A Flash in the Dark!

Wednesday, July 16, 2014

A Flash in the Dark!

We are delighted to welcome Esra Bulbul as a guest blogger. Esra led the new study reporting evidence for a mysterious X-ray signal in galaxy clusters, leading to our latest press release. She earned her master’s degree in physics from the Middle East Technical University in the capital city, Ankara, in Turkey in 2006. Four years later she graduated with a PhD in physics from the University of Alabama in Huntsville / NASA Marshall Space Flight Center. After receiving her Ph.D. she moved to the Harvard-Smithsonian Center for Astrophysics as a Smithsonian Astrophysical Fellow working jointly at the NASA Goddard Space Flight Center as a visiting scientist. She is now back at the Harvard-Smithsonian Center for Astrophysics and enjoys living in the greater Boston area.

When I started my first postdoc at the Harvard-Smithsonian Center for Astrophysics, I already knew that one alternative way to improve the sensitivity of current instruments like Chandra and XMM-Newton is to “stack” large numbers of observations of galaxy clusters, meaning that we layer one observation on top of another.

The great advantage of stacking observations is not only an increased signal-to-noise ratio (that is, the amount of useful signal compared to background noise), but also the diminished effects of detector and background features. The X-ray background emission and instrumental noise are the main obstacles in the analysis of faint objects, such as galaxy clusters.

I started by examining the large archive of the XMM-Newton satellite. After 15 years of operation, both XMM-Newton and Chandra have collected large amounts of data, which made this work possible. My primary goal was to refine previous upper limits on the properties of dark matter particles and maybe to find a weak emission line from a metal, which was not detected previously.

These weak emission lines from metals originate from the known atomic transitions taking place in the hot atmospheres of galaxy clusters. After spending a year reducing, carefully examining, and stacking the XMM-Newton X-ray observations of 73 galaxy clusters, I noticed an unexpected emission line at about 3.56 kiloelectron volts (keV), a specific energy in the X-ray range.

I remember being so puzzled when I first saw the line. Its wavelength did not correspond to any of the known atomic transitions. I remember running to my collaborator's office with excitement to show this new emission line. A second surprise came from my doctor at the time. I learned that I was pregnant with my first baby.

To convince myself that this line is not an XMM-Newton artifact I have further investigated the Chandra X-ray observations of the bright core of the Perseus Cluster. The line was also detected in these observations, confirming that it is not an instrumental feature. The next goal was to find the origin of this new line.

My team and I came up with a few astrophysical processes, which could explain this line. We went through these processes one by one carefully. However none of them could produce an emission line at 3.56 keV. Since 80% of galaxy clusters consists of dark matter, one possibility we considered was the decay signature of sterile neutrinos.

According to theory, a well-motivated warm dark matter candidate – a sterile neutrino – decays into an active neutrino by emitting an X-ray photon in the keV range. This X-ray photon can be detectable through X-ray spectroscopy. We found that our results indeed were consistent with the theoretical expectations and the upper limits placed by previous X-ray searches.

It took me a year to confirm the existence of the line in different subsamples and write the paper. Within a few hours of having submitted the paper to ApJ and posted it to the archive, I ran to the hospital and I delivered my baby, Adrian Batu. It was the most rewarding time of my life; I had two babies in a few days.

What is next? Since this line is weak, it is important to confirm it with other satellites. I received a NASA grant to continue searching for this line in the accumulated observations of galaxy clusters with Suzaku, a Japanese X-ray satellite that specializes in looking at the spectra from objects in space. At this point, it is still early to tell if this line originates from dark matter. The next Japanese X-ray mission, Astro-H, will fly in 2015 carrying a high-resolution instrument. With its ability to see better detail in the spectra, we hope we will be able to unambiguously distinguish an astrophysical line from a dark matter signal and tell us what this new X-ray emission truly is.

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The National Aeronautics and Space Administration (NASA) is the United States government agency responsible for the civilian space program as well as aeronautics and aerospace research. President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA's predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

UFO SIGHTINGS PHOTO PHOTOGRAPHY

The Oxford English Dictionary defines a UFO as "An unidentified flying object; a 'flying saucer'." The first published book to use the word was authored by Donald E. Keyhoe. The acronym "UFO" was coined by Captain Edward J. Ruppelt, who headed Project Blue Book, then the USAF's official investigation of UFOs. He wrote, "Obviously the term 'flying saucer' is misleading when applied to objects of every conceivable shape and performance. For this reason the military prefers the more general, if less colorful, name: unidentified flying objects. UFO (pronounced Yoo-foe) for short." Other phrases that were used officially and that predate the UFO acronym include "flying flapjack", "flying disc", "unexplained flying discs", "unidentifiable object", and "flying saucer". The phrase "flying saucer" had gained widespread attention after the summer of 1947. On June 24, a civilian pilot named Kenneth Arnold reported seeing nine objects flying in formation near Mount Rainier. Arnold timed the sighting and estimated the speed of discs to be over 1,200 mph (1,931 km/h). At the time, he described the objects' shape as being somewhat disc-like or saucer-like, leading to newspaper accounts of "flying saucers" and "flying discs". In popular usage the term UFO came to be used to refer to claims of alien spacecraft. and because of the public and media ridicule associated with the topic, some investigators prefer to use such terms as unidentified aerial phenomenon (or UAP) or anomalous phenomena, as in the title of the National Aviation Reporting Center on Anomalous Phenomena (NARCAP).

UFO PHOTO PHOTOGRAPHY

UFO - Unidentified Flying Object An unidentified flying object, or UFO, in its most general definition, is any apparent anomaly in the sky that is not identifiable as a known object or phenomenon. Culturally, UFOs are associated with claims of visitation by extraterrestrial life or government-related conspiracy theories, and have become popular subjects in fiction. While UFOs are often later identified, sometimes identification may not be possible owing to the usually low quality of evidence related to UFO sightings (generally anecdotal evidence and eyewitness accounts). Stories of fantastical celestial apparitions have been told since antiquity, but the term "UFO" (or "UFOB") was officially created in 1953 by the United States Air Force (USAF) to serve as a catch-all for all such reports. In its initial definition, the USAF stated that a "UFOB" was "any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type, or which cannot be positively identified as a familiar object." Accordingly, the term was initially restricted to that fraction of cases which remained unidentified after investigation, as the USAF was interested in potential national security reasons and/or "technical aspects" (see Air Force Regulation 200-2). During the late 1940s and through the 1950s, UFOs were often referred to popularly as "flying saucers" or "flying discs". The term UFO became more widespread during the 1950s, at first in technical literature, but later in popular use. UFOs garnered considerable interest during the Cold War, an era associated with a heightened concern for national security. Various studies have concluded that the phenomenon does not represent a threat to national security nor does it contain anything worthy of scientific pursuit (e.g., 1951 Flying Saucer Working Party, 1953 CIA Robertson Panel, USAF Project Blue Book, Condon Committee).

Photos of Nature | Nature Photography What is The Universe

Photos of Nature | Nature Photography What is The Universe

Wednesday, July 16, 2014