“We Truly Don’t Know What It Is” –Mystery Milky-Way Spectrum of Light Observed

 

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"We use special telescopes to catch X-ray light in the sky, and while looking at these X-rays, the telescopes noticed an unexpected feature and captured a spectrum of light, which is not produced by any known atomic emission," said University of Miami astrophysicist Nico Cappelluti. "This emission line is now called the 3.5 kiloelectron volt (keV). One interpretation of this emission line is that it's produced by the decay of dark matter."


"This 3.5 keV emission line is unidentified. We truly don't know what it is," said Esra Bulbul, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics and co-author in Cappelluti's study. "But one theory is that it could be a sterile neutrino, which is also known as decaying dark matter. What is truly interesting about Dr. Cappelluti's study is that he found this 3.5 keV line within our own galaxy."

 

In 2014, a team of astronomers led by Bulbul discovered a noticeable spike in intensity at a very specific energy level. While studying the hot gas within the Perseus galaxy cluster (image above), the Chandra and XMM-Newton observatories revealed an unexpected spike, or emission line, corresponding to an energy of 3.5 kiloelectron volts (keV). This wavelength is very difficult to explain, as it cannot be described by previously observed – or even predicted – astronomical objects.

"If confirmed, this will tell us what dark matter is and could be one of the major discoveries in physics," said Cappelluti. "We know that the Milky Way is surrounded by dark matter. Think of it as if we are living in a bubble of dark matter. But we also want to have the statistical certainty of our detection, so now we are putting together a Sterile Neutrino Task Force."

Cappelluti is intrigued by the cosmic phenomena of super massive black holes, the nature of dark matter, and active galactic nuclei, which is the very bright light source found at the center of many galaxies.His recent published findings that could give insight on a subject scientists and astrophysicists have been investigating for decades: What is dark matter and where does it come from?

Cappelluti's study, published in The Astrophysical Journal and entitled, "Searching for the 3.5 keV line in the deep fields with Chandra: the 10 MS observations," examines an interesting light source that was captured by four different telescopes each pointing in a different direction in the sky. The source of light is unfamiliar and unrecognizable to scientists and has caused quite a stir in the world of astrophysics. Bulbul also found the emission line while studying clusters of galaxies in 2014. 

The atomic emission spectra is shown below for various elements. Each thin band in each spectrum corresponds to a single, unique transition between energy levels in an atom. (Rochester Institute of Technology, CC BY-NC-SA 2.0).

 

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The four telescopes that captured the 3.5 keV emission were NASA's NuSTAR telescope, the European Space Agency's (ESA) XMM-Newton telescope, the Chandra telescope, and the Suzaku telescope from Japan.

This fall, several scientists from around the world, including Harvard's Bulbul, plan to gather at the University of Miami to organize a massive data-mining project to investigate and research this 3.5 keV emission line.

"The goal now is to continue to look at the sky until we obtain more powerful operating telescopes with better resolution, which won't be ready until 2021, and share and analyze data from other scientists who are trying to uncover the secrets of dark matter," said Bulbul.

The Daily Galaxy via University of Miami

 

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