This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

Banner image is by Ludie Cochrane..

Susan Kieffer can be contacted at s1kieffer at gmail.com

Tuesday, August 30, 2011

Truly cool! Black hole devours a star!

Black hole just about finished munching on wayward star!
NASA Swift satellite. NASA Goddard Space Flight Center
Terrestrial natural disasters don't seem so bad after you watch what happened to the wayward star that got too close to a black hole about 3.9 billion years ago! 

Last March 28 scientists on NASA's Swift satellite mission detected flares at Xray wavelengths coming from a black hole, now designated as Swift J1644+57. They were initially assumed to be from a gamma-ray burst, short blasts of high-energy radiation that are associated with the death of a massive star and the birth of a black hole. However, the emission from this area continued to increase, radio wavelength waves were detected, and astronomers began to think that a star was undergoing tidal disruption.  By March 30, the source was located on a faint galaxy that proved that the galaxy, the source of the X-rays and radio waves, and the event that produced the flares were linked.

(Great video with music, as well as the NASA press release, are here. I couldn't figure out how to get the video to play on this post.)

Most galaxies possess a central huge black hole, typically weighing millions of times the mass of our own sun. The star-gobbling black hole may be about twice the mass of the 4-million-solar-mass black hole in the center of our Milky Way galaxy. As a star gets too close to such an object, it is catastrophically stretched by tidal forces, and its gas falls into a disk swirling around the black hole. There it becomes heated to temperatures of millions of degrees, before being spit back out through funnels, defined by electric and magnetic fields. Matter moving at about 90% of the speed of light erupts along the black hole's spin axis.  One of these jets was pointing straight at the Earth, leading to the discovery in March.

As Zauderer, et al., say in the abstract to their Nature paper: "We conclude that we are seeing a newly formed relativistic outflow, launched by a transient accretion onto a million-solar-mass black hole." They point out that the relativistic outflow was not predicted for these events, so I guess that it's back to the drawing board for the astronomers!

References: Burrows, D.N., and many others, Relativistic jet activity from the tidal disruption of a star by a massive black hole, Nature, 476, 421-424, 2011.

Zauderer, B.A., and many others, Birth of a relativistic outflow in the unusual gamma-ray transient Swift J164449.3+573451, Nature, 476, 425-428, 2011.

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