There’s just something about the word “quasar”. It sounds so technical. So cutting edge. So borderline-indecipherable astrophysics. Come to think of it, what is a quasar, anyway?
Let’s start with the word. Quasar is a portmanteau of “quasi-stellar radio source”. Given that I think etymology is the hidden key to the universe, I maintain that most (not all) you need to know about quasars is contained in that word. Quasi-stellar? Star-like. Viewed through a telescope, a quasar appears as a bright point of light - very similar to a star. They are, however, not stars. Working out how far from Earth that bright point of light originated makes it very clear that the light is coming from too far away, and in the wrong direction, to be a recognizable star. And by “very far away”, I mean “well beyond the boundaries of the Milky Way”. So, quasars are non-stellar bodies visible from other galaxies. Radio source? Quasars were first identified by radio waves - astronomers discovered certain point regions of space that were emitting radio waves. Eventually, other non-stellar points of light that did not emit radio waves were discovered, but the name “quasar” applies to all such quasi-stellar objects. Quick tangent for less physics-inclined readers: when I say radio waves, I’m referring to a specific range of wavelengths on the electromagnetic spectrum. Other ranges of wavelength correspond to visible light, microwaves, and the ever exciting gamma rays.
One more note about radio waves - they are part of the suite of EM rays emitted by stellar bodies. So, quasars emit radio waves like stars (sometimes), and appear as points of light like stars, but by virtue of their distance from Earth and direction of travel, can not be stars. What exactly are they, then?
Astronomy can be very counterintuitive. Even when they are not emitting radio waves, astronomical measurements show quasars to be emitting huge amounts of EM energy (way more than even the brightest or hottest star) from a small source. They are, in fact, the most luminous objects in the universe. Now, what astronomical body can you think of that is the complete opposite of a massive, visible from unimaginable distances emission of light? If you said a black hole, go talk to NASA. They could use people like you.
Yes, quasars are energy emitters powered by black holes. Black holes are another astronomical bizarrity - their origins are better understood (and more widely known) than those of quasars, but a quick review. Sometimes when a star explodes, or goes supernova, the matter left behind is drawn together by gravity. Gravity, as used in astronomy, refers to the attractive force between any two objects. Gravity is a function of mass, but this only really comes into play with very massive (large) objects (Earth, Sun, etc.). I’ve seen the force of gravity visualized as a sheet drawn taut over a frame. Put a tennis ball in one corner, and a basketball in another corner. See how the tennis ball causes a smaller indentation than the more massive basketball? Correspondingly, the total area of the sheet that slopes in towards the basketball (anything placed on it will roll towards the ball) is greater than the total area of the sheet sloping in towards the tennis ball. So, in the remains of that supernova, massive quantities of matter are drawn together, combine, exert an even stronger gravitational pull...eventually, the pull gets so strong that even light can not escape. All of this matter is crammed into an area as few as twenty or thirty kilometers across, creating unbelievably dense matter.
When black holes form in the center of a galaxy, there is quite a lot of matter to be drawn into said hole. Through a process that astronomers are still working out, the process of drawing all of that matter into a black hole generates enormous volumes of energy, which are expressed as EM waves and, presumably, heat.
For me, the hardest part of astronomy to grasp is the light-years. Given how long it takes light to reach the Earth, we view most things in the past. When we observe light emitted by a star 35 light-years away, that light was emitted 35 years prior to the instant of viewing. Our galaxy has a diameter of 100,000 light years, and the closest galaxy is 250,000 light years away. So, when we view light from the relatively near-by Canis Major galaxy, that light was emitted 250,000 light years ago. The Chandra X-ray observatory routinely captures quasars 4.6 billion light years away. If we were to somehow develop faster-than-light travel and go to the sites of the quasars we now observe, those quasars would, in all likelihood, be long gone. The further out you observe from the Earth (correspondingly, the further back in time), the more quasars there are. It is currently theorized that the universe was more likely to manifest quasars earlier in its history, and that we are currently well past the peak of quasar formation. Why this might be so is still being investigated, but the answer is sure to be interesting.
So there you have it - quasars! Many of the odder elements of theoretical astrophysics made manifest - proof that while there may be an equation for everything, the phenomena those equations describe is no less strange and wonderful for being explicable.
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