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Catherine Donovan

Mrs. Natalie Hartford

Physics

17 December 2018

The Milky Way Monster

Beginning Paragraph Black holes strike terror into the hearts of most people. After all, nothing can escape these sucking vortexes, not even light. They tear apart stars and destroy worlds, even the home world of everybody’s favorite Vulcan, Mr. Spock (Star Trek). The term “supermassive black hole” therefore should give everyone the creeps, especially knowing that one such monster lurks in the heart of Earth’s own Milky Way Galaxy. Thesis Statement However, earthlings have little to fear from the incredibly dense object around which their sun and the rest of the galaxy revolves.

Topic Sentence The Milky Way’s supermassive black hole is called Sagittarius A*—pronounced Sagittarius A Star and abbreviated Sgr A* (Cain). The first part of the name comes from the constellation Sagittarius, which lies between Earth and the center of the galaxy. In 1932, astrophysicists identified a powerful source of radio waves at this location and named it Sagittarius A. More recently, the Chandra X-ray Observatory discovered that a very small region within Sagittarius A emits X-rays as well In-Text Citation (Garlick 166-167). The types of emissions, the size of the region, and the centrality all hinted at a very exotic object. The presence of high-velocity stars in orbit around that compact center pinpointed Sgr A* (Wolpert).

Middle Paragraphs Just how exotic is Sagittarius A*? Imagine our own solar system, with the sun at the center and Mercury orbiting 36 million miles away. If Sgr A* wandered into our solar system, it would more than fill the space between the sun and Mercury—and would swallow both instantly (Cain). Statistics Indeed,

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Sgr A* has feasted on many suns during its 13+ billion-year lifespan, consuming about 4 million solar masses at last count (Garlick 167).

These grim statistics may inspire panic, but Earth is quite safe from Sgr A*. First of all, the supermassive black hole lies 26,000 light years away from Earth (Cain). If the solar system suddenly plunged at light speed toward the center of the galaxy, it wouldn’t reach Sgr A* for 26,000 years. By the way, the solar system isn’t moving toward the supermassive black hole at all, but rather speeding 483,000 miles per hour in its orbit around the galactic center (Fraknoi). Secondly, Sgr A* hasn’t been actively feeding for quite a while. Aside from munching on the occasional gas cloud, it has cleared its vicinity of most other matter. In fact, the massive stars that do orbit Sgr A* come only as close as about 17 light hours (three times the distance from the sun to Pluto) and are in no danger of getting gobbled up (Cain).

More importantly, every large galaxy centers quite safely on a supermassive black hole like Sgr A*, and these objects have actually driven the galaxies’ evolutions. The mass of the central black hole directly correlates to the mass of the central galactic bulge as well as the speed of outer stars orbiting the galaxy. These supermassive black holes most likely preceded their galaxies, providing the seed that drew in matter and stimulated the formation of stars, including the sun (“Singular”). In other words, instead of being a cosmic bogeyman intent on eating the earth, Sgr A* is the force that brought the Milky Way, the sun, and the earth into being.

We may owe our existence to Sagittarius A*, but we still wouldn't want to get too close to it. Traveling into any black hole would be a one-way trip. To escape the gravity well, an object must travel at a speed that exceeds the force of gravity, which increases as the distance to the object decreases. At 36 million miles from the center of Sgr A*, an object would have to exceed

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the speed of light to escape. That inescapable sphere forms the black hole’s “event horizon” (Cain). Anything that crosses that boundary is gone.

But an unlucky traveler’s specific demise depends on the size of the black hole. A stellar-mass black hole creates a heart-rending end because its compact event horizon causes uneven tidal forces on the traveler. The difference in gravitation from head to foot would stretch the person until snapping at the center. Then each half would stretch until it snaps and so on until every tissue is pulled apart into a long string of atoms. Direct Quotation As astrophysicist Neil deGrasse Tyson puts it, “To all the words in the English language that describe ways to die . . . we add the term ‘spaghettification’ ” (285).

In a supermassive black hole, however, the event horizon lies much farther from its center, so the tidal forces from head to toe would be unnoticeable. In fact, a traveler moving at the speed of light into the event horizon wouldn’t sense any change at all (Tyson 286). What happens next, though, is anyone’s guess. Time actually stops at the event horizon, and then swaps places with space. The laws of physics break down entirely at the infinitely dense singularity at the black-hole’s center—just as they did in the singularity of the big bang. Some scientists even suggest that black holes lead to new big bangs (Finkel)!

Ending Paragraph So, though Sgr A* might sound terrifying at first, it actually has made the galaxy, the sun, the earth, and human existence possible. The universe itself might be inside such a forbidding place. In the past 50 years, scientists have learned a great deal about the monster at the center of the Milky Way, but with every discovery, Sgr A* somehow becomes less monstrous and more mysterious.

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Works-Cited Entries Works Cited

Cain, Fraser. “What Is Sagittarius A*?” Universe Today, 8 Nov. 2016, www.universetoday.com/39828/sagittarius-a/.

Finkel, Michael. “Are We Living in a Black Hole?” National Geographic, 19 Feb. 2014, news.nationalgeographic.com/news/2014/02/140218-black-hole-blast-explains-big-bang.

Fraknoi, Andrew. “How Fast Are You Moving When You Are Sitting Still?” The Universe in the Classroom, Astronomical Society of the Pacific, Spring 2007, www.astrosociety.org/edu/publications/tnl/71/howfast.html.

Garlick, Mark A., and Wil Tirion. The Illustrated Atlas of the Universe. Metro Books, 2012, pp. 166-67.

“A Singular Place: The Relationship Between Black Holes and Galaxies.” Cosmotography, www.cosmotography.com/images/supermassive_blackholes_drive_galaxy_evolution_2.html. Accessed 6 March 2018.

Star Trek. Dir. J.J. Abrams. Paramount, 2009.

Tyson, Neil deGrasse. Death by Black Hole. W. W. Norton, 2007, pp. 285-86.