Artist's impression of the black hole guzzling the gas cloud.
Image: ESO/MPE/M.Schartmann
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By Ron Cowen of Nature magazine
A gas cloud that is careering towards the supermassive black hole at the centre of the Milky Way may be the visible trail of a planet-forming disk surrounding a young, low-mass star, astrophysicists propose.
Modeling work by Ruth Murray-Clay and Avi Loeb of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, suggests that planets can form within the powerful gravitational field of a giant black hole. And it heightens expectations about what astronomers might learn as the cloud nears the galaxy’s biggest black hole — an event expected to cause a spectacular light show that could begin as early as next year. The model is published today in Nature Communications.
Murray-Clay and Loeb began their study last autumn after hearing one of the first public talks about the gas cloud. The team that discovered it proposed that the cloud formed when gas flowing out from two stars collided. But Murray-Clay and Loeb immediately seized on the idea that the cloud's mixture of gas and ionized dust might come from a planet-forming disk surrounding a single young star.
The idea isn’t as far-fetched as it might sound, because a ring of young stars is known to orbit at about 0.03 parsecs (one-tenth of a light year) from Sagittarius A*, the black hole of four million solar masses that lies at the Milky Way’s centre. In star-forming regions throughout the Galaxy, young stars often have planet-spawning disks, and Murray-Clay and Loeb reasoned that those in the region immediately surrounding a black hole might be no different.
According to their model, gravitational interactions dislodged a young, low-mass star orbiting near the ring’s inner edge. The ejected star, now heading towards Sagittarius A*, is too small and faint to be detected. However, material from the star’s disk — boiled off by ultraviolet radiation from other young stars and then stretched out by the black hole’s tidal gravitational forces to form an elongated cloud — can be observed.
Orbit problem
The simulated gas cloud matches key features of the observed cloud, Murray-Clay and Loeb report. However, they calculate that there is only a 0.1% chance that a recently dislodged star would have the same orbit as the gas cloud. This small percentage “is the main theoretical problem” with the model, says Stefan Gillessen at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, a member of the team behind the cloud's discovery.
The duo's model predicts that the gas cloud should have a dense core, which would be revealed by an increase in brightness as the cloud ventures closer to the black hole, Loeb notes. If the model is confirmed, it would suggest that young, low-mass stars that remained in the ring have disks stable enough to forge planets.
Regardless of the cloud’s origin, it could take decades for the whole of it to plunge into the black hole. Material could start falling onto a swirling accretion disk surrounding the black hole by the end of 2013 and continue for 20–40 years, says astronomer Andreas Burkert of the Ludwig Maximilians University in Munich, Germany, another member of the cloud-discovery team. And infalling gas must still make its way from the accretion disk to the black hole itself before most of the fireworks begin, he says.
The activity could come in bursts or appear as a steady brightening, and could also include a jet of hot gas shooting out of the black hole, says Burkert. The nature of the light show could help researchers to answer an enduring puzzle — why Sagittarius A* is so quiescent compared with other supermassive black holes, seemingly not having guzzled a substantial meal of gas and stars for years. But even before it dives into the black hole, the gas will heat up and glow brightly — at around the time of the cloud’s closest approach to Sagittarius A* next summer, Loeb says.
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14 Comments
Add CommentIs it possible that the gas cloud can never make it past the event horizon? In other words, black holes grow only by merging with other black holes.
Reply | Report Abuse | Link to thisIt will make it past the event horizon, but we will not see it after that.
Reply | Report Abuse | Link to thisI believe black holes at the centre of galaxies are anti-matter stars, made from all the anti-matter that was formed simultaneously with matter. Perhaps anti-matter clumps more and was the first to form stars. Now you should have 2 event horizons, one between the black hole and all the matter it is attracting and another between the antimatter star and the region where matter and antimatter annihilates itself.
When two black holes will merge, matter within event horizons of two BHs will merge effectively.
Reply | Report Abuse | Link to thisYou said "within" the event horizon. I referred only to matter outside the event horizon.
Reply | Report Abuse | Link to thismatter that is falling towards the black hole will pass through the event horizon from its point of view. It's only from a distant observer's point of view that the matter appears to never pass the event horizon.
Reply | Report Abuse | Link to thisTherefore, the matter within the event horizon is basically the matter that makes up the black hole, and when two black holes merge, that matter will also merge.
If matter from outside an event horizon can not enter event horizon of a BH, how matter within event horizon of another BH, on merging of two BHs, will enter the combined event horizon of submerged BH.
Reply | Report Abuse | Link to thisGravitational interaction resulting from merging of two BHs may be much more intense than as applicable upon matter lying outside the event horizon of a single BH, therefore, TD may also be equally high.
It is my understanding that the Gravitational Time Distortion at the event horizon is so great that (from our perspective) the matter is just frozen at the horizon and never actually enters. Meanwhile, from the matter's own perspective, it travels through in normal time. I have seen Leonard Susskind describe this on various documentaries. I believe that is the solution to the problem of lost information that black holes present.
Reply | Report Abuse | Link to thisOf course, any of the answers given to this are completely theoretical. Nobody knows what really happens...although hopefully the coming observations will help to correct that.
New observations made this year of G2 have improved ephemerides wrt the encounter next year with Sag A*. Not only is the speed and degree of tidal disruption of G2 greater than predicted (due to increased orbital eccentricity), but the estimated closest passage of the cloud has decreased to 2200 Schwarzschild radii and the predicted perihelion passage has now shifted to early September 2013 (specifically Sep 10, 2013).
Reply | Report Abuse | Link to thisDetails of the new observations have been submitted to the Astrophysical Journal and posted online: http://arxiv.org/abs/1209.2272v1
Thanks for the interesting link.
Reply | Report Abuse | Link to thisThat report states that that the infalling gas cloud has a mass ~3 Earth masses.
While the Nature article's referenced report argues somewhat convincingly that the cloud contains a low mass star (0.3 Solar masses - minimum to form a stable disk) surrounded by a (diminished) tidally stretched protoplanetary disk, this seems to conflict with your reference's mass estimate of 3 Earth masses for the entire cloud. In fact, your reference concludes:
"Overall, a simple ballistic gas cloud, which is being tidally sheared, is an excellent description of the
data available. The origin of such a cloud remains puzzling."
For the Nature article source report, please see:
Ruth A. Murray-Clay & Abraham Loeb, (2012), "Disruption of a proto-planetary disc by the black hole at the milky way centre",
http://www.nature.com/ncomms/journal/v3/n9/full/ncomms2044.html
http://arxiv.org/pdf/1112.4822.pdf
BTW, even if the (low-mass) stars within the ring of stars encircling the MW's SMBH can or do include protoplanetary disks, that is not evidence that they form planets.
Reply | Report Abuse | Link to thisAs I understand, almost all protostars accreted within a molecular cloud form a protoplanetary disk, even though most (especially low mass) stars do not form planetary systems. Please see
http://en.wikipedia.org/wiki/Protoplanetary_disks#Formation
In reviewing other references to G2 wrt mass, I found Burkert et al point out that the total mass of the system "could be substantially larger than G2's estimated mass".
Reply | Report Abuse | Link to thisThis same paper looks at two likely scenarios for the formation of G2.
1)Diffuse cloud scenario - the cloud consists of shocked wind material ejected from a Wolf-Rayet or Luminous Blue Variable(LBV) star.
2)Compact source scenario - the cloud is associated with a compact source eg:
a. Low mass star with a protoplanetary disk (ala Murray-Clay & Loeb)
b. A compact planetary nebula
c. An evaporating low mass star, brown dwarf, or Jupiter-mass planet.
Future observations should help determine the precise nature and origin of the cloud. The Burkert et al paper "Physics of the Galactic Center Cloud G2, on its Way towards the Super-Massive Black Hole" can be found here:
http://arxiv.org/abs/1201.1414
If the 2013 date for infalling gas is correct, we will experience a solar response? The cold infalling gas is heated and jetted outward? Is this jet a way to see 'action at a distance'? I am not convinced the AGN eats planets; I see the gas as the convertible agency.
Reply | Report Abuse | Link to thisScientists have found not one but two stars at the galaxy center hole that orbit each other. Wonderful info.
There are theories that tie a galactic center activity to our solar system such as Miles Mathis'.
Nov 22 says black hole at galaxy center flaring. Is it our gas cloud?
Reply | Report Abuse | Link to thisThe problem with these info briefs is that there never is any connection and leaves us without follow up.
The article contains several contradictions. From our point of view, the falling material will never cross the event horizon. It doesn't have to be as seen by a "distant observer" as posted earlier, but any observer not traveling with the matter being pulled in. From wikipedia:
Reply | Report Abuse | Link to this"Likewise, any object approaching the horizon from the observer's side appears to slow down and never quite pass through the horizon, with its image becoming more and more redshifted as time elapses." http://en.wikipedia.org/wiki/Event_horizon