14 December 2011

from BBC Website




Simulation of cloud path around black hole (ESO/MPE/Marc Schartmann)

Simulations suggest that the cloud will be ripped to bits

and partially swallowed by the black hole

Researchers have spotted a giant gas cloud spiraling into the super-massive black hole at our galaxy's centre.

Though it is known that black holes draw in nearby material, it will be the first chance to see one consume such a cloud. As it is torn apart, the turbulent area around the black hole will become unusually bright, giving astronomers a chance to learn more about it.

An article in Nature suggests the spectacle should be visible in 2013.

Researchers using the European Southern Observatory's Very Large Telescope estimate that despite its size, the cloud has a total mass of only about three times that of Earth.

They have plotted the cloud's squashed, oval-shaped path and estimate it has doubled its speed in the last seven years - to 2,350km per second.

It should spiral in to within about 40 billion kilometers of the black hole in the middle of 2013.

ESO images of gas cloud

Reviews of existing pictures from the VLT

show the cloud speeding up in recent years


Our local super-massive black hole, dubbed Sagittarius A*, lies about 27,000 light-years away, and has a mass about four million times that of our Sun.

As the name implies, beyond a certain threshold point - the event horizon - nothing can escape its pull, not even light itself. But outside that regime is a swirling mass of material, not unlike water circling a drain. In astronomical terms, it is a relatively quiet zone about which little is known.

That looks set to change, though, as the gas cloud approaches.



Spaghetti tester

It does not comprise enough matter to hold itself together under its own gravity, as a star might, so the cloud will begin to elongate as it meets its doom.

"The idea of an astronaut close to a black hole being stretched out to resemble spaghetti is familiar from science fiction," said lead author of the study Stefan Gillessen, from Max Planck Institute for Extraterrestrial Physics in Germany.

"But we can now see this happening for real to the newly discovered cloud. It is not going to survive the experience."

It is likely that about half of the cloud will be swallowed up, with the remainder flung back out into space.

But this violent process will literally shed light on the closest example we have of an enigmatic celestial object. The acceleration of the cloud's constituent material will create a shower of X-rays that will help astronomers learn more about our local black hole.

And as astronomer Mark Morris of the University of California Los Angeles put it in an accompanying article in Nature,

"many telescopes are likely to be watching".



Supermassive Black Hole and Gas Cloud












A Gas Cloud on Its Way Towards The...

Supermassive Black Hole at The Galactic Center
by S. Gillessen et. al.
14 December 2011

from Nature Website

Measurements of stellar orbits provide compelling evidence that the compact radio source Sagittarius A* (Sgr A*) at the Galactic Centre is a black hole four million times the mass of the Sun.


With the exception of modest X-ray and infrared flares, Sgr A* is surprisingly faint, suggesting that the accretion rate and radiation efficiency near the event horizon are currently very low. Here we report the presence of a dense gas cloud approximately three times the mass of Earth that is falling into the accretion zone of Sgr A*.


Our observations tightly constrain the cloud’s orbit to be highly eccentric, with an innermost radius of approach of only ~3,100 times the event horizon that will be reached in 2013.



Over the past three years the cloud has begun to disrupt, probably mainly through tidal shearing arising from the black hole’s gravitational force.


The cloud’s dynamic evolution and radiation in the next few years will probe the properties of the accretion flow and the feeding processes of the super-massive black hole.


The kilo-electronvolt X-ray emission of Sgr A* may brighten significantly when the cloud reaches pericenter. There may also be a giant radiation flare several years from now if the cloud breaks up and its fragments feed gas into the central accretion zone.


Complete report: A Gas Cloud on Its Way Towards The Super-Massive Black Hole in The Galactic Centre