromagnetic spectrum, and they also produce strong emission lines. They are the source of a wide range of photon energies, suggesting that they contain matter with wide ranges of temperatures. Their power output is so extraordinary that they swamp the light of their own galaxies making it extremely hard to detect surrounding galaxies.
As a result, ever since their discovery, astronomers have puzzled as to the source of such vast release of energy from small central volumes. It turns out that the energy and fabulous luminosity of quasars comes from matter that has fallen into a super massive black hole (its mass is usually millions to billions that of the mass of the sun). When the energy of matter falls towards a black hole it generates incredible amounts of energy. It is converted into kinetic energy, and as the particles falling in collide, this kinetic energy is converted into thermal energy causing matter to emit the fabulously intense radiation we observe in quasars. The matter that falls into a super massive black hole swirls through a gigantic accretion disk surrounding a supermassive black hole, before matter disappears beneath the event horizon. Indeed, to produce such vast luminosity, the amount of matter has to be greater than the mass of the sun to pass through the accretion disk and fall into the black hole. Similarly, the faster the rotation of a black hole, the more energy it releases. In this way, the super massive black hole theory explains what we observe in quasars or in the brightest active galactic nuclei: their extreme luminosities, the vast emission of radiation in many wavelengths from radio waves to X rays, and the existence of their powerful jets. Indeed, there is plenty of evidence that verifies to date the hypothesis that super massive black holes cause quasars, active galactic nuclei and radio galaxies.
31 Chaisson, McMillan. Astronomy Today. Volume II. Stars and Galaxies. 565.
32 Bennet, Donahue, Schneider, Voit. The Cosmic Perspective. 6th Edition. Volume II. Stars and Galaxies. 637, 636-641.
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