Antimatter in the Milky Way: Searching for the Source of Gamma Rays
Since the infancy of our 13.8-billion-year-old universe, matter has had its counterpart, antimatter. Identical in every single way to ordinary matter (protons, electrons, etc.), only with an opposite charge. Yet, while our familiar normal matter drastically dominates the universe, antimatter still exists, even in our own galaxy. But, what causes antimatter in the Milky Way?
The love-hate history of matter and antimatter
Firstly, as a backstory, during our universe’s very young age only shortly after the big bang, matter and antimatter existed in equal amounts. Positively charged protons produced in equal amounts as negatively charged antiprotons. And, negative electrons equal to positive positrons, and so on.
However, upon interacting, the counterparts instantly destroy each other, leaving behind only pure energy. Seems to be a fair fight, no?
Actually, somewhere along the universe’s early life, our now familiar and “normal” matter won, all but defeating its doppelgänger particles. As a result, matter, as we know it, exists everywhere compared to meager amounts of antimatter. Planets, galaxies, cars, people, it’s all made from normal matter, not antimatter. Fortunately, this allowed life and humans to exist in general.
Gamma ray emissions: evidence of antimatter in the Milky Way?
Today, we detect antimatter in various places of the universe. In fact, surprisingly large amounts exist in our own Milky Way galaxy, especially toward the center, or bulge. But, what causes the antimatter in the Milky Way?
Astronomers find antimatter in the Milky Way by detecting gamma ray emissions. Simply put, gamma rays are extremely powerful radiation, emitted when electrons and positrons (matter-antimatter opposites) destroy one another in very large quantities.
Therefore, we know large quantities of antimatter must exist, especially toward the center of the Milky Way. Could the supermassive black hole in our galaxy’s center by our culprit? Or, does mysterious and unknown dark matter cause it?
Could antimatter in the Milky Way come from white dwarf stars merging?
Recently, researchers from Australia began investigating white dwarf stars as potential causes of both positrons, and thus, gamma ray emissions.
When stars similar to our Sun’s mass die, they leave behind tiny hot core remnants called white dwarfs. In some cases, mass transfer occurs in which gas gets passed between the two stars.
Eventually, the two white dwarfs can even merge completely. The result, type IA supernova (pronounced “one A”) explosions generating loads of radioactive material, capable of decaying into none other than positrons. More specifically, tremendous amounts of positrons, likely capable of explaining the large gamma ray emissions.
Alas, such supernovae are far rarer than the type II (type 2) supernova, caused by a large star’s core collapsing. Proving white dwarf mergers indeed produce positron amounts needed to explain Milky Way gamma ray emissions requires much deeper and sharper investigation. Researchers hope to accomplish this in upcoming months.