X-RAY WHISPERS IN A NOISY PUB

Wednesday, July 16, 2014

X-RAY WHISPERS IN A NOISY PUB

X-RAY WHISPERS IN A NOISY PUB:

We are delighted to welcome Katja Poppenhaeger as a guest blogger today. Katja is the first author of a new paper describing the first exoplanet transit ever seen in X-rays, the subject of our latest press release [URL to be added]. Katja studied physics at Frankfurt University in Germany, followed by a PhD in astrophysics at Hamburg Observatory in Germany, before coming to Harvard-Smithsonian Center for Astrophysics (CfA) as a postdoc. She will be a Sagan Fellow at CfA beginning in September 2013.

Credit: K.PoppenhaegerI remember when, back in grad school, my colleagues and I were watching the launch of the Kepler space telescope on the internet. We were really excited because this telescope would - and, in retrospect, has - discovered thousands of planet candidates around other stars, using the transit method. Back then I thought to myself, wouldn't it be cool if I could observe such a transit in X-rays? X-rays are absorbed high up in our Earth's atmosphere, which makes the Earth's X-ray radius about 100 km larger than its optical radius - that is about 1.5% in terms of extra radius. I wanted to use that effect to test how far the outer atmosphere of a Hot Jupiter extends. These Hot Jupiters orbit so close to their central star that they get heated up to temperatures over 1000 K, and their atmospheres can even boil away (which let me hope that there might be more than just an extra 1.5% in radius to find for such planets).

So the first thing I did was to check the data archives of the two big X-ray telescopes, Chandra and XMM-Newton, to see if someone had - by chance or on purpose - observed a planet-hosting star in X-rays while its planet was transiting in front of it. And I couldn't believe my luck: there was indeed a fifteen hour long observation of the star HD 189733 with XMM-Newton, and its Hot Jupiter HD 189733b was crossing in front of the star during that observation.

But when I looked at the light curve, I was rather disappointed: The star is magnetically active, meaning that its corona is bright and flickering, so its X-ray light curve showed lots of scatter. Looking for a transit signal in this light curve was like trying to hear a whisper in a noisy pub. But playing with the light curve for a bit, I realized that during the two hours of the observation where I knew the transit was happening, the X-ray signal was slightly weaker than before and after the transit. It might just have been luck, but I was determined: I had to get more data. With more transits that I could add up, the flickering of the corona would finally average out, and the transit signal would become clearer.

An artist's impression of the HD 189773 system, showing the Hot Jupiter transiting the star.
Credit: NASA/CXC/M.WeissSo I applied for new observations and was granted time to observe six transits with the Chandra X-ray Observatory. When the data arrived, I combined the signal of all observations and was finally successful: I could detect the transit of the planet in X-rays. What surprised me was how deep the transit was: The planet swallowed about 6-8% of the X-ray light from the star, while it only blocked 2.4% of the starlight at optical wavelengths. That means that the planet's atmosphere blocks X-rays at altitudes of more than 60,000 km above its optical radius - a 75% larger radius in X-rays! That is pretty big, and I calculated that the outer atmosphere has to be heated up to about 20,000 K to sustain itself at such high altitudes. The bigger X-ray radius also means that the planet loses its atmosphere about 40% faster than thought before.

So what's next? I'd like to know if the X-ray radius of other hot exoplanets is extended as well - and if yes, does the extent depend on the heating of the planet by the host star, or more on things like the overall density of the planet? Together with my former colleagues from Hamburg Observatory, we will test this for the even hotter Jupiter CoRoT-2b, using XMM-Newton. Personally, I'd like it best if the CoRoT-2b experiment had a completely surprising outcome as well - we'll know next year!

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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