Dark Matter: The Invisible Force At The Heart Of A Galactic Mystery

Dark matter, invisible and enigmatic, may be the solution to a riddle posed by a star that is speeding through our galaxy. The recent discovery of the star system throws existing theories about the center of the galaxy into question – unless dark matter enters the equation.

As reported in The Astrophysical Journal, Péter Németh leads a team of astronomers at the Friedrich-Alexander University Erlangen-Nürnberg in Germany, aided by researchers at the California Institute of Technology. They theorize that dark matter can explain anomalies raised by their data.

His team discovered PB3877, a so-called hypervelocity star, one of about two dozen known to be traveling through our galaxy at the escape velocity. That means they are traveling fast enough to escape the gravitational pull of the sun that is holding earth and the other planets in orbit. PB3877 is different than the other hypervelocity (or super fast) stars in that it is actually a binary, or two-star system. One of the stars is about 5,000 times hotter than our sun while its partner is about 1,000 degrees cooler.

Previously, scientists theorized that these hypervelocity stars originated with a supermassive black hole located at the center of our galaxy. The black hole, with its gravitational force, can essentially spit stars right out of the galaxy.

However, the discovery of PB3877 has put that theory to the test. Scientists calculated the trajectory or path of P3877 as it travels through the galaxy and realized it could not have come from the galactic center. Any other current model or theory, such as an interstellar collision, would have knocked the binary system apart into two separate stars. It leaves PB3877 shrouded in mystery unless dark matter enters the picture.

A so-called “dark matter halo” could account for its anomalies. The amount of invisible dark matter will determine whether or not PB3877 remains bound to our galaxy. Scientists are eager to continue their study of PB3877 to learn more. Andreas Irrgang, a research associate at the Dr. Karl Remeis-Observatory, spoke to The Astrophysical Journal.

“We used different mass models to calculate the probability that the star will actually remain bound to the Galaxy. Only for the most massive Galaxy model this is the case. This makes PB3877 an excellent target to probe dark matter halo models.”

The theory of dark matter, which is invisible to our eyes and any of our current instrumentation, holds that it works, in essence, like a binding agent that holds galaxies and other stellar formations together through its gravitational force. Dark matter cannot be detected because it does not emit any light – current instrumentation is based on detecting light waves on the electromagnetic spectrum. Essentially, dark matter fills up the gaps in our universe after accounting for the gravitational force produced by all the visible objects. It is believed that there are about five times as much dark matter in the universe as there is ordinary matter that we can already detect.

The DAMA (for “Dark Matter”) collaboration project uses detectors situated at the world’s largest underground laboratory, located beneath the mountains at Gran Sasso just east of Rome, Italy. It has been the only source of a stream of data on dark matter for more than a decade. The detectors use sodium iodide crystals to detect the dark matter.

While there is a great deal of evidence that points to the existence of dark matter, it remains an enigma. Many scientists theorize that some part of dark matter is made up of what they are calling WIMPS, or “weakly interacting massive particles.”

If that hypothesis is true, then the sodium iodide crystals will produce a flash of light as they encounter dark matter. That’s the result the DAMA collaboration has been producing reliably now for more than a decade – but it has not been duplicated by any other such experiment. That fact has puzzled researchers around the globe, leading to the idea of trying to reproduce the same results in the exact same way as DAMA. Soon, a second detector in Seoul, South Korea, will go online, to be joined by others in Australia and Spain, and another near Rome over the next three years.

The scientists involved are certain that their experiments will either prove or disprove the DAMA dark matter results once and for all. Frank Calaprice of Princeton University in New Jersey leads the team of researchers at the Yangyang Underground Laboratory, about 100 miles east of Seoul. He spoke to Nature magazine.

“This will get resolved.”

While scientists have never seen dark matter, they are fairly certain it exists because they can observe its gravitational effects. NASA Jet Propulsion Laboratory scientists have used images from the Hubble Space Telescope among others to study galaxies and galaxy clusters. They believe many of the differences they observe between them can be accounted for by invisible dark matter.

[Image via NASA/JPL]

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