ACCORDING to Augusto Morales II, Physics professor of the UST Graduate School, dark matter is matter that cannot be seen or touched. Because it cannot be directly observed, its presence can be inferred from the effect of gravity on visible matter.

“Since gravity holds almost all astronomical masses together, it is standard practice in astronomy to use gravity to estimate the masses of objects in space,” Morales said.

Morales claims that there is insufficient scientific basis on what dark matter is made that studies about its origin is limited.

The missing mass

According to Morales, in order to determine the existence of potential sources of energy in the universe, scientists must first determine the overall mass of the universe.

“If we know the amount of energy possessed by the universe after determining its mass, we can determine the existence of not only astronomical objects, but also potential sources of energy,” he said.

One method in determining the mass of a galaxy or clusters of galaxies is by measuring the amount of light generated by the stars. Once the amount of light is determined, the number of stars in the galaxy, which will be used to mathematically calculate the galaxy’s mass, can be estimated.

Another method in determining a galaxy’s mass is using Doppler shift, which is a light source’s tendency to emit bluish light when it is moving closer to the observer, and reddish light when it is moving away from the observer. This can be observed in the rotation of a galaxy. Through using Doppler shift, the velocity of a galaxy as it rotates can be discovered. Once the rotational velocity of a galaxy is determined, a galaxy’s mass can be calculated mathematically.

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Dark matter’s existence was hypothesized in 1933 when physicist Fritz Zwicky calculated the mass of a cluster of galaxies, and found that he couldn’t account for the “missing mass,” which is responsible for the speed of a galaxy’s spin, which is faster than what should be expected.

According to a paper written by Chris Miller in 1995, dark matter may be found as either a massive astrophysical compact halo object (Macho) or a weakly interacting massive particle (Wimp).

A Macho is one type of object that could account for dark matter. According to Miller, it is a non-luminous object that makes up the halos around galaxies. He said that Machos can be found as brown dwarfs and black holes. Brown dwarfs, like ordinary stars, are accumulated hydrogen held together by gravity. However, its gravity is not strong enough to ignite when it forms. Black holes, on the other hand, occur due to an overabundance of matter, which causes its collapse. Any object, such as light, that comes close to a black hole is pulled to its gravitational field.

Wimps, which are smaller than an atom, are alternative hypothetical particles made of extraordinary matter. Because Wimps interact with ordinary matter gravitationally, they appear dark and invisible through normal electromagnetic observations. However, there has been no experimental evidence confirming the existence of Wimps.

Hide and seek

In May 2007, a group of astronomers led by Andrew Gould from Ohio State University were able to discover a way to estimate a certain dark matter’s location, particularly a Macho in a galaxy’s outer reaches, and its mass using triangulation, a method for solving a triangle based on ancient Greek geometry, which involves the gravitational lensing event.

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According to Baer, the gravitational lensing effect occurs when dark matter distorts the light of objects behind it. Dark matter acts like a lens to magnify the light from a star shining behind it, through its gravitational field. Because dark matter constantly moves, astronomers determine a gravitational lensing event by observing how the light from a star brightens and fades as the object passes by.

Triangulation was employed by using the earth, the National Aeronautics and Space Administration’s Spitzer space telescope, and the dark matter, as the vertices of a triangle. To calculate for the velocity of the dark matter, astronomers used the vertices and speed with which the light brightens and fades when seen from the earth and the Spitzer space telescope.

Once the velocity is determined, astronomers can classify whether the dark matter belongs to the Milky Way galaxy or any other galaxy, based on the predetermined velocity of heavenly bodies belonging to Milky Way galaxy.

With a new way to observe dark matter’s behavior, the once unobservable, untouchable, and invisible dark matter can now be perceived so that more light can be shed on its mystery.

Question from Teodulo Torres Jr., fourth year, College of Nursing

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