VLT watches in real time as gas cloud makes closest approach to the monster at the centre of the Milky Way

Jul 17, 2013
Ripped apart by a black hole
New observations from ESO's Very Large Telescope show for the first time a gas cloud being ripped apart by the supermassive black hole at the center of the galaxy. Shown here are VLT observations from 2006, 2010 and 2013, colored blue, green and red respectively. Credit: ESO/S. Gillessen

In 2011 ESO's Very Large Telescope (VLT) discovered a gas cloud with several times the mass of the Earth accelerating towards the black hole at the centre of the Milky Way (eso1151. This cloud is now making its closest approach and new VLT observations show that it is being grossly stretched by the black hole's extreme gravitational field.

"The gas at the head of the cloud is now stretched over more than 160 billion kilometres around the closest point of the orbit to the black hole. And the closest approach is only a bit more than 25 billion kilometres from the black hole itself—barely escaping falling right in," explains Stefan Gillessen (Max Planck Institute for Extraterrestrial Physics, Garching, Germany) who led the observing team . "The cloud is so stretched that the close approach is not a single event but rather a process that extends over a period of at least one year."

As the is stretched its light gets harder to see. But by staring at the region close to the black hole for more than 20 hours of total exposure time with the SINFONI instrument on the VLT—the deepest exposure of this region ever with an integral field spectrometer —the team was able to measure the velocities of different parts of the cloud as it streaks past the central black hole.

"The most exciting thing we now see in the new observations is the head of the cloud coming back towards us at more than 10 million km/h along the orbit—about 1% of the speed of light," adds Reinhard Genzel, leader of the research group that has been studied this region for nearly twenty years. "This means that the front end of the cloud has already made its closest approach to the black hole."

The origin of the gas cloud remains mysterious, although there is no shortage of ideas. The new observations narrow down the possibilities.

"Like an unfortunate astronaut in a science fiction film, we see that the cloud is now being stretched so much that it resembles spaghetti. This means that it probably doesn't have a star in it," concludes Gillessen. "At the moment we think that the gas probably came from the stars we see orbiting the black hole."

The climax of this unique event at the centre of the galaxy is now unfolding and being closely watched by astronomers around the world. This intense observing campaign will provide a wealth of data, not only revealing more about the gas cloud [6], but also probing the regions close to the black hole that have not been previously studied and the effects of super-strong gravity.

This research was presented in a paper "Pericenter passage of the gas cloud G2 in the Galactic Center", by S. Gillessen et al, to appear in the Astrophysical Journal.

Explore further: Gravitational waves according to Planck

More information: www.eso.org/public/archives/re… eso1332/eso1332a.pdf

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yyz
5 / 5 (6) Jul 17, 2013
It's interesting to study a series of images of the G2 cloud taken over time, such as this sequence obtained with the 8 meter VLT in the Brackett gamma line of hydrogen: http://www.eso.or...332e.jpg

We should also see some early Xray data on this encounter soon from the likes of Chandra, XMM-Newton and NuStar. Interesting times indeed.
HannesAlfven
1 / 5 (8) Jul 17, 2013
Re: "Like an unfortunate astronaut in a science fiction film, we see that the cloud is now being stretched so much that it resembles spaghetti."

Of course, spaghetti (alongside elephant trunks) is the analogy which has already been used to describe the interstellar "gas" much further from the galaxy's center. Radio astronomer, Gerrit Verschuur, has many times explained in his papers that the interstellar medium is extremely filamentary. So, to simply assume that the center of the galaxy is the cause would appear to simply ignore observations of HI hydrogen at the 21-cm wavelength which have been going on for a few decades now. It is of course equally possible that rotating filaments of "gas" at this location might transition between the various states of illuminated plasma which we see within the laboratory, and in novelty plasma globes.
Fleetfoot
5 / 5 (3) Jul 18, 2013
So, to simply assume that the center of the galaxy is the cause ...


That's why they measure the velocity of the cloud. Like the other orbiting stars in that regon, the motion is Keplerian hence we know it is the gravity of the central object that provides the cloud's acceleration. It is your own alternative that simply assumes these must be filaments because that's what they look like but with on evidence to justify the claim.

It is of course equally possible that rotating filaments of "gas" at this location might transition between the various states of illuminated plasma which we see within the laboratory, and in novelty plasma globes.


No, it's not possible at all. The gas cloud is an isolated entity with no electrical current such as occur in novelty globes. Switch off the power to the globe and you get a more representative lab test of your speculation.
GSwift7
5 / 5 (2) Jul 19, 2013
Radio astronomer, Gerrit Verschuur, has many times explained in his papers that the interstellar medium is extremely filamentary.


But this gas cloud wasn't filamentary until it got close to the black hole, and it will return to something like its original globular shape as it leaves the black hole area. In fact, only the leading edge has been stretched out into spighetti, while the back part will be stretched once it gets close enough.

Besides, I don't think Verschuur would have a problem with this. The thing that got him in the headlines was that he believed the CMBR doesn't exist. More recent work has proven he was wrong about that though. The original work only looked at correlation by position, but the more recent work also included radial velocity (towards and away from us). Once that was done, Verschuur's apparent correlation between HI and CMB seeds completely disapeared.