#1: Introduction

My name is Sharvani and I am a senior at BASIS Independent Silicon Valley. The goal of my project is to quantify and analyze the effects of a galaxy's orientation angle on the galaxy's measured dark matter content.

Imagine throwing a ball in the air. You would expect the ball to come back to Earth because of gravity; the gravitational force dictates that objects will return to Earth unless they achieve enough velocity to escape the Earth’s gravitational pull.

Similarly, planets and galaxies also experience gravitational pulls. The gravitational pull from a massive object is what keeps planets in orbit and galaxies intact –the Sun is the massive source of gravitational pull in our solar system and analogously, black holes are the source of gravitational pull in galaxies. Both the planets in the Solar System and the objects in galaxies (planets, stars, asteroids, and so on) experience this gravitational pull and thus orbit their respective centers of mass. This motion is governed by Kepler’s Laws (more so for the Solar System.)

Now, imagine that you throw a ball in the air and instead of coming straight back down, the ball shoots to the left. This is an unexpected action which goes against what the laws of gravity dictate, moving us to assume something else is affecting the way the laws of gravity work on the ball. A situation analogous to this resulted in the creation of the theory of dark matter. Refer to Fig 1 below:

Fig 1 (above): Two rotation curves. Distance refers to distance from the center of the galaxy. Velocity refers to the velocity of that part of that specific part of the galaxy. A represents what scientists expected a galaxy’s rotation curve to look like, and B is what a typical galaxy’s rotation curve actually looked like.

Scientists expected the velocity of a galaxy to slow down as they got farther from the center of the source of the gravitational pull (see A in Fig 1), but instead the galaxy’s velocity remained constant (see B in Fig 1). Scientists attributed this discrepancy by theorizing that there must be more mass in the galaxy than they could see, causing a greater gravitational pull between the center of the galaxy and its components and accounting for the consistent velocity. Since this matter was invisible and unable to be detected using conventional methods, scientists called this theoretical extra matter “dark matter.”

The dark matter of a galaxy is typically quantified by comparing the dynamical mass of a galaxy to the luminous mass of a galaxy. The dynamical mass of a galaxy is the mass of a galaxy calculated through gravitational force. Dynamical mass includes the dark matter content of a galaxy because gravity acts on all matter, including dark matter. The luminous mass of a galaxy is calculated by analyzing the stars in a galaxy and their various luminosities – their brightness – as well as other objects in the galaxy such as gas to determine the total mass of the galaxy based on visible content. These two values are then compared, and the difference between the two proves there is another factor that must be accounted for, and the dark matter theory accounts for this difference.

My senior research project matters because it helps determine more accurate dark matter measurements, and these values are the foundation for the entire theory of dark matter. It is important to account for potential sources of error in dark matter in order to confirm that there actually is a difference between a galaxy's stellar mass and dynamical mass.

I will complete my project by using data from the HALO7D survey (provided to me by my off-site mentor, the University of California, Santa Cruz's Professor Puragra Guhathakurta) and the Rainbow database to find data on the orientation angle of galaxies. I will also work with my faculty advisor, Mr. Hrin, to ensure I am going through the research process as thoroughly and formally as I can.

Since so little is known about dark matter, this is a critical first step to understanding this mysterious substance's nature. Completing this project will develop a reliable system for determining whether a certain galaxy can have its dark matter content measured through the aforementioned rotational velocity-dependent method and implement this system to provide an accurate value for a galaxy's dark matter content given its original dark matter content value, type, and orientation angle. Similar projects have been done by astrophysicists on a larger scale (mainly galaxy clusters - one such paper can be found here and my project is a stepping stone to analyzing these larger effects that help explain the structure of the universe.

Currently, dark matter research is focusing on the detection of particles believed to compose dark matter. Researchers are theorizing what kinds of particles make up dark matter and are building large detectors to detect these specific particles. Dark matter's composition still remains a mystery.

Overall, dark matter is one of the biggest mysteries astronomers and astrophysicists face today. My project, although not extremely ambitious, is critical in that it helps provide dark matter measurements that are as accurate as possible and thus provides a more reliable foundation off of which the scientific community can attempt to understand this mysterious matter.

I hope this introduction conveys my enthusiasm for this project, and I look forward to going through the challenging but exciting research research project. If you would like to learn more about my project, here is a link to my full research proposal.

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