Astronomers See a Massive Black Hole Tear a Star Apart

Thursday, January 29, 2015

Astronomers See a Massive Black Hole Tear a Star Apart

Astronomers See a Massive Black Hole Tear a Star Apart:

When a star encounters a black hole, tidal forces stretch the star into an elongated blob before tearing it apart, as seen in these images from a computer simulation by James Guillochon of Harvard University.

A telescope peers into the blackness of deep space. Suddenly – a brilliant flash of light appears that wasn’t there before. What could it be? A supernova? Two massively dense stars fusing together? Perhaps a gamma ray burst?

Five years ago, researchers using the ROTSE IIIb telescope at McDonald Observatory noticed just such an event. But far from being your run-of-the-mill stellar explosion or neutron star merger, the astronomers believe that this tiny flare was, in fact, evidence of a supermassive black hole at the center of a distant galaxy, tearing a star to shreds.

Astronomers at McDonald had been using the telescope to scan the skies for such nascent flashes for years, as part of the ROTSE Supernova Verification Project (SNVP). And at first blush, the event seen in early 2009, which the researches nicknamed “Dougie,” looked just like many of the other supernovae they had discovered over the course of the project. With a blazing – 22.5-magnitude absolute brightness, the event fit squarely within the class of superluminous supernovae that the researchers were already familiar with.

But as time went on and more data on Dougie rolled in, the astronomers began to change their minds. X-ray observations made by the orbiting Swift satellite and optical spectra taken by McDonald’s Hobby-Eberly Telescope revealed an evolving light curve and chemical makeup that didn’t fit with computer simulations of superluminous supernovae. Likewise, Dougie didn’t appear to be a neutron star merger, which would have reached peak luminosity far more quickly than was observed, or a gamma ray burst, which, even at an angle, would have appeared far brighter in x-ray light.

That left only one option: a so-called “tidal disruption event,” or the carnage and spaghettification that occurs when a star wanders too close to a black hole’s horizon. J. Craig Wheeler, head of the supernova group at The University of Texas at Austin and a member of the team that discovered Dougie, explained that at short distances, a black hole’s gravity exerts a much stronger pull on the side of the star nearest to it than it does on the star’s opposite side. He explained, “These especially large tides can be strong enough that you pull the star out into a noodle.”

The team refined their models of the event and came to a surprising conclusion: having drawn in Dougie’s stellar material a bit faster than it could handle, the black hole was now “choking” on its latest meal. This is due to an astrophysical principle called the Eddington Limit, which states that a black hole of a given size can only handle so much infalling material. After this limit has been reached, any additional intake of matter exerts more outward pressure than the black hole’s gravity can compensate for. This pressure increase has a kind of rebound effect, throwing off material from the black hole’s accretion disk along with heat and light. Such a burst of energy accounts for at least part of Dougie’s brightness, but also indicates that the original dying star – a star not unlike our own Sun – wasn’t going down without a fight.

Combining these observations with the mathematics of the Eddington Limit, the researchers estimated the black hole’s size to be about 1 million solar masses – a rather small black hole, at the center of a rather small galaxy, three billion light years away. Discoveries like these not only allow astronomers to better understand the physics of black holes, but also properties of their often unassuming home galaxies. After all, mused Wheeler, “Who knew this little guy had a black hole?”

To get a simulated glimpse of Dougie for yourself, check out the amazing animation below, courtesy of team member James Guillochon:

The research is published in this month’s issue of The Astrophysical Journal. A pre-print of the paper is available here.

About Vanessa Janek

Vanessa earned her bachelor's degree in Astronomy and Physics in 2009 from Wheaton College in Massachusetts. Her credits in astronomy include observing and analyzing eclipsing binary star systems and taking a walk on the theory side as a NSF REU intern, investigating the expansion of the Universe by analyzing its traces in observations of type 1a supernovae. In her spare time she enjoys writing about astrophysics, cosmology, biology, and medicine, making delicious vegetarian meals, taking adventures with her husband and/or Nikon D50, and saving the world.

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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).

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Photos of Nature | Nature Photography What is The Universe

Thursday, January 29, 2015