Colossal Ancient Galaxies Die from the Inside Out

Thursday, April 16, 2015

Colossal Ancient Galaxies Die from the Inside Out

Colossal Ancient Galaxies Die from the Inside Out:

by Elizabeth Howell, Space.com Contributor

Date: 16 April 2015 Time: 02:01 PM ET

The elliptical galaxy IC 2006 as seen by the Hubble Space Telescope. A new study suggests that the most massive elliptical galaxies stopped star formation near their centers roughly three billion years after the Big Bang

CREDIT: ESA/Hubble & NASA

The largest ancient galaxies stopped forming stars in their cores about three billion years after the Big Bang, with this end of star birth spreading from the inside out in so-called "dead" galaxies, scientists say.

A new survey of 22 elliptical galaxies (most of which were the same size or larger than our own Milky Way) revealed that the most massive galaxies from about 10 billion years ago have stopped forming stars in their centers while formation continued on the outskirts.

"These galaxies lived 10 billion years in the past — three billion years after the Big Bang — and are star-forming at high rates, and are the progenitors of the massive dead galaxies of today's universe," lead author Sandro Tacchella, a Ph.D. student at ETH Zurich's institute for astronomy in Switzerland, told Space.com. [Top 10 Star Mysteries of All Time]

The survey of ancient elliptical galaxies adds fuel to an ongoing debate about how the star shutdown occurs. One leading theory says that a supermassive black hole drives gas out and disrupts star formation, while the other supposes there is a yet-unexplained mechanism that switches off the gas supply in the center.

Tacchella said data from his study would support either of these two contentions, or even a combination of the two. Also interesting was the smaller, elliptical galaxies from this era were still churning out stars throughout their masses. Why is still poorly understood.

"The smaller galaxies are doubling their mass at the same pace in their inner and outer parts," he said. He added this same phenomenon was observed in younger galaxies closer to us.

This graphic shows how star formation stops in the heart of an elliptical galaxy, then spreads out to the outermost edges to create a so-called "red and dead" galaxy.
Credit: European Southern Observatory

Solving the mystery

Tacchella said he tackled this research problem because he is interested in how galaxies form stars in terms of physical mechanisms.

Figuring out what stopped the star formation in these massive galaxies will require more observations, he said. Astronomers call these elliptical galaxies "red and dead" as they contain a lot of old, dead red stars, but fewer blue youngsters.

The study of 22 galaxies ate up 300 hours of observing time between the orbiting Hubble Space Telescope and the European Southern Observatory's Very Large Telescope in Chile. The VLT looked at the spectra (light distribution) of stars, showing where the young ones were. Hubble was used to trace the older stars, showing the stellar mass distribution of galaxies.

The sheer amount of time would be difficult to replicate given the high observing time demands on these observatories, Tacchella said. He plans a further, focused study with Hubble that will look at the 10 largest galaxies to study their star formation habits more closely.

Better resolution will soon be available to astronomers as well as new observatories come online that can peer further back in time to galaxies that formed closer to the Big Bang, Tacchella said.

NASA's James Webb Space Telescope is set to fly in 2018. On the ground, the most massive optical telescope in the world – the European Extremely Large Telescope (E-ELT), with a 39-meter (128-foot) mirror – is expected to be finished by 2024.

The research was published today in the April 16 edition of the journal Science.

Follow Elizabeth Howell @howellspace, or Space.com @Spacedotcom. We're also on Facebook and Google+. Originally published on Space.com .

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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).

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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

Thursday, April 16, 2015