Naval Research Laboratory Brightens Perspective of Mysterious Mini-Halos

Saturday, August 5, 2017

Naval Research Laboratory Brightens Perspective of Mysterious Mini-Halos

Naval Research Laboratory Brightens Perspective of Mysterious Mini-Halos:

Image shows emission surrounding the Perseus Cluster (NGC 1275) from the 270-430 megahertz (MHz) radio map. In this image the main structures of the mini-halo are identified as: the northern extension; the two eastern spurs; the concave edge to the south; and the south-western edge and a plume of emission to the south-south-west. The small knob at the end of the western tail is the galaxy NGC 1272. The bar at top left shows a distance of 90 kpc or roughly 240,000 light years.

The largest gravitationally bound objects in the universe are galaxy clusters that form at the intersection of cosmic web filaments. These entities are shaped and grow through massive collisions as material streams into their gravitational pull. Within the heart of some galaxy clusters are mysterious and little known radio mini-halos. These rare, dispersed, and steep-spectrum (brighter at low frequencies) radio sources surround a bright central radio galaxy and are highly luminous at radio wavelengths.

Studying this phenomenon is Dr. Tracy Clarke, a radio astronomer at the U.S. Naval Research Laboratory (NRL) Radio Astrophysics and Sensing Section and co-author of research on the topic titled, "Deep 230-470 [megahertz] VLA Observations of the mini-halo in the Perseus Cluster." She works in conjunction with the National Radio Astronomy Observatory (NRAO), the research team uses the upgraded Karl G. Jansky Very Large Array (JVLA) to peer into the cluster of galaxies in the constellation Perseus, 250 million light-years from Earth.

"In 2011, an upgrade to the receivers on the JVLA sacrificed the observatory's capability for operation at frequencies between 30 MHz and 300 MHz," said Clarke. "However, in 2013 all 27 of the 25-meter antennas of the JVLA were outfitted with new receivers, providing the bandwidth necessary for these observations."

According to Clarke the Perseus cluster is one of the most massive objects in the known universe, containing thousands of galaxies immersed in a vast cloud of multimillion-degree gas and harbors a minihalo. Mini-halo systems are thought to provide a window on the otherwise elusive turbulence driven by minor mergers between galaxy clusters and less massive systems.

Funded by NRL, the new broadband low frequency receivers have widened the VHF/UHF receiver bandwidth from 300-340 MHz to 230-470 MHz, significantly increasing the sensitivity of the telescope. The new JVLA facilities have also produced an order of magnitude of deeper image quality than previous high fidelity data, which lets the mini-halo emissions be seen clearly at the 270-430 MHz range.

“Overall, the recently upgraded JVLA has enabled a breakthrough in radio astronomy by providing a radio telescope with unprecedented sensitivity, resolution, and imaging capabilities," said Julie Hlavacek Larrondo, Universite de Montreal astrophysicist and a lead author of the paper. "The new JVLA images of the Perseus cluster demonstrate the unique and state-of-the-art capabilities that this telescope offers to the community."

The deep JVLA observations of the Perseus cluster, combined with the cluster's properties, offer researchers a unique opportunity to study mini-halo structures. Lead author Marie-Lou Gendron-Marsolais, Ph.D. student at Universite de Montreal notes, "The results demonstrate the sensitivity of the new low frequency JVLA receivers, as well as the necessity to obtain deeper, higher-fidelity radio images of minihalos in clusters to trace complex structures and further understand their origin."

Recognizing the power of the new VHF/UHF receiver, NRL wanted to enhance the availability of this new resource. In 2014, NRL and NRAO researchers worked to develop the VLA Low Band Ionospheric and Transient Experiment (VLITE) to tap into the new broadband low frequency receivers and piggyback on the $300 million dollar infrastructure of the JVLA.

"The data stream from this new system can be tapped to expand our understanding of objects such as these mini-halos while at the same time providing real-time monitoring of ionospheric weather conditions over the U.S. southwest," Clarke said.

At present, VLITE is being further expanded (eVLITE) to more than double the number of baselines from the original 45 baselines to 104 and should be fully operational by the end of August 2017. The expansion, to date, has brought a total of 66 baselines to VLITE.

Astronomers use VLITE for a wide range of astrophysics, which includes exploring the sky for shortlived bursts of radio waves. This type of research continues to grow in importance, since a small number of such events have led astronomers to suspect still-undiscovered phenomena in the universe may be producing many such powerful bursts.

Credit: nrl.navy.mil

No comments:

Post a Comment

NASA Photos Photography

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

Saturday, August 5, 2017