Hubble Spots the Ghostly Light From Dead Galaxies

Monday, November 3, 2014

Hubble Spots the Ghostly Light From Dead Galaxies

Hubble Spots the Ghostly Light From Dead Galaxies:

Hubble Frontier Fields view of Abell 2744

In a patch of sky 3.5 billion light-years away there are hazy elliptical galaxies, colorful spirals, blue arcs and distorted shapes seen clumping together. It’s the result of a vast cosmic collision that took place over the course of 350 million years.

The mess is a treasure trove of information for astronomers, allowing them to piece together the history of a cosmic pile-up of multiple galaxy clusters.

But now astronomers are digging through the nearby darkness. They’re eyeing the remnant stars that were cast adrift in intergalactic space. These stars should emit a faint glow known as intracluster light that — until now — has mostly remained a subject of speculation.

Mireia Montes and Ignacio Trujillo, both from the University of La Laguna, Spain, have used the Hubble Space Telescope to observe the aforementioned cluster, Abel 2744, in exquisite detail. The cluster has already earned the nickname Pandora’s Cluster for its violent past.

The team looked at both visible and near-infrared color images of the cluster, and then split these color images by brightness. This allowed Montes and Trujillo to pinpoint the color of the cluster’s faintest glow and therefore glean the ghost stars’ age, chemical content, and total mass.

Compared to stars within the cluster’s galaxies, the ghost stars emit bluer light and are therefore rich in heavier elements like oxygen, carbon, and nitrogen. So the scattered stars must be second- or third-generation stars enriched by previous supernovae. But they’re still between three and nine billion years younger than the stars within the cluster’s galaxies.

The team estimates that the combined light of about 100 billion outcast stars contributes approximately six percent of the cluster’s brightness.

But how did the stars get thrown from their respective galaxies in the first place? This new forensic evidence suggests that violent collisions tore apart between four and six Milky Way-size galaxies, scattering their stars into intergalactic space.

“The Hubble data revealing the ghost light are important steps forward in understanding the evolution of galaxy clusters,” said Trujillo in a news release. “It is also amazingly beautiful in that we found the telltale glow by utilizing Hubble’s unique capabilities.”

Abell 2744 is only one target in Hubble’s Frontier Fields program, which will map five more galaxy clusters in superb detail.

The results have been published in the Astrophysical Journal and are available online.

About Shannon Hall

Shannon Hall is a freelance science journalist. She holds two B.A.'s from Whitman College in physics-astronomy and philosophy, and an M.S. in astronomy from the University of Wyoming. Currently, she is working toward a second M.S. from NYU's Science, Health and Environmental Reporting program. You can follow her on Twitter @ShannonWHall.

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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.

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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).

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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

Monday, November 3, 2014