Daxton Matthews
Physics Research Paper
Black Holes
Over the past two centuries, scientists have puzzled over the idea of the existence of black holes
in the universe. Could there be an object so massive that nothing-even light itself-could escape its
gravitational pull? The idea became more plausible when Einstein’s theory of relativity, which provides
a unified description of gravity as a geometric property of space and time, was published in 1916. With
this new understanding, German astrophysicist Karl Schwarzschild was the first to begin calculating the
gravitational force surrounding stars. He also determined, by the same method, the gravitational effects
on space and time inside a star. His research was later coined as the “Schwarzschild singularity”, and
prompted further study and speculation into, what are now known as, black holes.
Many scientists and astronomers, including Einstein, thought the concept of black holes to be
too bizarre and abstract for sincere investigation, even though it corresponded logically with established
laws and theories within the realm of physics. Black holes, unlike most other astronomical discoveries
up to this point, could not be seen directly, making it hard to prove their actuality. Astronomers have
found other ways to detect them, mostly through acute observation of their effect on surrounding
particles. One method has been to watch the results of an object actually falling into a black hole.
Roeland van der Marel, a researcher with the Space Telescope Science Institute, explains, “If material
actually falls into a black hole, it gets shredded apart and it heats up. As it heats up, it starts emitting
radiation and this radiation we can observe. In particular, we can often see X-rays coming from black
holes.” These X-rays do not penetrate the Earth’s atmosphere and, therefore, are only visible to
telescopes positioned in space. Once a particle enters, what is called, the “event horizon”, or the point
of no return, they can no longer emit light or radiation-it is all sucked in by the black hole’s massive
gravitational pull. Another technique used to locate and identify black holes is observing the behavior of
objects that are neighboring one. Scientists have found that, because black holes are quite massive, any
material, for example stars, that move close to it will feel an immense gravitational pull. As a result of
this, stars will move much faster than they normally would. In their search for these invisible giants,
scientists will look for objects in the universe that seem to be moving unusually fast. These, and a
handful of other methods, give us greater ability to study, observe, and hypothesize over this puzzling
enigma living within our universe.
Scientists believe the majority of black holes are formed by the gravitational collapse of large,
heavy objects, such as stars. A star will collapse when its temperature is no longer high enough to
prevent it from collapsing under its own weight. Then, its gravitational force will suck everything inward
causing the entire mass of the star to be squeezed into a very small space, forming a singularity, or a
region where the spacetime curvature becomes infinite. Black holes will continue to grow as they
absorb additional matter, including gas and interstellar dust, and as they merge with other bodies such
as stars, or even other black holes. Black holes can be big or small. Scientists think the smallest black
holes can be as small as one atom. Although it may seem tiny, a black hole of this size would have the
mass of a large mountain. Stars that are really massive can become stellar-mass black holes when their
lives end in supernova explosions. Stellar-mass black holes can be up to twenty times more than the
mass of the sun. The largest black holes we know of are called supermassive black holes, and can be
formed by the slow accretion of matter by a stellar-mass black hole. These can range from hundreds of
thousands to billions of solar masses.
Not only are black holes dispersed throughout the universe, but also, in our own galaxy. It is
widely accepted that, at the center of every galaxy there lies a black hole. Astronomers have located a
supermassive black hole at the center of our Milky Way, which they’ve named Sagittarius-A. NASA’s
Chandra X-ray Observatory has been observing radiation patterns from Sgr A over the course of several
years, and has detected X-ray flares released about once a day. Fortunately, unless an object comes
within its event location, a black hole’s gravitational force acts just the same as if it were still an active
star, so there is no need to be worried that planet Earth will be sucked into its core. Since the discovery
of black holes, many have wondered, and worried, about the possibility of our planet being “eaten” by
one of these monsters. Scientists suggest that there are no black holes even close enough to be a
threat. Even if a black hole the size of the sun were to take place of the sun (or if the sun were to
become a black hole), the Earth still would not fall in. The black hole would have the same gravity as the
sun currently has, and the planets would continue their orbit in ordinary fashion. In addition, because of
the sun’s relatively small size, it could never turn into a black hole.
Although we have learned a lot about these puzzling, celestial bodies, there is still a lot that we
don’t know. When asked to give a description of a black hole, Andrea Ghez, an astrophysicist with the
University of California stated, “We don’t know! We’d like to know, but we don’t actually know. The
real problem is that we can’t make any measurements inside the event horizon. Which leaves
everything inside to the realm of theory. [But] a black hole is a region of space where the pull of gravity
is so immense that not even light can escape it. That’s sort of the simple definition. So that means we
can introduce the concept of an event horizon around the black hole. That’s the last point at which we
can get any information or light can escape from the pull of the black hole. You can also think of a black
hole as an object where the pull of gravity got so strong that there’s no other force that can oppose it,
and the object collapses to an infinitely small volume.” Roger Blandford, an astrophysicist of Standford
University, when asked the same question, stated, “Well, what it is really is a region of space and time
where the properties are very different from those we encounter in the space and time around us. It
has lots of weird effects that it can exhibit—and then those we think we can understand as physicists.
But right at the heart of a black hole is the center nugget, which we call the singularity, and there we
don’t know what goes on. There I can’t answer your question, I’m afraid.” In conclusion, there is still a
lot that we don’t know, and much to be learned, regarding these mysterious, invisible creatures in our
universe. I hope that I can live to see even further discoveries emerge that will give us greater
understanding into the black hole.
Works Cited
"Black Holes Explained Transcript." PBS. PBS, Sept. 2006. Web. 01 May 2012.
<http://www.pbs.org/wgbh/nova/blackhole/expl-text.html>.
Boen, Brooke. "NASA - National Aeronautics and Space Administration." NASA. NASA Educational
Technology Services, 8 Feb. 2012. Web. 01 May 2012.
<http://www.nasa.gov/mission_pages/chandra/multimedia/saga.html>.
"A Brief History of Black Holes." NCSA Web Archive Bounce Page. The Board of Trustees of the
University of Illinois, 1995. Web. 01 May 2012.
<http://archive.ncsa.illinois.edu/Cyberia/NumRel/BlackHoleHistory.html>.
Goudarzi, Sara. "The Tricky Task of Detecting Black Holes." Space.com. Space.com, 21 Feb. 2007.
Web. 01 May 2012. <http://www.space.com/3457-tricky-task-detecting-black-holes.html>.
O'Neill, Lan. "Hunting Black Holes Through A Gravitational Lens." Discovery News. Discovery News,
11 Feb. 2012. Web. 1 May 2012.
Smith, Heather R. "NASA - National Aeronautics and Space Administration." NASA. NASA
Educational Technology Services, 30 Dec. 2009. Web. 01 May 2012.
<http://www.nasa.gov/audience/forstudents/k-4/stories/what-is-a-black-hole-k4.html>.